Hereditary non-polyposis colorectal cancer HNPCC

Hereditary non-polyposis colorectal cancer (HNPCC) is due to defects in mismatch repair (MMR) and thus to deficiencies in removing nucleotides mi-spaired by DNA polymerases as well as insertion/deletion loops (1-10 bases). This dramatically increases the mutation rate. The affected genes are MLHl (60%),MSH2 and MSH6. 

Mismatched bases produced during DNA replication are those not conforming to or A=T base pairing. They are identified and corrected in the new strand by the mismatch-repair enzyme complex . The mismatched nucleotides are identified and excised, and the gap filled by DNA polymerase. Mutations in this complex result in failure to correct mismatched base pairs and cause hereditary non-polyposis colorectal cancer (HNPCC). 

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