BRCA1 and breast cancer: The spectra of BRCA1 and BRCA2 mutations have been characterized in a number of different populations worldwide, with significant variation among populations in the contributions of these genes to hereditary breast and ovarian cancer.29 Founder mutations account for differing proportions of cancer in different populations; for example in the Ashkenazi Jewish population [12], three founder mutations have a combined population frequency of 2% and represent 60% of breast cancer families with a BRCA1 or BRCA2 gene mutation.