Assuming a 5‐year difference in the age of cancer development between ALDH2 GG and GA/AA genotypes, we estimated that 100 cases with the BRCA1 or BRCA2 mutation would be necessary to detect the difference with an acceptable statistical power (expected mean age 55 in GG, 50 in GA/AA with standard deviation 10 with alpha error (0.05) and beta error (0.30)). The gene discussed is BRCA2; the disease is cancer.