Genetic epidemiology of BRCA mutations--family history detects less than 50% of the mutation carriers.

Ten BRCA mutations were demonstrated to be frequent in the Norwegian population. We present maps verifying the uneven distribution of prevalences according to municipality. We tested incident breast cancer cases treated in Mid-Norway from 1999 onwards for these mutations. Uptake of testing was 97% and 2.5% were demonstrated to be mutation carriers. Ten (77%) were outside families previously known to carry a mutation. Ten (77%) did not meet clinical criteria to be selected for mutation testing. We tested incident ovarian cancer cases in South-West Norway from 2001 onwards. Uptake of testing was 80% and 23% were mutation carriers. Twenty-one (88%) were outside families previously known. Twelve (67%) did not meet clinical criteria to be selected for testing. All patients with mutation collaborated actively to give our offer of predictive genetic testing to their relatives. No complaint on the activity was received.