Medical genetics: Friedreich ataxia: practice question

A Anatomy 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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Anatomy · Medical genetics: Friedreich ataxia

Sample item

A 14-year-old boy has progressive gait ataxia, scoliosis, pes cavus, loss of vibration and joint position sense, absent ankle jerks and hypertrophic cardiomyopathy. His parents are healthy and a sibling is affected. Which molecular lesion is responsible?

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

The answer and the reasoning

A. GAA expansion in the frataxin gene

Friedreich ataxia is autosomal recessive and caused by an intronic GAA repeat expansion in the frataxin gene, which reduces frataxin and damages mitochondrial iron handling. Degeneration of the dorsal columns, spinocerebellar tracts and corticospinal tracts explains the signs.

Option by option

  • A. GAA expansion in the frataxin gene (correct)

    Correct. GAA expansion in frataxin explains ataxia, dorsal column loss and cardiomyopathy in a recessive pedigree.

  • B. CAG expansion in the huntingtin gene

    CAG expansion in huntingtin causes autosomal dominant Huntington disease with chorea.

  • C. CGG expansion in the FMR1 gene

    CGG expansion in FMR1 causes fragile X syndrome.

  • D. CTG expansion in the DMPK gene

    CTG expansion in DMPK causes myotonic dystrophy.

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.

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Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is A, GAA expansion in the frataxin gene. Friedreich ataxia is autosomal recessive and caused by an intronic GAA repeat expansion in the frataxin gene, which reduces frataxin and damages mitochondrial iron handling.

Why is "CAG expansion in the huntingtin gene" not the answer?

CAG expansion in huntingtin causes autosomal dominant Huntington disease with chorea.

Why is "CGG expansion in the FMR1 gene" not the answer?

CGG expansion in FMR1 causes fragile X syndrome.

Why is "CTG expansion in the DMPK gene" not the answer?

CTG expansion in DMPK causes myotonic dystrophy.

What concept does this question test?

It tests Medical genetics: Friedreich ataxia in Anatomy. Degeneration of the dorsal columns, spinocerebellar tracts and corticospinal tracts explains the signs.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Medical genetics: Friedreich ataxia?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy 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.