A novel BRCA1 mutation in an identical twin pair with similar clinical histories

Factors affecting the penetrance and expression of BRCA1 are not understood. Breast cancer risk and ovarian cancer risk, in general, are known to be associated with non-Mendelian factors. However, whether and how these various factors influence tumor development in BRCA1 mutation carriers is not known. Here we report the breast and ovarian cancer syndrome in an identical twin pair. These female identical twins had remarkably similar clinical histories. Both twins developed histologically similar ovarian cancer in their mid-fifties. One twin was diagnosed with stage III disease and died of refractory metastatic disease. The other twin was diagnosed with stage I disease but ultimately died of recurrent disease. Neither twin developed breast or colon cancer. The twins have both similarities and differences in terms of nongenetic cancer-related risk factors. Results of BRCA1 analysis of DNA from both twins revealed a novel mutation, 2711delA, which resulted in a premature termination at codon 892. This report has intriguing implications concerning the role of genotype in the ultimate penetrance and expression of disease among BRCA1 mutation carriers.