Abstract

BACKGROUND

Hypospadias is a common congenital malformation of the male external genitalia. Most cases have an unknown aetiology, which is probably a mix of monogenic and multifactorial forms, implicating both genes and environmental factors. This review summarizes current knowledge about the aetiology of hypospadias.

METHODS

Pubmed was used to identify studies on hypospadias aetiology published between January 1995 and February 2011. Reference lists of the selected manuscripts were also searched to identify additional studies, including those published before 1995.

RESULTS

The search provided 922 articles and 169 articles were selected for this review. Studies screening groups of patients with hypospadias for single gene defects found mutations in WT1, SF1, BMP4, BMP7, HOXA4, HOXB6, FGF8, FGFR2, AR, HSD3B2, SRD5A2, ATF3, MAMLD1, MID1 and BNC2. However, most investigators are convinced that single mutations do not cause the majority of isolated hypospadias cases. Indeed, associations were found with polymorphisms in FGF8, FGFR2, AR, HSD17B3, SRD5A2, ESR1, ESR2, ATF3, MAMLD1, DGKK, MID1, CYP1A1, GSTM1 and GSTT1. In addition, gene expression studies indentified CTGF, CYR61 and EGF as candidate genes. Environmental factors consistently implicated in hypospadias are low birthweight, maternal hypertension and pre-eclampsia, suggesting that placental insufficiency may play an important role in hypospadias aetiology. Exogenous endocrine-disrupting chemicals have the potential to induce hypospadias but it is unclear whether human exposure is high enough to exert this effect. Other environmental factors have also been associated with hypospadias but, for most, the results are inconsistent.

CONCLUSIONS

Although a number of contributors to the aetiology of hypospadias have been identified, the majority of risk factors remain unknown.

Introduction

Hypospadias is a congenital hypoplasia of the penis, with displacement of the urethral opening along the ventral surface, often associated with dorsal hooded foreskin and chordee. More than 50% of cases have anterior hypospadias, with a small displacement of the meatus in the glandular region (Fredell et al., 2002b; van der Zanden et al., 2010). Other patients have more substantial displacements, with middle (penile) or posterior (penoscrotal, scrotal and perineal) openings (Fig. 1). Hypospadias is usually diagnosed during physical examination of the newborn but localization is best established during surgery, after chordee release. Compared with healthy children, boys born with hypospadias more often have additional congenital anomalies (Latifoğlu et al., 1998; Akre et al., 1999; Aschim et al., 2004a; Nassar et al., 2007), an association that appears to be stronger for posterior compared with anterior cases (Latifoğlu et al., 1998; Wu et al., 2002; Nassar et al., 2007). Cryptorchidism in particular and other urogenital anomalies are frequently found with hypospadias (Weidner et al., 1999; Nassar et al., 2007; Schnack et al., 2009; Akin et al., 2011).

Figure 1

Hypospadias subgroups.

Figure 1

Hypospadias subgroups.

Even when patients receive surgery in their first 2 years of life, they may encounter severe medical, social and sexual problems later in life. After long-term follow-up (10 years) of mainly patients with anterior hypospadias who underwent 1-stage repair, different rates of complications in up to 50% of patients were reported, depending on the inclusion of different aspects (Nuininga et al., 2005). Although most studies conclude that psychosocial development is not seriously altered, patients do suffer from negative genital appraisal, sexual inhibition and more erection and ejaculation problems (Mieusset and Soulié, 2005; Schönbucher et al., 2008).

Prevalence

Figures on the birth prevalence of hypospadias vary considerably across countries, ranging from 4 to 43 cases per 10 000 births (Kurahashi et al., 2004; Nassar et al., 2007). Hypospadias occurs most frequently in whites, less frequently in blacks and rates are lowest among Asians and Hispanics (Gallentine et al., 2001; Carmichael et al., 2003, 2007; Yang et al., 2004; Nelson et al., 2005; Porter et al., 2005; Forrester and Merz, 2006; Meyer et al., 2006; Carmichael et al., 2007; Nassar et al., 2010). There is debate about whether or not the prevalence of hypospadias is increasing. Some researchers reported increasing prevalences in China (Sun et al., 2009; Jin et al., 2010), Australia (Nassar et al., 2007), the USA (Paulozzi et al., 1997; Nelson et al., 2005) and Europe (Lund et al., 2009), whereas others did not find an increase in Canada, the USA (Fisch et al., 2001; Carmichael et al., 2003; Porter et al., 2005), Europe (Aho et al., 2000; Ahmed et al., 2004; Abdullah et al., 2007) and Japan (Kurahashi et al., 2004). However, the results of different studies are difficult to compare because some are based on hospital discharge registries, including only surgically treated patients or all newborns diagnosed with hypospadias, whereas others are based on birth defects surveillance systems, including all registered hypospadias cases or excluding cases with glandular hypospadias. In addition, the diagnosis and definition of hypospadias may have changed over time.

Embryology of the male external genitalia

Indifferent stage

Early development of the external genitalia is similar for males and females. The embryonic cloaca, the far end of the hind gut, is separated from the amniotic cavity by the cloacal membrane. Early in the fifth week of development, a swelling develops on both sides of this membrane, the cloacal folds, which meet in the midline anterior to the cloacal membrane, forming the genital tubercle (GT) (Schoenwolf et al., 2009; Fig. 2). At the same time, the genital ridges, the precursors of the gonads, develop. Studies in mice showed that this process requires Wilms tumour 1 (Wt1) activity, which activates splicing factor 1 (Sf1; Wilhelm and Englert, 2002), thus preventing degeneration of the developing gonads (Luo et al., 1994). During the seventh week of human development, the urorectal septum fuses with the cloacal membrane, dividing the cloaca into the primitive urogenital sinus and the rectum, and dividing the cloacal membrane into the urogenital and the anal membrane. The swellings next to the urogenital membrane are then called the urogenital folds and a new pair of swellings, the labioscrotal swellings, appears on either side of these folds. In addition, the urogenital membrane breaks down (Schoenwolf et al., 2009).

Figure 2

Simple schematic drawing of the normal embryology of the human male external genitalia, which is disturbed in the case of hypospadias development.

Figure 2

Simple schematic drawing of the normal embryology of the human male external genitalia, which is disturbed in the case of hypospadias development.

Early patterning

The GT masculinizes if exposed to androgens but early patterning is androgen independent. Studies on genes and proteins involved in this patterning process have mainly been performed in mice and showed that the distal urethral plate epithelium is the signalling centre regulating GT outgrowth (Perriton et al., 2002). Fibroblast growth factor protein (Fgf) and wingless-type MMTV integration site family member 5A (Wnt5a) signalling have a growth-promoting role in this outgrowth (Yamaguchi et al., 1999), whereas bone morphogenetic proteins (Bmps) stimulate apoptosis (Morgan et al., 2003; Suzuki et al., 2003). The expression of Fgf8 in the urethral plate is regulated by sonic hedgehog (Shh) and homeobox A13 (Hoxa13; Haraguchi et al., 2001; Perriton et al., 2002; Morgan et al., 2003), while Hoxa13 also regulates the expression of Bmp7 (Morgan et al., 2003). Shh induces, either directly or via Fgf8 or other factors, the expression of Fgf10, Bmp2, Bmp4, Wnt5a, Patched 1 (Ptch1), Msh homeobox 1 (Msx1) and Hoxd13 (Haraguchi et al., 2001; Perriton et al., 2002). Shh thus modulates the balance between proliferation and apoptosis (Haraguchi et al., 2001) and regulates the initiation of GT outgrowth (Perriton et al., 2002). Immunohistochemical staining of human fetal penises showed the expression of SHH, its receptor PTCH1, and its downstream genes smoothened, frizzled family receptor (SMO) and GLI family zinc finger 1 (GLI1) around the time of urethral closure (Shehata et al., 2011). Studies in mice showed that Wnt-β-catenin signalling also seems to play a role in GT development, either in early androgen-independent GT development (Lin et al., 2008) or as a downstream effector of androgen signalling essential for GT masculinization (Miyagawa et al., 2009).

Masculinization

Subsequent masculinization relies on hormones produced by the testes. The expression of the sex-determining region Y gene (SRY) induces a cascade of gene interactions, involving SRY-box 9 (SOX9; Schoenwolf et al., 2009), resulting in differentiation of the gonads into the testes (Sinclair et al., 1990). SRY leads to the differentiation of Sertoli cells (Schoenwolf et al., 2009), which secrete anti-Müllerian hormone (AMH). Studies in mice showed that AMH secretion happens under the influence of Sf1 (Giuili et al., 1997). AMH causes regression of the Müllerian ducts that would otherwise form part of the female genital structures (Schoenwolf et al., 2009). HCG, produced by the placenta, controls fetal Leydig cell growth and stimulates fetal testicular steroidogenesis, the generation of steroids from cholesterol (Misrahi et al., 1998). The enzymatic steps of steroidogenesis, mainly taking place in the Leydig cell, are well documented, and the expression of key genes in this pathway is dependent on the expression of SF1 (Scott et al., 2009; Fig. 3). Testosterone leaves the Leydig cell and is converted into dihydrotestosterone (DHT) by steroid-5-alpha-reductase (SRD5A). Testosterone promotes the formation of the internal reproductive structures from the Wolffian ducts, whereas DHT induces the development of the external genitalia (Schoenwolf et al., 2009), both through their effect on the androgen receptor (AR). The expression of estrogen receptors (ESRs) in male genital tissue during development suggests that the balance between androgens and estrogens is important as well (Crescioli et al., 2003).

Figure 3

Steroidogenesis in the mitochondrium (top) and smooth endoplasmic reticulum (bottom) of the fetal Leydig cell.

Figure 3

Steroidogenesis in the mitochondrium (top) and smooth endoplasmic reticulum (bottom) of the fetal Leydig cell.

During masculinization of the external genitalia, between the 12th and 14th weeks after conception (Schoenwolf et al., 2009), the GT develops into the penis, the labioscrotal swellings fuse to form the scrotum (Ammini et al., 1997; Schoenwolf et al., 2009) and the urogenital folds close in a proximal to distal direction to form the penile urethra (Ammini et al., 1997; van der Werff et al., 2000; Yamada et al., 2003; Hynes and Fraher, 2004b; Schoenwolf et al., 2009; Fig. 2). Several hypotheses have been proposed about the formation of the glandular portion of the urethra. One of these states that, while the penile urethra is created by fusion and primary luminization, the glandular urethra develops by fusion and secondary luminization (van der Werff et al., 2000). According to another hypothesis, the complete urethra arises by the fusion of the urogenital folds (Ammini et al., 1997; Baskin et al., 2001). Still others believe that the glandular portion of the urethra originates from a different set of folds (Hynes and Fraher, 2004a), ingrowth of surface cells (Jones, 1910) or canalization of the urethral plate (Schoenwolf et al., 2009).

As a result, the development of hypospadias is also controversial. From a clinical point of view, the development of the urethra, corpora, glans and penile skin are directly correlated. In posterior hypospadias, there is non-fusion of the labioscrotal swellings with a distal dysplasia of the urethral plate and corpora, as well as non-fusion of the glans and skin in the midline. In middle hypospadias, the distal part of the penis shows a persistence of the urethral plate and non-tubularization of the glans with disturbed penile skin formation. In glandular hypospadias, there is a dimple or a short tubular tract with a septum in between this tract and the urethral plate or tube and no closure of the skin in the midline. In the most minimal form, hypospadias sine hypospadias, only non-fusion of the preputial skin on the ventral side is seen, with dorsal hooded foreskin with or without some chordee.

Aim of this review

In 30% of the least frequently occurring posterior hypospadias cases a cause can be identified, for example, a complex genetic syndrome, partial androgen insensitivity related to AR mutations, or SRD5A type II deficiency (Albers et al., 1997; Boehmer et al., 2001). The aetiology of most other hypospadias cases, however, is not yet solved in spite of intensive research. In this review, we will summarize the current knowledge about the causes of the isolated, non-syndromic form of this common birth defect in humans, from both a genetic and an environmental point of view. In addition, we will provide recommendations for further research.

Methods

Pubmed was used to identify all relevant manuscripts on the aetiology of hypospadias. We searched for papers published between January 1995 and February 2011 in the English language using the following keywords in the title or abstract: ‘(hypospadia OR hypospadias) NOT surgical NOT surgery NOT reconstruction NOT repair NOT incised NOT procedure’. This search provided 922 articles, of which we used the titles and abstracts to identify relevant papers. We focused our review on the aetiology of isolated hypospadias in humans. Therefore, we excluded all animal studies (n = 99), articles that were not about hypospadias or the aetiology of hypospadias (n = 235) and articles or case reports that described the phenotype of patients suffering from syndromes including hypospadias, or that investigated or described the most likely cause of the syndrome in these boys (n = 308). To systematically exclude articles with a lesser degree of evidence, we excluded all ecological studies (n = 11). For epidemiological studies reporting negative findings for environmental factors, we took the power into consideration before reporting that it showed no association. In general, we excluded negative results on environmental factors from studies describing <100 cases, as these have, for example, only 37% power to significantly (P< 0.05) detect a 2-fold increased risk, assuming a prevalence of 10% (15 studies were completely excluded because of this criterion). To guarantee that all information was included only once in the article, we excluded all reviews and meta-analyses (n = 79). In addition, when a study was supplemented with new data in a later publication (n = 3), we only included the article reporting the most complete data. Finally, all commentaries were excluded (n = 32). Reference lists of the selected manuscripts were searched to identify additional studies, including those published before 1995, although these were only included if they reported results that were not found in one of the more recently published articles (n = 29). This selection process resulted in 169 original articles that were included in this review and are described below.

Results

Aetiology of hypospadias is multifactorial

Hypospadias shows familial clustering, with 7% of cases having affected first, second or third degree relatives (Fredell et al., 2002b). Familial occurrence seems to be more common for anterior and middle forms of hypospadias than for posterior types (Fredell et al., 2002b; Brouwers et al., 2010). The chance that a brother of an affected boy will also have hypospadias is 9–17% (Calzolari et al., 1986; Stoll et al., 1990; Schnack et al., 2008). In two family studies and one small twin study, the heritability of hypospadias was estimated to be 57–77% (Calzolari et al., 1986; Stoll et al., 1990; Schnack et al., 2008), meaning that 57–77% of the phenotypic variability can be attributed to genetic variability. Because hypospadias is equally transmitted through the maternal and paternal sides of the family and recurrence risks for brothers and sons of hypospadias cases are similar, genetic rather than shared environmental factors may play a principal role in familial hypospadias (Schnack et al., 2008). Segregation analysis, however, suggested that the majority of cases have a multifactorial aetiology, involving both genes and environmental factors (Fredell et al., 2002a).

Genes implicated in the aetiology of isolated hypospadias

Much of the genetic research on hypospadias has been focused on identification of causal mutations. In Table I, we summarize the exonic (including 3′-untranslated and splice acceptor site) mutations found in studies screening candidate genes in groups of patients with hypospadias, ordered according to the different stages of embryonic development. Whether these mutations have functional consequences remains unclear in most cases, as only few studies reported conservation and function of the region in which the mutation is located, or predicted potential influence of the mutation on protein function using bioinformatics. The majority of mutations were found only once and were identified in posterior or penile cases. The latter has contributed to the view that there is a difference in the genetic models underlying posterior versus anterior hypospadias, with posterior cases being more common in monogenic forms of hypospadias and anterior cases having a polygenic or multifactorial aetiology. The studies investigating associations between genetic polymorphisms and hypospadias are summarized in Table II (following the same order as Table I).

Table I

Mutations found in studies screening candidate genes in groups of patients with hypospadias.

Gene Locus n cases n controls Ethnicity Mutation Phenotype Heterozygosity Remarks Reference 
Indifferent stage of development 
WT1 11p13 35  Different ethnicities     Nordenskjöld et al. (1999
  90 276 Chinese N130N Penoscrotal, micropenis Hetero  Wang et al., 2004
      Penile Hetero  
     A131T Penile Hetero  
     S159S Glandular, also has BMP7 mutation Hetero  
WTAP 6q25-q27 37 20 Controls are Caucasian, ethnicity cases ?     Utsch et al. (2003
SF1 11q13 60a 100 Q107X Penoscrotal, bilateral cryptorchidism Hetero  Showed that variant impairs transcriptional activity Köhler et al. (2009
     c.103−3C>Ab Scrotal, micropenis, bilateral cryptorchidism Hetero  
     E11X Penoscrotal, micropenis, bilateral cryptorchidism Hetero Showed that variant impairs transcriptional activity 
Early patterning stage of development 
BMP4 14q22-q23 90 190 Chinese H207D Penoscrotal, micropenis Hetero  Chen et al. (2007
     R223H Penoscrotal Hetero  
     H251Y Penile, micropenis Hetero  
BMP7 20q13 60c 96 Different ethnicities     Beleza-Meireles et al. (2007c
  90 190 Chinese R303C Glandular, also has WT1 mutation Hetero  Chen et al. (2007
     Q199Q Penile Hetero  
     c.1465T>Ad Penoscrotal, micropenis Hetero  
     c.1567A>Gd Penile Hetero  
HOXA4 7p15.2 90 190 Chinese G129C Penoscrotal, micropenis Hetero  Chen et al. (2007
     S290C Penile, bifid scrotum, cryptorchidism Hetero  
      Penile, micropenis, also has SRD5A2 mutation Hetero  
HOXB6 17q21.3 90 190 Chinese P42T Scrotal, micropenis, bifid scrotum, cryptorchidism, also has SRD5A2 and MID1 mutations Hetero Mother heterozygous Chen et al. (2007
     C123R Penile Hetero  
HOXA13 7p15.2 37 20 Controls are Caucasian, ethnicity cases ?     Utsch et al. (2003
FGF8 10q24 60c 96 Different ethnicities c.590C>Ge Homo Swedish patient Beleza-Meireles et al. (2007c
FGF10 5p13-p12 60c 96 Different ethnicities     Beleza-Meireles et al. (2007c
FGFR2 10q26 60c 96 Different ethnicities M186Tf Midpenile Hetero Swedish patient Beleza-Meireles et al. (2007c
     c.2454C > Te Hetero Swedish patient 
Masculinization stage of development 
SRY 90 276 Chinese     Wang et al. (2004
SOX9 17q23 90 276 Chinese     Wang et al. (2004
AR Xq12 21 90 V870A Penoscrotal, bilateral cryptorchidism Hemi  Hiort et al. (1994
  9g  G566V Perineal Hemi Family history suggested familial component Alléra et al. (1995
  40h  P546S Distal penile shaft Hemi  Sutherland et al. (1996
  35  Different ethnicities F725V Hypospadias and cryptorchidism, clinically diagnosed with PAIS based on sparse body hair, gynaecomastia and heredity for intersex malformations Hemi  Nordenskjöld et al. (1999
     S597T Severe hypospadias, cryptorchidism, bifid scrotum Hemi  
  21 100 Japanese     Muroya et al. (2001
AR Xq12 90 276 Chinese I664T Glandular, gynaecomastia Hemi  Wang et al. (2004
     R840H Perineal, micropenis, bifid scrotum Hemi Mother heterozygous, variant previously described in ambiguous genitalia patient and shown by others to reduce androgen-binding affinity and transcriptional activity 
     I842T Scrotal, micropenis, bifid scrotum Hemi Mother heterozygous 
     R855H Perineal, micropenis, bifid scrotum Hemi Mother heterozygous, uncle has same mutation and phenotype, variant previously described in two brothers with perineal hypospadias, bilateral cryptorchidism and micropenis 
     L859L Penile Hemi  
  37i  Different ethnicities Q798E Scrotal Hemi Variant previously described in various genital defects and shown by others to affect AR transactivation function Thai et al. (2005
  92 190 Iranian     Radpour et al. (2007
FKBP4 12p13.33 91  Different ethnicities     Beleza-Meireles et al. (2007a
HSD3B2 1p13.1 90g 101 S213T Scrotal, bilateral cryptorchidism Hetero Mother and brother heterozygous, showed that variant reduces enzyme activity Codner et al. (2004
     S284R Midshaft Hetero De novo, showed that variant reduces enzyme activity 
     A238A Midshaft Hetero  
     T259T Proximal penile, micropenis and Wilms' tumour but no WT1 mutation Hetero De novo 
     T320T Subcoronal Hetero Father heterozygous has bifid preputium and a wide meatus  
HSD17B3 9q22 19j  Different ethnicities     Thai et al. (2005
SRD5A2 2p23 35  Different ethnicities     Nordenskjöld et al. (1999
  81k 100 Different ethnicities L113V Penoscrotal Hetero  Silver and Russell (1999
     H231R Scrotal Hetero Variant previously described in 5α-reductase deficiency 
  90 276 Chinese R227Q Penile, bifid scrotum, also has HOXA4 mutation Homo Variant previously described in patient with scrotal hypospadias, bifid scrotum and micropenis and shown by others to inhibit NADPH binding, reduce testosterone binding and reduce enzyme half-life Wang et al. (2004
      Scrotal, micropenis, bifid scrotum Homo  
      Glandular Hetero  
     R246Q Scrotal, bifid scrotum, cryptorchidism Homo Variant previously described in two patients with perineoscrotal hypospadias, micropenis and cryptorchidism and shown by others to reduce enzyme activity 
     Q6X Scrotal, micropenis, bifid scrotum, cryptorchidism Homo  
      Scrotal, micropenis, bifid scrotum, cryptorchidism, also has G203S variant (also found in controls) and HOXB6 and MID1 mutation Hetero Father heterozygous 
     L224H Scrotal, micropenis, bifid scrotum, also has G203S variant Hetero Father heterozygous, two brothers of patient have same genotype and phenotype as patient 
     656delT Perineal, micropenis, bifid scrotum, cryptorchidism Hetero  
SRD5A2 2p23 37i  Different ethnicities G196S Scrotal Hetero Mother heterozygous, variant previously described in homozygous form in eight patients with scrotal hypospadias and micropenis and shown by ohers to partly disrupt NADPH binding Thai et al. (2005
SRD5A1 5p15 10l 49     Tria et al. (2004
Other genes 
ESR1 6q25.1 60 94 Different ethnicities     Beleza-Meireles et al. (2006
ESR2 14q23.2 60 94 Different ethnicities     Beleza-Meireles et al. (2006
ATF3 1q32.3 93 96 Different ethnicities A90G Moderate Swedish patient Beleza-Meireles et al. (2008
     c.817C>Td Moderate/severe Middle Eastern patient 
      Moderate/severe Swedish patient 
  41 30 L23M Anterior Hetero  Kalfa et al. (2008a
MAMLD1 Xq28 166 460 Different ethnicities E124X Penoscrotal, cryptorchidism, bifid scrotum Hemi Japanese patient, mother heterozygous, maternal half-brother has same mutation and similar phenotype Fukami et al. (2006
     Q197X Penoscrotal, micropenis, bifid scrotum Hemi Japanese patient 
     R653X Penoscrotal, micropenis, cryptorchidism, bifid scrotum Hemi Japanese patient, mother heterozygous 
  41 30 Different ethnicities V432Am Proximal penile Hemi  Kalfa et al. (2008b
     L121X Proximal penile, cryptorchidism Hemi  
      Penoscrotal Hemi de novo 
     p.531ins3Qn Coronal Hemi  
  99o 95 Q529K Severe, bilateral cryptorchidism Hemi  Chen et al. (2010
     D686D Hemi  
MID1 Xp22 114 95 E238X Penoscrotal, hypertelorism Hemi Mother heterozygous, brother has same mutation and phenotype, variant previously describeded in Opitz syndrome Zhang et al. (2011
     K560R Penoscrotal, hypertelorism Hemi  
INSL3 19p13.2-p12 94 270 Moroccan     El Houate et al. (2007
BNC2 9p22.2 48p 23 Different ethnicities A923V Distal Hetero Caucasian patient Bhoj et al. (2011
      Distal Hetero African-American patient 
     L414V Distal Hetero Caucasian patient 
     P306A Distal Hetero Caucasian patient 
     P579L Distal Hetero Caucasian patient 
     E240G, R283G and Q152R Distal Hetero for all variants Caucasian patient 
         
