The proportion of the total breast cancer familial variance explained by the hypothetical gene was 21.6% at age 20–29 years and decreased steadily with age thereafter; in terms of the residual familial variance after adjusting for the effects of BRCA1, BRCA2, PALB2, CHEK2, ATM, and TP53, the proportion was 39.7% at age 20–29 years and decreased thereafter (Figure 1; Table S6). This evidence concerns the gene CHEK2 and breast cancer.