What Does Microsatellite Instability Have to Do With HNPCC?
If a tumor is found to have microsatellite instability, scientists are more likely to find a mutation in one of the known DNA mismatch repair genes during genetic testing. The genes that cause HNPCC are DNA repair genes. Everyone has two copies of each gene one from their mother and one from their father. However, every cell in people with HNPCC has inherited one mutated copy of a DNA repair gene. If the remaining nonmutated copy of that DNA repair gene is deactivated in any cell, that cell’s ability to repair DNA is impaired. When a cell can’t repair damaged DNA, many mutations accumulate, and a tumor can result. In addition to making tumors more likely, the cell’s difficulty in repairing DNA causes another phenomenon called microsatellite instability. Microsatellites are repeated sequences of DNA. Although the length of these microsatellites is highly variable from person to person, each individual has microsatellites of a set length. These repeated sequences are common, and normal.
