The molecular mechanisms behind MSI involve defects in the MMR pathway. Normally, MMR proteins recognize and repair erroneous insertions, deletions, and misincorporations of bases that can occur during DNA replication. When MMR proteins are nonfunctional due to genetic mutations, these errors accumulate, resulting in MSI. Key proteins involved in the MMR system include MLH1, MSH2, MSH6, and PMS2.
