Lynch syndrome (LS), also was known as Hereditary non-polyposis colorectal cancer, is the most common hereditary colon cancer syndrome which is an autosomal dominant disease and is caused by germline mutations in one of several DNA mismatch repair (MMR) genes, including MSH2 on chromosome 2p16, MLH1 on chromosome 3p21, MSH6 on chromosome 2p16, and PSM2 on chromosome 7p22 (Lynch et al., 2009[32]). The gene discussed is MLH1; the disease is Lynch syndrome.