Detection of Microsatellite Instability

In 1993, three groups independently discovered that the lengths of microsatellites in tumors could vary from the normally constant pattern defined at birth (5 –5 ) (see review in ref. 4 ). This discovery has been designated either microsatellite instability (MSI) or replication errors (RER). A recent international consensus conference convened by the National Cancer Institute defined MSI/RER as “a change in length due to either insertion or deletion of repeating units, in a microsatellite within a tumor when compared to normal tissue” (5 ). Microsatellites are regions of repetitive DNA in which the repeating unit is small, varying in length from 1 to 6 nucleotides, and in which the number of repeating units in a microsatellite can vary from 10–60 (6 –7 ). Because microsatellite lengths generally vary from person to person, they have received widespread use in forensics, gene mapping, parentage testing,