Identification of a novel pathogenic MLH1 mutation and recommended genetic screening strategy: An investigation of three Chinese Lynch syndrome pedigrees

BACKGROUND: Lynch syndrome (LS) is an autosomal‐dominant disorder that increases the risk of many cancers. The genetic basis of LS is germline mutations in DNA mismatch repair genes. METHODS: We performed next‐generation sequencing on blood cells obtained from the members of three unrelated LS pedigrees. Immunohistochemistry staining was performed to analyze protein expression. RESULTS: Multigene panel screening revealed three mutL homolog 1 (MLH1) pathogenic mutations (c.199G>A, c.790 + 1G>A, and c.1557_1558 + 8delGGGTACGTAA, unreported) confirmed by Sanger sequencing. Immunohistochemistry showed a loss of MLH1 protein expression. We also confirmed that the unreported mutant allele was inherited for at least three generations. CONCLUSION: These results provide new insights into the molecular mechanisms underlying the pathogenicity of MLH1 mutations and reaffirm the importance of genetic screening for the early diagnosis of LS.