Discovery of BRCA1/BRCA2 Founder Variants by Haplotype Analysis

A significant number of hereditary breast or ovarian cancers are caused by germline variants, mostly BRCA1/BRCA2 genes. Because genetic predispositions vary by ethnicity, several studies have reported founder variants of BRCA1/BRCA2 genes. Such founder variants were reported primarily based on their relevant population frequencies. We reviewed the variant data relating to BRCA1 and BRCA2 genes from January, 2012 to March 2019 at Samsung Medical Center, Seoul, Korea. Among the cases with pathogenic variants (PVs) or likely pathogenic variants (LPVs), we defined recurrent variants as those found in more than five unrelated patients. Using single nucleotide polymorphisms, we analyzed patient haplotypes. There were 14 recurrent variants in the BRCA1 gene and seven variants in the BRCA2 gene. Of note, three variants in each gene were primarily detected in Korean populations. Among them, the c.5339T > C BRCA1 variant had a long block sized 74.5 kb. In BRCA2 , the c.1399A > T variant had a long block sized 35.5 kb. We suggest that BRCA1 c.5339T > C and BRCA2 c.1399A > T are founder variants of the Korean population. These two recurrent variants were ethnicity-prevalent, primarily found in Korean populations, and the sizes of the linkage disequilibrium blocks are longer than others.