Response: Re: HRAS1 Rare Minisatellite Alleles and Breast Cancer in Australian Women Under Age Forty Years

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We welcome Dr. Krontiris' offer to exchange samples for repeat genotyping between our laboratories to help resolve the issues raised by our report and his letter.

Dr. Krontiris considers our study to have two flaws. On the technical side, we do not believe that our polymerase chain reaction (PCR)-based genotyping system is failing to detect large HRAS1 variable number of tandem repeats (VNTR) alleles due to “allele steal” (dropout). We were well aware of this phenomenon when we commenced this work and undertook considerable PCR optimization to reduce or eliminate it (1). We used a proofreading enzyme system. Trials with dimethyl sulfoxide and multistage cycling protocols did not provide improvements. (Betaine was not tested.) Our technique allowed us to amplify HRAS1 allele heterozygote combinations with large size differences; i.e., a1, a4 + 3, and a1, a4 + 8 (see Table 1 from our study) and a1, a4 + 15 (unpublished results). We did not experience allele dropout.