Deficient MMR (dMMR) can occur either by germline mutations of genes encoding for MLH 1, MSH 2, MSH 6, and PMS2 protein as in Lynch syndrome (also called hereditary nonpolyposis colorectal cancer (HNPCC)) or by sporadic hypermethylation of the MLH 1 gene promoter [37]. The gene discussed is PMS2; the disease is hereditary nonpolyposis colon cancer.