Genetics: Marfan 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 · Genetics: Marfan syndrome

Sample item

A 17-year-old tall boy has an arm span greater than his height, arachnodactyly, upward dislocation of the lens and aortic root dilatation. Which gene and protein are defective?

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

The answer and the reasoning

C. FBN1, fibrillin-1

Marfan syndrome is autosomal dominant, caused by mutations in FBN1 on chromosome 15, which encodes fibrillin-1, a component of microfibrils; defective fibrillin increases TGF-beta signalling. Features include superotemporal ectopia lentis, aortic root dilatation with dissection risk and mitral valve prolapse. Homocystinuria mimics the habitus but lens dislocation is downward.

Option by option

  • A. COL1A1, type I collagen

    COL1A1 mutations cause osteogenesis imperfecta, with fragile bones and blue sclerae.

  • B. COL3A1, type III collagen

    COL3A1 mutations cause vascular Ehlers-Danlos syndrome, with arterial and bowel rupture.

  • C. FBN1, fibrillin-1 (correct)

    Correct. Fibrillin-1 defects produce the skeletal, ocular and aortic features of Marfan syndrome.

  • D. CBS, cystathionine beta-synthase

    CBS deficiency causes homocystinuria, with downward lens dislocation and thrombosis.

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, FBN1, fibrillin-1. Marfan syndrome is autosomal dominant, caused by mutations in FBN1 on chromosome 15, which encodes fibrillin-1, a component of microfibrils; defective fibrillin increases TGF-beta signalling.

Why is "COL1A1, type I collagen" not the answer?

COL1A1 mutations cause osteogenesis imperfecta, with fragile bones and blue sclerae.

Why is "COL3A1, type III collagen" not the answer?

COL3A1 mutations cause vascular Ehlers-Danlos syndrome, with arterial and bowel rupture.

Why is "CBS, cystathionine beta-synthase" not the answer?

CBS deficiency causes homocystinuria, with downward lens dislocation and thrombosis.

What concept does this question test?

It tests Genetics: Marfan syndrome in Anatomy. Features include superotemporal ectopia lentis, aortic root dilatation with dissection risk and mitral valve prolapse. Homocystinuria mimics the habitus but lens dislocation is downward.

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: Marfan 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.