Download MYH-associated polyposis fact sheet

MAP
MYH-associated polyposis fact sheet
Clinical features
Individuals with MYH-associated polyposis (MAP) most commonly develop dozens (sometimes
hundreds) of polyps in their colons. The phenotype is similar to those with
familial adenomatous polyposis (FAP) or attenuated familial adenomatous polyposis (AFAP).
Rarely, those with MAP have no polyps. Patients with MAP have a nearly 100 percent risk of
developing colon cancer (CRC) by the age of 65.
Inheritance
Autosomal recessive
Gene
MYH gene on chromosome 1
Genetic testing
DNA testing is commercially available and warranted in individuals with more than 10 polyps
but who do not have a mutation in the APC gene. Since the clinical features of MAP are similar
to those of FAP/AFAP, FAP/AFAP should first be ruled out by testing for a mutation in APC. If
no mutation is found in APC, then testing for MYH mutations can be pursued. There are two
common MYH mutations seen in most cases of MAP: Y165C and G382D. Identification of an
MYH mutation confirms the diagnosis of MAP and allows for genetic testing in family members,
particularly siblings.
Risk for CRC
Nearly 100 percent by the age of 65; average age at onset is approximately 48–56 years. MYH
heterozygotes may have an increased risk for CRC, but data is unclear.
Risks for other cancers
Research is ongoing to determine what other cancers are linked to MYH mutations.
Non-cancer findings
None known
Colorectal Cancer Fact Sheets: MAP | 1
MAP
Screening recommendations
If patient is asymptomatic, but has sibling with MAP:
• Colonoscopy starting age 25–30 and every three to five years if negative
(consider shorter intervals with advancing age)
• Consider upper endoscopy and side viewing duodenoscopy starting age 30–35 and every
three to five years
• Patients with duodenal adenomas are treated as in FAP
• Genetic counseling and testing for the familial MYH polyposis mutation(s) is
recommended
If patient has a personal history of adenomatous polyps with negative APC testing:
• No MYH testing + polyposis + negative APC testing
■ Genetic counseling and testing for MYH polyposis mutation(s) is recommended; if
negative, refer to increased risk colorectal cancer screening guidelines for multiple
adenomatous polyps
If patient has a personal history of being MYH mutation-positive:
• MYH positive + adenomas manageable with colonoscopy and polypectomy
■ Colonoscopy and polypectomy every one to two years
■ Consider upper endoscopy and side viewing duodenoscopy starting age 30–35 every
three to five years
■ Patients with duodenal adenomas treated as in FAP
• MYH positive + dense or large polyps not manageable with colonoscopy and
polypectomy
■ Counseling regarding surgical options
■ Subtotal colectomy or proctocolectomy depending on ademona density and
distribution; counseling regarding surgical option
■ Upper endoscopy and side viewing duodenoscopy starting age 30–35 every three to
five years
■ Patients with duodenal adenomas treated as in FAP
Screening references:
NCCN Colorectal Cancer Screening guidelines, V.2.2011.
nccn.org/professionals/physician_gls/f_guidelines.asp
ACG Guidelines for Colorectal Cancer Screening 2009.
http://s3.gi.org/physicians/guidelines/CCSJournalPublicationFebruary2009.pdf
11-0456:2/12:jt:Updated Feb 2012
Colorectal Cancer Fact Sheets: MAP | 2