What is microsatellite instability or MSI?
Microsatellites are stretches of nucleotide repeats within the genome that can act as hot spots where errors in DNA replication occur frequently. Normally these errors are repaired by the four major
mismatch repair or MMR proteins.
Sometimes in cancer cells the ability to correct replication errors is disrupted by mutations or methylation silencing of these MMR proteins. This is called mismatch repair deficiency or dMMR and allows replication errors to accumulate. While all microsatellites accumulate replication errors mononucleotide sequences are most sensitive and specific as biomarkers for dMMR.
This accumulation of errors due to mismatch repair deficiency in microsatellite regions is known as microsatellite instability or MSI.
