Extracellular matrix: Marfan syndrome: practice question

A Biochemistry 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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Biochemistry · Extracellular matrix: Marfan syndrome

Sample item

A 20-year-old tall man with arm span exceeding height, arachnodactyly, upward dislocation of the lens and a dilated aortic root has a mutation in which protein?

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

The answer and the reasoning

B. Fibrillin-1

Marfan syndrome is an autosomal dominant defect of fibrillin-1 (FBN1 on chromosome 15), a microfibril glycoprotein that scaffolds elastin and sequesters TGF-beta. Loss of fibrillin raises TGF-beta signalling and causes aortic root dilatation. Lens dislocation is upward, whereas it is downward in homocystinuria.

Option by option

  • A. Type III collagen

    Type III collagen mutations cause vascular Ehlers-Danlos syndrome without lens dislocation.

  • B. Fibrillin-1 (correct)

    Correct. Fibrillin-1 mutation is the cause of Marfan syndrome.

  • C. Elastin

    Elastin mutations cause supravalvular aortic stenosis or cutis laxa, not this skeletal and ocular pattern.

  • D. Lysyl oxidase

    Lysyl oxidase deficiency would be linked to copper disorders and is not the cause of Marfan syndrome.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Fibrillin-1. Marfan syndrome is an autosomal dominant defect of fibrillin-1 (FBN1 on chromosome 15), a microfibril glycoprotein that scaffolds elastin and sequesters TGF-beta.

Why is "Type III collagen" not the answer?

Type III collagen mutations cause vascular Ehlers-Danlos syndrome without lens dislocation.

Why is "Elastin" not the answer?

Elastin mutations cause supravalvular aortic stenosis or cutis laxa, not this skeletal and ocular pattern.

Why is "Lysyl oxidase" not the answer?

Lysyl oxidase deficiency would be linked to copper disorders and is not the cause of Marfan syndrome.

What concept does this question test?

It tests Extracellular matrix: Marfan syndrome in Biochemistry. Loss of fibrillin raises TGF-beta signalling and causes aortic root dilatation. Lens dislocation is upward, whereas it is downward in homocystinuria.

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 Extracellular matrix: Marfan syndrome?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.