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".
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This instability is usually due to the propensity of these regions to misalign during DNA repair, exacerbated by defects of the appearance of replication proteins (like FEN1 or Pol δ) that ubiquitously affect the integrity of the genome.
DNA polymerase delta is an enzyme complex found in eukaryotes that is involved in DNA replication and repair, and it consists of the proliferating cell nuclear antigen (PCNA), the multisubunit replication factor C, and the 4 subunit polymerase complex: POLD1, POLD2, POLD3, and POLD4.
Exonucleases remove these unpaired nucleotides and the gaps are filled by DNA synthesis and repair machinery.
# 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.