For example, in hereditary nonpolyposis colon cancer (HNPCC), MLH1 inactivation via mutation can lead to microsatellite instability (MSI) and tumorigenesis, whereas in sporadic colon cancers, MLH1 is frequently silenced by methylation (Kane et al., 1997; Veigl et al., 1998). The gene discussed is MLH1; the disease is hereditary nonpolyposis colon cancer.