WBR0120
| Author | PageAuthor::William J Gibson |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Genetics |
| Sub Category | SubCategory::Cardiology |
| Prompt | [[Prompt::An 18 year old boy collapses while playing in a basketball game. Despite CPR, he died before ambulances arrived. Distraught, the parents order an autopsy. Toxicological screening is negative for alcohol or illicit drugs. The pathologist notes a large, thick myocardium with disarrayed muscle fibers on autopsy. The pathologist concludes that the left ventricular septum “bulged” outward into the left ventricular outflow tract, obstructing blood flow out of the heart and causing a myocardial ischemia. The patient likely died of an arrhythmia following said ischemia. Which of the following most likely describes the inheritance of the patient’s condition?]] |
| Answer A | AnswerA::Mutation in sarcomere; Autosomal dominant |
| Answer A Explanation | AnswerAExp::'''Correct''' - See explanation |
| Answer B | AnswerB::Mutation in sarcomere; Autosomal recessive |
| Answer B Explanation | AnswerBExp::'''Incorrect''' - HCM is inherited in an autosomal dominant fashion. |
| Answer C | AnswerC::Mutation in calcium channel; Autosomal dominant |
| Answer C Explanation | AnswerCExp::'''Incorrect''' - HCM is not caused by mutations in the calcium channels. However, HCM can be treated with a calcium channel blocker to decrease myocardial contractility. |
| Answer D | AnswerD::Mutation in ryanodine receptor; Autosomal recessive |
| Answer D Explanation | AnswerDExp::'''Incorrect''' - HCM is not caused by mutations in the ryanodine receptor. |
| Answer E | AnswerE::Mutation in myostatin; Autosomal dominant |
| Answer E Explanation | AnswerEExp::'''Incorrect''' - Mutations of myostatin are extremely rare and cause widespread, gross muscle hypertrophy. |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::The patient in this vignette suffered from hypertrophic cardiomyopathy, sometimes called Hypertrophic Obstructive Cardiomyopathy (HOCM). HCM is most commonly due to a mutation in one of 9 sarcomeric genes that results in a mutated protein in the sarcomere, the primary component of the myocyte (the muscle cell of the heart). It is inherited in an autosomal dominant pattern.
Educational Objective: Hypertrophic cardiomyopathy is caused by mutation of sarcomere proteins and is inherited in an autosomal dominant fashion. References: First Aid 2012 page 299. |
| Approved | Approved::Yes |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |