Carbohydrate metabolism: PDH complex 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: PDH complex deficiency

Sample item

A 6-month-old boy has hypotonia, developmental delay and persistent lactic acidosis. Pyruvate is raised in proportion to lactate. Enzyme assay shows deficiency of the E1 alpha subunit of the pyruvate dehydrogenase complex. Which dietary measure is most appropriate?

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

The answer and the reasoning

A. High-fat, low-carbohydrate ketogenic diet

In PDH deficiency, pyruvate cannot be converted to acetyl-CoA, so carbohydrate loads worsen lactic acidosis. A ketogenic diet supplies acetyl-CoA through fatty acid and ketone body metabolism, bypassing the block, and ketones serve as an alternative brain fuel. Thiamine can be trialled as a cofactor.

Option by option

  • A. High-fat, low-carbohydrate ketogenic diet (correct)

    Fat and ketones bypass the PDH block and lower the lactate load.

  • B. Protein-restricted diet

    Protein restriction does not bypass the enzyme block and does not address lactate production.

  • C. Fructose-loaded diet

    Fructose enters glycolysis and also produces pyruvate and lactate that cannot be oxidised.

  • D. High-carbohydrate diet with frequent feeds

    More carbohydrate increases pyruvate flux and worsens lactic acidosis.

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 A, High-fat, low-carbohydrate ketogenic diet. In PDH deficiency, pyruvate cannot be converted to acetyl-CoA, so carbohydrate loads worsen lactic acidosis.

Why is "Protein-restricted diet" not the answer?

Protein restriction does not bypass the enzyme block and does not address lactate production.

Why is "Fructose-loaded diet" not the answer?

Fructose enters glycolysis and also produces pyruvate and lactate that cannot be oxidised.

Why is "High-carbohydrate diet with frequent feeds" not the answer?

More carbohydrate increases pyruvate flux and worsens lactic acidosis.

What concept does this question test?

It tests Carbohydrate metabolism: PDH complex deficiency in Biochemistry. A ketogenic diet supplies acetyl-CoA through fatty acid and ketone body metabolism, bypassing the block, and ketones serve as an alternative brain fuel. Thiamine can be trialled as a cofactor.

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 Carbohydrate metabolism: PDH complex 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.