Metabolic bone disease: carbonic anhydrase II deficiency: practice question

A Orthopaedics 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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Orthopaedics · Metabolic bone disease: carbonic anhydrase II deficiency

Sample item

A child with dense bones and recurrent fractures also has renal tubular acidosis and intracranial calcification. Which enzyme deficiency explains this combination?

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

The answer and the reasoning

D. Carbonic anhydrase II

Carbonic anhydrase II deficiency produces osteopetrosis with renal tubular acidosis and cerebral calcification. The enzyme is needed by osteoclasts to acidify the resorption lacuna and by the renal tubule to handle hydrogen ions.

Option by option

  • A. Glucocerebrosidase

    Glucocerebrosidase deficiency causes Gaucher disease with hepatosplenomegaly.

  • B. Cathepsin K

    Cathepsin K deficiency causes pyknodysostosis, which lacks renal acidosis and cerebral calcification.

  • C. Alkaline phosphatase

    Alkaline phosphatase deficiency causes hypophosphatasia with soft bone.

  • D. Carbonic anhydrase II (correct)

    Correct. The triad of osteopetrosis, tubular acidosis and cerebral calcification is carbonic anhydrase II deficiency.

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 Orthopaedics question

What is the answer to this Orthopaedics question?

The best answer is D, Carbonic anhydrase II. Carbonic anhydrase II deficiency produces osteopetrosis with renal tubular acidosis and cerebral calcification.

Why is "Glucocerebrosidase" not the answer?

Glucocerebrosidase deficiency causes Gaucher disease with hepatosplenomegaly.

Why is "Cathepsin K" not the answer?

Cathepsin K deficiency causes pyknodysostosis, which lacks renal acidosis and cerebral calcification.

Why is "Alkaline phosphatase" not the answer?

Alkaline phosphatase deficiency causes hypophosphatasia with soft bone.

What concept does this question test?

It tests Metabolic bone disease: carbonic anhydrase II deficiency in Orthopaedics. The enzyme is needed by osteoclasts to acidify the resorption lacuna and by the renal tubule to handle hydrogen ions.

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 Metabolic bone disease: carbonic anhydrase II deficiency?

Pair each fracture with its classic complication and nerve injured. Then use the flashcards and the other Orthopaedics 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.