Lipoproteins: familial dysbetalipoproteinaemia: 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 · Lipoproteins: familial dysbetalipoproteinaemia

Sample item

A 40-year-old man has orange-yellow creases in the palms, tuberoeruptive xanthomas over the elbows, total cholesterol 420 mg/dL and triglycerides 450 mg/dL. Lipoprotein electrophoresis shows a broad beta band, and he is homozygous for apoE2. Which lipoproteins accumulate?

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

The answer and the reasoning

C. Chylomicron remnants and IDL, because apoE2 binds poorly to hepatic remnant receptors

ApoE on chylomicron remnants and IDL is the ligand for hepatic remnant uptake. The E2 isoform binds receptors poorly, so remnants accumulate, raising cholesterol and triglyceride in similar proportions. Palmar xanthomas (xanthoma striata palmaris) are almost characteristic, and the condition is Fredrickson type III.

Option by option

  • A. Chylomicrons, because lipoprotein lipase is absent

    Absent lipoprotein lipase raises chylomicrons and causes eruptive xanthomas and pancreatitis, not a broad beta band.

  • B. LDL, because the LDL receptor is absent

    LDL receptor absence causes familial hypercholesterolaemia with raised LDL and tendon xanthomas but normal triglyceride.

  • C. Chylomicron remnants and IDL, because apoE2 binds poorly to hepatic remnant receptors (correct)

    Impaired remnant clearance with apoE2 explains the raised cholesterol and triglyceride and the broad beta band.

  • D. HDL, because apoA-I is deficient

    ApoA-I deficiency lowers HDL and does not cause remnant accumulation.

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, Chylomicron remnants and IDL, because apoE2 binds poorly to hepatic remnant receptors. ApoE on chylomicron remnants and IDL is the ligand for hepatic remnant uptake.

Why is "Chylomicrons, because lipoprotein lipase is absent" not the answer?

Absent lipoprotein lipase raises chylomicrons and causes eruptive xanthomas and pancreatitis, not a broad beta band.

Why is "LDL, because the LDL receptor is absent" not the answer?

LDL receptor absence causes familial hypercholesterolaemia with raised LDL and tendon xanthomas but normal triglyceride.

Why is "HDL, because apoA-I is deficient" not the answer?

ApoA-I deficiency lowers HDL and does not cause remnant accumulation.

What concept does this question test?

It tests Lipoproteins: familial dysbetalipoproteinaemia in Biochemistry. The E2 isoform binds receptors poorly, so remnants accumulate, raising cholesterol and triglyceride in similar proportions. Palmar xanthomas (xanthoma striata palmaris) are almost characteristic, and the condition is Fredrickson type III.

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 Lipoproteins: familial dysbetalipoproteinaemia?

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.