Carbohydrate metabolism: glycerol kinase deficiency: 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 · Carbohydrate metabolism: glycerol kinase deficiency

Sample item

A boy with Duchenne muscular dystrophy and adrenal hypoplasia is found to have a markedly raised triglyceride level on a routine lipid profile, yet his plasma is clear and he has no xanthomas. Glycerol is excreted in urine. Which enzyme is deficient?

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

The answer and the reasoning

C. Glycerol kinase

Glycerol kinase deficiency is X-linked and can arise from a contiguous gene deletion at Xp21 that also involves the dystrophin and adrenal hypoplasia genes. Free glycerol accumulates, and enzymatic triglyceride assays that measure released glycerol give a falsely high reading.

Option by option

  • A. Lipoprotein lipase

    Lipoprotein lipase deficiency causes true chylomicronaemia with milky plasma, which this boy does not have.

  • B. Hormone-sensitive lipase

    Hormone-sensitive lipase mobilises stored fat in adipose tissue and its loss does not raise plasma free glycerol.

  • C. Glycerol kinase (correct)

    Correct. Absent glycerol kinase raises free glycerol, producing pseudohypertriglyceridaemia.

  • D. Glycerol-3-phosphate dehydrogenase

    Glycerol-3-phosphate dehydrogenase deficiency affects the shuttle and triglyceride synthesis but is not linked to dystrophin and adrenal genes.

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 C, Glycerol kinase. Glycerol kinase deficiency is X-linked and can arise from a contiguous gene deletion at Xp21 that also involves the dystrophin and adrenal hypoplasia genes.

Why is "Lipoprotein lipase" not the answer?

Lipoprotein lipase deficiency causes true chylomicronaemia with milky plasma, which this boy does not have.

Why is "Hormone-sensitive lipase" not the answer?

Hormone-sensitive lipase mobilises stored fat in adipose tissue and its loss does not raise plasma free glycerol.

Why is "Glycerol-3-phosphate dehydrogenase" not the answer?

Glycerol-3-phosphate dehydrogenase deficiency affects the shuttle and triglyceride synthesis but is not linked to dystrophin and adrenal genes.

What concept does this question test?

It tests Carbohydrate metabolism: glycerol kinase deficiency in Biochemistry. Free glycerol accumulates, and enzymatic triglyceride assays that measure released glycerol give a falsely high reading.

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 Carbohydrate metabolism: glycerol kinase deficiency?

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.