BRCA1 and breast cancer: Women with pathogenetic variants in high-risk breast cancer susceptible genes such as BRCA1 and BRCA2 have a greater breast cancer risk, especially at young ages [20, 21]; however, the proportions of women with such pathogenetic variants are similar between participants in the UK Biobank and the population [21, 22], so that the elevated SIR in ages < 45 years is unlikely to be due to this.