Neurology: Charcot-Marie-Tooth disease genetics: practice question

A General Medicine question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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General Medicine · Neurology: Charcot-Marie-Tooth disease genetics

Sample item

A 20-year-old has high-arched feet, hammer toes, distal leg wasting and a steppage gait with absent ankle jerks. His father has similar features. Nerve conduction studies show uniformly slowed velocities. Which genetic abnormality is the commonest cause?

AFrataxin GAA repeat expansionBPMP22 gene duplicationCSMN1 gene deletionDDystrophin gene deletion

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. PMP22 gene duplication

Charcot-Marie-Tooth type 1A is a demyelinating hereditary neuropathy caused by duplication of PMP22 on chromosome 17. It gives pes cavus, distal wasting with a champagne bottle appearance, and uniformly slowed conduction.

Option by option

A. Frataxin GAA repeat expansion
A frataxin repeat expansion causes Friedreich ataxia with sensory ataxia and cardiomyopathy.
B. PMP22 gene duplication (correct)
Correct. PMP22 duplication is the commonest cause of this demyelinating neuropathy.
C. SMN1 gene deletion
SMN1 deletion causes spinal muscular atrophy with anterior horn cell loss.
D. Dystrophin gene deletion
Dystrophin deletion causes Duchenne muscular dystrophy in boys.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this General Medicine question

What is the answer to this General Medicine question?

The best answer is B, PMP22 gene duplication. Charcot-Marie-Tooth type 1A is a demyelinating hereditary neuropathy caused by duplication of PMP22 on chromosome 17.

Why is "Frataxin GAA repeat expansion" not the answer?

A frataxin repeat expansion causes Friedreich ataxia with sensory ataxia and cardiomyopathy.

Why is "SMN1 gene deletion" not the answer?

SMN1 deletion causes spinal muscular atrophy with anterior horn cell loss.

Why is "Dystrophin gene deletion" not the answer?

Dystrophin deletion causes Duchenne muscular dystrophy in boys.

What concept does this question test?

It tests Neurology: Charcot-Marie-Tooth disease genetics in General Medicine. It gives pes cavus, distal wasting with a champagne bottle appearance, and uniformly slowed conduction.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Neurology: Charcot-Marie-Tooth disease genetics?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.