Carbohydrate metabolism: galactose: 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: galactose

Sample item

A 10-day-old breastfed neonate has jaundice, vomiting, poor feeding and hepatomegaly. Blood culture grows Escherichia coli. Urine is positive for reducing substances with Benedict reagent but negative with a glucose oxidase strip. Which enzyme is most likely deficient?

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

The answer and the reasoning

B. Galactose-1-phosphate uridyltransferase

Classic galactosemia results from deficiency of galactose-1-phosphate uridyltransferase, so galactose-1-phosphate and galactitol accumulate after lactose feeding. It presents in the first weeks with jaundice, liver dysfunction, cataract and a predisposition to E. coli sepsis. Treatment is lifelong exclusion of lactose and galactose.

Option by option

  • A. Aldolase B

    Aldolase B deficiency causes hereditary fructose intolerance after fructose or sucrose, not milk feeding.

  • B. Galactose-1-phosphate uridyltransferase (correct)

    Accumulation of galactose-1-phosphate damages liver, kidney and brain, and explains the sepsis-prone, jaundiced neonate.

  • C. Galactokinase

    Galactokinase deficiency usually causes only cataract from galactitol, without liver failure or sepsis.

  • D. Glucose-6-phosphatase

    Glucose-6-phosphatase deficiency causes fasting hypoglycaemia and lactic acidosis, and the urine is not reducing-positive.

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, Galactose-1-phosphate uridyltransferase. Classic galactosemia results from deficiency of galactose-1-phosphate uridyltransferase, so galactose-1-phosphate and galactitol accumulate after lactose feeding.

Why is "Aldolase B" not the answer?

Aldolase B deficiency causes hereditary fructose intolerance after fructose or sucrose, not milk feeding.

Why is "Galactokinase" not the answer?

Galactokinase deficiency usually causes only cataract from galactitol, without liver failure or sepsis.

Why is "Glucose-6-phosphatase" not the answer?

Glucose-6-phosphatase deficiency causes fasting hypoglycaemia and lactic acidosis, and the urine is not reducing-positive.

What concept does this question test?

It tests Carbohydrate metabolism: galactose in Biochemistry. It presents in the first weeks with jaundice, liver dysfunction, cataract and a predisposition to E. coli sepsis. Treatment is lifelong exclusion of lactose and galactose.

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: galactose?

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.