Usefulness of polymorphic markers in exclusion of BRCA1/BRCA2 mutations in families with aggregation of breast/ovarian cancers.

Founder mutations can account for a large proportion of BRCA1/BRCA2 gene abnormalities in a given population. However there is still a need to study the entire gene in many families, even in countries where founder mutations have been identified. It is possible to decrease the number of cases which are studied by complex and expensive sequencing/Southern blot analyses of BRCA1/BRCA2 genes by exclusion of common BRCA1/BRCA2 alleles in a given family by using polymorphic dinucleotide markers. The goal of o ur study was to assess the effectiveness of this method in exclusion of BRCA1/BRCA2 constitutional mutations. In each family, blood samples for genetic analyses were taken from two affected relatives from the same generation. Six polymorphic microsatellite markers linked to BRCA1/BRCA2 genes were analysed. Results obtained with these markers were verified by applying BRCA1 testing for the most common founder mutations in Poland and using exon by exon" sequencing of coding fragments of the BRCA2 gene. Polymorphic markers useful in BRCA1/BRCA2 analyses included only 3 of 6 examined - D17S855, D13S260 and D13S267. Occurrence of commoalleles of BRCA1 was excluded in 3 families and BRCA2 in 5 out of 30 families. Results obtained by testing for BRCA1 Polish founder mutations and BRCA2 sequencing were in agreement with BRCA1 findings based on polymorphic markers. The only exception was family 994 with BRCA1 exon 5 300T/G mutation, in which BRCA1 mutation carrier was excluded by using D17S855. Among 14 families without BRCA1 Polish founder mutations in this gene were excluded in 2 families and BRCA2 mutation was excluded in one family.