Genetics: neurofibromatosis type 1: 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 · Genetics: neurofibromatosis type 1

Sample item

A 10-year-old child has six café-au-lait macules larger than 5 mm, axillary freckling and Lisch nodules, and the father has similar skin findings. Which gene is mutated and what is its normal function?

ATSC2 on chromosome 16, encoding tuberinBVHL on chromosome 3, encoding pVHLCNF2 on chromosome 22, encoding merlinDNF1 on chromosome 17, encoding neurofibromin that inactivates Ras

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

The answer and the reasoning

D. NF1 on chromosome 17, encoding neurofibromin that inactivates Ras

Neurofibromatosis type 1 is autosomal dominant, due to mutations in NF1 on chromosome 17, which encodes neurofibromin, a GTPase-activating protein that inhibits Ras. Loss of this tumour suppressor causes neurofibromas, optic gliomas and Lisch nodules. Half of cases are new mutations.

Option by option

A. TSC2 on chromosome 16, encoding tuberin
TSC2 mutations cause tuberous sclerosis, with ash-leaf macules and angiofibromas.
B. VHL on chromosome 3, encoding pVHL
VHL mutations cause von Hippel-Lindau disease, with haemangioblastomas and renal cell carcinoma.
C. NF2 on chromosome 22, encoding merlin
NF2 mutations cause bilateral vestibular schwannomas.
D. NF1 on chromosome 17, encoding neurofibromin that inactivates Ras (correct)
Correct. Neurofibromin is a negative regulator of Ras.

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.

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is D, NF1 on chromosome 17, encoding neurofibromin that inactivates Ras. Neurofibromatosis type 1 is autosomal dominant, due to mutations in NF1 on chromosome 17, which encodes neurofibromin, a GTPase-activating protein that inhibits Ras.

Why is "TSC2 on chromosome 16, encoding tuberin" not the answer?

TSC2 mutations cause tuberous sclerosis, with ash-leaf macules and angiofibromas.

Why is "VHL on chromosome 3, encoding pVHL" not the answer?

VHL mutations cause von Hippel-Lindau disease, with haemangioblastomas and renal cell carcinoma.

Why is "NF2 on chromosome 22, encoding merlin" not the answer?

NF2 mutations cause bilateral vestibular schwannomas.

What concept does this question test?

It tests Genetics: neurofibromatosis type 1 in Anatomy. Loss of this tumour suppressor causes neurofibromas, optic gliomas and Lisch nodules. Half of cases are new mutations.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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: neurofibromatosis type 1?

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.