Medical genetics: Prader-Willi syndrome: 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: Prader-Willi syndrome

Sample item

An infant with severe hypotonia and poor feeding later develops hyperphagia, obesity, hypogonadism and learning difficulty. What is the most common genetic mechanism?

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

The answer and the reasoning

A. Deletion of paternal chromosome 15q11-q13

About 70% of Prader-Willi cases are due to a paternal 15q11-q13 deletion, because the maternal copy of this region is imprinted and silenced. Maternal uniparental disomy accounts for most of the rest, and a maternal deletion causes Angelman syndrome.

Option by option

  • A. Deletion of paternal chromosome 15q11-q13 (correct)

    Correct. The paternal copy is the only active one, so its deletion produces Prader-Willi syndrome.

  • B. Expanded CGG repeat at Xq27.3

    A CGG expansion at Xq27.3 causes fragile X syndrome.

  • C. Deletion of maternal chromosome 15q11-q13

    A maternal deletion gives Angelman syndrome with seizures and a happy affect.

  • D. Paternal uniparental disomy of chromosome 15

    Paternal disomy of 15 gives Angelman syndrome, since no maternal contribution exists.

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 Anatomy questions

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is A, Deletion of paternal chromosome 15q11-q13. About 70% of Prader-Willi cases are due to a paternal 15q11-q13 deletion, because the maternal copy of this region is imprinted and silenced.

Why is "Expanded CGG repeat at Xq27.3" not the answer?

A CGG expansion at Xq27.3 causes fragile X syndrome.

Why is "Deletion of maternal chromosome 15q11-q13" not the answer?

A maternal deletion gives Angelman syndrome with seizures and a happy affect.

Why is "Paternal uniparental disomy of chromosome 15" not the answer?

Paternal disomy of 15 gives Angelman syndrome, since no maternal contribution exists.

What concept does this question test?

It tests Medical genetics: Prader-Willi syndrome in Anatomy. Maternal uniparental disomy accounts for most of the rest, and a maternal deletion causes Angelman syndrome.

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: Prader-Willi syndrome?

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.