BRCA1-positive patients are small for gestational age compared with their unaffected relatives.

The BRCA1 gene is thought to exert its main function early in life. We, therefore, studied the effects of BRCA1 mutations on birth weight and birth length. This was carried out by comparing 33 women with and without mutations. Birth weight and length were obtained from a self-administered questionnaire. BRCA1 mutations carriers had a significantly lower birth weight (P = 0.0041) compared with non-carriers, after adjustment for gestational age. They were also significantly shorter at birth compared with their unaffected relatives (P = 0.0060), after adjustment for gestational age. The BRCA1 gene thus seems to influence the carriers in utero. The findings could imply that humans heterozygotic for the BRCA1 mutations may be influenced by the mutations during development in utero.