Gender Identity Disorder in Twins: A Review of the Case Report Literature

ABSTRACT

Introduction

The etiology of gender identity disorder (GID) remains largely unknown. In recent literature, increased attention has been attributed to possible biological factors in addition to psychological variables.

Aim

To review the current literature on case studies of twins concordant or discordant for GID.

Methods

A systematic, comprehensive literature review.

Results

Of 23 monozygotic female and male twins, nine (39.1%) were concordant for GID; in contrast, none of the 21 same-sex dizygotic female and male twins were concordant for GID, a statistically significant difference (P = 0.005). Of the seven opposite-sex twins, all were discordant for GID.

Conclusions

These findings suggest a role for genetic factors in the development of GID.

Twins, Gender Identity Disorder, Genetics, Biologic Factors in GID, Transsexualism

© International Society for Sexual Medicine 2011