Microsatellite instability

Mutations in mismatch repair proteins were found in tumor cells from individuals with an inherited cancer predisposition called HNPCC (heritable nonpolyposis colon cancer).

Germ-line mutations in the genes for five different mismatch repair proteins have been found to be associated with HNPCC.

Tumor cells from those affected with HNPCC exhibit phenomenon called microsatellite instability—a large number of mutations in regions of the genome containing repeats of single-, double-, and triple-nucleotide sequences, usually with large increases in the numbers of repeating units in such sequences.

These data suggest that the product and template strands can normally slip at such sites so that DNA polymerase copies a short repeating sequence more than once, or else skips a segment.

This creates a heteroduplex with a short loop.