Familial Adenomatous polyposis

Q. All are true about adenomatous polyposis syndrome except? ( Repeated in NOV INI SS) 
A. 25% do not have family history
B. Attenuated FAP has less than 100 polyps and delayed onset (50-55 yrs)
C. More than 20 rectal polyps have to be operated as there is high risk of Carcinoma
D. Attenuated FAP don’t have extracolonic manifestations and carry APC mutation

Ans d

Attenuated FAP is a phenotypically distinct variant of FAP in which

(1) affected individuals have fewer than 100 adenomas

(2) the polyps are more proximally distributed in the colon, and

(3) the onset of colorectal cancer is about 15 years later than in patients with FAP.

Germline mutations in the APC gene are found in 80% to 90% of patients with classic FAP and in 10% to 30% of patients with AFAP.

About 25% of patients with FAP have a de novo mutation and thus have no family history.

Attenuated FAP is a milder form of classic familial adenomatous polyposis (FAP) and is characterized by fewer colon polyps (an average of 30) and a delay in the development of colon cancer (average age 50 to 55 years) (True)

 AFAP is caused by mutations in the APC gene and is inherited in an autosomal dominant manner. 

Mutations responsible for this variant occur in the extreme upstream or downstream
portions of the APC gene.

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