PubMed:10627141 JSONTXT 9 Projects

Four new mutations in the DNA mismatch repair gene MLH1 in colorectal cancers with microsatellite instability. Mutations in brief no. 157. Online. Hereditary nonpolyposis colorectal cancer (HNPCC) is frequently associated with inherited mutation in one of four DNA mismatch repair genes. Somatic mutations in the same genes are also found in a subset of sporadic colorectal cancers. A defect in DNA mismatch repair results in a RER (replication error) tumor phenotype. We screened 110 archival and 11 prospectively acquired colorectal cancers for the RER phenotype. A total of 22 cancers were RER-positive. RER-positive tumors were investigated for mutations in the DNA mismatch repair gene MLH1 using single-strand-conformation-polymorphism (SSCP) analysis. We identified four previously undescribed mutations in four different samples. Three mutations were exonic: a point mutation at codon 69 (AGG-->AAG(arg-->lys]); a single base pair deletion at codon 42/43 (GCAAAATCC-->GCAAATCC) leading to a new stop codon downstream; and a point mutation at codon 757 (TAA-->TAT [termination-->tyr] which extend the MLH1 peptide by 36 ammino acids. The fourth mutation was a 1 base pair insertion six base pairs 5' to the start of exon 14 (tttgtttt-->tttggtttt). The mutations were not seen in the patients' constitutional DNA. The somatic MLHI mutations identified appear to be causally associated with the RER phenotype.