Definition of MYH

MYH: A base excision repair gene responsible for an hereditary colon cancer syndrome. MYH is located on the short (p) arm of chromosome 1 in region 1p34.3-p32.1. MYH encodes an enzyme that removes the base adenine from mispairs (with 8-oxoguanine) that arise during the replication of oxidized DNA. MYH is also known as MUTYH.

A substantial proportion of people with multiple polyps in the colon, perhaps as many as 30% of those who have 15 to 100 polyps, have biallelic MYH mutations. (Both of their MYH genes are mutant.) From another perspective, up to 10% of families thought to have FAP (familial adenomatous polyposis) but who do not have the usual mutation in the APC gene, have biallelic mutations in the MYH gene.

The MYH syndrome is inherited in an autosomal recessive manner. Most people with the syndrome do not have a multigenerational family history of polyps or cancer of the colon but may have brothers or sisters with it. The MYH syndrome can result in very few or several hundred polyps in the colon. There is no tendency to extracolonic tumors (growths outside the colon and rectum) associated with MYH.

In sum, the MYH syndrome is an autosomal recessive form of colorectal adenomatous polyposis (familial adenomatous polyposis or familial polyposis of the colon and rectum).