MUTYH-associated polyposis (MAP) is an autosomal recessive disorder characterized by a variable number of colorectal adenomas with a high risk of developing colorectal cancer. MAP is caused by biallelic germline mutations in MUTYH gene, but there is also evidence that monoallelic mutation carriers have an increased risk for developing colorectal cancer. The clinical symptoms of MAP are often undistinguishable from that of familial adenomatous polyposis (FAP) or attenuated FAP (AFAP) caused by mutations in adenomatous polyposis coli (APC) gene, but the age of onset is usually later compared to FAP patients. The two most common mutations in Caucasians, accounting for about 80% of mutant MUTYH alleles, are p.Y179C and p.G396D (also known as Y165C and G382D).
Indications for genetic testing:
- Testing of individuals with clinical symptoms similar to FAP or AFAP but in whom no APC gene mutation has been identified
- Testing of first degree relatives of the affected individuals
- Genetic counseling