The N-terminus of the Breast Cancer-1 predisposition protein (BRCA1) associates with the BRCA1-associated RING domain-1 protein (BARD1) to form a heterodimer, which exhibits ubiquitin ligase activity that is abrogated by known cancer-associated BRCA1 missense mutations.
Twenty patients (19%) were identified to carry deleterious mutations, of whom 13 (12%) were in the BRCA1 or BRCA2, 6 (6%) were in five other known breast cancer predisposition genes and 1 patient had a mutation in both BRCA2 and BARD1.
BARD1 is indispensable for cell viability, so loss-of-function mutations are rare, but mutations and truncations that alter its function might be involved in the pathogenesis of breast cancer.
Further analysis of haplotypes at BARD1 also revealed no evidence that additional common genetic variation not captured by Cys557Ser was associated with breast cancer risk.
Carriers of the common Icelandic BRCA2 999del5 mutation were found to have their risk of breast cancer further increased if they also carried the BARD1 variant: the frequency of the BARD1 variant allele was 0.047 (OR = 3.11, 95% CI 1.16-8.40, p = 0.046) in 999del5 carriers with breast cancer.
Using DHPLC analysis we screened the coding region of BARD1 for variants in 210 probands of breast cancer families including 129 families with no mutations in BRCA1 or BRCA2.
Germline pathogenic variants in BARD1, BRCA1, BRCA2, PALB2, and RAD51D were associated with high risk (odds ratio > 5.0) of TNBC and greater than 20% lifetime risk for overall breast cancer among Caucasians.
The connections between BRCA1/BARD1 and PR activity suggested by our findings may help explain why host mutations in BRCA1 exert a tissue specificity in preferentially elevating the risk of breast cancer.
BARD1-mutated BC index patients showed a significantly younger mean age at first diagnosis (AAD; 42.3 years, range 24-60 years) compared with the overall study sample (48.6 years, range 17-92 years; P = 0.00347).
Furthermore, the BARD1Cys557Ser allele does not appear to modify the risk of breast cancers among carriers of BRCA1 mutations, or of other predisposing mutations.
Here, we observe that purified RINGs from a variety of functionally unrelated proteins, including promyelocytic leukemia protein, KAP-1TIF1beta, Z, Mel18, breast cancer susceptibility gene product 1 (BRCA1), and BRCA1-associated RING domain (BARD1), self-assemble into supramolecular structures in vitro that resemble those they form in cells.
These results suggest that the contribution of the BARD1 germline variants to breast cancer predisposition is very limited, and that neither Cys557Ser nor Val507Met have an effect on familial breast cancer susceptibility.
The breast cancer susceptibility gene BARD1 (BRCA1-associated RING domain protein, MIM# 601593) acts with BRCA1 in DNA double-strand break (DSB) repair and also in apoptosis initiation.
BRCA1 or BRCA2 mutations were found in 7.3% of the subjects, 6.3% had a mutation in other breast cancer genes (PALB2, CHEK2, ATM, and BARD1), and 1.6% had mutations in genes not associated with breast cancer.