MLH1 and neoplasm: Within tumours of the digestive system, the microinstability of satellites, which is an alteration in the repair system due to DNA mismatch, leads to the accumulation of a great variety of mutations (primarily in the MLH1, PMS2, MSH2, and MSH6 genes) that are detectable using immunohistochemistry, and DNA polymerase generates alterations in the length of the microsatellites (i.e., in consecutive repeats of noncoding DNA) in tumour cells.