Genetics: Noonan syndrome: 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.

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Pediatrics · Genetics: Noonan syndrome

Sample item

A boy has short stature, webbed neck, pectus excavatum, ptosis and pulmonary valve stenosis, with normal karyotype. Which gene is most often mutated?

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

The answer and the reasoning

D. PTPN11

Noonan syndrome is autosomal dominant, with PTPN11 mutation in about half, affecting the RAS-MAPK pathway. It resembles Turner syndrome but occurs in both sexes with normal karyotype, and the common cardiac lesion is pulmonary stenosis rather than coarctation. Bleeding diathesis may occur.

Option by option

  • A. DMD

    DMD mutation causes Duchenne muscular dystrophy.

  • B. CFTR

    CFTR mutation causes cystic fibrosis.

  • C. FBN1

    FBN1 mutation causes Marfan syndrome.

  • D. PTPN11 (correct)

    Correct. PTPN11 is mutated in about half.

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 Pediatrics question

What is the answer to this Pediatrics question?

The best answer is D, PTPN11. Noonan syndrome is autosomal dominant, with PTPN11 mutation in about half, affecting the RAS-MAPK pathway.

Why is "DMD" not the answer?

DMD mutation causes Duchenne muscular dystrophy.

Why is "CFTR" not the answer?

CFTR mutation causes cystic fibrosis.

Why is "FBN1" not the answer?

FBN1 mutation causes Marfan syndrome.

What concept does this question test?

It tests Genetics: Noonan syndrome in Pediatrics. It resembles Turner syndrome but occurs in both sexes with normal karyotype, and the common cardiac lesion is pulmonary stenosis rather than coarctation. Bleeding diathesis may occur.

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 Genetics: Noonan syndrome?

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.