Genetics of Colorectal Cancer (PDQ®): Genetics - Health Professional Information [NCI] - Major Genetic Syndromes
Table 8. Clinical Practice Guidelines for Diagnosis and Colon Surveillance of Familial Adenomatous Polyposis (FAP) continued...
MMR genes may interact with MYH and increase the risk of CRC. An association between MYH and MSH6 has been reported. Both proteins interact together in base excision repair processes. A study reported a significant increase of MSH6 mutations in monoallelic MYH mutation carriers with CRC compared to noncarriers (11.5% vs. 0%; P = .037).
Mut Y Homolog
The Mut Y homolog gene, which is also known as MUTYH and MYH, is located on chromosome 1p34.3-32.1. The protein encoded by MYH is a base excision repair glycosylase. It repairs one of the most common forms of oxidative damage. Over 100 unique sequence variants of MYH have been reported (Leiden Open Variation Database). A founder mutation with ethnic differentiation is assumed for MYH mutations. In Caucasian populations, two major variants (Y165C and/or G382D) account for 70% of biallelic mutations in MYH-associated polyposis patients, and 90% of these patients carry at least one of these mutations. Biallelic MYH mutations are associated with a 93-fold excess risk of CRC with near complete penetrance by age 60 years.
Lynch Syndrome (LS)
Between 1900 and 1990, numerous case reports of families with apparent increases in CRC were reported. As series of such reports accumulated, certain characteristic clinical features emerged: early age at onset; high risk of second primary tumors; preferential involvement of the right colon; improved clinical outcome; and a range of associated extracolonic sites including the endometrium, ovaries, other sites in the GI tract, uroepithelium, brain, and skin (sebaceous tumors). Terms such as Lynch 1 (families with CRC only), Lynch 2 (families with CRC and extracolonic tumors), cancer family syndrome, and later, hereditary nonpolyposis colorectal cancer (HNPCC), were commonly employed.
By 1990, the need for enhanced surveillance (colonoscopy at an early age and repeated frequently) was recognized. However, the need to limit this aggressive regimen to families most likely to have an inherited susceptibility or "true" HNPCC led to development of the so-called Amsterdam criteria: three or more cases of CRC over two or more generations, with at least one diagnosed before age 50 years, and no evidence of FAP.