Mutation or epigenetic silencing of the human mismatch repair (MMR) genes MSH2, MSH6, MLH1 or PMS2 is the cause of Lynch syndrome or hereditary non-polyposis colorectal cancer (LS/HNPCC) as well as 10-40% of sporadic cancers [19]. The gene discussed is MLH1; the disease is hereditary nonpolyposis colon cancer.