LAUSR

Abstract 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.