Lipoproteins: abetalipoproteinaemia: 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: abetalipoproteinaemia

Sample item

A 3-year-old child has chronic steatorrhoea, failure to thrive, acanthocytes on the blood film and very low plasma cholesterol and triglycerides. Later he develops ataxia and retinitis pigmentosa. Which defect is responsible?

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

The answer and the reasoning

B. Deficiency of microsomal triglyceride transfer protein, which prevents assembly of apoB-containing lipoproteins

Microsomal triglyceride transfer protein loads lipid onto apoB-48 and apoB-100 in enterocytes and hepatocytes. Without it chylomicrons, VLDL and LDL are not formed, fat accumulates in enterocytes, and fat-soluble vitamins (especially vitamin E) are malabsorbed, producing neuropathy, ataxia and retinopathy.

Option by option

  • A. Deficiency of lipoprotein lipase, which prevents hydrolysis of chylomicron triglyceride

    Lipoprotein lipase deficiency causes massive hypertriglyceridaemia, not very low triglycerides.

  • B. Deficiency of microsomal triglyceride transfer protein, which prevents assembly of apoB-containing lipoproteins (correct)

    Failure to assemble apoB lipoproteins explains low lipids, steatorrhoea and vitamin E deficiency.

  • C. Deficiency of the LDL receptor, which prevents hepatic uptake of LDL

    LDL receptor deficiency causes very high LDL cholesterol with xanthomas.

  • D. Deficiency of lecithin-cholesterol acyltransferase, which prevents esterification of HDL cholesterol

    LCAT deficiency causes low HDL with corneal opacity and anaemia, not acanthocytosis and steatorrhoea.

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 B, Deficiency of microsomal triglyceride transfer protein, which prevents assembly of apoB-containing lipoproteins. Microsomal triglyceride transfer protein loads lipid onto apoB-48 and apoB-100 in enterocytes and hepatocytes.

Why is "Deficiency of lipoprotein lipase, which prevents hydrolysis of chylom…" not the answer?

Lipoprotein lipase deficiency causes massive hypertriglyceridaemia, not very low triglycerides.

Why is "Deficiency of the LDL receptor, which prevents hepatic uptake of LDL" not the answer?

LDL receptor deficiency causes very high LDL cholesterol with xanthomas.

Why is "Deficiency of lecithin-cholesterol acyltransferase, which prevents es…" not the answer?

LCAT deficiency causes low HDL with corneal opacity and anaemia, not acanthocytosis and steatorrhoea.

What concept does this question test?

It tests Lipoproteins: abetalipoproteinaemia in Biochemistry. Without it chylomicrons, VLDL and LDL are not formed, fat accumulates in enterocytes, and fat-soluble vitamins (especially vitamin E) are malabsorbed, producing neuropathy, ataxia and retinopathy.

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: abetalipoproteinaemia?

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.