         
Gene Locus n cases n controls Ethnicity Mutation Phenotype Heterozygosity Remarks Reference 
Indifferent stage of development 
WT1 11p13 35  Different ethnicities     Nordenskjöld et al. (1999
  90 276 Chinese N130N Penoscrotal, micropenis Hetero  Wang et al., 2004
      Penile Hetero  
     A131T Penile Hetero  
     S159S Glandular, also has BMP7 mutation Hetero  
WTAP 6q25-q27 37 20 Controls are Caucasian, ethnicity cases ?     Utsch et al. (2003
SF1 11q13 60a 100 Q107X Penoscrotal, bilateral cryptorchidism Hetero  Showed that variant impairs transcriptional activity Köhler et al. (2009
     c.103−3C>Ab Scrotal, micropenis, bilateral cryptorchidism Hetero  
     E11X Penoscrotal, micropenis, bilateral cryptorchidism Hetero Showed that variant impairs transcriptional activity 
Early patterning stage of development 
BMP4 14q22-q23 90 190 Chinese H207D Penoscrotal, micropenis Hetero  Chen et al. (2007
     R223H Penoscrotal Hetero  
     H251Y Penile, micropenis Hetero  
BMP7 20q13 60c 96 Different ethnicities     Beleza-Meireles et al. (2007c
  90 190 Chinese R303C Glandular, also has WT1 mutation Hetero  Chen et al. (2007
     Q199Q Penile Hetero  
     c.1465T>Ad Penoscrotal, micropenis Hetero  
     c.1567A>Gd Penile Hetero  
HOXA4 7p15.2 90 190 Chinese G129C Penoscrotal, micropenis Hetero  Chen et al. (2007
     S290C Penile, bifid scrotum, cryptorchidism Hetero  
      Penile, micropenis, also has SRD5A2 mutation Hetero  
HOXB6 17q21.3 90 190 Chinese P42T Scrotal, micropenis, bifid scrotum, cryptorchidism, also has SRD5A2 and MID1 mutations Hetero Mother heterozygous Chen et al. (2007
     C123R Penile Hetero  
HOXA13 7p15.2 37 20 Controls are Caucasian, ethnicity cases ?     Utsch et al. (2003
FGF8 10q24 60c 96 Different ethnicities c.590C>Ge Homo Swedish patient Beleza-Meireles et al. (2007c
FGF10 5p13-p12 60c 96 Different ethnicities     Beleza-Meireles et al. (2007c
FGFR2 10q26 60c 96 Different ethnicities M186Tf Midpenile Hetero Swedish patient Beleza-Meireles et al. (2007c
     c.2454C > Te Hetero Swedish patient 
Masculinization stage of development 
SRY 90 276 Chinese     Wang et al. (2004
SOX9 17q23 90 276 Chinese     Wang et al. (2004
AR Xq12 21 90 V870A Penoscrotal, bilateral cryptorchidism Hemi  Hiort et al. (1994
  9g  G566V Perineal Hemi Family history suggested familial component Alléra et al. (1995
  40h  P546S Distal penile shaft Hemi  Sutherland et al. (1996
  35  Different ethnicities F725V Hypospadias and cryptorchidism, clinically diagnosed with PAIS based on sparse body hair, gynaecomastia and heredity for intersex malformations Hemi  Nordenskjöld et al. (1999
     S597T Severe hypospadias, cryptorchidism, bifid scrotum Hemi  
  21 100 Japanese     Muroya et al. (2001
AR Xq12 90 276 Chinese I664T Glandular, gynaecomastia Hemi  Wang et al. (2004
     R840H Perineal, micropenis, bifid scrotum Hemi Mother heterozygous, variant previously described in ambiguous genitalia patient and shown by others to reduce androgen-binding affinity and transcriptional activity 
     I842T Scrotal, micropenis, bifid scrotum Hemi Mother heterozygous 
     R855H Perineal, micropenis, bifid scrotum Hemi Mother heterozygous, uncle has same mutation and phenotype, variant previously described in two brothers with perineal hypospadias, bilateral cryptorchidism and micropenis 
     L859L Penile Hemi  
  37i  Different ethnicities Q798E Scrotal Hemi Variant previously described in various genital defects and shown by others to affect AR transactivation function Thai et al. (2005
  92 190 Iranian     Radpour et al. (2007
FKBP4 12p13.33 91  Different ethnicities     Beleza-Meireles et al. (2007a
HSD3B2 1p13.1 90g 101 S213T Scrotal, bilateral cryptorchidism Hetero Mother and brother heterozygous, showed that variant reduces enzyme activity Codner et al. (2004
     S284R Midshaft Hetero De novo, showed that variant reduces enzyme activity 
     A238A Midshaft Hetero  
     T259T Proximal penile, micropenis and Wilms' tumour but no WT1 mutation Hetero De novo 
     T320T Subcoronal Hetero Father heterozygous has bifid preputium and a wide meatus  
HSD17B3 9q22 19j  Different ethnicities     Thai et al. (2005
SRD5A2 2p23 35  Different ethnicities     Nordenskjöld et al. (1999
  81k 100 Different ethnicities L113V Penoscrotal Hetero  Silver and Russell (1999
     H231R Scrotal Hetero Variant previously described in 5α-reductase deficiency 
  90 276 Chinese R227Q Penile, bifid scrotum, also has HOXA4 mutation Homo Variant previously described in patient with scrotal hypospadias, bifid scrotum and micropenis and shown by others to inhibit NADPH binding, reduce testosterone binding and reduce enzyme half-life Wang et al. (2004
      Scrotal, micropenis, bifid scrotum Homo  
      Glandular Hetero  
     R246Q Scrotal, bifid scrotum, cryptorchidism Homo Variant previously described in two patients with perineoscrotal hypospadias, micropenis and cryptorchidism and shown by others to reduce enzyme activity 
     Q6X Scrotal, micropenis, bifid scrotum, cryptorchidism Homo  
      Scrotal, micropenis, bifid scrotum, cryptorchidism, also has G203S variant (also found in controls) and HOXB6 and MID1 mutation Hetero Father heterozygous 
     L224H Scrotal, micropenis, bifid scrotum, also has G203S variant Hetero Father heterozygous, two brothers of patient have same genotype and phenotype as patient 
     656delT Perineal, micropenis, bifid scrotum, cryptorchidism Hetero  
SRD5A2 2p23 37i  Different ethnicities G196S Scrotal Hetero Mother heterozygous, variant previously described in homozygous form in eight patients with scrotal hypospadias and micropenis and shown by ohers to partly disrupt NADPH binding Thai et al. (2005
SRD5A1 5p15 10l 49     Tria et al. (2004
Other genes 
ESR1 6q25.1 60 94 Different ethnicities     Beleza-Meireles et al. (2006
ESR2 14q23.2 60 94 Different ethnicities     Beleza-Meireles et al. (2006
ATF3 1q32.3 93 96 Different ethnicities A90G Moderate Swedish patient Beleza-Meireles et al. (2008
     c.817C>Td Moderate/severe Middle Eastern patient 
      Moderate/severe Swedish patient 
  41 30 L23M Anterior Hetero  Kalfa et al. (2008a
MAMLD1 Xq28 166 460 Different ethnicities E124X Penoscrotal, cryptorchidism, bifid scrotum Hemi Japanese patient, mother heterozygous, maternal half-brother has same mutation and similar phenotype Fukami et al. (2006
     Q197X Penoscrotal, micropenis, bifid scrotum Hemi Japanese patient 
     R653X Penoscrotal, micropenis, cryptorchidism, bifid scrotum Hemi Japanese patient, mother heterozygous 
  41 30 Different ethnicities V432Am Proximal penile Hemi  Kalfa et al. (2008b
     L121X Proximal penile, cryptorchidism Hemi  
      Penoscrotal Hemi de novo 
     p.531ins3Qn Coronal Hemi  
  99o 95 Q529K Severe, bilateral cryptorchidism Hemi  Chen et al. (2010
     D686D Hemi  
MID1 Xp22 114 95 E238X Penoscrotal, hypertelorism Hemi Mother heterozygous, brother has same mutation and phenotype, variant previously describeded in Opitz syndrome Zhang et al. (2011
     K560R Penoscrotal, hypertelorism Hemi  
INSL3 19p13.2-p12 94 270 Moroccan     El Houate et al. (2007
BNC2 9p22.2 48p 23 Different ethnicities A923V Distal Hetero Caucasian patient Bhoj et al. (2011
      Distal Hetero African-American patient 
     L414V Distal Hetero Caucasian patient 
     P306A Distal Hetero Caucasian patient 
     P579L Distal Hetero Caucasian patient 
     E240G, R283G and Q152R Distal Hetero for all variants Caucasian patient 
         
         

All studies included in this table screened patients with hypospadias for mutations in specific genes. Most studies checked whether mutations were present in healthy controls. The table includes only exonic (including 3’-UTR and splice acceptor site) mutations that were not found in healthy controls, were not previously reported polymorphisms and were not described as a polymorphism by the authors of the article. Results from functional analyses, either performed by the study reporting the mutation or performed by earlier studies and referred to by the study reporting the mutation, are included in the table. Most studies included patients with different degrees of hypospadias or information about phenotype was not reported. Most studies excluded syndromal patients, but did not exclude patients with cryptorchidism, micropenis, bifid scrotum or other associated anomalies, or information about associated anomalies was not reported. Most studies did not exclude patients with affected relatives or information about affected relatives was not reported. Family members carrying the same mutation were unaffected, unless indicated differently. n, number; hetero, heterozygous; homo, homozygous; hemi, hemizygous; PAIS, partial androgen insensitivity syndrome.

aOnly DSD (disorders of sex development) patients with severe penile to penoscrotal hypospadias included.

bSplice acceptor site.

cOnly patients with at least one affected relative included.

d3′-UTR.

eSynonymous variant, not mentioned in which amino acid.

fVariant is known as rs755793, but with allele frequency of 0% in Caucasians.

gOnly patients with severe hypospadias included.

hOnly patients without other genitourinary abnormalities included.

iOnly patients with severe hypospadias or a familial form included.

jOnly patients from families contributing most to a linkage peak in the vicinity of HSD17B3 included.

kPatients with cryptorchidism, intersex condition or endocrine abnormalities excluded.

lOnly patients with elevated testosterone/DHT ratios without mutations in AR or SRD5A2 included.

mVariant was later found in two more patients and in two controls (Chen et al., 2010).

nVariant was later found in three more patients and in one control (Chen et al., 2010).

oOnly sporadic patients included.

pOnly patients with distal hypospadias included.

Table II

Genetic association results for hypospadias.

Gene Locus SNP n cases n controls Controls Ethnicity Genotypes/alleles associated with increased risk (P < 0.05) Reference 
Early patterning stage of development 
FGF8 10q24 rs3218238 or rs3218233a 60b 96 Healthy voluntary blood donors Different ethnicities A allelec Beleza-Meireles et al. (2007c)d 
FGFR2 10q26 c.382+52→G 60b 96 Healthy voluntary blood donors Different ethnicities G allele of c.382+52 → Ge Beleza-Meireles et al. (2007c)d 
  c.550+27T>C     C/T allele of c.550+27T>Ce 
  c.727+180T>G     G allele of c.727+180T>Gc 
Masculinization stage of development 
AR Xq12 CAG repeat 78f 425 Anonymous females Longer repeat Lim et al. (2000
   21 100 Boys with short stature and normal external genitalia and fertile males Japanese No association Muroya et al. (2001
   51 210 Males from military service, no history of hypospadias or cryptorchidism Cases are Caucasian, controls have Swedish mothers No association Aschim et al. (2004b
   92 190 Fertile males Iranian No association Radpour et al. (2007
  GGN repeat 51 210 Males from military service, no history of hypospadias or cryptorchidism Cases are Caucasian, controls have Swedish mothers Longer repeatg Aschim et al. (2004b
   92 190 Fertile males Iranian Longer repeatg Radpour et al. (2007
FKBP4 12p13.33 rs1062478rs3021522 333 380 Voluntary blood donors Different ethnicities No association Beleza-Meireles et al. (2007a
         
HSD17B3 9q22 rs4743709 89h 291 Male newborns without malformations Japanese A allele of rs2066479 Sata et al. (2010
  rs2066476     AA genotype of rs2066479 
  rs2066474      
  rs2066480      
  rs2066479      
SRD5A2 2p23 rs9282858 81i 100+ Normal controls Different ethnicities T allele Silver and Russell (1999)j 
   rs523349 90 87 Normal males Chinese G allele Wang et al. (2004
       CG and GG genotypes 
   158 96 Unaffected persons Cases have different ethnicities, controls are Caucasian G alleleCG and GG genotypes Thai et al. (2005
        
   89h 281 Male newborns without malformations Japanese CG genotypek Sata et al. (2010
   620 596 Unaffected males Caucasian No association van der Zanden et al. (2010)l 
Other genes 
ESR1 6q25.1 rs6932902m 43 135 Boys with short stature and normal external genitalia and fertile males Japanese A alleleAA genotype Watanabe et al. (2007
        
   620 596 Unaffected males Caucasian A allele van der Zanden et al. (2010)l 
  TA repeat 90 94 Voluntary blood donors Different ethnicities No association Beleza-Meireles et al. (2006
  rs1801132      
  rs2234693 59h 286 Boys without malformations Japanese A allele of rs9340799 Ban et al. (2008
  rs9340799      
ESR2 14q23.2 CA repeat 90 94 Voluntary blood donors Different ethnicities Longer repeat Beleza-Meireles et al. (2006
   354 380 Healthy voluntary blood donors Different ethnicities Longer repeat Beleza-Meireles et al. (2007b
  rs1887994 354 380 Healthy voluntary blood donors Different ethnicities G allele of rs10483774 Beleza-Meireles et al. (2007b
  rs1256040     AG genotype of rs10483774 
  rs1256062      
  rs10483774      
  rs1271572      
  rs944050 90 94 Voluntary blood donors Different ethnicities AG genotypen Beleza-Meireles et al. (2006
   59h 286 Boys without malformations Japanese AG genotypeo Ban et al. (2008
   rs2987983 354 380 Healthy voluntary blood donors Different ethnicities G allele Beleza-Meireles et al. (2007b
       GG genotype 
   620 596 Unaffected males Caucasian AG genotypeo van der Zanden et al. (2010)l 
  rs1256049rs4986938 51 186 Control males from military service without genital anomalies and with sperm concentrations >5×106 spermatozoa/ml Cases are Caucasian, controls have Swedish parents No association Aschim et al. (2005
        
ATF3 1q32.3 rs11119982 330 380 Healthy voluntary blood donors Different ethnicities C allele Beleza-Meireles et al. (2008
       CC genotype 
   620 596 Unaffected males Caucasian T allele van der Zanden et al. (2010)l 
       TT and CT genotypes 
  rs2137424 330 380 Healthy voluntary blood donors Different ethnicities T allele of rs3125289 Beleza-Meireles et al. (2008
  rs3125289     TT genotype of rs3125289 
  rs1877474     T allele of rs1877474 
  rs10735510     TT genotype of rs1877474 
  rs9429889rs12070345rs10475     Strongest association for combination of risk alleles: rs3125289 (T), rs1877474 (T) and rs11119982 (C) 
MAMLD1 Xq28 rs61740566 370 380 Healthy voluntary blood donors No association Chen et al. (2010
  rs41313406 370 418 Male healthy voluntary blood donors T allele of rs41313406 Chen et al. (2010
  rs2073043     G allele of rs2073043 
DGKK Xp11.22 rs1934179 436p 449 Healthy control males Caucasian A allele of rs1934179 van der Zanden et al. (2011)r 
  rs7063116 133p 133 Mothersq  A allele of rs7063116 
   266p 402 Male healthy voluntary blood donors   
MID1 Xp22 rs16986145 366 405 Male controls A alleles Zhang et al. (2011
CYP1A1 15q24.1 31t 64 Mothers of boys without any malformation Japanese Heterozygous CYP1A1 genotypeo Kurahashi et al. (2005
GSTM1 1p13.3 Gene deletion      
GSTT1 22q11.23 Gene deletion      
CYP1A1 15q24.1 80 120 Age-matched boys Concomitant deletion of GSTM1 and GSTT1 Yadav et al. (2011
GSTM1 1p13.3 Gene deletion      
GSTT1 22q11.23 Gene deletion      
Gene Locus SNP n cases n controls Controls Ethnicity Genotypes/alleles associated with increased risk (P < 0.05) Reference 
Early patterning stage of development 
FGF8 10q24 rs3218238 or rs3218233a 60b 96 Healthy voluntary blood donors Different ethnicities A allelec Beleza-Meireles et al. (2007c)d 
FGFR2 10q26 c.382+52→G 60b 96 Healthy voluntary blood donors Different ethnicities G allele of c.382+52 → Ge Beleza-Meireles et al. (2007c)d 
  c.550+27T>C     C/T allele of c.550+27T>Ce 
  c.727+180T>G     G allele of c.727+180T>Gc 
Masculinization stage of development 
AR Xq12 CAG repeat 78f 425 Anonymous females Longer repeat Lim et al. (2000
   21 100 Boys with short stature and normal external genitalia and fertile males Japanese No association Muroya et al. (2001
   51 210 Males from military service, no history of hypospadias or cryptorchidism Cases are Caucasian, controls have Swedish mothers No association Aschim et al. (2004b
   92 190 Fertile males Iranian No association Radpour et al. (2007
  GGN repeat 51 210 Males from military service, no history of hypospadias or cryptorchidism Cases are Caucasian, controls have Swedish mothers Longer repeatg Aschim et al. (2004b
   92 190 Fertile males Iranian Longer repeatg Radpour et al. (2007
FKBP4 12p13.33 rs1062478rs3021522 333 380 Voluntary blood donors Different ethnicities No association Beleza-Meireles et al. (2007a
         
