Microsatellite Instability

                          Microsatellite instability (MSI) has been shown to be relevant to various diseases, including cancers. Cells with mutations in one of the genes responsible for DNA mismatch repair (MMR) accumulate mutations at a very high rate. 

                            Because DNA mismatches are more likely to occur in DNA microsatellites, defective DNA MMR leads to the phenomenon of MSI, in which the progeny of the defective cells have  varying lengths of a given microsatellite. The microsatellite reference panel to study MSI is BAT25, BAT26, D5S346, D2S123, and D17S250. 

                            Studies of MSI are performed routinely in patients with colorectal cancer because of the defective MMR phenotype of colorectal carcinomas. The electrophoretic profile of the amplified products is compared between tumor and normal DNA from the same patient.