The syndrome results from a germline mutation in genes for mismatch repair (MMR) proteins leading to insufficient DNA repair and development of tumors characterized by high levels of instability in short tandem repeat DNA sequences (microsatellites) or "microsatellite instability-high" (MSI-H).
The syndrome is explained by germline mutations in DNA mismatch repair (MMR) genes, and there is a need for diagnostic tools to preselect patients for genetic testing to diagnose those with HNPCC.