Targeted sequencing for hereditary breast and ovarian cancer in BRCA1/2-negative families from the Lynch Memorial Biobank reveals complex genetic architecture and phenocopies

In this study, we applied an efficient and inexpensive targeted sequencing approach to provide molecular diagnoses in 245 human samples representing 134 BRCA mutation negative (BRCAX) hereditary breast and ovarian cancer (HBOC) families recruited from 1973-2019 by Dr. Henry Lynch. Sequencing identified 391 variants, which were functionally annotated and ranked based on their predicted clinical impact. Known pathogenic CHEK2 breast cancer variants were identified in five BRCAX families in this study. While BRCAX was an inclusion criterion for this study, we still identified a pathogenic BRCA2 variant (p.Met192ValfsTer13) in one family. A portion of BRCAX families could be explained by other hereditary cancer syndromes that increase HBOC risk: Li-Fraumeni Syndrome (gene: TP53) and Lynch Syndrome (gene: MSH6). Interestingly, many families carried additional Variants of Undetermined Significance (VOUSs) that may further modify phenotypes of syndromic family members. Ten families carried more than one potential VOUS suggesting the presence of complex multi-variant families. Overall, nine BRCAX HBOC families in our study may be explained by known likely-pathogenic/pathogenic variants, and six families carried potential VOUSs, which require further functional testing.