False about familial polyposis colon cancer syndrome:

Familial adenomatous polyposis (FAP) is an autosomal dominant disorder in which patients develop numerous colorectal adenomas as teenagers. It is caused by mutations of the adenomatous polyposis coli, or APC, gene, which you will recall is a key negative regulator of the Wnt signalling pathway. Approximately 75% of cases are inherited, while the remaining appear to be caused by de novo mutations. At least 100 polyps are necessary for a diagnosis of classic FAP. Colorectal adenocarcinoma develops in 100% of untreated FAP patients, often before age 30 and nearly always by age 50. As a result, prophylactic colectomy is the standard therapy for individuals carrying APC mutations. Colectomy prevents colorectal cancer, but patients remain at risk for neoplasia at other sites. Adenomas may develop elsewhere in the GI tract, paicularly adjacent to the ampulla of Vater and in the stomach. FAP is associated with a variety of extraintestinal manifestations including congenital hyperophy of the retinal pigment epithelium, which can generally be detected at bih, and therefore may be an adjunct to early screening. Specific APC mutations have been associated with the development of other manifestations of FAP and paly explain variants such as Gardner syndrome and Turcot syndrome. Gardner syndrome: FAP + Fibroma + Osteoma Turcot syndrome: FAP + Medulloblastoma/Glioblastoma