Familial adenomatous polyposis

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Familial adenomatous polyposis


Genetic disorders


Alagille syndrome (NORD)

Familial adenomatous polyposis

Familial hypercholesterolemia

Hereditary spherocytosis

Huntington disease

Li-Fraumeni syndrome

Marfan syndrome

Multiple endocrine neoplasia

Myotonic dystrophy


Polycystic kidney disease

Treacher Collins syndrome

Tuberous sclerosis

von Hippel-Lindau disease




Cystic fibrosis

Friedreich ataxia

Gaucher disease (NORD)

Glycogen storage disease type I

Glycogen storage disease type II (NORD)

Glycogen storage disease type III

Glycogen storage disease type IV

Glycogen storage disease type V


Krabbe disease


Mucopolysaccharide storage disease type 1 (Hurler syndrome) (NORD)

Niemann-Pick disease type C

Niemann-Pick disease types A and B (NORD)

Phenylketonuria (NORD)

Polycystic kidney disease

Primary ciliary dyskinesia

Sickle cell disease (NORD)

Tay-Sachs disease (NORD)

Wilson disease

Cri du chat syndrome

Williams syndrome

Angelman syndrome

Prader-Willi syndrome

Beckwith-Wiedemann syndrome

Mitochondrial myopathy

Klinefelter syndrome

Turner syndrome

Fragile X syndrome

Friedreich ataxia

Huntington disease

Myotonic dystrophy

Down syndrome (Trisomy 21)

Edwards syndrome (Trisomy 18)

Patau syndrome (Trisomy 13)

Alport syndrome

Fragile X syndrome

Fabry disease (NORD)

Glucose-6-phosphate dehydrogenase (G6PD) deficiency


Lesch-Nyhan syndrome

Mucopolysaccharide storage disease type 2 (Hunter syndrome) (NORD)

Muscular dystrophy

Ornithine transcarbamylase deficiency

Wiskott-Aldrich syndrome

X-linked agammaglobulinemia

Autosomal trisomies: Pathology review

Miscellaneous genetic disorders: Pathology review

Muscular dystrophies and mitochondrial myopathies: Pathology review


Familial adenomatous polyposis


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USMLE® Step 1 questions

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High Yield Notes

8 pages


Familial adenomatous polyposis

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USMLE® Step 1 style questions USMLE

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A heterosexual couple comes to the genetic counselor’s office for prenatal counseling. The woman has no significant past medical history, and her family history is not notable for any cancers. The man has a history of prophylactic colectomy at the age of 16 after a colonoscopy revealed hundreds of polyps. His father died at the age of 39 due to colorectal cancer, but his mother has been healthy. The couple is worried their children may also inherit this condition. What is the probability that this couple’s first child will inherit the disease?  

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APC gene p. 222

familial adenomatous polyposis and p. 396


adenomatous polyposis p. 396

Colorectal cancer p. 397

adenomatous polyposis and p. 396

Familial adenomatous polyposis p. 396

APC gene and p. 396

chromosome association p. 62

labs/findings p. 721


familial adenomatous polyposis p. 396


With familial adenomatous polyposis, or simply FAP, familial refers to the fact that the disease runs in the family, and adenomatous polyposis refers to the fact that people affected develop multiple polyps that arise from the glands in the large intestine, which includes the colon and the rectum.

Now, the walls of the gastrointestinal tract are composed of four layers.

The outermost layer is called serosa.

Then there’s the muscular layer, which contracts in a synchronized way to move food through the bowel.

Then there is the submucosa, which consists of a dense layer of tissue through which blood vessels, lymphatics, and nerves run and branch into the mucosa and the muscular layer.

Finally, the inner lining of the intestine is called the mucosa; it surrounds the lumen of the gastrointestinal tract, and comes into direct contact with digested food.

The mucosa is organized as invaginations called the intestinal glands or colonic crypts, lined with large cells that are specialized in absorption.

Familial adenomatous polyposis is caused by an autosomal dominant mutation in the adenomatous polyposis coli gene or APC gene on chromosome 5q, which is a tumor suppressor gene.

Tumor suppressor genes stop cells from dividing uncontrollably.

But if the gene is mutated and the cell is without a functioning APC, the intestinal gland cells are more likely to accumulate mutations and start dividing faster than usual - ultimately giving rise to polyps, which are benign outgrowths of intestinal gland tissue.

Even though for any single polyp the chance that it evolves into cancer is generally quite low, polyps might accumulate additional mutations in other genes like the p53 gene (another tumor suppressor) or K-ras gene (a proto-oncogene), and with enough mutations, a cell might become completely unregulated and might start invading nearby tissue and become malignant.


Familial adenomatous polyposis (FAP) is a rare, autosomal dominant condition characterized by the development of many polyps in the colon and rectum. These polyps can become cancerous over time, leading to a high risk of developing colorectal cancer. Surgery is often recommended to remove the polyps and prevent cancer from developing.

FAP is caused by mutations in the adenomatous polyposis coli (APC) gene. This gene normally helps to suppress tumor growth in the colon. When it is mutated, this function is lost, resulting in an increased risk of developing tumors. FAP can be diagnosed through genetic testing.


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