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.