HSD17B3 9q22 rs4743709 89h 291 Male newborns without malformations Japanese A allele of rs2066479 Sata et al. (2010
  rs2066476     AA genotype of rs2066479 
  rs2066474      
  rs2066480      
  rs2066479      
SRD5A2 2p23 rs9282858 81i 100+ Normal controls Different ethnicities T allele Silver and Russell (1999)j 
   rs523349 90 87 Normal males Chinese G allele Wang et al. (2004
       CG and GG genotypes 
   158 96 Unaffected persons Cases have different ethnicities, controls are Caucasian G alleleCG and GG genotypes Thai et al. (2005
        
   89h 281 Male newborns without malformations Japanese CG genotypek Sata et al. (2010
   620 596 Unaffected males Caucasian No association van der Zanden et al. (2010)l 
Other genes 
ESR1 6q25.1 rs6932902m 43 135 Boys with short stature and normal external genitalia and fertile males Japanese A alleleAA genotype Watanabe et al. (2007
        
   620 596 Unaffected males Caucasian A allele van der Zanden et al. (2010)l 
  TA repeat 90 94 Voluntary blood donors Different ethnicities No association Beleza-Meireles et al. (2006
  rs1801132      
  rs2234693 59h 286 Boys without malformations Japanese A allele of rs9340799 Ban et al. (2008
  rs9340799      
ESR2 14q23.2 CA repeat 90 94 Voluntary blood donors Different ethnicities Longer repeat Beleza-Meireles et al. (2006
   354 380 Healthy voluntary blood donors Different ethnicities Longer repeat Beleza-Meireles et al. (2007b
  rs1887994 354 380 Healthy voluntary blood donors Different ethnicities G allele of rs10483774 Beleza-Meireles et al. (2007b
  rs1256040     AG genotype of rs10483774 
  rs1256062      
  rs10483774      
  rs1271572      
  rs944050 90 94 Voluntary blood donors Different ethnicities AG genotypen Beleza-Meireles et al. (2006
   59h 286 Boys without malformations Japanese AG genotypeo Ban et al. (2008
   rs2987983 354 380 Healthy voluntary blood donors Different ethnicities G allele Beleza-Meireles et al. (2007b
       GG genotype 
   620 596 Unaffected males Caucasian AG genotypeo van der Zanden et al. (2010)l 
  rs1256049rs4986938 51 186 Control males from military service without genital anomalies and with sperm concentrations >5×106 spermatozoa/ml Cases are Caucasian, controls have Swedish parents No association Aschim et al. (2005
        
ATF3 1q32.3 rs11119982 330 380 Healthy voluntary blood donors Different ethnicities C allele Beleza-Meireles et al. (2008
       CC genotype 
   620 596 Unaffected males Caucasian T allele van der Zanden et al. (2010)l 
       TT and CT genotypes 
  rs2137424 330 380 Healthy voluntary blood donors Different ethnicities T allele of rs3125289 Beleza-Meireles et al. (2008
  rs3125289     TT genotype of rs3125289 
  rs1877474     T allele of rs1877474 
  rs10735510     TT genotype of rs1877474 
  rs9429889rs12070345rs10475     Strongest association for combination of risk alleles: rs3125289 (T), rs1877474 (T) and rs11119982 (C) 
MAMLD1 Xq28 rs61740566 370 380 Healthy voluntary blood donors No association Chen et al. (2010
  rs41313406 370 418 Male healthy voluntary blood donors T allele of rs41313406 Chen et al. (2010
  rs2073043     G allele of rs2073043 
DGKK Xp11.22 rs1934179 436p 449 Healthy control males Caucasian A allele of rs1934179 van der Zanden et al. (2011)r 
  rs7063116 133p 133 Mothersq  A allele of rs7063116 
   266p 402 Male healthy voluntary blood donors   
MID1 Xp22 rs16986145 366 405 Male controls A alleles Zhang et al. (2011
CYP1A1 15q24.1 31t 64 Mothers of boys without any malformation Japanese Heterozygous CYP1A1 genotypeo Kurahashi et al. (2005
GSTM1 1p13.3 Gene deletion      
GSTT1 22q11.23 Gene deletion      
CYP1A1 15q24.1 80 120 Age-matched boys Concomitant deletion of GSTM1 and GSTT1 Yadav et al. (2011
GSTM1 1p13.3 Gene deletion      
GSTT1 22q11.23 Gene deletion      

Most studies were association studies with a case–control design. Most studies included patients with different degrees of hypospadias. Most studies excluded syndromal patients, but did not exclude patients with cryptorchidism, micropenis, bifid scrotum or other associated anomalies or information about associated anomalies was not reported. Most studies did not exclude patients with affected relatives or information about affected relatives was not reported. Deviations from these statements are included in the specified footnotes. n, number.

aThe SNP reported in the text was different from the SNP reported in the table.

bAll patients have at least one affected relative.

cThis SNP was found in a heterozygous form in three patients, while it was not found in controls.

dThis was not an association study, but a study screening FGF8 and FGFR2 for mutations.

eThese SNPs were found in heterozygous form in one patient, while they were not found in controls. For c.550+27T>C it is not clear whether T or C is the risk allele because the SNP reported in the text was different from the SNP reported in the table (c.550+27T>C and c.550+27C>T).

fUndermasculinized patients, most of them with perineoscrotal openings and unfused or partially fused scrotum.

gOnly penile patients have longer repeats.

hPatients with affected family members excluded.

iPatients with cryptorchidism, intersex condition or endocrine abnormalities excluded.

jThis was not an association study, but a study screening SRD5A2 for mutations. This SNP was found in homozygous form in two patients and in heterozygous form in three patients, while it was not found in controls. In another study, this SNP was found in 1 out of 37 patients, but as that study did not genotype controls to perform an association analysis, it was not included in the table (Thai et al., 2005).

kOnly associated with severe hypospadias.

lThis was an association study with a case–parent triad design analyzed using the transmission disequilibrium test.

mSNP tagged the ‘AGATA’ haplotype of rs926779, rs3020364, rs6932902, rs3020371 and rs3020375.

nAll six patients with this genotype had affected family members, and the SNP was inherited from the affected line twice.

oAssociated with decreased risk.

pOnly patients with anterior and middle hypospadias included.

qThis part of the study was an association study with a case–parent triad design analyzed using the transmission disequilibrium test, but as this in an X-chromosomal SNP, only mothers were taken into account.

rThis was a genome-wide association study with a case–control design, suggesting more associations with hypospadias than reported in this table.

sFour cases were familial. Two affected relatives carried the variant and one did not. Five of the nine cases with the variant had at least one parent born in North Africa, where the A allele is more prevalent.

tMothers of patients with hypospadias.

Indifferent stage

All genes involved in the development of the male external genitalia are obvious candidate genes for hypospadias. Because Wt1 and Sf1 play major roles in early embryonic development of the kidneys and the urogenital system, mutations in these genes are likely to cause not only hypospadias but also more severe defects. Indeed, SF1 mutations were found in severe penoscrotal hypospadias cases with cryptorchidism (Köhler et al., 2009), while a mutation in WT1 was described in a boy with penoscrotal hypospadias and micropenis and also in three boys with isolated penile or glandular hypospadias (Wang et al., 2004; Table I).

Early patterning

Genes involved in GT patterning are additional candidates for hypospadias. Mutation screening in hypospadias cases revealed mutations in BMP4, BMP7, HOXA4, HOXB6, FGF8 and the Fgf receptor FGFR2 (Chen et al., 2007; Beleza-Meireles et al., 2007c; Table I), while associations with hypospadias were also observed for polymophisms in FGF8 and FGFR2 (Beleza-Meireles et al., 2007c; Table II).

Masculinization

The expression of the SRY gene, located on the Y chromosome, is crucial for development of the testis from the indifferent gonad (Gubbay et al., 1990; Sinclair et al., 1990). Sex chromosome abnormalities were noticed in 4 out of 100 patients with hypospadias (Moreno-García and Miranda, 2002) but no mutations in SRY were found in 90 patients in another study (Wang et al., 2004). In addition, screening Yq for microdeletions in 44 cases did not reveal any abnormalities (Tateno et al., 2000) and neither did screening the segments of the Y chromosome associated with infertility in 20 cases with middle or posterior hypospadias and cryptorchidism (Castro et al., 2004).

Genetic research has been focused on the hormone-dependent stage of sexual development as well. The gene encoding AR in particular was investigated extensively. AR is expressed in the developing human penis and urethra (Kim et al., 2002) and several studies reported rare mutations in the gene encoding AR in patients with hypospadias (Hiort et al., 1994; Alléra et al., 1995; Sutherland et al., 1996; Nordenskjöld et al., 1999; Wang et al., 2004; Thai et al., 2005; Table I). In addition, polymorphisms in AR have been investigated for associations with the anomaly and may increase hypospadias risk. For example, the expansion of the polyglutamine (CAG) repeat in the N-terminus of AR, shown to decrease AR transactivation function (Chamberlain et al., 1994), was found to be associated with undermasculinization (Lim et al., 2000). Two studies reported that longer GGN repeat length increased the risk of penile hypospadias (Aschim et al., 2004b; Radpour et al., 2007) but these two (and one other) studies did not find an association between CAG repeat length and hypospadias (Muroya et al., 2001; Aschim et al., 2004b; Radpour et al., 2007; Table II). DHT binding capacity of the AR in genital skin fibroblasts was reported to be decreased in some patients with hypospadias (Schweikert et al., 1989; Alléra et al., 1995), whereas normal binding capacity was found in others (Gearhart et al., 1988; Terakawa et al., 1990). In addition, AR levels were similar in foreskin samples of hypospadias cases and controls (Bentvelsen et al., 1995).

Several proteins are needed for AR function. The FK506 binding protein 4, 59 kDa (FKBP4, also known as FKBP52), for example, is a component of AR complexes, enhancing AR-mediated transactivation (Cheung-Flynn et al., 2005). However, no differences in FKBP4 expression were noted between patients with hypospadias and controls and no mutations in FKBP4 were observed (Beleza-Meireles et al., 2007a).

As normal male urethral development requires testosterone and DHT, defects in steroidogenesis could also account for hypospadias. One article stated that up to 50% of patients with hypospadias have a testosterone biosynthesis defect (Aaronson et al., 1997), a conclusion that could not be confirmed in two other studies that found no enzymatic defects (Feyaerts et al., 2002; Holmes et al., 2004). Nevertheless, mutations have been found in hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 2 (HSD3B2; Codner et al., 2004) and SRD5A type II (SRD5A2; Silver and Russell, 1999; Wang et al., 2004; Thai et al., 2005).

The gene encoding SRD5A2 is particularly interesting because this enzyme is expressed during male genital development around the ventral part of the remodelling urethra and it converts testosterone to the more potent androgen DHT, which induces formation of the external genitalia (Kim et al., 2002). Two single nucleotide polymorphisms (SNPs) in this gene seemed to be associated with hypospadias in some but not all studies (Silver and Russell, 1999; Wang et al., 2004; Thai et al., 2005; Sata et al., 2010; van der Zanden et al., 2010; Table II). One of these SNPs (rs523349) causes a valine to leucine substitution (V89L), resulting in a decrease in enzyme activity by ∼30% (Makridakis et al., 1997, 2000), whereas the other SNP (rs9282858) results in an alanine to threonine replacement (A49T), which causes an increase in enzyme function (Makridakis et al., 2000). Another SNP that seems to be associated with hypospadias and to have functional consequences is rs2066479 in HSD17B3. The glycine to serine substitution (G289S) caused by this SNP results in reduced HSD17B3 mRNA expression levels in utero (Sata et al., 2010).

Other genes

Not only steroidogenesis but also the balance between androgens and estrogens appears to be important in the development of the male external genitalia. The ESRs, ESR1 and ESR2, are expressed in the developing human male GT (Crescioli et al., 2003) and associations have been reported between hypospadias and several SNPs in the genes encoding these receptors, as well as with the CA-repeat in ESR2 (Beleza-Meireles et al., 2006, 2007b; Watanabe et al., 2007; Ban et al., 2008; van der Zanden et al., 2010; Table II). One of the SNPs in ESR1, rs9340799, was shown to increase enhancer activity of ESR1 (Maruyama et al., 2000).

Some additional genes are also suggested to be involved in the development of hypospadias. Activating transcription factor 3 (ATF3) is an estrogen-responsive gene showing strong up-regulation in hypospadias patients (Liu et al., 2005; Wang et al., 2007; Kalfa et al., 2008a; Gurbuz et al., 2010). Studies focusing on the relation between this gene and hypospadias found mutations and associations with several SNPs (Beleza-Meireles et al., 2008; Kalfa et al., 2008a) but not all associations could be replicated (van der Zanden et al., 2010; Tables I and II). Recently, mastermind-like domain containing 1 (MAMLD1, previously known as CXorf6) was identified as a causal gene for hypospadias. MAMLD1 contains the SF1 target sequence (Fukami et al., 2008) and mutations and polymorphisms in MAMLD1 have been found in patients with hypospadias (Fukami et al., 2006; Kalfa et al., 2008b; Chen et al., 2010; Tables I and II). A recent genome-wide association study using pooled DNA samples identified diacylglycerol kinase, kappa (DGKK) as a major risk gene for hypospadias (van der Zanden et al., 2011). An intronic SNP was associated with a 2.5 times increased hypospadias risk, while DGKK expression in preputial skin was shown to be lower in boys carrying the risk allele. In the van der Zanden et al. (2011) study, additional candidate genes, i.e. peroxisome proliferator-activated receptor gamma, coactivator 1 beta (PPARGC1B), glutamate receptor, ionotropic, delta 1 (GRID1) and KIAA2022 were also identified but these still need to be confirmed. One study investigated MID1 in relation to hypospadias and found mutations in patients with hypospadias as well as a SNP in this gene to be associated with the disorder (Zhang et al., 2011; Tables I and II). Insulin-like 3 (INSL3) mutations have been found in patients with cryptorchidism but no alterations were detected in 94 hypospadias cases (El Houate et al., 2007; Table I).

Expression studies have also identified some candidate genes. Using prepuce samples of patients with hypospadias and controls, Wang et al. (2007) not only found ATF3 to be up-regulated in patients but also connective tissue growth factor (CTGF) and cysteine-rich, angiogenic inducer, 61 (CYR61), two other estrogen-responsive genes. In addition, epidermal growth factor (EGF) staining in prepuce showed lower expression of EGF within the penile skin adjacent to the urethra in patients with hypospadias compared with controls (el-Galley et al., 1997).

A balanced translocation in a man with hypospadias and other congenital anomalies indicated basonuclin 2 (BNC2) as a candidate gene. This gene is expressed in developing human periurethral tissue and mutations were found in 6 out of 48 patients with hypospadias but also in 2 out of 23 controls (Bhoj et al., 2011; Table I).

As exposure to environmental toxicants has also been suggested to cause hypospadias, and cytochrome P4501A1 (CYP1A1) and glutathione S-transferases (GSTM1 and GSTT1) are involved in the metabolism of various toxicants, two studies evaluated the effect of polymorphisms in the genes encoding these enzymes on hypospadias risk. One study found an association with hypospadias for concomitant deletion of GSTM1 and GSTT1 (Yadav et al., 2011; Table II). The other study investigated associations between maternal smoking, maternal SNPs in the genes and the risk of hypospadias in offspring. They found an association between a SNP in CYP1A1 and hypospadias, which was not modified by smoking behaviour (Kurahashi et al., 2005).

One genome-wide linkage analysis in 69 families with at least 2 members with hypospadias found suggestive linkage at 9q22, 2p11, 10p15 and 10q21 (Frisen et al., 2004), while another linkage study in a three-generational family showing autosomal dominant inheritance of hypospadias found a peak on 7q32.2–q36.1 (Thai et al., 2008). Mutation analysis of two genes in this region, AKRID1 and PTN, failed to reveal any mutations (Thai et al., 2008).

Screening 17 isolated patients with hypospadias and 12 patients with associated anomalies for copy number variants (CNVs) revealed clinically significant CNVs in 3 patients with isolated hypospadias (5p15, 12p13 and Xq28) and in 2 patients with an associated anomaly, which were cryptorchidism (2q22) and cleft palate (16p11; Tannour-Louet et al., 2010).

The role of environmental factors in the aetiology of hypospadias

Introduction

While genes involved in the aetiology of hypospadias have received a considerable amount of attention, research on environmental factors has been even more extensive. Despite the large number of studies, however, clear evidence for causal environmental factors is still lacking, although some consistent associations have been reported. Table III gives a summary of environmental factors investigated in relation to hypospadias.

Table III

Clinical, behavioural, occupational and environmental factors investigated for their association with hypospadias in more than one study.

Factors frequently investigated 
Factors with consistent results in all studies 
 Factors consistently associated with hypospadias  Factors consistently not associated with hypospadias 
  Low birthweight/being small for gestational age   Gestational diabetes 
  Placental insufficiency   Maternal alcohol consumption 
  Maternal hypertension  
  Pre-eclampsia  
  Maternal intrauterine DES exposure  
Factors with consistent results in most studies 
 Factors associated with hypospadias in most studies  Factors not associated with hypospadias in most studies 
  Use of ICSI   Use of oral contraceptives during pregnancy 
  Prolonged TTP   Use of IVF 
  High maternal BMI   Use of hormonal stimulation to induce pregnancy 
  Primiparity   Maternal medication use: loratadine Maternal folate supplementation Paternal age Maternal smoking Maternal exposure to water disinfection by-products 
  Multiple pregnancy Pre-existing maternal diabetes Maternal medication use: anti-epileptic drugs 
Factors showing inconsistent results 
 Preterm delivery  Maternal occupational exposure to: 
 Maternal iron supplementation   Endocrine disruptors 
 Maternal age   Heavy metals 
 Maternal vegetarian diet   Phthalates 
 Maternal fish consumption  Maternal serum levels of PCBs 
 Maternal and paternal exposure to pesticides  Seasonal trend 
Factors not frequently investigated 
 Factors that seem to be associated with hypospadias  Factors that do not seem to be associated with hypospadias 
  Paternal subfertility   Amount of weight gain during pregnancy 
  Absence of nausea and vomiting in early pregnancy   Maternal medication use: corticosteroids and antibiotics Most maternal and paternal occupational exposures 
  Bleeding during pregnancy 
  Complications during labour 
  Maternal medication use: antihypertensive drugs  
  Father being a vehicle mechanic or manufacturer  
Factors showing inconsistent results 
 Early age at menarche  Use of progestogens/progestins for threatened abortion 
 Maternal thyroid disease  Paternal occupational exposure to heavy metals 
 Fever during first trimester of pregnancy  Living in rural or urban areas 
Factors frequently investigated 
Factors with consistent results in all studies 
 Factors consistently associated with hypospadias  Factors consistently not associated with hypospadias 
  Low birthweight/being small for gestational age   Gestational diabetes 
  Placental insufficiency   Maternal alcohol consumption 
  Maternal hypertension  
  Pre-eclampsia  
  Maternal intrauterine DES exposure  
Factors with consistent results in most studies 
 Factors associated with hypospadias in most studies  Factors not associated with hypospadias in most studies 
  Use of ICSI   Use of oral contraceptives during pregnancy 
  Prolonged TTP   Use of IVF 
  High maternal BMI   Use of hormonal stimulation to induce pregnancy 
  Primiparity   Maternal medication use: loratadine Maternal folate supplementation Paternal age Maternal smoking Maternal exposure to water disinfection by-products 
  Multiple pregnancy Pre-existing maternal diabetes Maternal medication use: anti-epileptic drugs 
Factors showing inconsistent results 
 Preterm delivery  Maternal occupational exposure to: 
 Maternal iron supplementation   Endocrine disruptors 
 Maternal age   Heavy metals 
 Maternal vegetarian diet   Phthalates 
 Maternal fish consumption  Maternal serum levels of PCBs 
 Maternal and paternal exposure to pesticides  Seasonal trend 
Factors not frequently investigated 
 Factors that seem to be associated with hypospadias  Factors that do not seem to be associated with hypospadias 
  Paternal subfertility   Amount of weight gain during pregnancy 
  Absence of nausea and vomiting in early pregnancy   Maternal medication use: corticosteroids and antibiotics Most maternal and paternal occupational exposures 
  Bleeding during pregnancy 
  Complications during labour 
  Maternal medication use: antihypertensive drugs  
  Father being a vehicle mechanic or manufacturer  
Factors showing inconsistent results 
 Early age at menarche  Use of progestogens/progestins for threatened abortion 
 Maternal thyroid disease  Paternal occupational exposure to heavy metals 
 Fever during first trimester of pregnancy  Living in rural or urban areas 
Testicular dysgenesis syndrome

In 2001, Skakkebæk et al. (2001) suggested that poor sperm quality, testicular cancer, undescended testes and hypospadias are symptoms of one underlying entity, the testicular dysgenesis syndrome (TDS). They were convinced of its existence because countries with high incidences of testicular cancer also had high prevalence rates of hypospadias, cryptorchidism and poor sperm quality (Virtanen et al., 2005). Other researchers question whether TDS actually exists as there is little evidence of shared causes (Akre and Richiardi, 2009), only a few patients display all features, and incidences of the four components of the syndrome did not increase over time at the same rate (Thorup et al., 2010). Although testicular germ cell cancer risk was increased in patients with hypospadias or undescended testis, risk was not increased in their family members. This does not support the hypothesis of shared heritability (Schnack et al., 2010). Recently, Skakkebæk et al. concluded that TDS does exist but that it encompasses only a fraction of hypospadias and impaired spermatogenesis cases (Jørgensen et al., 2010).

