Affected individuals from 431 families gave blood for mutational analysis in BRCA1 and BRCA2 mainly to develop genetic tests for their family. Individuals were eligible if there was at least a 50% chance of a gene predisposing to breast cancer (not necessarily BRCA1/2) in their family. Assessment was made using the Cancer and Steroid Hormone (CASH) dataset and the Claus curves.1,2 A minimal requirement was two close relatives with breast cancer before the age of 50 years, but combinations of male and female breast cancer, and breast and ovarian cancer were particularly identified. An exception to this were two research projects where population based cases of breast cancer before the age of 31 years3 and sporadic breast cancer before the age of 36 years4 were screened for both genes. Male breast cancer (MBC) families presenting to the clinic with at least one MBC before the age of 60 years or at any age if female breast cancer had occurred were screened for BRCA2.5

Initial screening for mutations involved a whole gene assessment using single strand conformational polymorphism (SSCP) analysis and protein truncation testing (PTT) of exon 11 in each gene. All mutations were confirmed, in both orientations, by direct fluorescent sequencing of the appropriate exon. We excluded one exon 13 duplication and two exonic deletions detected on screening 95 BRCA1 negative breast/ovarian families. A further two exon 13 duplications in five subsequent BRCA1 negative breast/ovary families originating from east of the Pennines were also excluded. Of the non large-scale rearrangement mutations, 26/78 (33%) were detected outside the commonly screened regions of BRCA1 (exons 2, 11, 20) in the UK (table 1). Similarly 15/50 (30%) BRCA2 mutations were detected outside exons 10 and 11.