Mismatch repair (MMR) proteins is a group of nuclear enzymes, which in all proliferating cells participate in repair of base-base mismatch, that occur during DNA replication. The proteins form complexes that bind to areas of abnormal DNA and initiates its removal. MMR can ensure the integrity and stability of genetic materials, avoid mutation of genetic substances, and ensure high fidelity of DNA replication, which is composed of MLH1, MSH2, MSH6, PMS2, etc. Loss of MMR proteins leads to an accumulation of DNA replication errors in the proliferating cells, particularly in areas of the genome with short repetitive nucleotide sequences, a phenomenon known as microsatellite instability (MSI). About 3-5% of all colorectal carcinomas are related to a mutation in the MMR proteins. Carriers of an MLH1 or MSH2 mutation has a more than 70% lifetime risk of developing a colorectal carcinoma. At present, MSH2 with combinated to MSH6, MLH1 and PMS2 is commonly used in Lynch syndrome screening.