MRC1 and hereditary nonpolyposis colon cancer: Although mutations in MMR genes are believed to account for most HNPCC, the mechanism responsible for the MSI-H phenotype in sporadic CRC seems to involve methylation of MMR gene sequences, resulting in downregulation of gene expression (transcription) and subsequently less functional protein (Kane et al, 1997; Cunningham et al, 1998; Herman et al, 1998; Kuismanen et al, 1999).