BRCA1 and BRCA2 mutation carriers have increased risks of breast and ovarian cancer. In this Dutch study the authors examined these risks and their variation. We found that the average risks of breast and ovarian cancer by age 70 were 45% and 31%, respectively, for BRCA1 and 27% and 6%, respectively, for BRCA2 mutation carriers. Among BRCA1 carriers the relatively low average risk estimates result from the lower risks in older generations and the lower risks in families with a moderate family history. Founder mutations also played a role. For BRCA2 we did not find such explanations. (By Dr Matti A Rookus, http://jmg.bmj.com/content/early/2013/11/27/jmedgenet-2013-101974 )