Genetic and metabolic disorders: Charcot-Marie-Tooth disease: practice question

A Pediatrics 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.

Try it

Pediatrics · Genetic and metabolic disorders: Charcot-Marie-Tooth disease

Sample item

A 14-year-old has high-arched feet, hammer toes, distal leg wasting, foot drop and absent ankle jerks. There is no ataxia or cardiomyopathy, and nerve conduction velocities are uniformly slow at about 20 m/s. Which genetic abnormality is the commonest cause?

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

The answer and the reasoning

B. Duplication of PMP22 on chromosome 17

Charcot-Marie-Tooth disease type 1A is the commonest hereditary motor and sensory neuropathy, caused by duplication of PMP22 on chromosome 17p. It gives a demyelinating neuropathy with uniformly slow conduction, pes cavus and distal wasting.

Option by option

  • A. Homozygous deletion of the SMN1 gene

    SMN1 deletion causes spinal muscular atrophy, a motor neuron disease with normal conduction velocities.

  • B. Duplication of PMP22 on chromosome 17 (correct)

    Correct. PMP22 duplication causes the commonest demyelinating hereditary neuropathy.

  • C. GAA repeat expansion in the frataxin gene

    Frataxin GAA expansion causes Friedreich ataxia, which has ataxia, cardiomyopathy and diabetes.

  • D. Deletion of exons in the dystrophin gene

    Dystrophin exon deletions cause muscular dystrophy with proximal weakness and calf hypertrophy.

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.

More Pediatrics questions

Questions about this Pediatrics question

What is the answer to this Pediatrics question?

The best answer is B, Duplication of PMP22 on chromosome 17. Charcot-Marie-Tooth disease type 1A is the commonest hereditary motor and sensory neuropathy, caused by duplication of PMP22 on chromosome 17p.

Why is "Homozygous deletion of the SMN1 gene" not the answer?

SMN1 deletion causes spinal muscular atrophy, a motor neuron disease with normal conduction velocities.

Why is "GAA repeat expansion in the frataxin gene" not the answer?

Frataxin GAA expansion causes Friedreich ataxia, which has ataxia, cardiomyopathy and diabetes.

Why is "Deletion of exons in the dystrophin gene" not the answer?

Dystrophin exon deletions cause muscular dystrophy with proximal weakness and calf hypertrophy.

What concept does this question test?

It tests Genetic and metabolic disorders: Charcot-Marie-Tooth disease in Pediatrics. It gives a demyelinating neuropathy with uniformly slow conduction, pes cavus and distal wasting.

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 Genetic and metabolic disorders: Charcot-Marie-Tooth disease?

Memorise milestones and the vaccine schedule as tables and revise them often. Then use the flashcards and the other Pediatrics 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.