Gluconeogenesis: fructose-1,6-bisphosphatase 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 · Gluconeogenesis: fructose-1,6-bisphosphatase deficiency

Sample item

A 9-month-old develops hypoglycaemia, lactic acidosis, ketosis and hepatomegaly during a febrile illness with poor feeding. Symptoms are worse after fructose or sucrose, but he is well when fed regularly. Which enzyme is deficient?

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

The answer and the reasoning

C. Fructose-1,6-bisphosphatase

Fructose-1,6-bisphosphatase is a key irreversible enzyme of gluconeogenesis. When it is deficient, lactate, alanine and glycerol cannot be converted to glucose, so fasting or illness causes hypoglycaemia with lactic acidosis and ketosis. Treatment is avoidance of fasting and of fructose and sucrose.

Option by option

  • A. Glycogen debranching enzyme

    Debranching enzyme deficiency spares gluconeogenesis, so lactate is normal and fructose has no special effect.

  • B. Pyruvate kinase

    Pyruvate kinase deficiency causes haemolytic anaemia and not fasting hypoglycaemia.

  • C. Fructose-1,6-bisphosphatase (correct)

    Blocked gluconeogenesis explains fasting hypoglycaemia with lactate and ketone accumulation.

  • D. Galactokinase

    Galactokinase deficiency causes cataract after galactose feeding, not hypoglycaemia.

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.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Fructose-1,6-bisphosphatase. Fructose-1,6-bisphosphatase is a key irreversible enzyme of gluconeogenesis.

Why is "Glycogen debranching enzyme" not the answer?

Debranching enzyme deficiency spares gluconeogenesis, so lactate is normal and fructose has no special effect.

Why is "Pyruvate kinase" not the answer?

Pyruvate kinase deficiency causes haemolytic anaemia and not fasting hypoglycaemia.

Why is "Galactokinase" not the answer?

Galactokinase deficiency causes cataract after galactose feeding, not hypoglycaemia.

What concept does this question test?

It tests Gluconeogenesis: fructose-1,6-bisphosphatase deficiency in Biochemistry. When it is deficient, lactate, alanine and glycerol cannot be converted to glucose, so fasting or illness causes hypoglycaemia with lactic acidosis and ketosis. Treatment is avoidance of fasting and of fructose and sucrose.

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 Gluconeogenesis: fructose-1,6-bisphosphatase 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.