sentences:  Mutations in MSH2 and other mismatch repair genes cause DNA damage to go unrepaired, resulting in an increase in mutation frequency.These mutations build up over a person's life that otherwise would not have occurred had the DNA been repaired properly.The viability of MMR genes including "MSH2" can be tracked via microsatellite instability, a biomarker test that analyzes short sequence repeats which are very difficult for cells to replicate without a functioning mismatch repair system.