The goal of this study was to examine if low levels of constitutional DNA methylation corresponding to high levels of tumor DNA methylation could be identified at breast cancer predisposition genes other than BRCA1. We included blood and tumor-derived DNA from young affected women participating in the Australian Breast Cancer Family Study (ABCFS), using the Infinium HumanMethylation450 (HM450K) beadchip assay. This evidence concerns the gene BRCA1 and breast carcinoma.