All are true regarding familial adenomatous polyposis except
Correct Answer: Autosomal recessive
Description: C i.e. Autosomal recessiveRef: Bailey and Love, Short Practice of Surgery, 5th edition, chapter 1, page 94-95, 1149Explanation:FAMILIAL ADENOMATOUS POLYPOSIS (FAP)Autosomal Dominant DisorderPatients develop numerous colorectal adenomas as teenagers.It is caused by mutations of the adenomatous polyposis coli, or APC gene (5q21).Some FAP patients without APC loss have mutations of the base-excision repair gene MUTYH.At least 100 polyps are necessary for a diagnosis of classic FAP, and as many as several thousand may be present.These growths are morphologically indistinguishable from sporadic adenomas.Colorectal adenocarcinoma develops in 100% of untreated FAP patients before age 30.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 Gl tract, particularly adjacent to the ampulla of Vater and in the stomach.FAP is associated with a variety of extra-intestinal manifestations including:Congenital hypertrophy of the retinal pigment epithelium.Gardner syndrome, andTurcot syndrome.Gardner SyndromeOsteomas of mandible, skull, and long bones.Epidermal cysts.Desmoid tumors.Thyroid tumors.Dental abnormalities (Unerupted and supernumerary teeth).Turcot SyndromeIntestinal adenomas.Tumors of the central nervous system.Two third patients have APC gene mutation and develop medulloblastomas.The remaining one third have mutations genes involved in DNA repair and develop glioblastomas.Associated TumoursColorectal cancer under the age of 25 years.Papillary carcinoma of the thyroid.Cancer of the ampulla of Vater.Hepatoblastomas.Primary brain tumours (Turcot's syndrome).Osteomas of the jaw.CHRPE (congenital hypertrophy of the retinal pigment epithelium).Gardner's syndrome can cause the development of cutaneous pathology, such as multiple epidermoid cysts and lipomata.Clinical Features and Pathological OutlinesPatients may develop gastric fundic gland polyps, gastric or small bowel flat adenomas, and gastric/ duodenal carcinomas.Duodenal adenomas are very common.Extracolonic manifestations of classical FAP are less common in attenuated FAP.Classically reserved for patients with fewer than 100 colonic adenomatous polyps.Polyps are usually more proximal (i.e., right sided) than in classic FAP.Rectum often spared.Polyps are flat, slightly raised, or plaque-like.May have minute central depression or umbilication.Adenomatous polyps are microscopically similar to sporadic-type adenomas.Extra-colorectal polyps and cancers are important primarily for surveillance purposes.STRATEGIES FOR PREVENTION Clinical Testing of APC GeneFlexible proctosigmoidoscopy at age 10-12 years; repeat every 1-2 years until age 35; after age 35 repeat every 3 years.Upper Gl endoscopy every 1-3 years starting when polyps first identified.Prophylactic panprotocolectomy.Here are the estimated cancer risks associated with classic FAP.CancersIncidenceColorectal cancerAlmost 100% if not treatedDesmoid tumor10% to 20%Small bowel (intestines)4% to 12%Pancreatic cancer2%Papillary thyroid cancer2%Hepatoblastoma (a type of liver cancer)1.5%Brain or central nervous system tumorLess than 1 %Stomach cancer0.5%Bile duct cancerSmall, but increasedAdrenal gland cancerSmall, but increased
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