Our current understanding of breast cancer susceptibility involves mutations in the 2 major genes BRCA1 and BRCA2, found in about 25% of high-risk families, as well as few other low penetrance genes such as ATM and CHEK2. Approximately two-thirds of the multiple cases families remain to be explained by mutations in still unknown genes. In a candidate gene approach to identify new genes potentially involved in breast cancer susceptibility, we analyzed genomic variants in the ZBRK1 gene, a co-repressor implicated in BRCA1-mediated repression of GADD45. Direct sequencing of ZBRK1 entire coding region in affected breast cancer individuals from 97 high-risk French Canadian breast/ovarian cancer families and 94 healthy controls led to the identification of 18 genomic variants. Haplotype analyses, using PHASE, COCAPHASE and HaploStats programs, put in evidence 3 specific haplotypes which could potentially modulate breast cancer risk, and among which 2 that are associated with a potential protective effect (p = 0.01135 and p = 0.00268), while another haplotype is over-represented in the case group (p = 0.00143). Further analyses of these haplotypes indicated that a strong component of the observed difference between both groups emerge from the first 5 variants (out of 12 used for haplotype determination). The present study also permitted to determine a set of tagging SNPs that could be useful for subsequent analyses in large scale association studies. Additional studies in large cohorts and other populations will however be needed to further evaluate if common and/or rare ZBRK1 sequence variants and haplotypes could be associated with a modest/intermediate breast cancer risk.
Copyright 2007 Wiley-Liss, Inc.