WBR0368
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| Author | [[PageAuthor::Mahmoud Sakr M.D. (Reviewed by Serge Korjian M.D.)]] |
|---|---|
| Exam Type | USMLE Step 1 |
| Main Category | Genetics |
| Sub Category | Neurology |
| Prompt | A 20-year-old man presents to the neurology clinic for left foot weakness and gradual loss sensation in the both lower extremities. His symptoms have been progressive over the past 2 years. On physical examination, the physician notes significant pes cavus with left foot drop, lower extremity weakness and muscle wasting giving the legs an inverted champagne bottle appearance. The patient explains that several of his family members have had the same condition. A mutation in which of the following gene is likely to be responsible for this patient's condition? |
| Answer A | CMT gene |
| Answer A Explanation | Charcot–Marie–Tooth (CMT) disease is caused by mutations in one of several CMT genes involved in the structure and function of either the peripheral nerve axon or the myelin sheath. |
| Answer B | FXN gene |
| Answer B Explanation | Friedreich's ataxia (FRDA) is caused by FXN gene mutation that results in reduced expression of frataxin protein. |
| Answer C | DUX4 gene |
| Answer C Explanation | Facioscapulohumeral muscular dystrophy is caused by DUX4 gene mutation. |
| Answer D | Dystrophin gene |
| Answer D Explanation | Duchenne muscular dystrophy (DMD) is caused by Dystrophin gene frameshift mutation. |
| Answer E | DYSF gene |
| Answer E Explanation | Distal muscular dystrophy is caused by a mutation in the DYSF. The disease is characterized by relatively late-onset of symptoms (20-60 years of age), which include weakness and wasting of muscles of the hands, forearms, and lower legs. It is usually progressive but not life-threatening. |
| Right Answer | A |
| Explanation | [[Explanation::Charcot–Marie–Tooth (CMT) disease is a common inherited disorder occurring in approximately 1 in 2500 people in the United States. CMT is caused by mutations in CMT genes involved in the structure and function of either the peripheral nerve axon or the myelin sheath. This leads to slowly progressive degeneration of peripheral motor and sensory nerves. Patients with CMT typically present in late childhood or early adulthood with sensorimotor neuropathy. 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 champagne bottle" appearance. Educational Objective: Charcot–Marie–Tooth (CMT) disease is caused by mutations in CMT genes involved in the structure and function of either the peripheral nerve axon or the myelin sheath. |
| Approved | Yes |
| Keyword | Charcot-Marie-Tooth, CMT, Neuropathy, Mutation |
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