Studies in western countries indicate that among BRCA1 and BRCA2 mutation carriers, breast cancer risks, age for age, are significantly higher among women born more recently than among women born earlier, even with the same mutations in the same families.22,23 The causes of the increase in risk by birth cohort are not genetic but are changes in the same aforementioned features of reproductive history. The gene discussed is BRCA1; the disease is breast carcinoma.