Medical genetics: Noonan 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: Noonan syndrome

Sample item

A 9-year-old boy has webbed neck, short stature, pectus excavatum and pulmonary valve stenosis. His karyotype is 46,XY. Which description fits this condition?

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

The answer and the reasoning

C. Autosomal dominant, PTPN11 mutation, normal karyotype

Noonan syndrome is an autosomal dominant RASopathy, most often from PTPN11 mutations, and affects both sexes with a normal karyotype. Pulmonary stenosis is typical, whereas coarctation of the aorta is typical of Turner syndrome. The phenotype resembles Turner syndrome, hence the term male Turner.

Option by option

  • A. Mosaic 45,X/46,XY with ambiguous genitalia

    Mosaic 45,X/46,XY is mixed gonadal dysgenesis with ambiguous genitalia.

  • B. Monosomy X with streak gonads

    Monosomy X with streak gonads defines Turner syndrome.

  • C. Autosomal dominant, PTPN11 mutation, normal karyotype (correct)

    Correct. It is autosomal dominant with a normal karyotype and PTPN11 mutations.

  • D. 47,XXY with hypogonadism

    47,XXY is Klinefelter syndrome, with tall stature and hypogonadism.

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 C, Autosomal dominant, PTPN11 mutation, normal karyotype. Noonan syndrome is an autosomal dominant RASopathy, most often from PTPN11 mutations, and affects both sexes with a normal karyotype.

Why is "Mosaic 45,X/46,XY with ambiguous genitalia" not the answer?

Mosaic 45,X/46,XY is mixed gonadal dysgenesis with ambiguous genitalia.

Why is "Monosomy X with streak gonads" not the answer?

Monosomy X with streak gonads defines Turner syndrome.

Why is "47,XXY with hypogonadism" not the answer?

47,XXY is Klinefelter syndrome, with tall stature and hypogonadism.

What concept does this question test?

It tests Medical genetics: Noonan syndrome in Anatomy. Pulmonary stenosis is typical, whereas coarctation of the aorta is typical of Turner syndrome. The phenotype resembles Turner syndrome, hence the term male Turner.

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: Noonan 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.