Estrogen hypothesis

In 1993, Sharpe and Skakkebæk (1993) hypothesized that the increasing incidence of reproductive abnormalities in males may have a common cause, namely increased estrogen exposure in utero, leading to disturbances in AMH secretion or impairment of Leydig cell development. Ten years after the introduction of this hypothesis, Sharpe (2003) concluded that evidence for fetal estrogen exposure inducing TDS had strengthened. New pathways were identified through which estrogens could induce TDS, including the suppression of testosterone production, AR expression and insulin-like 3 secretion. Whether increased estrogen exposure will turn out to be an important aetiological factor for TDS is not so certain, however.

The initial ‘estrogen hypothesis’ was superseded by a more refined definition of endocrine-disrupting chemicals (EDCs), suggesting that chemicals may act on the endocrine systems in a plethora of ways (Fisher, 2004). In 2008, Sharpe and Skakkebæk (2008) highlighted the central role of deficient androgen production or action during fetal testis development in the origin of the downstream disorders of TDS. However, the question remains whether levels of exposure to EDCs are sufficient to influence male reproductive health (Fisher, 2004) and several reviews concluded that there is little evidence for a role of environmental EDCs (Raman-Wilms et al., 1995; Chia, 2000; Safe, 2000; Vidaeff and Sever, 2005; Storgaard et al., 2006; Martin et al., 2008).

Exogenous exposure to estrogens

Oral contraceptives

Although oral contraceptives probably provide the strongest estrogen exposure that humans can experience, an association between hypospadias and use of oral contraceptives for some time during pregnancy was not found in most studies (Morera et al., 2006; Wogelius et al., 2006; Brouwers et al., 2007, 2010; Akre et al., 2008; Nørgaard et al., 2009).

Assisted reproductive technology

Assisted reproductive technologies (ARTs) frequently involve hormonal stimulation and some studies showed an increased risk of hypospadias with ART (Brouwers et al., 2007, 2010; Carmichael et al., 2007). More specifically, ICSI increased hypospadias risk in most (Wennerholm et al., 2000; Ericson and Källén, 2001; Pinborg et al., 2004; Källén et al., 2005; Fedder et al., 2007; Funke et al., 2010) but not all studies (Bonduelle et al., 2002; Källén et al., 2010), whereas studies on IVF did not report increased risks or were inconclusive (Ericson and Källén, 2001; Bonduelle et al., 2002; Morera et al., 2006; Funke et al., 2010; Källén et al., 2010), except for one study that did not report whether ICSI was excluded (Silver et al., 1999). In one study, increased hypospadias risk was associated with hormonal stimulation (Carmichael et al., 2005a) but this was not confirmed in other studies (Källén et al., 2002; Sørensen et al., 2005b; Meijer et al., 2006; Morera et al., 2006).

Other authors assumed that the increased hypospadias risk may be explained by reduced maternal or paternal fertility. Fathers of hypospadias cases were reported to have lower sperm concentration, sperm count (Asklund et al., 2007) and sperm motility, as well as a higher proportion of abnormal sperm morphology (Fritz and Czeizel, 1996). In addition, several studies reported a prolonged time-to-pregnancy (TTP) for parents of patients with hypospadias (Källén, 2002; Pierik et al., 2004; Asklund et al., 2007; Brouwers et al., 2010) and only one study did not confirm these results (Akre et al., 1999). The fact that ICSI, rather that IVF, and sperm quality are associated with hypospadias supports the idea that paternal fertility problems in particular play a role in hypospadias (Brouwers et al., 2007, 2010).

ART may be associated with genomic imprinting disorders (Laprise, 2009). This possible interference with epigenetic regulation is another mechanism by which ART could increase hypospadias risk. A very recent study indicated that alterations in the methylation pattern of AR, leading to abnormal expression of the gene in foreskin tissue from patients, may contribute to the development of hypospadias (Vottero et al., 2011).

Endogenous hormone levels

Endogenous estradiol levels

Endogenous levels of free estradiol increase with increasing BMI and are elevated in women with an early age at menarche (Apter and Vihko, 1983; Emaus et al., 2008). Several studies found associations between hypospadias and mothers being overweight (25 ≤ BMI < 30 kg/m2; Waller et al., 2007) or severely overweight or obese (BMI > 29 or 30 kg/m2; Waller et al., 2007; Akre et al., 2008; Blomberg and Källén, 2010; Giordano et al., 2010) but one study did not (Brouwers et al., 2010). Another study found increased risks for underweight but not for overweight or obese women (Rankin et al., 2010). The results for early age at menarche were inconsistent (Morera et al., 2006; Giordano et al., 2010). Estradiol levels are also higher in first pregnancies and twin pregnancies (Kappel et al., 1985; Bernstein et al., 1986), which were both repeatedly investigated for their association with hypospadias. Most studies showed that women in their first pregnancy (Akre et al., 1999; Weidner et al., 1999; Hussain et al., 2002; Källén, 2002; Carmichael et al., 2003, 2007; Aschim et al., 2004a; Sørensen et al., 2005a; Meyer et al., 2006; Morera et al., 2006; Nassar et al., 2010; Jin et al., 2010) or with a twin or triplet pregnancy (Akre et al., 1999; Fredell et al., 2002b; Morera et al., 2006; Brouwers et al., 2007, 2010; Carmichael et al., 2007; Sun et al., 2009; Funke et al., 2010; Jin et al., 2010; Nassar et al., 2010) were at increased risk of having a son with hypospadias but a few studies could not replicate the findings for primiparity or for multiple pregnancies (Weidner et al., 1999; Carmichael et al., 2003; Aschim et al., 2004a; Sørensen et al., 2005a; Ghirri et al., 2009). The latter may be caused by overadjustment for birthweight in some studies. As only early-onset intrauterine growth restriction (IUGR) could be a risk factor for hypospadias, it is more likely that low birthweight and hypospadias share an underlying cause rather than low birthweight being a risk factor for hypospadias.

Fetal hCG provision

Placental hCG stimulates fetal testicular steroidogenesis before the fetus's own pituitary–gonadal axis is established. Placental insufficiency may result in inadequate fetal hCG provision and IUGR, possibly explaining the association between hypospadias and low birthweight or being small for gestational age (SGA) that was consistently reported, although not always statistically significant (Akre et al., 1999, 2008; Weidner et al., 1999; Gatti et al., 2001; Fredell et al., 2002b; Hughes et al., 2002; Hussain et al., 2002; Carmichael et al., 2003; Aschim et al., 2004a; Pierik et al., 2004; Boisen et al., 2005; Chong et al., 2006; Morera et al., 2006; Brouwers et al., 2007, 2010; Giordano et al., 2008; Ghirri et al., 2009; Sun et al., 2009; Funke et al., 2010; Giordano et al., 2010; Jin et al., 2010; Nassar et al., 2010). However, because hCG levels were similar in maternal serum samples of hypospadias cases and controls, this is unlikely to be related to decreased maternal hCG production (Kiely et al., 1995). IUGR was also found more often in the affected twin of same-sex twin pairs discordant for hypospadias (Fredell et al., 1998; Chambers et al., 2006). Direct proof of a link between placental insufficiency and hypospadias was provided by research showing an association between hypospadias and low placental weight (Stoll et al., 1990), an increased frequency of placental infarction among extremely low birthweight boys with hypospadias (Fujimoto et al., 2008) and a high rate of early-onset IUGR related to placental insufficiency among SGA newborns with hypospadias, with the more posterior cases having more severe IUGR (Yinon et al., 2010). The association with low birthweight also seems to be stronger for more posterior forms of hypospadias (Carmichael et al., 2003; Carlson et al., 2009; Ghirri et al., 2009; Brouwers et al., 2010).

Nausea in early pregnancy may be caused by the early surge of hCG (Furneaux et al., 2001), suggesting that placental insufficiency may cause absence of nausea. Indeed, vomiting and nausea during early pregnancy were shown to decrease hypospadias risk (Carmichael et al., 2007; Akre et al., 2008). Maternal hypertension during pregnancy (Morera et al., 2006; Akre et al., 2008; Caton et al., 2008; Sun et al., 2009; Brouwers et al., 2010) and pre-eclampsia (Akre et al., 1999; Aschim et al., 2004a; Sørensen et al., 2005a; Chong et al., 2006; Morera et al., 2006; Sun et al., 2009; Brouwers et al., 2010) were consistently associated with hypospadias, and both factors may be associated with placental dysfunction, possibly by compromising uteroplacental perfusion (Caton et al., 2008). Preterm delivery may be associated with late placental dysfunction and several studies demonstrated an association with hypospadias (Pierik et al., 2004; Meyer et al., 2006; Akre et al., 2008; Sun et al., 2009; Funke et al., 2010; Giordano et al., 2010; Jin et al., 2010; Nassar et al., 2010; Akin et al., 2011) while others could not confirm this (Akre et al., 1999; Weidner et al., 1999; Carmichael et al., 2003; Aschim et al., 2004a; Chong et al., 2006; Ghirri et al., 2009), again possibly because of overadjustment for birthweight in some studies.

Clinical factors

Pregnancy complications

In a few studies, associations were investigated between hypospadias and complications during pregnancy, such as maternal bleeding, which seemed to be more prevalent among cases (Aschim et al., 2004a; Jin et al., 2010). The amount of weight gain was not associated with hypospadias (Meyer et al., 2006; Morera et al., 2006). Complications during labour, such as labour induction and Caesarean section, occurred more frequently among mothers of hypospadias cases (Aschim et al., 2004a; Meyer et al., 2006), indicating that pregnancies affected by hypospadias are associated with other difficulties that make them prone to these complications. Diabetes has been another focus of research, but most studies were too small to draw conclusions (Hussain et al., 2002; Sørensen et al., 2005a; Morera et al., 2006; Sun et al., 2009; Brouwers et al., 2010). One study found maternal gestational and pre-existing diabetes not to be associated with occurrence of hypospadias (Aschim et al., 2004a), whereas others reported an increased risk for pre-existing but not for gestational diabetes (Åberg et al., 2001; Porter et al., 2005). Results were inconsistent for thyroid disease (Aschim et al., 2004a; Browne et al., 2009) and fever during pregnancy (Stoll et al., 1990; Jin et al., 2010). Women with gynaecological diseases (ovarian cysts or benign uterine tumours; Giordano et al., 2008), those who are carriers of hepatitis B antigen (Sun et al., 2009) and women experiencing a viral infection or influenza in the first trimester of pregnancy (North and Golding, 2000; Morera et al., 2006) seem to be at increased risk of giving birth to a son with hypospadias but evidence was derived from only one study. Urinary infections and anaemia do not seem to increase hypospadias risk (Aschim et al., 2004a).

Maternal drug use

Most therapeutic drugs, such as corticosteroids, antibiotics, antipsychotics, antifungal and anti-asthmatic drugs, do not seem to be associated with hypospadias, although some studies may suffer from under reporting (Czeizel and Rockenbauer, 1997; Czeizel et al., 2001; Brouwers et al., 2007, 2010; Källén and Otterblad, 2007; Carter et al., 2008; Carmichael et al., 2009a). Based on data from the Swedish Medical Birth Register 1995–2001, Källén and Olausson (2001) reported 15 hypospadias cases in 2780 infants born after maternal use of loratadine, an antihistamine, during pregnancy but in 2001–2004 only two cases were identified among 1911 infants exposed to loratadine, indicating that the primary finding occurred by chance (Källén and Olausson, 2006). Other studies also failed to find an association between loratadine and hypospadias (CDC, 2004; Pedersen et al., 2008). The results for progestogens/progestins used for threatened abortion vary (Katz et al., 1985; Calzolari et al., 1986). The use of loperamide (Källén et al., 2008), antiretroviral therapy (Watts et al., 2007), antihypertensive drugs (Caton et al., 2008; Brouwers et al., 2010), nystatin (Czeizel et al., 2003) or paroxetine (Reis and Källén, 2010) during early pregnancy may increase hypospadias risk, while codeine (North and Golding, 2000) may decrease the risk but most of these associations were reported only once. In contrast, the use of anti-epileptic drugs was linked to hypospadias several times (Arpino et al., 2000; Hunt et al., 2008; Rodríguez-Pinilla et al., 2008; Jentink et al., 2010; Bánhidy et al., 2011). Most studies showed no effects of folate (Källén, 2007; Carmichael et al., 2009b; Brouwers et al., 2010) or iron supplementation (Morera et al., 2006; Brouwers et al., 2010) on hypospadias risk, although one study showed a reduced risk of folate (Ormond et al., 2009) and two others an increased risk of iron supplementation (North and Golding, 2000; Brouwers et al., 2007).

Maternal intrauterine DES exposure

In 2002, Klip et al. (2002) reported a 21 times increased hypospadias risk among sons of women exposed to diethylstilbestrol (DES) in utero in a cohort of women with fertility problems. Thereafter, other studies were consistent in showing an increased risk for sons of DES daughters, although less strong (Palmer et al., 2005; Pons et al., 2005; Brouwers et al., 2006, 2010). This transgenerational effect may have been related to genetic or epigenetic changes in primordial oocytes, which were transmitted to the next generation, or in somatic cells of the DES daughter, resulting in disturbed hormonal balance in adult life (Klip et al., 2002). Another explanation would be that pathology of the DES daughter's reproductive structures interferes with normal fetal development (Brouwers et al., 2006).

Behavioural factors

Parental age

Women become pregnant at different ages but, overall, maternal and paternal age at the time of conception did not seem to increase the risk of having a son with hypospadias (Akre et al., 1999, 2008; Weidner et al., 1999; Hussain et al., 2002; Källén, 2002; Aschim et al., 2004a; Sørensen et al., 2005a; Meyer et al., 2006; Morera et al., 2006; Brouwers et al., 2007, 2010; Ghirri et al., 2009; Lund et al., 2009; Materna-Kiryluk et al., 2009; Sun et al., 2009; Nassar et al., 2010). However, some studies reported a higher maternal age (Fisch et al., 2001; Hussain et al., 2002; Carmichael et al., 2003, 2007; Reefhuis and Honein, 2004; Porter et al., 2005; Fisch et al., 2009; Akin et al., 2011) or lower or higher paternal age (McIntosh et al., 1995; Materna-Kiryluk et al., 2009) to increase hypospadias risk.

Maternal diet

In 2000, North and Golding (2000) reported a five times increased risk of a hypospadias-affected son for women with a vegetarian diet, a finding that was confirmed in one study (Akre et al., 2008) but not in others (Brouwers et al., 2007, 2010; Ormond et al., 2009). However, all of these results were based on case–control studies with relatively few exposed cases and controls (<15) except for a study in England reporting no association in >75 cases and >90 controls who were vegetarian (Ormond et al., 2009). The suggestion that an increased risk might be related to intake of phytoestrogens was refuted by a small study involving phytoestrogen-specific questionnaires that did not find an association (Pierik et al., 2004). Another dietary factor found to be associated with hypospadias in two small studies is the frequent consumption of fish, possibly associated with the bioaccumulation of contaminants in fish (Giordano et al., 2008, 2010). However, a larger case–control study found a decreased hypospadias risk for frequent fish consumption (Akre et al., 2008).

Other lifestyle factors

Alcohol consumption during pregnancy was consistently found not to be associated with hypospadias (Hussain et al., 2002; Meyer et al., 2006; Brouwers et al., 2007). For maternal smoking, most studies showed no association (Akre et al., 1999, 2008; Hussain et al., 2002; Källén, 2002; Carmichael et al., 2005b; Meyer et al., 2006; Morera et al., 2006; Brouwers et al., 2007, 2010). One small study found maternal cocaine use to be associated with hypospadias (Battin et al., 1995).

Occupational factors

Exposure to pesticides

Occupational exposures have been a major focus in hypospadias research, especially exposure to pesticides, with contradicting results. Paternal exposure to pesticides before pregnancy does not seem to be associated with hypospadias (Weidner et al., 1998; Brouwers et al., 2007, 2010; Nassar et al., 2010), although one small study reported a possibly increased risk (Giordano et al., 2008). In addition, an increased risk was found among farmers who were indicated as exposed to pesticides in a register-based study (Kristensen et al., 1997). Most studies showed no association with maternal occupational exposure to pesticides (Weidner et al., 1998; Vrijheid et al., 2003; Brouwers et al., 2007, 2010; Nassar et al., 2010; Morales-Suárez-Varela et al., 2011) but being involved in agricultural activities (Sun et al., 2009) or using insect repellents (Dugas et al., 2010) seemed to increase hypospadias risk in two studies. Maternal serum levels of dichlorodiphenyltrichloroethane and dichlorodiphenyldichloroethane during pregnancy were not associated with hypospadias (Longnecker et al., 2002; Bhatia et al., 2005) but maternal serum hexachlorobenzene concentrations ∼1 year after birth were more often above the median of all subjects among hypospadias cases than among controls (Giordano et al., 2010).

Other occupational exposures

Boys conceived to mothers employed in the leather industry (García and Fletcher, 1998) and post-war to mothers who served in the Gulf war (Araneta et al., 2003) seemed to have a higher prevalence of hypospadias. Most other maternal occupational exposures were not associated with hypospadias, although results for EDCs, heavy metals and phthalates vary, while exposure to hairspray increased the risk in one study (Vrijheid et al., 2003; Brouwers et al., 2007, 2010; Ormond et al., 2009; Giordano et al., 2010; Nassar et al., 2010; Morales-Suárez-Varela et al., 2011). For fathers, being a vehicle mechanic or manufacturer (Schnitzer et al., 1995; Irgens et al., 2000), police officer or fire fighter (Schnitzer et al., 1995) and occupational exposure to dusts from grinding metals (Brouwers et al., 2010) seemed to increase the risk of having a son with hypospadias. Results on heavy metals vary (Nassar et al., 2010; Morales-Suárez-Varela et al., 2011) but most other paternal occupational exposures were not associated with hypospadias (Brouwers et al., 2007, 2010; Nassar et al., 2010; Morales-Suárez-Varela et al., 2011).

Living environment

Results on living in rural or (sub)urban areas are contradictory (Sun et al., 2009; Nassar et al., 2010), whereas living close to a landfill site seemed to be associated with an increased hypospadias risk (Dolk et al., 1998). Maternal serum levels of polychlorinated biphenyls (PCBs) were elevated during pregnancies affected by hypospadias in two small studies but these results were not statistically significant (Carmichael et al., 2010; Giordano et al., 2010). Another study found marginally increased PCB levels in serum samples of women pregnant with a hypospadias-affected son, but the study samples were collected in the 1960s, when PCB exposure was substantially higher than nowadays (McGlynn et al., 2009). Maternal exposure to water disinfection by-products was also suggested to increase hypospadias risk but most studies provided little evidence for this association (Källén and Robert, 2000; Luben et al., 2008; Iszatt et al., 2011).

In one study, the prevalence of hypospadias seemed to be higher in areas of intensive pesticide use or in agricultural areas (Morera et al., 2006). Another study showed an increased risk of hypospadias for living in an area where diclofop-methyl was applied but a decreased risk for alachlor and permethrin, or for pesticide application in aggregate (Meyer et al., 2006).

