BRCA1 and breast cancer: In the families with two or more breast cancer cases and at least two of them diagnosed under the age of 50 and no ovarian cancer (Group A), the mutation detection rate for BRCA1 is 23% and for BRCA2 is 13% or 36% for both genes in the Slovenian population, 27% in the Dutch population and 37% in the German population [15,17].