WBR0368

Author	PageAuthor::Mahmoud Sakr M.D.
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Genetics
Sub Category	SubCategory::Musculoskeletal/Rheumatology
Prompt	[[Prompt::17 year-old-boy presents to your office with a chief complaint of foot drop as well as loss of touch sensation in the feet, ankles and legs. His symptoms have been progressive over the past several years. On exam, he has wasting of muscle tissue of the lower parts of the legs with an "inverted bottle" appearance. You also notice high arched feet or pes cavus. He tells you he has several family members with a similar condition. Disorders in which of the following genes are likely responsible for this inherited disease?]]
Answer A	AnswerA::CMT gene
Answer A Explanation	[[AnswerAExp::Correct! Charcot–Marie–Tooth disease (CMT) is caused by mutations that cause defects in neuronal proteins. Loss of touch sensation in the feet, ankles and legs, as well as in the hands, wrists and arms is characteristic in various types of the disease. Sensory and proprioceptive nerves in the hands and feet are often damaged, while pain nerves are left intact. Wasting of muscle tissue of the lower parts of the legs may give rise to a "stork leg" or "inverted bottle" appearance.]]
Answer B	AnswerB::FXN gene
Answer B Explanation	AnswerBExp::FXN gene associated reduced expression of frataxin protein is the cause of Friedreich's ataxia (FRDA).
Answer C	AnswerC::DUX4 gene
Answer C Explanation	AnswerCExp::DUX4 gene associated facioscapulohumeral muscular dystrophy (FSHD) initially affects the muscles of the face, shoulders, and upper arms with progressive weakness.
Answer D	AnswerD::Dystrophin gene
Answer D Explanation	[[AnswerDExp::Dystrophin gene disorder is responsible for Duchenne muscular dystrophy (DMD), which is the most common childhood form of muscular dystrophy; it generally affects only boys (with extremely rare exceptions), becoming clinically evident when a child begins walking. By age 10, the child may need braces for walking and by age 12, most patients are confined to a wheelchair]]
Answer E	AnswerE::DYSF gene
Answer E Explanation	AnswerEExp::DYSF gene relates to distal muscular dystrophies; age at onset: 20 to 60 years; symptoms include weakness and wasting of muscles of the hands, forearms, and lower legs; progress is slow and not life-threatening.
Right Answer	RightAnswer::A
Explanation	[[Explanation::Charcot–Marie–Tooth disease (CMT) is caused by mutations that cause defects in neuronal proteins. Loss of touch sensation in the feet, ankles and legs, as well as in the hands, wrists and arms is characteristic in various types of the disease. Sensory and proprioceptive nerves in the hands and feet are often damaged, while pain nerves are left intact. Wasting of muscle tissue of the lower parts of the legs may give rise to a "stork leg" or "inverted bottle" appearance. Educational Objective: References: ]]
Approved	Approved::Yes
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