In some older studies, a seasonal trend for hypospadias was identified (Wehrung and Hay, 1970; Roberts and Lloyd, 1973; Avellan, 1977), which was attributed to factors such as hours of daylight, climate or temperature, whereas more recent studies did not find seasonal variation (Skriver et al., 2004; Morera et al., 2006; Jin et al., 2010).

Conclusion

Most hypospadias cases have an unknown aetiology, which is likely to be a mix of monogenic and multifactorial forms, implicating both genes and environmental factors. Several mutations have been found that might cause hypospadias but most investigators are convinced that single mutations are not likely to be the cause for the majority of isolated hypospadias cases. Neverteheless, studies screening patients with hypospadias for single-gene defects found mutations in the genes WT1, SF1, BMP4, BMP7, HOXA4, HOXB6, FGF8, FGFR2, AR, HSD3B2, SRD5A2, ATF3, MAMLD1, MID1 and BNC2. Association studies found polymorphisms in FGF8, FGFR2, AR, HSD17B3, SRD5A2, ESR1, ESR2, ATF3, MAMLD1, DGKK, MID1, CYP1A1, GSTM1 and GSTT1 to be risk factors for hypospadias. In addition, gene expression studies indentified CTGF, CYR61 and EGF as candidate genes.

Additional evidence for the involvement of genes can be derived from syndromes commonly associated with hypospadias, which were not reviewed in this article. For example, additional evidence for the involvement of WT1 comes from the fact that WT1 mutations cause syndromes such as Denys-Drash and Frasier syndromes, characterized by progressive nephropathy, intersex and predisposition to develop genitourinary tumours (Morrison et al., 2008). Male cases having hypospadias were reported for both syndromes (Sherbotie et al., 2000; Melo et al., 2002; Kaltenis et al., 2004). Syndromes which are commonly associated with hypospadias can also help in the indentification of new candidate genes. One example is hand–foot–genital syndrome, which is caused by mutations in HOXA13 (Mortlock and Innis, 1997; Goodman and Scambler, 2001). Hoxa13 mutant mice also exhibited hypospadias (Morgan et al., 2003) and expansion of a polyalanine tract in HOXD13 found in synpolydactyly families also seems to be associated with hypospadias (Goodman et al., 1997; Tüzel et al., 2007). Mutations in zinc finger E-box binding homeobox 2 (ZEB2) cause Mowat–Wilson syndrome, which is associated with hypospadias in >50% of affected males (Mowat et al., 2003; Zweier et al., 2005; Adam et al., 2006; Garavelli and Mainardi, 2007; Garavelli et al., 2009).

Additional candidate genes for hypospadias aetiology include genes for which mutations were described in case reports, such as CYP11A1 (Rubtsov et al., 2009), CYP17A1 (Sherbet et al., 2003) and HSD17B3 (Lee et al., 2007).

Animal studies also provide some additional candidate genes, such as the genes encoding the cell-surface molecules ephrins and their receptors, EPH receptor B2 (EphB2) and Ephrin-B2 (Efnb2; Lorenzo et al., 2003; Dravis et al., 2004). EFNB2 has been suggested as the gene underlying genital malformations in patients with a 13q33–34 deletion (Garcia et al., 2006; Walczak-Sztulpa et al., 2008; Andresen et al., 2010).

In conclusion, many candidate genes have been suggested for hypospadias. Although some associations with hypospadias were found, none of these associations were replicated consistently, with the possible exception of DGKK. Therefore, we suggest that a genome-wide association study using individual genotyping of a large group of cases and controls is the way forward to generate more knowledge about the genetic factors underlying isolated hypospadias. In addition, the novel exome or even whole-genome sequencing techniques generate new opportunities. Currently, the high costs make these techniques only suitable for identification of causes of monogenic forms of hypospadias but with falling prices, the techniques may also be applied to large cohorts of patients with isolated hypospadias in the future.

As for environmental factors, the development of the male external genitalia is dependent on the balance between androgens and estrogens. The fact that maternal exposure to synthetic estrogens can induce hypospadias in murine models (Kim et al., 2004) and that antiandrogens acting as inhibitors of steroid hormone synthesis or AR antagonists can induce male reproductive abnormalities in animal models (Gray et al., 2001) suggests that EDCs have the potential to induce hypospadias. However, because of considerable species differences and markedly different estrogen levels in human compared with rodent pregnancy, it is debatable whether EDCs also induce hypospadias in humans. Phthalates inhibit steroidogenesis in the fetal rat testis but this does not occur in vitro with human fetal Leydig cells (van Gelder et al., 2010). The question remains as to whether exposure levels in humans are high enough to exert an effect on the occurrence of hypospadias. Given that even exposures to high levels of exogenous hormones, such as in case of hormonal stimulation used to induce pregnancy and use of oral contraceptives for some time while pregnant, do not show consistent associations with hypospadias, we suggest that exogenous hormones and EDCs may not be as important in the aetiology of hypospadias as has previously been assumed.

The consistent association of hypospadias with low birthweight, maternal hypertension and pre-eclampsia suggests that placental insufficiency may be a major risk factor for hypospadias, possibly through inadequate provision of hCG to the fetus. A role for endogenous hormones is suggested by free estradiol levels linked to high maternal BMI, primiparity and multiple pregnancies that appear to contribute to susceptibility to hypospadias.

In addition, maternal intrauterine DES exposure, use of anti-epileptic drugs, pre-existing diabetes, prolonged TTP and pregnancies resulting from ICSI have been associated with hypospadias in most studies. Other potential environmental risk factors were not, or not consistently, associated with hypospadias or studied too infrequently to draw conclusions.

In our opinion, the lack of replication of results for both genetic and environmental factors associated with hypospadias may be related to subtle isolated effects of factors that may have larger influences in combination with other factors (e.g. gene–gene or gene–environment interactions). While a different genetic background of a population may affect its vulnerability to an environmental exposure, different environmental exposures may influence the effect of a genotype. Therefore, we think that the challenges for future research in disentangling the pathogenesis of hypospadias mainly lie in studies focussing on gene–gene or gene–environment interactions.

Authors' roles

L.v.d.Z. performed the literature search and selected the relevant articles. I.v.R and N.R. contributed to the appraisal of the epidemiological manuscripts and the inclusion or exclusion of these articles, whereas B.F. and N.K. assisted with the interpretation of the genetic studies and W.F. helped with understanding the embryology. L.v.d.Z. took primary responsibility for drafting the manuscript with intellectual contributions, editing and approval from all other authors.

Funding

This research is performed within a PhD project supported by the Radboud University Nijmegen Medical Centre.

Conflict of interest

None declared.

References

Aaronson
IA
Cakmak
MA
Key
LL
Defects of the testosterone biosynthetic pathway in boys with hypospadias
J Urol
 , 
1997
, vol. 
157
 (pg. 
1884
-
1888
)
Abdullah
NA
Pearce
MS
Parker
L
Wilkinson
JR
Jaffray
B
McNally
RJQ
Birth prevalence of cryptorchidism and hypospadias in northern England, 1993–2000
Arch Dis Child
 , 
2007
, vol. 
92
 (pg. 
576
-
579
)
Åberg
A
Westbom
L
Källén
B
Congenital malformations among infants whose mothers had gestational diabetes or preexisting diabetes
Early Hum Dev
 , 
2001
, vol. 
61
 (pg. 
85
-
95
)
Adam
MP
Schelley
S
Gallagher
R
Brady
AN
Barr
K
Blumberg
B
Shieh
JTC
Graham
J
Slavotinek
A
Martin
M
, et al.  . 
Clinical features and management issues in Mowat-Wilson syndrome
Am J Med Genet A
 , 
2006
, vol. 
140
 (pg. 
2730
-
2741
)
Ahmed
SF
Dobbie
R
Finlayson
AR
Gilbert
J
Youngson
G
Chalmers
J
Stone
D
Prevalence of hypospadias and other genital anomalies among singleton births, 1988–1997, in Scotland
Arch Dis Child Fetal Neonatal Ed
 , 
2004
, vol. 
89
 (pg. 
F149
-
F151
)
Aho
M
Koivisto
AM
Tammela
TLJ
Auvinen
A
Is the incidence of hypospadias increasing? Analysis of Finnish hospital discharge data 1970–1994
Environ Health Perspect
 , 
2000
, vol. 
108
 (pg. 
463
-
465
)
Akin
Y
Ercan
O
Telatar
B
Tarhan
F
Comert
S
The incidence and risk factors of hypospadias: a study from Istanbul
Pediatr Int
 , 
2011
, vol. 
53
 (pg. 
754
-
760
)
Akre
O
Richiardi
L
Does a testicular dysgenesis syndrome exist?
Hum Reprod
 , 
2009
, vol. 
24
 (pg. 
2053
-
2060
)
Akre
O
Lipworth
L
Cnattingius
S
Sparén
P
Ekbom
A
Risk factor patterns for cryptorchidism and hypospadias
Epidemiology
 , 
1999
, vol. 
10
 (pg. 
364
-
369
)
Akre
O
Boyd
HA
Ahlgren
M
Wilbrand
K
Westergaard
T
Hjalgrim
H
Nordenskjöld
A
Ekbom
A
Melbye
M
Maternal and gestational risk factors for hypospadias
Environ Health Perspect
 , 
2008
, vol. 
116
 (pg. 
1071
-
1076
)
Albers
N
Ulrichs
C
Glüer
S
Hiort
O
Sinnecker
GHG
Mildenberger
H
Brodehl
J
Etiologic classification of severe hypospadias: implications for prognosis and management
J Pediatr
 , 
1997
, vol. 
131
 (pg. 
386
-
392
)
Alléra
A
Herbst
MA
Griffin
JE
Wilson
JD
Schweikert
HU
McPhaul
MJ
Mutations of the androgen receptor coding sequence are infrequent in patients with isolated hypospadias
J Clin Endocrinol Metab
 , 
1995
, vol. 
80
 (pg. 
2697
-
2699
)
Ammini
AC
Sabherwal
U
Mukhopadhyay
C
Vijayaraghavan
M
Pandey
J
Morphogenesis of the human external male genitalia
Pediatr Surg Int
 , 
1997
, vol. 
12
 (pg. 
401
-
406
)
Andresen
JH
Aftimos
S
Doherty
E
Love
DR
Battin
M
13q33.2 deletion: a rare cause of ambiguous genitalia in a male newborn with growth restriction
Acta Paediatr
 , 
2010
, vol. 
99
 (pg. 
784
-
786
)
Apter
D
Vihko
R
Early menarche, a risk factor for breast cancer, indicates early onset of ovulatory cycles
J Clin Endocrinol Metab
 , 
1983
, vol. 
57
 (pg. 
82
-
86
)
Araneta
MRG
Schlangen
KM
Edmonds
LD
Destiche
DA
Merz
RD
Hobbs
CA
Flood
TJ
Harris
JA
Krishnamurti
D
Gray
GC
Prevalence of birth defects among infants of Gulf War veterans in Arkansas, Arizona, California, Georgia, Hawaii, Iowa, 1989–1993
Birth Defects Res A Clin Mol Teratol
 , 
2003
, vol. 
67
 (pg. 
246
-
260
)
Arpino
C
Brescianini
S
Robert
E
Castilla
EE
Cocchi
G
Cornel
MC
de Vigan
C
Lancaster
PA
Merlob
P
Sumiyoshi
Y
, et al.  . 
Teratogenic effects of antiepileptic drugs: use of an International Database on Malformations and Drug Exposure (MADRE)
Epilepsia
 , 
2000
, vol. 
41
 (pg. 
1436
-
1443
)
Aschim
EL
Haugen
TB
Tretli
S
Daltveit
AK
Grotmol
T
Risk factors for hypospadias in Norwegian boys—association with testicular dysgenesis syndrome?
Int J Androl
 , 
2004
, vol. 
27
 (pg. 
213
-
221
)
Aschim
EL
Nordenskjöld
A
Giwercman
A
Lundin
KB
Ruhayel
Y
Haugen
TB
Grotmol
T
Giwercman
YL
Linkage between cryptorchidism, hypospadias, GGN repeat length in the androgen receptor gene
J Clin Endocrinol Metab
 , 
2004
, vol. 
89
 (pg. 
5105
-
5109
)
Aschim
EL
Giwercman
A
Ståhl
O
Eberhard
J
Cwikiel
M
Nordenskjöld
A
Haugen
TB
Grotmol
T
Giwercman
YL
The RsaI polymorphism in the estrogen receptor-beta gene is associated with male infertility
J Clin Endocrinol Metab
 , 
2005
, vol. 
90
 (pg. 
5343
-
5348
)
Asklund
C
Jørgensen
N
Skakkebæk
NE
Jensen
TK
Increased frequency of reproductive health problems among fathers of boys with hypospadias
Hum Reprod
 , 
2007
, vol. 
22
 (pg. 
2639
-
2646
)
Avellan
L
On aetiological factors in hypospadias
Scand J Plast Reconstr Surg
 , 
1977
, vol. 
11
 (pg. 
115
-
123
)
Ban
S
Sata
F
Kurahashi
N
Kasai
S
Moriya
K
Kakizaki
H
Nonomura
K
Kishi
R
Genetic polymorphisms of ESR1 and ESR2 that may influence estrogen activity and the risk of hypospadias
Hum Reprod
 , 
2008
, vol. 
23
 (pg. 
1466
-
1471
)
Bánhidy
F
Puhó
EH
Czeizel
AE
Efficacy of medical care of epileptic pregnant women based on the rate of congenital abnormalities in their offspring
Congenit Anom (Kyoto)
 , 
2011
, vol. 
51
 (pg. 
34
-
42
)
Baskin
LS
Erol
A
Jegatheesan
P
Li
Y
Liu
W
Cunha
GR
Urethral seam formation and hypospadias
Cell Tissue Res
 , 
2001
, vol. 
305
 (pg. 
379
-
387
)
Battin
M
Albersheim
S
Newman
D
Congenital genitourinary tract abnormalities following cocaine exposure in utero
Am J Perinatol
 , 
1995
, vol. 
12
 (pg. 
425
-
428
)
Beleza-Meireles
A
Omrani
D
Kockum
I
Frisén
L
Lagerstedt
K
Nordenskjöld
A
Polymorphisms of estrogen receptor beta gene are associated with hypospadias
J Endocrinol Invest
 , 
2006
, vol. 
29
 (pg. 
5
-
10
)
Beleza-Meireles
A
Barbaro
M
Wedell
A
Töhönen
V
Nordenskjöld
A
Studies of a co-chaperone of the androgen receptor, FKBP52, as candidate for hypospadias
Reprod Biol Endocrinol
 , 
2007
, vol. 
5
 pg. 
8
 
Beleza-Meireles
A
Kockum
I
Lundberg
F
Söderhäll
C
Nordenskjöld
A
Risk factors for hypospadias in the estrogen receptor 2 gene
J Clin Endocrinol Metab
 , 
2007
, vol. 
92
 (pg. 
3712
-
3718
)
Beleza-Meireles
A
Lundberg
F
Lagerstedt
K
Zhou
X
Omrani
D
Frisén
L
Nordenskjöld
A
FGFR2, FGF8, FGF10 and BMP7 as candidate genes for hypospadias
Eur J Hum Genet
 , 
2007
, vol. 
15
 (pg. 
405
-
410
)
Beleza-Meireles
A
Töhönen
V
Söderhäll
C
Schwentner
C
Radmayr
C
Kockum
I
Nordenskjöld
A
Activating transcription factor 3: a hormone responsive gene in the etiology of hypospadias
Eur J Endocrinol
 , 
2008
, vol. 
158
 (pg. 
729
-
739
)
Bentvelsen
FM
Brinkmann
AO
van der Linden
JE
Schroder
FH
Nijman
JM
Decreased immunoreactive androgen receptor levels are not the cause of isolated hypospadias
Br J Urol
 , 
1995
, vol. 
76
 (pg. 
384
-
388
)
Bernstein
L
Depue
RH
Ross
RK
Judd
HL
Pike
MC
Henderson
BE
Higher maternal levels of free estradiol in first compared to second pregnancy: early gestational differences
J Natl Cancer Inst
 , 
1986
, vol. 
76
 (pg. 
1035
-
1039
)
Bhatia
R
Shiau
R
Petreas
M
Weintraub
JM
Farhang
L
Eskenazi
B
Organochlorine pesticides and male genital anomalies in the child health and development studies
Environ Health Perspect
 , 
2005
, vol. 
113
 (pg. 
220
-
224
)
Bhoj
EJ
Ramos
P
Baker
LA
Cost
N
Nordenskjöld
A
Elder
FF
Bleyl
SB
Bowles
NE
Arrington
CB
Delhomme
B
, et al.  . 
Human balanced translocation and mouse gene inactivation implicate Basonuclin 2 in distal urethral development
Eur J Hum Genet
 , 
2011
, vol. 
19
 (pg. 
540
-
546
)
Blomberg
MI
Källén
B
Maternal obesity and morbid obesity: the risk for birth defects in the offspring
Birth Defects Res A Clin Mol Teratol
 , 
2010
, vol. 
88
 (pg. 
35
-
40
)
Boehmer
ALM
Nijman
RJM
Lammers
BAS
de Coninck
SJF
van Hemel
JO
Themmen
APN
Mureau
MAM
de Jong
FH
Brinkmann
AO
Niermeijer
MF
, et al.  . 
Etiological studies of severe or familial hypospadias
J Urol
 , 
2001
, vol. 
165
 (pg. 
1246
-
1254
)
Boisen
KA
Chellakooty
M
Schmidt
IM
Kai
CM
Damgaard
IN
Suomi
AM
Toppari
J
Skakkebæk
NE
Main
KM
Hypospadias in a cohort of 1072 Danish newborn boys: prevalence and relationship to placental weight, anthropometrical measurements at birth, reproductive hormone levels at three months of age
J Clin Endocrinol Metab
 , 
2005
, vol. 
90
 (pg. 
4041
-
4046
)
Bonduelle
M
Liebaers
I
Deketelaere
V
Derde
MP
Camus
M
Devroey
P
van Steirteghem
A
Neonatal data on a cohort of 2889 infants born after ICSI (1991–1999) and of 2995 infants born after IVF (1983–1999)
Hum Reprod
 , 
2002
, vol. 
17
 (pg. 
671
-
694
)
Brouwers
MM
Feitz
WFJ
Roelofs
LAJ
Kiemeney
LALM
de Gier
RPE
Roeleveld
N
Hypospadias: a transgenerational effect of diethylstilbestrol?
Hum Reprod
 , 
2006
, vol. 
21
 (pg. 
666
-
669
)
Brouwers
MM
Feitz
WFJ
Roelofs
LAJ
Kiemeney
LALM
de Gier
RPE
Roeleveld
N
Risk factors for hypospadias
Eur J Pediatr
 , 
2007
, vol. 
166
 (pg. 
671
-
678
)
Brouwers
MM
van der Zanden
LFM
de Gier
RPE
Barten
EJ
Zielhuis
GA
Feitz
WFJ
Roeleveld
N
Hypospadias: risk factor patterns and different phenotypes
BJU Int
 , 
2010
, vol. 
105
 (pg. 
254
-
262
)
Browne
ML
Rasmussen
SA
Hoyt
AT
Waller
DK
Druschel
CM
Caton
AR
Canfield
MA
Lin
AE
Carmichael
SL
Romitti
PA
Maternal thyroid disease, thyroid medication use, selected birth defects in the National Birth Defects Prevention Study
Birth Defects Res A Clin Mol Teratol
 , 
2009
, vol. 
85
 (pg. 
621
-
628
)
Calzolari
E
Contiero
MR
Roncarati
E
Mattiuz
PL
Volpato
S
Aetiological factors in hypospadias
J Med Genet
 , 
1986
, vol. 
23
 (pg. 
333
-
337
)
Carlson
WH
Kisely
SR
MacLellan
DL
Maternal and fetal risk factors associated with severity of hypospadias: a comparison of mild and severe cases
J Pediatr Urol
 , 
2009
, vol. 
5
 (pg. 
283
-
286
)
Carmichael
SL
Shaw
GM
Nelson
V
Selvin
S
Torfs
CP
Curry
CJ
Hypospadias in California: trends and descriptive epidemiology
Epidemiology
 , 
2003
, vol. 
14
 (pg. 
701
-
706
)
Carmichael
SL
Shaw
GM
Laurent
C
Croughan
MS
Olney
RS
Lammer
EJ
Maternal progestin intake and risk of hypospadias
Arch Pediatr Adolesc Med
 , 
2005
, vol. 
159
 (pg. 
957
-
962
)
Carmichael
SL
Shaw
GM
Laurent
C
Lammer
EJ
Olney
RS
Hypospadias and maternal exposures to cigarette smoke
Paediatr Perinat Epidemiol
 , 
2005
, vol. 
19
 (pg. 
406
-
412
)
Carmichael
SL
Shaw
GM
Laurent
C
Olney
RS
Lammer
EJ
Maternal reproductive and demographic characteristics as risk factors for hypospadias
Paediatr Perinat Epidemiol
 , 
2007
, vol. 
21
 (pg. 
210
-
218
)
Carmichael
SL
Ma
C
Werler
MM
Olney
RS
Shaw
GM
Maternal corticosteroid use and hypospadias
J Pediatr
 , 
2009
, vol. 
155
 (pg. 
39
-
44
)
Carmichael
SL
Yang
W
Correa
A
Olney
RS
Shaw
GM
Hypospadias and intake of nutrients related to one-carbon metabolism
J Urol
 , 
2009
, vol. 
181
 (pg. 
315
-
321
)
Carmichael
SL
Herring
AH
Sjödin
A
Jones
R
Needham
L
Ma
C
Ding
K
Shaw
GM
Hypospadias and halogenated organic pollutant levels in maternal mid-pregnancy serum samples
Chemosphere
 , 
2010
, vol. 
80
 (pg. 
641
-
646
)
Carter
TC
Druschel
CM
Romitti
PA
Bell
EM
Werler
MM
Mitchell
AA
Antifungal drugs and the risk of selected birth defects
Am J Obstet Gynecol
 , 
2008
, vol. 
198
 (pg. 
191
-
197
)
Castro
A
Codner
E
Kaune
H
Lopez
P
Vantman
D
Cassorla
F
Absence of Y chromosome microdeletions in patients with cryptorchidism and hypospadias
J Pediatr Endocrinol Metab
 , 
2004
, vol. 
17
 (pg. 
143
-
148
)
Caton
AR
Bell
EM
Druschel
CM
Werler
MM
Mitchell
AA
Browne
ML
McNutt
LA
Romitti
PA
Olney
RS
Correa
A
Maternal hypertension, antihypertensive medication use, the risk of severe hypospadias
Birth Defects Res A Clin Mol Teratol
 , 
2008
, vol. 
82
 (pg. 
34
-
40
)
Centers for Disease Control and Prevention (CDC)
Evaluation of an association between loratadine and hypospadias—United States, 1997–2001
MMWR Morb Mortal Wkly Rep
 , 
2004
, vol. 
53
 (pg. 
219
-
221
)
Chamberlain
NL
Driver
ED
Miesfeld
RL
The length and location of CAG trinucleotide repeats in the androgen receptor N-terminal domain affect transactivation function
Nucleic Acids Res
 , 
1994
, vol. 
22
 (pg. 
3181
-
3186
)
Chambers
CD
Castilla
EE
Orioli
I
Jones
KL
Intrauterine growth restriction in like-sex twins discordant for structural defects
Birth Defects Res A Clin Mol Teratol
 , 
2006
, vol. 
76
 (pg. 
246
-
248
)
Chen
T
Li
Q
Xu
J
Ding
K
Wang
Y
Wang
W
Li
S
Shen
Y
Mutation screening of BMP4, BMP7, HOXA4 and HOXB6 genes in Chinese patients with hypospadias
Eur J Hum Genet
 , 
2007
, vol. 
15
 (pg. 
23
-
28
)
Chen
Y
Thai
HTT
Lundin
J
Lagerstedt-Robinson
K
Zhao
S
Markljung
E
Nordenskjöld
A
Mutational study of the MAMLD1-gene in hypospadias
Eur J Med Genet
 , 
2010
, vol. 
53
 (pg. 
122
-
126
)
Cheung-Flynn
J
Prapapanich
V
Cox
MB
Riggs
DL
Suarez-Quian
C
Smith
DF
Physiological role for the cochaperone FKBP52 in androgen receptor signaling
Mol Endocrinol
 , 
2005
, vol. 
19
 (pg. 
1654
-
1666
)
Chia
SE
Endocrine disruptors and male reproductive function—a short review
Int J Androl
 , 
2000
, vol. 
23
 
Suppl. 2)
(pg. 
45
-
46
)
Chong
JH
Wee
CK
Ho
SK
Chan
DK
Factors associated with hypospadias in Asian newborn babies
J Perinat Med
 , 
2006
, vol. 
34
 (pg. 
497
-
500
)
Codner
E
Okuma
C
Iñiguez
G
Boric
MA
Avila
A
Johnson
MC
Cassorla
FG
Molecular study of the 3 beta-hydroxysteroid dehydrogenase gene type II in patients with hypospadias
J Clin Endocrinol Metab
 , 
2004
, vol. 
89
 (pg. 
957
-
964
)
Crescioli
C
Maggi
M
Vannelli
GB
Ferruzzi
P
Granchi
S
Mancina
R
Muratori
M
Forti
G
Serio
M
Luconi
M
Expression of functional estrogen receptors in human fetal male external genitalia
J Clin Endocrinol Metab
 , 
2003
, vol. 
88
 (pg. 
1815
-
1824
)
Czeizel
AE
Rockenbauer
M
Population-based case–control study of teratogenic potential of corticosteroids
Teratology
 , 
1997
, vol. 
56
 (pg. 
335
-
340
)
Czeizel
AE
Rockenbauer
M
Sørensen
HT
Olsen
J
The teratogenic risk of trimethoprim-sulfonamides: a population based case–control study
Reprod Toxicol
 , 
2001
, vol. 
15
 (pg. 
637
-
646
)
Czeizel
AE
Kazy
Z
Puho
E
A population-based case–control teratological study of oral nystatin treatment during pregnancy
Scand J Infect Dis
 , 
2003
, vol. 
35
 (pg. 
830
-
835
)
Dolk
H
Vrijheid
M
Armstrong
B
Abramsky
L
Bianchi
F
Garne
E
Nelen
V
Robert
E
Scott
JES
Stone
D
, et al.  . 
Risk of congenital anomalies near hazardous-waste landfill sites in Europe: the EUROHAZCON study
Lancet
 , 
1998
, vol. 
352
 (pg. 
423
-
427
)
Dravis
C
Yokoyama
N
Chumley
MJ
Cowan
CA
Silvany
RE
Shay
J
Baker
LA
Henkemeyer
M
Bidirectional signaling mediated by ephrin-B2 and EphB2 controls urorectal development
Dev Biol
 , 
2004
, vol. 
271
 (pg. 
272
-
290
)
Dugas
J
Nieuwenhuijsen
MJ
Martinez
D
Iszatt
N
Nelson
P
Elliott
P
Use of biocides and insect repellents and risk of hypospadias
Occup Environ Med
 , 
2010
, vol. 
67
 (pg. 
196
-
200
)
El Houate
B
Rouba
H
Sibai
H
Barakat
A
Chafik
A
Chadli
EB
Imken
L
Bogatcheva
NV
Feng
S
Agoulnik
AI
, et al.  . 
Novel mutations involving the INSL3 gene associated with cryptorchidism
J Urol
 , 
2007
, vol. 
177
 (pg. 
1947
-
1951
)
el-Galley
RES
Smith
E
Cohen
C
Petros
JA
Woodard
J
Galloway
NTM
Epidermal growth factor (EGF) and EGF receptor in hypospadias
Br J Urol
 , 
1997
, vol. 
79
 (pg. 
116
-
119
)
Emaus
A
Espetvedt
S
Veierød
MB
Ballard-Barbash
R
Furberg
AS
Ellison
PT
Jasienska
G
Hjartåker
A
Thune
I
17-beta-estradiol in relation to age at menarche and adult obesity in premenopausal women
Hum Reprod
 , 
2008
, vol. 
23
 (pg. 
919
-
927
)
Ericson
A
Källén
B
Congenital malformations in infants born after IVF: a population-based study
Hum Reprod
 , 
2001
, vol. 
16
 (pg. 
504
-
509
)
Fedder
J
Gabrielsen
A
Humaidan
P
Erb
K
Ernst
E
Loft
A
Malformation rate and sex ratio in 412 children conceived with epididymal or testicular sperm
Hum Reprod
 , 
2007
, vol. 
22
 (pg. 
1080
-
1085
)
Feyaerts
A
Forest
MG
Morel
Y
Mure
PY
Morel-Journel
N
Mallet
D
Nicolino
M
Chatelain
P
David
M
Mouriquand
P
Endocrine screening in 32 consecutive patients with hypospadias
J Urol
 , 
2002
, vol. 
168
 (pg. 
720
-
725
)
Fisch
H
Golden
RJ
Libersen
GL
Hyun
GS
Madsen
P
New
MI
Hensle
TW
Maternal age as a risk factor for hypospadias
J Urol
 , 
2001
, vol. 
165
 (pg. 
934
-
936
)
Fisch
H
Lambert
SM
Hensle
TW
Hyun
G
Hypospadias rates in New York state are not increasing
J Urol
 , 
2009
, vol. 
181
 (pg. 
2291
-
2294
)
Fisher
JS
Environmental anti-androgens and male reproductive health: focus on phthalates and testicular dysgenesis syndrome
Reproduction
 , 
2004
, vol. 
127
 (pg. 
305
-
315
)
Forrester
MB
Merz
RD
Rates for specific birth defects among offspring of Japanese mothers, Hawaii, 1986–2002
Congenit Anom (Kyoto)
 , 
2006
, vol. 
46
 (pg. 
76
-
80
)
Fredell
L
Lichtenstein
P
Pedersen
NL
Svensson
J
Nordenskjöld
A
Hypospadias is related to birth weight in discordant monozygotic twins
J Urol
 , 
1998
, vol. 
160
 (pg. 
2197
-
2199
)
Fredell
L
Iselius
L
Collins
A
Hansson
E
Holmner
S
Lundquist
L
Läckgren
G
Pedersen
J
Stenberg
A
Westbacke
G
, et al.  . 
Complex segregation analysis of hypospadias
Hum Genet
 , 
2002
, vol. 
111
 (pg. 
231
-
234
)
Fredell
L
Kockum
I
Hansson
E
Holmner
S
Lundquist
L
Läckgren
G
Pedersen
J
Stenberg
A
Westbacke
G
Nordenskjöld
A
Heredity of hypospadias and the significance of low birth weight
J Urol
 , 
2002
, vol. 
167
 (pg. 
1423
-
1427
)
Frisen
L
Soderhall
C
Tapper-Persson
M
Luthman
H
Kockum
I
Nordenskjöld
A
Genome-wide linkage analysis for hypospadias susceptibility genes
J Urol
 , 
2004
, vol. 
172
 (pg. 
1460
-
1463
)
Fritz
G
Czeizel
AE
Abnormal sperm morphology and function in the fathers of hypospadiacs
J Reprod Fertil
 , 
1996
, vol. 
106
 (pg. 
63
-
66
)
Fujimoto
T
Suwa
T
Kabe
K
Adachi
T
Nakabayashi
M
Amamiya
T
Placental insufficiency in early gestation is associated with hypospadias
J Pediatr Surg
 , 
2008
, vol. 
43
 (pg. 
358
-
361
)
Fukami
M
Wada
Y
Miyabayashi
K
Nishino
I
Hasegawa
T
Nordenskjöld
A
Camerino
G
Kretz
C
Buj-Bello
A
Laporte
J
, et al.  . 
CXorf6 is a causative gene for hypospadias
Nat Genet
 , 
2006
, vol. 
38
 (pg. 
1369
-
1371
)
Fukami
M
Wada
Y
Okada
M
Kato
F
Katsumata
N
Baba
T
Morohashi
K
Laporte
J
Kitagawa
M
Ogata
T
Mastermind-like domain-containing 1 (MAMLD1 or CXorf6) transactivates the Hes3 promoter, augments testosterone production, contains the SF1 target sequence
J Biol Chem
 , 
2008
, vol. 
283
 (pg. 
5525
-
5532
)
Funke
S
Flach
E
Kiss
I
Sandor
J
Vida
G
Bodis
J
Ertl
T
Male reproductive tract abnormalities: more common after assisted reproduction?
Early Hum Dev
 , 
2010
, vol. 
86
 (pg. 
547
-
550
)
Furneaux
EC
Langley-Evans
AJ
Langley-Evans
SC
Nausea and vomiting of pregnancy: endocrine basis and contribution to pregnancy outcome
Obstet Gynecol Surv
 , 
2001
, vol. 
56
 (pg. 
775
-
782
)
Gallentine
ML
Morey
AF
Thompson
IM
Jr
Hypospadias: a contemporary epidemiologic assessment
Urology
 , 
2001
, vol. 
57
 (pg. 
788
-
790
)
Garavelli
L
Mainardi
PC
Mowat-Wilson syndrome
Orphanet J Rare Dis
 , 
2007
, vol. 
2
 pg. 
42
 
Garavelli
L
Zollino
M
Mainardi
PC
Gurrieri
F
Rivieri
F
Soli
F
Verri
R
Albertini
E
Favaron
E
Zignani
M
, et al.  . 
Mowat-Wilson syndrome: facial phenotype changing with age: study of 19 Italian patients and review of the literature
Am J Med Genet A
 , 
2009
, vol. 
149A
 (pg. 
417
-
426
)
García
AM
Fletcher
T
Maternal occupation in the leather industry and selected congenital malformations
Occup Environ Med
 , 
1998
, vol. 
55
 (pg. 
284
-
286
)
Garcia
NM
Allgood
J
Santos
LJ
Lonergan
D
Batanian
JR
Henkemeyer
M
Bartsch
O
Schultz
RA
Zinn
AR
Baker
LA
Deletion mapping of critical region for hypospadias, penoscrotal transposition and imperforate anus on human chromosome 13
J Pediatr Urol
 , 
2006
, vol. 
2
 (pg. 
233
-
242
)
Gatti
JM
Kirsch
AJ
Troyer
WA
Perez-Brayfield
MR
Smith
EA
Scherz
HC
Increased incidence of hypospadias in small-for-gestational age infants in a neonatal intensive-care unit
BJU Int
 , 
2001
, vol. 
87
 (pg. 
548
-
550
)
Gearhart
JP
Linhard
HR
Berkovitz
GD
Jeffs
RD
Brown
TR
Androgen receptor levels and 5 alpha-reductase activities in preputial skin and chordee tissue of boys with isolated hypospadias
J Urol
 , 
1988
, vol. 
140
 (pg. 
1243
-
1246
)
Ghirri
P
Scaramuzzo
RT
Bertelloni
S
Pardi
D
Celandroni
A
Cocchi
G
Danieli
R
De Santis
L
Di Stefano
MC
Gerola
O
, et al.  . 
Prevalence of hypospadias in Italy according to severity, gestational age and birthweight: an epidemiological study
Ital J Pediatr
 , 
2009
, vol. 
35
 pg. 
18
 
