Identification of new susceptibility genes in familial breast cancer by exome sequencing.

Abstract

1538 Background: Familial breast cancer was described in the early 1970s with its syndromy confirmed by the discovery of BRCA germline mutations in the 1990s. BRCA mutations account for less than 10% of affected families. Efforts made in the past two decades have resulted in limited results in identifying additional susceptibility genes for familial breast cancer. Methods: Using exome sequencing, we analyzed eight members in a BRCA1-, BRCA2-, p53- and PTEN-negative breast cancer family; five with breast cancer and three unaffected. Mutation candidates were idenified by bioinformatics analysis, experimentally validated by Sanger sequencing and their damaging effect was predicted by the SIFT program. Validated mutations were also tested in 42 additional breast cancer samples from BRCA-negative breast cancer families. Results: We identified 55 non-synonymous germline mutations affecting 49 genes in multiple members of this family, 20 of 22 selected mutations predicted to cause damaging effects were validated. As an exemplar, two mutations in the MYST4 gene were detected at the C terminal (p.D1516Y and p.R1577C), validated, and predicted to cause damaging consequences. MYST4 is a histone acetyltransferase (Champagne, N. et al. JBC. 274, 28528-28536,1999). It contains a C2HC-type finger and a PHD-type zinc finger. Its N-terminal is involved in transcriptional repression while its C-terminal is involved in transcriptional activation and interacts with important transcriptional regulators RUNX1 and RUNX2. MYST4 is involved in DNA replication, transcriptional regulation, and epigenetic modification of chromatin structure. A translocation t(10;16)(q22;p13) between CREBBP and MYST4 was identified in acute myeloid leukemia. The 20 validated germline mutations were tested by Sanger sequencing in 42 additional breast cancer cases from 26 BRCA-negative families. None of the 20 mutations were detected. Conclusions: Results show that remaining unknown susceptibility genes are likely family-specific and can be detected in each affected family using genome sequencing approaches. These results may be the first reported in an exome sequencing study of BRCA-negative breast cancer families.