MRC1 and cancer: The discovery of a link between human cancer and MMR defects has led to an increased interest in eukaryotic MMR.13 Frameshift mutations of short-tandem repetitive sequences indicate instability of these sequences [microsatellite instability (MSI)] and represent a hallmark of MMR deficiency in human cancers.14, 15 Since MSI can be detected in colitis tissue without dysplasia, inactivation of the MMR system must be an early event in colon carcinogenesis in ulcerative colitis.