Giordano
F
Carbone
P
Nori
F
Mantovani
A
Taruscio
D
Figà-Talamanca
I
Maternal diet and the risk of hypospadias and cryptorchidism in the offspring
Paediatr Perinat Epidemiol
 , 
2008
, vol. 
22
 (pg. 
249
-
260
)
Giordano
F
Abballe
A
De Felip
E
di Dominico
A
Ferro
F
Grammatico
P
Ingelido
AM
Marra
V
Marrocco
G
Vallasciani
S
, et al.  . 
Maternal exposures to endocrine disrupting chemicals and hypospadias in offspring
Birth Defects Res A Clin Mol Teratol
 , 
2010
, vol. 
88
 (pg. 
241
-
250
)
Giuili
G
Shen
WH
Ingraham
HA
The nuclear receptor SF-1 mediates sexually dimorphic expression of Mullerian inhibiting substance, in vivo
Development
 , 
1997
, vol. 
124
 (pg. 
1799
-
1807
)
Goodman
FR
Scambler
PJ
Human HOX gene mutations
Clin Genet
 , 
2001
, vol. 
59
 (pg. 
1
-
11
)
Goodman
FR
Mundlos
S
Muragaki
Y
Donnai
D
Giovannucci-Uzielli
ML
Lapi
E
Majewski
F
McGaughran
J
McKeown
C
Reardon
W
, et al.  . 
Synpolydactyly phenotypes correlate with size of expansions in HOXD13 polyalanine tract
Proc Natl Acad Sci USA
 , 
1997
, vol. 
94
 (pg. 
7458
-
7463
)
Gray
LE
Ostby
J
Furr
J
Wolf
CJ
Lambright
C
Parks
L
Veeramachaneni
DN
Wilson
V
Price
M
Hotchkiss
A
, et al.  . 
Effects of environmental antiandrogens on reproductive development in experimental animals
Hum Reprod Update
 , 
2001
, vol. 
7
 (pg. 
248
-
264
)
Gubbay
J
Collignon
J
Koopman
P
Capel
B
Economou
A
Münsterberg
A
Vivian
N
Goodfellow
P
Lovell-Badge
R
A gene mapping to the sex-determining region of the mouse Y chromosome is a member of a novel family of embryonically expressed genes
Nature
 , 
1990
, vol. 
346
 (pg. 
245
-
250
)
Gurbuz
C
Demir
S
Zemheri
E
Canat
L
Kilic
M
Caskurlu
T
Is activating transcription factor 3 up-regulated in patients with hypospadias?
Korean J Urol
 , 
2010
, vol. 
51
 (pg. 
561
-
564
)
Haraguchi
R
Mo
R
Hui
C
Motoyama
J
Makino
S
Shiroishi
T
Gaffield
W
Yamada
G
Unique functions of Sonic hedgehog signaling during external genitalia development
Development
 , 
2001
, vol. 
128
 (pg. 
4241
-
4250
)
Hiort
O
Klauber
G
Cendron
M
Sinnecker
GHG
Keim
L
Schwinger
E
Wolfe
HJ
Yandell
DW
Molecular characterization of the androgen receptor gene in boys with hypospadias
Eur J Pediatr
 , 
1994
, vol. 
153
 (pg. 
317
-
321
)
Holmes
NM
Miller
WL
Baskin
LS
Lack of defects in androgen production in children with hypospadias
J Clin Endocrinol Metab
 , 
2004
, vol. 
89
 (pg. 
2811
-
2816
)
Hughes
IA
Northstone
K
Golding
J
Reduced birth weight in boys with hypospadias: an index of androgen dysfunction?
Arch Dis Child Fetal Neonatal Ed
 , 
2002
, vol. 
87
 (pg. 
F150
-
F151
)
Hunt
S
Russell
A
Smithson
WH
Parsons
L
Robertson
I
Waddell
R
Irwin
B
Morrison
PJ
Morrow
J
Craig
J
Topiramate in pregnancy: preliminary experience from the UK Epilepsy and Pregnancy Register
Neurology
 , 
2008
, vol. 
71
 (pg. 
272
-
276
)
Hussain
N
Chaghtai
A
Herndon
CDA
Herson
VC
Rosenkrantz
TS
McKenna
PH
Hypospadias and early gestation growth restriction in infants
Pediatrics
 , 
2002
, vol. 
109
 (pg. 
473
-
478
)
Hynes
PJ
Fraher
JP
The development of the male genitourinary system. I. The origin of the urorectal septum and the formation of the perineum
Br J Plast Surg
 , 
2004
, vol. 
57
 (pg. 
27
-
36
)
Hynes
PJ
Fraher
JP
The development of the male genitourinary system. III. The formation of the spongiose and glandar urethra
Br J Plast Surg
 , 
2004
, vol. 
57
 (pg. 
203
-
214
)
Irgens
A
Krüger
K
Skorve
AH
Irgens
LM
Birth defects and paternal occupational exposure. Hypotheses tested in a record linkage based dataset
Acta Obstet Gynecol Scand
 , 
2000
, vol. 
79
 (pg. 
465
-
470
)
Iszatt
N
Nieuwenhuijsen
MJ
Nelson
P
Elliott
P
Toledano
MB
Water consumption and use, trihalomethane exposure, the risk of hypospadias
Pediatrics
 , 
2011
, vol. 
127
 (pg. 
e389
-
e397
)
Jentink
J
Loane
MA
Dolk
H
Barisic
I
Garne
E
Morris
JK
de Jong-van den Berg
L
Valproic acid monotherapy in pregnancy and major congenital malformations
N Engl J Med
 , 
2010
, vol. 
362
 (pg. 
2185
-
2193
)
Jin
L
Ye
R
Zheng
J
Hong
S
Ren
A
Secular trends of hypospadias prevalence and factors associated with it in southeast China during 1993–2005
Birth Defects Res A Clin Mol Teratol
 , 
2010
, vol. 
88
 (pg. 
458
-
465
)
Jones
FW
The development and malformations of the glans and prepuce
Br Med J
 , 
1910
, vol. 
1
 (pg. 
137
-
138
)
Jørgensen
N
Meyts
ER
Main
KM
Skakkebæk
NE
Testicular dysgenesis syndrome comprises some but not all cases of hypospadias and impaired spermatogenesis
Int J Androl
 , 
2010
, vol. 
33
 (pg. 
298
-
303
)
Kalfa
N
Liu
B
Klein
O
Wang
MH
Cao
M
Baskin
LS
Genomic variants of ATF3 in patients with hypospadias
J Urol
 , 
2008
, vol. 
180
 (pg. 
2183
-
2188
)
Kalfa
N
Liu
B
Ophir
K
Audran
F
Wang
MH
Mei
C
Sultan
C
Baskin
LS
Mutations of CXorf6 are associated with a range of severities of hypospadias
Eur J Endocrinol
 , 
2008
, vol. 
159
 (pg. 
453
-
458
)
Källén
K
Role of maternal smoking and maternal reproductive history in the etiology of hypospadias in the offspring
Teratology
 , 
2002
, vol. 
66
 (pg. 
185
-
191
)
Källén
B
Congenital malformations in infants whose mothers reported the use of folic acid in early pregnancy in Sweden. A prospective population study
Congenit Anom (Kyoto)
 , 
2007
, vol. 
47
 (pg. 
119
-
124
)
Källén
B
Olausson
PO
Monitoring of maternal drug use and infant congenital malformations. Does loratadine cause hypospadias?
Int J Risk Saf Med
 , 
2001
, vol. 
14
 (pg. 
115
-
119
)
Källén
B
Olausson
PO
No increased risk of infant hypospadias after maternal use of loratadine in early pregnancy
Int J Med Sci
 , 
2006
, vol. 
3
 (pg. 
106
-
107
)
Källén
B
Otterblad
OP
Use of anti-asthmatic drugs during pregnancy. 3. Congenital malformations in the infants
Eur J Clin Pharmacol
 , 
2007
, vol. 
63
 (pg. 
383
-
388
)
Källén
BAJ
Robert
E
Drinking water chlorination and delivery outcome—a registry-based study in Sweden
Reprod Toxicol
 , 
2000
, vol. 
14
 (pg. 
303
-
309
)
Källén
B
Olausson
PO
Nygren
KG
Neonatal outcome in pregnancies from ovarian stimulation
Obstet Gynecol
 , 
2002
, vol. 
100
 (pg. 
414
-
419
)
Källén
B
Finnström
O
Nygren
KG
Olausson
PO
In vitro fertilization (IVF) in Sweden: risk for congenital malformations after different IVF methods
Birth Defects Res A Clin Mol Teratol
 , 
2005
, vol. 
73
 (pg. 
162
-
169
)
Källén
B
Nilsson
E
Otterblad
OP
Maternal use of loperamide in early pregnancy and delivery outcome
Acta Paediatr
 , 
2008
, vol. 
97
 (pg. 
541
-
545
)
Källén
B
Finnström
O
Lindam
A
Nilsson
E
Nygren
KG
Otterblad
PO
Congenital malformations in infants born after in vitro fertilization in Sweden
Birth Defects Res A Clin Mol Teratol
 , 
2010
, vol. 
88
 (pg. 
137
-
143
)
Kaltenis
P
Schumacher
V
Jankauskiené
A
Laurinavičius
A
Royer-Pokora
B
Slow progressive FSGS associated with an F392L WT1 mutation
Pediatr Nephrol
 , 
2004
, vol. 
19
 (pg. 
353
-
356
)
Kappel
B
Hansen
K
Moller
J
Faaborg-Andersen
J
Human placental lactogen and dU-estrogen levels in normal twin pregnancies
Acta Genet Med Gemellol (Roma)
 , 
1985
, vol. 
34
 (pg. 
59
-
65
)
Katz
Z
Lancet
M
Skornik
J
Chemke
J
Mogilner
BM
Klinberg
M
Teratogenicity of progestogens given during the first trimester of pregnancy
Obstet Gynecol
 , 
1985
, vol. 
65
 (pg. 
775
-
780
)
Kiely
EA
Chapman
RS
Bajoria
SK
Hollyer
JS
Hurley
R
Maternal serum human chorionic gonadotrophin during early pregnancy resulting in boys with hypospadias or cryptorchidism
Br J Urol
 , 
1995
, vol. 
76
 (pg. 
389
-
392
)
Kim
KS
Liu
W
Cunha
GR
Russell
DW
Huang
H
Shapiro
E
Baskin
LS
Expression of the androgen receptor and 5 alpha-reductase type 2 in the developing human fetal penis and urethra
Cell Tissue Res
 , 
2002
, vol. 
307
 (pg. 
145
-
153
)
Kim
KS
Torres
CR
Jr
Yucel
S
Raimondo
K
Cunha
GR
Baskin
LS
Induction of hypospadias in a murine model by maternal exposure to synthetic estrogens
Environ Res
 , 
2004
, vol. 
94
 (pg. 
267
-
275
)
Klip
H
Verloop
J
van Gool
JD
Koster
META
Burger
CW
van Leeuwen
FE
Hypospadias in sons of women exposed to diethylstilbestrol in utero: a cohort study
Lancet
 , 
2002
, vol. 
359
 (pg. 
1102
-
1107
)
Köhler
B
Lin
L
Mazen
I
Cetindag
C
Biebermann
H
Akkurt
I
Rossi
R
Hiort
O
Grüters
A
Achermann
JC
The spectrum of phenotypes associated with mutations in steroidogenic factor 1 (SF-1, NR5A1, Ad4BP) includes severe penoscrotal hypospadias in 46,XY males without adrenal insufficiency
Eur J Endocrinol
 , 
2009
, vol. 
161
 (pg. 
237
-
242
)
Kristensen
P
Irgens
LM
Andersen
A
Bye
AS
Sundheim
L
Birth defects among offspring of Norwegian farmers, 1967–1991
Epidemiology
 , 
1997
, vol. 
8
 (pg. 
537
-
544
)
Kurahashi
N
Murakumo
M
Kakizaki
H
Nonomura
K
Koyanagi
T
Kasai
S
Sata
F
Kishi
R
The estimated prevalence of hypospadias in Hokkaido, Japan
J Epidemiol
 , 
2004
, vol. 
14
 (pg. 
73
-
77
)
Kurahashi
N
Sata
F
Kasai
S
Shibata
T
Moriya
K
Yamada
H
Kakizaki
H
Minakami
H
Nonomura
K
Kishi
R
Maternal genetic polymorphisms in CYP1A1, GSTM1 and GSTT1 and the risk of hypospadias
Mol Hum Reprod
 , 
2005
, vol. 
11
 (pg. 
93
-
98
)
Laprise
SL
Implications of epigenetics and genomic imprinting in assisted reproductive technologies
Mol Reprod Dev
 , 
2009
, vol. 
76
 (pg. 
1006
-
1018
)
Latifoğlu
O
Yavuzer
R
Demirciler
N
Ünal
S
Atabay
K
Extraurogenital congenital anomalies associated with hypospadias: retrospective review of 700 patients
Ann Plast Surg
 , 
1998
, vol. 
41
 (pg. 
570
-
571
)
Lee
YS
Kirk
JMW
Stanhope
RG
Johnston
DI
Harland
S
Auchus
RJ
Andersson
S
Hughes
IA
Phenotypic variability in 17beta-hydroxysteroid dehydrogenase-3 deficiency and diagnostic pitfalls
Clin Endocrinol (Oxf)
 , 
2007
, vol. 
67
 (pg. 
20
-
28
)
Lim
HN
Chen
H
McBride
S
Dunning
AM
Nixon
RM
Hughes
IA
Hawkins
JR
Longer polyglutamine tracts in the androgen receptor are associated with moderate to severe undermasculinized genitalia in XY males
Hum Mol Genet
 , 
2000
, vol. 
9
 (pg. 
829
-
834
)
Lin
C
Yin
Y
Long
F
Ma
L
Tissue-specific requirements of beta-catenin in external genitalia development
Development
 , 
2008
, vol. 
135
 (pg. 
2815
-
2825
)
Liu
B
Wang
Z
Lin
G
Agras
K
Ebbers
M
Willingham
E
Baskin
LS
Activating transcription factor 3 is up-regulated in patients with hypospadias
Pediatr Res
 , 
2005
, vol. 
58
 (pg. 
1280
-
1283
)
Longnecker
MP
Klebanoff
MA
Brock
JW
Zhou
H
Gray
KA
Needham
LL
Wilcox
AJ
Maternal serum level of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene and risk of cryptorchidism, hypospadias, polythelia among male offspring
Am J Epidemiol
 , 
2002
, vol. 
155
 (pg. 
313
-
322
)
Lorenzo
AJ
Nguyen
MT
Sozubir
S
Henkemeyer
M
Baker
LA
Dihydrotestosterone induction of EPHB2 expression in the female genital tubercle mimics male pattern of expression during embryogenesis
J Urol
 , 
2003
, vol. 
170
 (pg. 
1618
-
1623
)
Luben
TJ
Nuckols
JR
Mosley
BS
Hobbs
C
Reif
JS
Maternal exposure to water disinfection by-products during gestation and risk of hypospadias
Occup Environ Med
 , 
2008
, vol. 
65
 (pg. 
420
-
429
)
Lund
L
Engebjerg
MC
Pedersen
L
Ehrenstein
V
Nørgaard
M
Sørensen
HT
Prevalence of hypospadias in Danish boys: a longitudinal study, 1977–2005
Eur Urol
 , 
2009
, vol. 
55
 (pg. 
1022
-
1026
)
Luo
X
Ikeda
Y
Parker
KL
A cell-specific nuclear receptor is essential for adrenal and gonadal development and sexual differentiation
Cell
 , 
1994
, vol. 
77
 (pg. 
481
-
490
)
Makridakis
N
Ross
RK
Pike
MC
Chang
L
Stanczyk
FZ
Kolonel
LN
Shi
CY
Yu
MC
Henderson
BE
Reichardt
JKV
A prevalent missense substitution that modulates activity of prostatic steroid 5alpha-reductase
Cancer Res
 , 
1997
, vol. 
57
 (pg. 
1020
-
1022
)
Makridakis
NM
di Salle
E
Reichardt
JKV
Biochemical and pharmacogenetic dissection of human steroid 5 alpha-reductase type II
Pharmacogenetics
 , 
2000
, vol. 
10
 (pg. 
407
-
413
)
Martin
OV
Shialis
T
Lester
JN
Scrimshaw
MD
Boobis
AR
Voulvoulis
N
Testicular dysgenesis syndrome and the estrogen hypothesis: a quantitative meta-analysis
Environ Health Perspect
 , 
2008
, vol. 
116
 (pg. 
149
-
157
)
Maruyama
H
Toji
H
Harrington
CR
Sasaki
K
Izumi
Y
Ohnuma
T
Arai
H
Yasuda
M
Tanaka
C
Emson
PC
, et al.  . 
Lack of an association of estrogen receptor alpha gene polymorphisms and transcriptional activity with Alzheimer disease
Arch Neurol
 , 
2000
, vol. 
57
 (pg. 
236
-
240
)
Materna-Kiryluk
A
Wiśniewska
K
Badura-Stronka
M
Mejnartowicz
J
Więckowska
B
Balcar-Boroń
A
Czerwionka-Szaflarska
M
Gajewska
E
Godula-Stuglik
U
Krawczyński
M
, et al.  . 
Parental age as a risk factor for isolated congenital malformations in a Polish population
Paediatr Perinat Epidemiol
 , 
2009
, vol. 
23
 (pg. 
29
-
40
)
McGlynn
KA
Guo
X
Graubard
BI
Brock
JW
Klebanoff
MA
Longnecker
MP
Maternal pregnancy levels of polychlorinated biphenyls and risk of hypospadias and cryptorchidism in male offspring
Environ Health Perspect
 , 
2009
, vol. 
117
 (pg. 
1472
-
1476
)
McIntosh
GC
Olshan
AF
Baird
PA
Paternal age and the risk of birth defects in offspring
Epidemiology
 , 
1995
, vol. 
6
 (pg. 
282
-
288
)
Meijer
WM
de Jong-Van den Berg
LTW
van den Berg
MD
Verheij
JBGM
de Walle
HEK
Clomiphene and hypospadias on a detailed level: signal or chance?
Birth Defects Res A Clin Mol Teratol
 , 
2006
, vol. 
76
 (pg. 
249
-
252
)
Melo
KFS
Martin
RM
Costa
EMF
Carvalho
FM
Jorge
AA
Arnhold
IJP
Mendonca
BB
An unusual phenotype of Frasier syndrome due to IVS9 +4C > T mutation in the WT1 gene: predominantly male ambiguous genitalia and absence of gonadal dysgenesis
J Clin Endocrinol Metab
 , 
2002
, vol. 
87
 (pg. 
2500
-
2505
)
Meyer
KJ
Reif
JS
Veeramachaneni
DNR
Luben
TJ
Mosley
BS
Nuckols
JR
Agricultural pesticide use and hypospadias in eastern Arkansas
Environ Health Perspect
 , 
2006
, vol. 
114
 (pg. 
1589
-
1595
)
Mieusset
R
Soulié
M
Hypospadias: psychosocial, sexual, reproductive consequences in adult life
J Androl
 , 
2005
, vol. 
26
 (pg. 
163
-
168
)
Misrahi
M
Beau
I
Meduri
G
Bouvattier
C
Atger
M
Loosfelt
H
Ghinea
N
Hai
MV
Bougneres
PF
Milgrom
E
Gonadotropin receptors and the control of gonadal steroidogenesis: physiology and pathology
Baillieres Clin Endocrinol Metab
 , 
1998
, vol. 
12
 (pg. 
35
-
66
)
Miyagawa
S
Satoh
Y
Haraguchi
R
Suzuki
K
Iguchi
T
Taketo
MM
Nakagata
N
Matsumoto
T
Takeyama
K
Kato
S
, et al.  . 
Genetic interactions of the androgen and Wnt/beta-catenin pathways for the masculinization of external genitalia
Mol Endocrinol
 , 
2009
, vol. 
23
 (pg. 
871
-
880
)
Morales-Suárez-Varela
MM
Toft
GV
Jensen
MS
Ramlau-Hansen
C
Kaerlev
L
Thulstrup
AM
Llopis-González
A
Olsen
J
Bonde
JP
Parental occupational exposure to endocrine disrupting chemicals and male genital malformations: a study in the Danish National Birth Cohort study
Environ Health
 , 
2011
, vol. 
10
 pg. 
3
 
