High frequency of BRCA1/2 germline mutations in 42 Belgian families with a small number of symptomatic subjects.

The initial risk assessments for BRCA1/2 mutation carriers and estimates of carrier frequencies were based on extended pedigrees with a large number of symptomatic subjects. When counselling based on BRCA gene mutation analysis was initiated, we faced requests for counselling mostly from members of small families with only two or three affected members. We report on the likelihood of finding a BRCA mutation in such small families.,In the first 100 families that came for oncogenetic counselling since September 1994, a BRCA1/2 gene mutation screen was initiated if there were two or more symptomatic first degree relatives, if one of them had ovarian cancer, or if one breast cancer was diagnosed before the age of 50 years.,BRCA gene mutations were found and confirmed by sequencing in 14 out of 42 families (33%); 10 mutations were in the BRCA1 gene and four in the BRCA2 gene. Our findings indicate an increased probability of detecting a BRCA gene mutation when ovarian cancer occurred in the family. There is no increased probability of detecting a mutation with increasing numbers of breast cancers. Only 22% of the eligible presymptomatic family members opted for testing. The presymptomatic female carriers currently prefer breast surveillance rather than prophylactic surgery.,BRCA1/2 gene mutation testing can be done with reasonable efficiency in the Belgian population when there are two symptomatic family members. The availability of testing does not lead to a high frequency of requests for testing by presymptomatic family members.