BRCA1 and Alzheimer disease: Initially, BRCA1 appears a good candidate gene for testing the theory of mutation accumulation because 1) when all BRCA1 mutations are taken together, the prevalence of breast and ovarian cancer linked to the BRCA1 locus is one of the highest among late-onset diseases and 2) in the absence of modern medicine, the disease leads to rapid and certain death (as opposed to slowly degenerative diseases, like Alzheimer dementia, whose effects on fitness are unclear).