Moreno-García
M
Miranda
EB
Chromosomal anomalies in cryptorchidism and hypospadias
J Urol
 , 
2002
, vol. 
168
 (pg. 
2170
-
2172
)
Morera
AM
Valmalle
AF
Asensio
MJ
Chossegros
L
Chauvin
MA
Durand
P
Mouriquand
PDE
A study of risk factors for hypospadias in the Rhône-Alpes region (France)
J Pediatr Urol
 , 
2006
, vol. 
2
 (pg. 
169
-
177
)
Morgan
EA
Nguyen
SB
Scott
V
Stadler
HS
Loss of Bmp7 and Fgf8 signaling in Hoxa13-mutant mice causes hypospadia
Development
 , 
2003
, vol. 
130
 (pg. 
3095
-
3109
)
Morrison
AA
Viney
RL
Saleem
MA
Ladomery
MR
New insights into the function of the Wilms tumor suppressor gene WT1 in podocytes
Am J Physiol Renal Physiol
 , 
2008
, vol. 
295
 (pg. 
F12
-
F17
)
Mortlock
DP
Innis
JW
Mutation of HOXA13 in hand-foot-genital syndrome
Nat Genet
 , 
1997
, vol. 
15
 (pg. 
179
-
180
)
Mowat
DR
Wilson
MJ
Goossens
M
Mowat-Wilson syndrome
J Med Genet
 , 
2003
, vol. 
40
 (pg. 
305
-
310
)
Muroya
K
Sasagawa
I
Suzuki
Y
Nakada
T
Ishii
T
Ogata
T
Hypospadias and the androgen receptor gene: mutation screening and CAG repeat length analysis
Mol Hum Reprod
 , 
2001
, vol. 
7
 (pg. 
409
-
413
)
Nassar
N
Bower
C
Barker
A
Increasing prevalence of hypospadias in Western Australia, 1980–2000
Arch Dis Child
 , 
2007
, vol. 
92
 (pg. 
580
-
584
)
Nassar
N
Abeywardana
P
Barker
A
Bower
C
Parental occupational exposure to potential endocrine disrupting chemicals and risk of hypospadias in infants
Occup Environ Med
 , 
2010
, vol. 
67
 (pg. 
585
-
589
)
Nelson
CP
Park
JM
Wan
J
Bloom
DA
Dunn
RL
Wei
JT
The increasing incidence of congenital penile anomalies in the United States
J Urol
 , 
2005
, vol. 
174
 (pg. 
1573
-
1576
)
Nordenskjöld
A
Friedman
E
Tapper-Persson
M
Söderhäll
C
Leviav
A
Svensson
J
Anvret
M
Screening for mutations in candidate genes for hypospadias
Urol Res
 , 
1999
, vol. 
27
 (pg. 
49
-
55
)
Nørgaard
M
Wogelius
P
Pedersen
L
Rothman
KJ
Sørensen
HT
Maternal use of oral contraceptives during early pregnancy and risk of hypospadias in male offspring
Urology
 , 
2009
, vol. 
74
 (pg. 
583
-
587
)
North
K
Golding
J
A maternal vegetarian diet in pregnancy is associated with hypospadias. The ALSPAC Study Team. Avon Longitudinal Study of Pregnancy and Childhood
BJU Int
 , 
2000
, vol. 
85
 (pg. 
107
-
113
)
Nuininga
JE
DE Gier
RPE
Verschuren
R
Feitz
WFJ
Long-term outcome of different types of 1-stage hypospadias repair
J Urol
 , 
2005
, vol. 
174
 (pg. 
1544
-
1548
)
Ormond
G
Nieuwenhuijsen
MJ
Nelson
P
Toledano
MB
Iszatt
N
Geneletti
S
Elliott
P
Endocrine disruptors in the workplace, hair spray, folate supplementation, risk of hypospadias: case–control study
Environ Health Perspect
 , 
2009
, vol. 
117
 (pg. 
303
-
307
)
Palmer
JR
Wise
LA
Robboy
SJ
Titus-Ernstoff
L
Noller
KL
Herbst
AL
Troisi
R
Hoover
RN
Hypospadias in sons of women exposed to diethylstilbestrol in utero
Epidemiology
 , 
2005
, vol. 
16
 (pg. 
583
-
586
)
Paulozzi
LJ
Erickson
JD
Jackson
RJ
Hypospadias trends in two US surveillance systems
Pediatrics
 , 
1997
, vol. 
100
 (pg. 
831
-
834
)
Pedersen
L
Nørgaard
M
Rothman
KJ
Sørensen
HT
Loratadine during pregnancy and hypospadias
Epidemiology
 , 
2008
, vol. 
19
 (pg. 
359
-
360
)
Perriton
CL
Powles
N
Chiang
C
Maconochie
MK
Cohn
MJ
Sonic hedgehog signaling from the urethral epithelium controls external genital development
Dev Biol
 , 
2002
, vol. 
247
 (pg. 
26
-
46
)
Pierik
FH
Burdorf
A
Deddens
JA
Juttmann
RE
Weber
RFA
Maternal and paternal risk factors for cryptorchidism and hypospadias: a case–control study in newborn boys
Environ Health Perspect
 , 
2004
, vol. 
112
 (pg. 
1570
-
1576
)
Pinborg
A
Loft
A
Nyboe
AA
Neonatal outcome in a Danish national cohort of 8602 children born after in vitro fertilization or intracytoplasmic sperm injection: the role of twin pregnancy
Acta Obstet Gynecol Scand
 , 
2004
, vol. 
83
 (pg. 
1071
-
1078
)
Pons
JC
Papiernik
E
Billon
A
Hessabi
M
Duyme
M
Hypospadias in sons of women exposed to diethylstilbestrol in utero
Prenat Diagn
 , 
2005
, vol. 
25
 (pg. 
418
-
419
)
Porter
MP
Faizan
MK
Grady
RW
Mueller
BA
Hypospadias in Washington State: maternal risk factors and prevalence trends
Pediatrics
 , 
2005
, vol. 
115
 (pg. 
e495
-
e499
)
Radpour
R
Rezaee
M
Tavasoly
A
Solati
S
Saleki
A
Association of long polyglycine tracts (GGN repeats) in exon 1 of the androgen receptor gene with cryptorchidism and penile hypospadias in Iranian patients
J Androl
 , 
2007
, vol. 
28
 (pg. 
164
-
169
)
Raman-Wilms
L
Tseng
AL
Wighardt
S
Einarson
TR
Koren
G
Fetal genital effects of first-trimester sex hormone exposure: a meta-analysis
Obstet Gynecol
 , 
1995
, vol. 
85
 (pg. 
141
-
149
)
Rankin
J
Tennant
PW
Stothard
KJ
Bythell
M
Summerbell
CD
Bell
R
Maternal body mass index and congenital anomaly risk: a cohort study
Int J Obes (Lond)
 , 
2010
, vol. 
34
 (pg. 
1371
-
1380
)
Reefhuis
J
Honein
MA
Maternal age and non-chromosomal birth defects, Atlanta—1968–2000: teenager or thirty-something, who is at risk?
Birth Defects Res A Clin Mol Teratol
 , 
2004
, vol. 
70
 (pg. 
572
-
579
)
Reis
M
Källén
B
Delivery outcome after maternal use of antidepressant drugs in pregnancy: an update using Swedish data
Psychol Med
 , 
2010
, vol. 
40
 (pg. 
1723
-
1733
)
Roberts
CJ
Lloyd
S
Observations on the epidemiology of simple hypospadias
Br Med J
 , 
1973
, vol. 
1
 (pg. 
768
-
770
)
Rodríguez-Pinilla
E
Mejías
C
Prieto-Merino
D
Fernández
P
Martínez-Frías
ML
Risk of hypospadias in newborn infants exposed to valproic acid during the first trimester of pregnancy: a case–control study in Spain
Drug Saf
 , 
2008
, vol. 
31
 (pg. 
537
-
543
)
Rubtsov
P
Karmanov
M
Sverdlova
P
Spirin
P
Tiulpakov
A
A novel homozygous mutation in CYP11A1 gene is associated with late-onset adrenal insufficiency and hypospadias in a 46,XY patient
J Clin Endocrinol Metab
 , 
2009
, vol. 
94
 (pg. 
936
-
939
)
Safe
SH
Endocrine disruptors and human health—is there a problem? An update
Environ Health Perspect
 , 
2000
, vol. 
108
 (pg. 
487
-
493
)
Sata
F
Kurahashi
N
Ban
S
Moriya
K
Tanaka
KD
Ishizuka
M
Nakao
H
Yahata
Y
Imai
H
Kakizaki
H
, et al.  . 
Genetic polymorphisms of 17beta-hydroxysteroid dehydrogenase 3 and the risk of hypospadias
J Sex Med
 , 
2010
, vol. 
7
 (pg. 
2729
-
2738
)
Schnack
TH
Zdravkovic
S
Myrup
C
Westergaard
T
Christensen
K
Wohlfahrt
J
Melbye
M
Familial aggregation of hypospadias: a cohort study
Am J Epidemiol
 , 
2008
, vol. 
167
 (pg. 
251
-
256
)
Schnack
TH
Poulsen
G
Myrup
C
Wohlfahrt
J
Melbye
M
Familial coaggregation of cryptorchidism and hypospadias
Epidemiology
 , 
2009
, vol. 
21
 (pg. 
109
-
113
)
Schnack
TH
Poulsen
G
Myrup
C
Wohlfahrt
J
Melbye
M
Familial coaggregation of cryptorchidism, hypospadias, testicular germ cell cancer: a nationwide cohort study
J Natl Cancer Inst
 , 
2010
, vol. 
102
 (pg. 
187
-
192
)
Schnitzer
PG
Olshan
AF
Erickson
JD
Paternal occupation and risk of birth defects in offspring
Epidemiology
 , 
1995
, vol. 
6
 (pg. 
577
-
583
)
Schoenwolf
GC
Bleyl
SB
Brauwer
PR
Francis-West
PH
Larsen's Human Embryology
 , 
2009
4th edn
Philadelphia, USA
Churchill Livingstone
Schönbucher
VB
Weber
DM
Landolt
MA
Psychosocial adjustment, health-related quality of life, psychosexual development of boys with hypospadias: a systematic review
J Pediatr Psychol
 , 
2008
, vol. 
33
 (pg. 
520
-
535
)
Schweikert
HU
Schlüter
M
Romalo
G
Intracellular and nuclear binding of [3H]dihydrotestosterone in cultured genital skin fibroblasts of patients with severe hypospadias
J Clin Invest
 , 
1989
, vol. 
83
 (pg. 
662
-
668
)
Scott
HM
Mason
JI
Sharpe
RM
Steroidogenesis in the fetal testis and its susceptibility to disruption by exogenous compounds
Endocr Rev
 , 
2009
, vol. 
30
 (pg. 
883
-
925
)
Sharpe
RM
The 'oestrogen hypothesis’—where do we stand now?
Int J Androl
 , 
2003
, vol. 
26
 (pg. 
2
-
15
)
Sharpe
RM
Skakkebæk
NE
Are oestrogens involved in falling sperm counts and disorders of the male reproductive tract?
Lancet
 , 
1993
, vol. 
341
 (pg. 
1392
-
1395
)
Sharpe
RM
Skakkebæk
NE
Testicular dysgenesis syndrome: mechanistic insights and potential new downstream effects
Fertil Steril
 , 
2008
, vol. 
89
 (pg. 
e33
-
e38
)
Shehata
BM
Elmore
JM
Bootwala
Y
Steelman
CK
Bare
JB
Shoffeitt
CJ
Wang
R
Zhau
HE
He
D
Zhu
G
, et al.  . 
Immunohistochemical characterization of sonic hedgehog and its downstream signaling molecules during human penile development
Fetal Pediatr Pathol
 , 
2011
, vol. 
30
 (pg. 
244
-
251
)
Sherbet
DP
Tiosano
D
Kwist
KM
Hochberg
Z
Auchus
RJ
CYP17 mutation E305G causes isolated 17,20-lyase deficiency by selectively altering substrate binding
J Biol Chem
 , 
2003
, vol. 
278
 (pg. 
48563
-
48569
)
Sherbotie
JR
van Heyningen
V
Axton
R
Williamson
K
Finn
LS
Kaplan
BS
Hemolytic uremic syndrome associated with Denys-Drash syndrome
Pediatr Nephrol
 , 
2000
, vol. 
14
 (pg. 
1092
-
1097
)
Silver
RI
Russell
DW
5alpha-reductase type 2 mutations are present in some boys with isolated hypospadias
J Urol
 , 
1999
, vol. 
162
 (pg. 
1142
-
1145
)
Silver
RI
Rodriguez
R
Chang
TSK
Gearhart
JP
In vitro fertilization is associated with an increased risk of hypospadias
J Urol
 , 
1999
, vol. 
161
 (pg. 
1954
-
1957
)
Sinclair
AH
Berta
P
Palmer
MS
Hawkins
JR
Griffiths
BL
Smith
MJ
Foster
JW
Frischauf
AM
Lovell-Badge
R
Goodfellow
PN
A gene from the human sex-determining region encodes a protein with homology to a conserved DNA-binding motif
Nature
 , 
1990
, vol. 
346
 (pg. 
240
-
244
)
Skakkebæk
NE
Rajpert-De Meyts
E
Main
KM
Testicular dysgenesis syndrome: an increasingly common developmental disorder with environmental aspects
Hum Reprod
 , 
2001
, vol. 
16
 (pg. 
972
-
978
)
Skriver
MV
Pedersen
L
Stang
P
Lund
L
Rothman
KJ
Sørensen
HT
The month of birth does not affect the risk of hypospadias
Eur J Epidemiol
 , 
2004
, vol. 
19
 (pg. 
1135
-
1136
)
Sørensen
HT
Pedersen
L
Nørgaard
M
Wogelius
P
Rothman
KJ
Maternal asthma, preeclampsia and risk of hypospadias
Epidemiology
 , 
2005
, vol. 
16
 (pg. 
806
-
807
)
Sørensen
HT
Pedersen
L
Skriver
MV
Nørgaard
M
Norgard
B
Hatch
EE
Use of clomifene during early pregnancy and risk of hypospadias: population based case–control study
BMJ
 , 
2005
, vol. 
330
 (pg. 
126
-
127
)
Stoll
C
Alembik
Y
Roth
MP
Dott
B
Genetic and environmental factors in hypospadias
J Med Genet
 , 
1990
, vol. 
27
 (pg. 
559
-
563
)
Storgaard
L
Bonde
JP
Olsen
J
Male reproductive disorders in humans and prenatal indicators of estrogen exposure. A review of published epidemiological studies
Reprod Toxicol
 , 
2006
, vol. 
21
 (pg. 
4
-
15
)
Sun
G
Tang
D
Liang
J
Wu
M
Increasing prevalence of hypospadias associated with various perinatal risk factors in Chinese newborns
Urology
 , 
2009
, vol. 
73
 (pg. 
1241
-
1245
)
Sutherland
RW
Wiener
JS
Hicks
JP
Marcelli
M
Gonzales
ET
Jr
Roth
DR
Lamb
DJ
Androgen receptor gene mutations are rarely associated with isolated penile hypospadias
J Urol
 , 
1996
, vol. 
156
 (pg. 
828
-
831
)
Suzuki
K
Bachiller
D
Chen
YP
Kamikawa
M
Ogi
H
Haraguchi
R
Ogino
Y
Minami
Y
Mishina
Y
Ahn
K
, et al.  . 
Regulation of outgrowth and apoptosis for the terminal appendage: external genitalia development by concerted actions of BMP signaling [corrected]
Development
 , 
2003
, vol. 
130
 (pg. 
6209
-
6220
)
Tannour-Louet
M
Han
S
Corbett
ST
Louet
JF
Yatsenko
S
Meyers
L
Shaw
CA
Kang
SH
Cheung
SW
Lamb
DJ
Identification of de novo copy number variants associated with human disorders of sexual development
PLoS One
 , 
2010
, vol. 
5
 pg. 
e15392
 
Tateno
T
Sasagawa
I
Ashida
J
Nakada
T
Ogata
T
Absence of Y-chromosome microdeletions in patients with isolated hypospadias
Fertil Steril
 , 
2000
, vol. 
74
 (pg. 
399
-
400
)
Terakawa
T
Shima
H
Yabumoto
H
Koyama
K
Ikoma
F
Androgen receptor levels in patients with isolated hypospadias
Acta Endocrinol (Copenh)
 , 
1990
, vol. 
123
 (pg. 
24
-
29
)
Thai
HTT
Kalbasi
M
Lagerstedt
K
Frisén
L
Kockum
I
Nordenskjöld
A
The valine allele of the V89L polymorphism in the 5-alpha-reductase gene confers a reduced risk for hypospadias
J Clin Endocrinol Metab
 , 
2005
, vol. 
90
 (pg. 
6695
-
6698
)
Thai
HT
Soderhall
C
Lagerstedt
K
Omrani
MD
Frisen
L
Lundin
J
Kockum
I
Nordenskjöld
A
A new susceptibility locus for hypospadias on chromosome 7q32.2-q36.1
Hum Genet
 , 
2008
, vol. 
124
 (pg. 
155
-
160
)
Thorup
J
McLachlan
R
Cortes
D
Nation
TR
Balic
A
Southwell
BR
Hutson
JM
What is new in cryptorchidism and hypospadias—a critical review on the testicular dysgenesis hypothesis
J Pediatr Surg
 , 
2010
, vol. 
45
 (pg. 
2074
-
2086
)
Tria
A
Hiort
O
Sinnecker
GHG
Steroid 5alpha-reductase 1 polymorphisms and testosterone/dihydrotestosterone ratio in male patients with hypospadias
Horm Res
 , 
2004
, vol. 
61
 (pg. 
180
-
183
)
Tüzel
E
Şamli
H
Kuru
I
Türkmen
S
Demir
Y
Maralcan
G
Güler
C
Association of hypospadias with hypoplastic synpolydactyly and role of HOXD13 gene mutations
Urology
 , 
2007
, vol. 
70
 (pg. 
161
-
164
)
Utsch
B
Kaya
A
Özburun
A
Lentze
MJ
Albers
N
Ludwig
M
Exclusion of WTAP and HOXA13 as candidate genes for isolated hypospadias
Scand J Urol Nephrol
 , 
2003
, vol. 
37
 (pg. 
498
-
501
)
van der Werff
JFA
Nievelstein
RAJ
Brands
E
Luijsterburg
AJM
Vermeij-Keers
C
Normal development of the male anterior urethra
Teratology
 , 
2000
, vol. 
61
 (pg. 
172
-
183
)
van der Zanden
LFM
van Rooij
IALM
Feitz
WFJ
Knight
J
Donders
ART
Renkema
KY
Bongers
EMHF
Vermeulen
SHHM
Kiemeney
LALM
Veltman
JA
, et al.  . 
Common variants in DGKK are strongly associated with risk of hypospadias
Nat Genet
 , 
2011
, vol. 
43
 (pg. 
48
-
50
)
van der Zanden
LFM
van Rooij
IALM
Feitz
WFJ
Vermeulen
SHHM
Kiemeney
LALM
Knoers
NVAM
Roeleveld
N
Franke
B
Genetics of hypospadias: are single-nucleotide polymorphisms in SRD5A2, ESR1, ESR2, ATF3 really associated with the malformation?
J Clin Endocrinol Metab
 , 
2010
, vol. 
95
 (pg. 
2384
-
2390
)
van Gelder
MMHJ
van Rooij
IALM
Miller
RK
Zielhuis
GA
de Jong-van den Berg
LTW
Roeleveld
N
Teratogenic mechanisms of medical drugs
Hum Reprod Update
 , 
2010
, vol. 
16
 (pg. 
378
-
394
)
Vidaeff
AC
Sever
LE
In utero exposure to environmental estrogens and male reproductive health: a systematic review of biological and epidemiologic evidence
Reprod Toxicol
 , 
2005
, vol. 
20
 (pg. 
5
-
20
)
Virtanen
HE
Rajpert-De Meyts
E
Main
KM
Skakkebæk
NE
Toppari
J
Testicular dysgenesis syndrome and the development and occurrence of male reproductive disorders
Toxicol Appl Pharmacol
 , 
2005
, vol. 
207
 (pg. 
501
-
505
)
Vottero
A
Minari
R
Viani
I
Tassi
F
Bonatti
F
Neri
TM
Bertolini
L
Bernasconi
S
Ghizzoni
L
Evidence for epigenetic abnormalities of the androgen receptor gene in foreskin from children with hypospadias
J Clin Endocrin Metab
 , 
2011
, vol. 
96
 (pg. 
E1953
-
E1962
)
Vrijheid
M
Armstrong
B
Dolk
H
van
TM
Botting
B
Risk of hypospadias in relation to maternal occupational exposure to potential endocrine disrupting chemicals
Occup Environ Med
 , 
2003
, vol. 
60
 (pg. 
543
-
550
)
Walczak-Sztulpa
J
Wisniewska
M
Latos-Bielenska
A
Linné
M
Kelbova
C
Belitz
B
Pfeiffer
L
Kalscheuer
V
Erdogan
F
Kuss
AW
, et al.  . 
Chromosome deletions in 13q33–34: report of four patients and review of the literature
Am J Med Genet A
 , 
2008
, vol. 
146
 (pg. 
337
-
342
)
Waller
DK
Shaw
GM
Rasmussen
SA
Hobbs
CA
Canfield
MA
Siega-Riz
AM
Gallaway
MS
Correa
A
Prepregnancy obesity as a risk factor for structural birth defects
Arch Pediatr Adolesc Med
 , 
2007
, vol. 
161
 (pg. 
745
-
750
)
Wang
Y
Li
Q
Xu
J
Liu
Q
Wang
W
Lin
Y
Ma
F
Chen
T
Li
S
Shen
Y
Mutation analysis of five candidate genes in Chinese patients with hypospadias
Eur J Hum Genet
 , 
2004
, vol. 
12
 (pg. 
706
-
712
)
Wang
Z
Liu
BC
Lin
GT
Lin
CS
Lue
TF
Willingham
E
Baskin
LS
Up-regulation of estrogen responsive genes in hypospadias: microarray analysis
J Urol
 , 
2007
, vol. 
177
 (pg. 
1939
-
1946
)
Watanabe
M
Yoshida
R
Ueoka
K
Aoki
K
Sasagawa
I
Hasegawa
T
Sueoka
K
Kamatani
N
Yoshimura
Y
Ogata
T
Haplotype analysis of the estrogen receptor 1 gene in male genital and reproductive abnormalities
Hum Reprod
 , 
2007
, vol. 
22
 (pg. 
1279
-
1284
)
Watts
DH
Li
D
Handelsman
E
Tilson
H
Paul
M
Foca
M
Vajaranant
M
Diaz
C
Tuomala
R
Thompson
B
Assessment of birth defects according to maternal therapy among infants in the Women and Infants Transmission Study
J Acquir Immune Defic Syndr
 , 
2007
, vol. 
44
 (pg. 
299
-
305
)
Wehrung
DA
Hay
S
A study of seasonal incidence of congenital malformations in the United States
Br J Prev Soc Med
 , 
1970
, vol. 
24
 (pg. 
24
-
32
)
Weidner
IS
Møller
H
Jensen
TK
Skakkebæk
NE
Cryptorchidism and hypospadias in sons of gardeners and farmers
Environ Health Perspect
 , 
1998
, vol. 
106
 (pg. 
793
-
796
)
Weidner
IS
Møller
H
Jensen
TK
Skakkebæk
NE
Risk factors for cryptorchidism and hypospadias
J Urol
 , 
1999
, vol. 
161
 (pg. 
1606
-
1609
)
Wennerholm
UB
Bergh
C
Hamberger
L
Lundin
K
Nilsson
L
Wikland
M
Källén
B
Incidence of congenital malformations in children born after ICSI
Hum Reprod
 , 
2000
, vol. 
15
 (pg. 
944
-
948
)
Wilhelm
D
Englert
C
The Wilms tumor suppressor WT1 regulates early gonad development by activation of Sf1
Genes Dev
 , 
2002
, vol. 
16
 (pg. 
1839
-
1851
)
Wogelius
P
Horváth-Puhó
E
Pedersen
L
Nørgaard
M
Czeizel
AE
Sørensen
HT
Maternal use of oral contraceptives and risk of hypospadias—a population-based case–control study
Eur J Epidemiol
 , 
2006
, vol. 
21
 (pg. 
777
-
781
)
Wu
WH
Chuang
JH
Ting
YC
Lee
SY
Hsieh
CS
Developmental anomalies and disabilities associated with hypospadias
J Urol
 , 
2002
, vol. 
168
 (pg. 
229
-
232
)
Yadav
C
Bajpai
M
Kumar
V
Ahmed
RS
Gupta
P
Banerjee
BD
Polymorphism in CYP1A1, GSTM 1, GSTT1 genes and organochlorine pesticides in the etiology of hypospadias
Hum Exp Toxicol
 , 
2011
, vol. 
30
 (pg. 
1464
-
1474
)
Yamada
G
Satoh
Y
Baskin
LS
Cunha
GR
Cellular and molecular mechanisms of development of the external genitalia
Differentiation
 , 
2003
, vol. 
71
 (pg. 
445
-
460
)
Yamaguchi
TP
Bradley
A
McMahon
AP
Jones
S
A Wnt5a pathway underlies outgrowth of multiple structures in the vertebrate embryo
Development
 , 
1999
, vol. 
126
 (pg. 
1211
-
1223
)
Yang
J
Carmichael
SL
Kaidarova
Z
Shaw
GM
Risks of selected congenital malformations among offspring of mixed race-ethnicity
Birth Defects Res A Clin Mol Teratol
 , 
2004
, vol. 
70
 (pg. 
820
-
824
)
Yinon
Y
Kingdom
JCP
Proctor
LK
Kelly
EN
Salle
JLP
Wherrett
D
Keating
S
Nevo
O
Chitayat
D
Hypospadias in males with intrauterine growth restriction due to placental insufficiency: the placental role in the embryogenesis of male external genitalia
Am J Med Genet A
 , 
2010
, vol. 
152A
 (pg. 
75
-
83
)
Zhang
X
Chen
Y
Zhao
S
Markljung
E
Nordenskjöld
A
Hypospadias associated with hypertelorism, the mildest phenotype of Opitz syndrome
J Hum Genet
 , 
2011
, vol. 
56
 (pg. 
348
-
351
)
Zweier
C
Thiel
CT
Dufke
A
Crow
YJ
Meinecke
P
Suri
M
Ala-Mello
S
Beemer
F
Bernasconi
S
Bianchi
P
, et al.  . 
Clinical and mutational spectrum of Mowat-Wilson syndrome
Eur J Med Genet
 , 
2005
, vol. 
48
 (pg. 
97
-
111
)