Endocrinology: McCune-Albright 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 · Endocrinology: McCune-Albright syndrome

Sample item

A 4-year-old girl has vaginal bleeding, large irregular cafe-au-lait macules and polyostotic fibrous dysplasia. What is the underlying defect?

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

The answer and the reasoning

B. Activating somatic mutation of GNAS (Gs alpha)

McCune-Albright syndrome results from postzygotic activating GNAS mutations, giving autonomous endocrine hyperfunction, with gonadotropin-independent precocious puberty. Features include fibrous dysplasia and large cafe-au-lait spots with ragged borders. Hyperthyroidism and growth hormone excess may occur.

Option by option

  • A. Loss of function of the LH receptor

    LH receptor loss would delay puberty.

  • B. Activating somatic mutation of GNAS (Gs alpha) (correct)

    Correct. GNAS activating mutation is causal.

  • C. Deletion of 11p15

    11p15 is linked to Beckwith-Wiedemann.

  • D. Mutation of the FGF23 gene

    FGF23 is linked to phosphate wasting.

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 B, Activating somatic mutation of GNAS (Gs alpha). McCune-Albright syndrome results from postzygotic activating GNAS mutations, giving autonomous endocrine hyperfunction, with gonadotropin-independent precocious puberty.

Why is "Loss of function of the LH receptor" not the answer?

LH receptor loss would delay puberty.

Why is "Deletion of 11p15" not the answer?

11p15 is linked to Beckwith-Wiedemann.

Why is "Mutation of the FGF23 gene" not the answer?

FGF23 is linked to phosphate wasting.

What concept does this question test?

It tests Endocrinology: McCune-Albright syndrome in Pediatrics. Features include fibrous dysplasia and large cafe-au-lait spots with ragged borders. Hyperthyroidism and growth hormone excess 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 Endocrinology: McCune-Albright 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.