Minerals: Menkes disease: 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 · Minerals: Menkes disease

Sample item

A 4-month-old boy has sparse, kinky, steel-coloured hair, seizures, hypotonia, tortuous arteries and metaphyseal spurring. Serum copper and ceruloplasmin are low. Deficiency of which enzyme best explains the arterial tortuosity and bone changes?

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

The answer and the reasoning

D. Lysyl oxidase

Menkes disease is an X-linked defect of the copper transporter ATP7A that impairs intestinal copper absorption and delivery to tissues. Lysyl oxidase is a copper-dependent enzyme that cross-links collagen and elastin, so vessels become tortuous and bone is fragile. Other copper enzymes explain the neurological features, hypopigmentation and hypothermia.

Option by option

  • A. Prolyl hydroxylase

    Prolyl hydroxylase requires iron and ascorbate, not copper.

  • B. Lysyl hydroxylase

    Lysyl hydroxylase requires iron and ascorbate, not copper, and its deficiency causes Ehlers-Danlos type VI.

  • C. Procollagen N-peptidase

    Procollagen N-peptidase deficiency causes a form of Ehlers-Danlos syndrome and is not copper dependent.

  • D. Lysyl oxidase (correct)

    Copper-dependent lysyl oxidase is needed for collagen and elastin cross-linking.

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 D, Lysyl oxidase. Menkes disease is an X-linked defect of the copper transporter ATP7A that impairs intestinal copper absorption and delivery to tissues.

Why is "Prolyl hydroxylase" not the answer?

Prolyl hydroxylase requires iron and ascorbate, not copper.

Why is "Lysyl hydroxylase" not the answer?

Lysyl hydroxylase requires iron and ascorbate, not copper, and its deficiency causes Ehlers-Danlos type VI.

Why is "Procollagen N-peptidase" not the answer?

Procollagen N-peptidase deficiency causes a form of Ehlers-Danlos syndrome and is not copper dependent.

What concept does this question test?

It tests Minerals: Menkes disease in Biochemistry. Lysyl oxidase is a copper-dependent enzyme that cross-links collagen and elastin, so vessels become tortuous and bone is fragile. Other copper enzymes explain the neurological features, hypopigmentation and hypothermia.

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 Minerals: Menkes disease?

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.