Yet the contribution of high- and medium-penetrance loci to breast-cancer risk varies markedly by ancestry: ATM shows limited relevance in Asians, founder BRCA2 mutations greatly elevate risk in Ashkenazi Jews, pathogenic BRCA2 and PALB2 variants are more common in Black women, and CHEK2 frequencies are lower in both Black and Asian populations. The gene discussed is ATM; the disease is breast cancer.