Specifically the overwhelming majority of hereditary nonpolyposis colorectal cancers (HNPCC) are attributed to mutations in the genes encoding the MutS and MutL homologues MSH2 and MLH1 respectively, which allows them to be classified as tumour suppressor genes.
Hereditary nonpolyposis colorectal cancer (HNPCC) is very often caused by a defective MSH2 gene leading to defective mismatch repair, but displays no symptoms of "accelerated aging".
Disruption of an exon splicing ehancer in exon 3 of MLH1 gene is the cause of HNPCC (hereditary non polyposis colorectal cancer) in a Quebec family.
The most frequent mutations in HNPCC are mutations in the MSH2 and MLH1 genes.
# DNA repair proteins are usually classified as tumor suppressors as well, as mutations in their genes increase the risk of cancer, for example mutations in HNPCC, MEN1 and BRCA.