BRCA1 and breast cancer: On the basis of the model with an age-decreasing σP2(t), the proportion of the total breast cancer familial variance attributed to TP53 was 3.5% at age 20–29 years and decreased with age thereafter; in terms of the residual familial variance after adjusting for the effects of BRCA1, BRCA2, PALB2, CHEK2, and ATM, the proportion decreased from 6.1% at age 20–29 years (Figure 1; Table S6).