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What is Familial adenomatous polyposis is characterized by all except: and explain in detail?
Ans. (a) Autosomal recessiveRef: Sabiston pages 1367-1369* 5q21 chromosome mutation.* The syndrome is associated with multiple colonic polyps; gastric, duodenal, and periampullary polyps.* Extraintestinal manifestations, including epidermoid cysts, desmoid tumors, osteomas, and brain tumors.* Gastric and duodenal polyps occur in approximately 50% of affected individuals.* Gastric polyps represent fundic gland hyperplasia, rather than adenomatous polyps, and have limited malignant potential.* Duodenal polyps are adenomatous in nature and should be considered premalignant.* Patients with FAP have an increased risk for ampullary cancer.* Adenomatous polyps and cancer have also been found in the jejunum and ileum of patients with FAP.* Extraintestinal malignant neoplasms in FAP patients include cancers of the extrahepatic bile ducts, gallbladder, pancreas, adrenals, thyroid, and liver.* An interesting marker for FAP is CHRPE, detected by indirect ophthalmoscopy in approximately 75% of affected individuals.* The gene is expressed in 100% of patients with the mutation.* Autosomal dominance results in expression in 50% of offspring* There is a negative family history in 10-20% of affected individuals (result of a spontaneous germline mutation)* The average age at discovery of a new patient with FAP is 29 years.