WBR0095
| Author | PageAuthor::William J Gibson |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Genetics |
| Sub Category | SubCategory::Gastrointestinal |
| Prompt | [[Prompt::A 16 year old girl presents to her primary care physician complaining of fatigue, gastrointestinal pain, and bloody stools. She denies changes in her diet, nor association of pain with her menstrual cycles. Flexible sigmoidoscopy reveals thousands of polyps lining her colon. Her father was diagnosed with a similar condition at the age of 20 and died shortly thereafter. Her gastrointestinal physician advices her that if she does not undergo colonic resection, she will also die. This condition is caused by defect in which of the following genes?]] |
| Answer A | AnswerA::APC gene |
| Answer A Explanation | AnswerAExp::Correct - See explanation |
| Answer B | AnswerB::STK11 gene |
| Answer B Explanation | [[AnswerBExp::Incorrect - this describes the genetic defect underlying Peutz-Jeghers Syndrome. Peutz–Jeghers syndrome, also known as hereditary intestinal polyposis syndrome, is an autosomal dominant genetic disease characterized by the development of benign hamartomatous polyps in the gastrointestinal tract and hyperpigmented macules on the lips and oral mucosa.]] |
| Answer C | AnswerC::Rb gene |
| Answer C Explanation | AnswerCExp::Incorrect - this describes retinoblastoma, a familial tumor of the eye in infants. |
| Answer D | AnswerD::Wnt gene |
| Answer D Explanation | [[AnswerDExp::Incorrect - Wnt binding to extracellular receptors can induce beta-catenin signaling, which can cause uncontrolled cell growth. However, activation of beta-catenin signaling is achieved in familial adenomatous polyposis is achieved via mutations in the APC gene.]] |
| Answer E | AnswerE::Beta catenin gene |
| Answer E Explanation | AnswerEExp::Incorrect - While beta catenin becomes dysregulated in familial adenomatis polyposis, this occurs due to loss of function mutations in APC. APC is a negative regulator of beta catenin. |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::The patient in this vignette is suffering from familial adenomatous polyposis syndrome (FAP). Familial adenomatous polyposis (FAP) is an inherited condition in which numerous polyps form mainly in the epithelium of the large intestine. While these polyps start out benign, malignant transformation into colon cancer occurs when left untreated. This condition most commonly results from mutations in the APC gene, and is inherited in an autosomal dominant pattern. Thus, one copy of the altered gene is sufficient to cause the disorder. The incidence of malignancy in these cases approaches 100%. Most individuals with the APC mutation will develop colon cancer by the age of 40. Therefore, prophylactic surgery is generally recommended before the age of 25. There are several surgical options that involve the removal of either the colon or both the colon and rectum.
Educational Objective: Familial adenomatous polyposis is caused by loss of function mutations in the APC gene. References: First Aid 2012 page 90,359 |
| Approved | Approved::Yes |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |