Genetics: connective tissue disorders: 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: connective tissue disorders

Sample item

A 15-year-old tall boy has arachnodactyly, aortic root dilatation and a dislocated lens displaced upward and outward, with normal intelligence. Which combination of gene defect and inheritance best fits?

ACystathionine beta-synthase deficiency, autosomal recessiveBType V collagen defect, autosomal dominantCFibrillin-1 defect, autosomal dominantDFibrillin-1 defect, X-linked recessive

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

The answer and the reasoning

C. Fibrillin-1 defect, autosomal dominant

Marfan syndrome is an autosomal dominant fibrillinopathy (FBN1), with superotemporal lens dislocation, aortic root dilatation and skeletal overgrowth. Homocystinuria mimics the habitus but is autosomal recessive, with inferonasal (downward) lens dislocation, intellectual disability and thromboembolism. Aortic root surveillance and beta-blocker or ARB therapy are used in Marfan syndrome.

Option by option

A. Cystathionine beta-synthase deficiency, autosomal recessive
Cystathionine beta-synthase deficiency causes homocystinuria, with downward lens dislocation and intellectual disability.
B. Type V collagen defect, autosomal dominant
Type V collagen defects cause classic Ehlers-Danlos syndrome, with skin hyperextensibility, without lens dislocation.
C. Fibrillin-1 defect, autosomal dominant (correct)
Correct. Upward lens dislocation with normal intelligence and aortic dilatation indicates fibrillin-1 and dominant inheritance.
D. Fibrillin-1 defect, X-linked recessive
Marfan syndrome is not X-linked, so this pairing is incorrect.

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 C, Fibrillin-1 defect, autosomal dominant. Marfan syndrome is an autosomal dominant fibrillinopathy (FBN1), with superotemporal lens dislocation, aortic root dilatation and skeletal overgrowth.

Why is "Cystathionine beta-synthase deficiency, autosomal recessive" not the answer?

Cystathionine beta-synthase deficiency causes homocystinuria, with downward lens dislocation and intellectual disability.

Why is "Type V collagen defect, autosomal dominant" not the answer?

Type V collagen defects cause classic Ehlers-Danlos syndrome, with skin hyperextensibility, without lens dislocation.

Why is "Fibrillin-1 defect, X-linked recessive" not the answer?

Marfan syndrome is not X-linked, so this pairing is incorrect.

What concept does this question test?

It tests Genetics: connective tissue disorders in Anatomy. Homocystinuria mimics the habitus but is autosomal recessive, with inferonasal (downward) lens dislocation, intellectual disability and thromboembolism. Aortic root surveillance and beta-blocker or ARB therapy are used in Marfan syndrome.

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 Genetics: connective tissue disorders?

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.