Metabolic: phenylketonuria: practice question

A Pediatrics 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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Pediatrics · Metabolic: phenylketonuria

Sample item

A 4-month-old fair-skinned infant has a mousy odour, developmental delay and eczema. Which enzyme is deficient and what is the treatment?

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

The answer and the reasoning

C. Phenylalanine hydroxylase; phenylalanine-restricted diet

Classic PKU is an autosomal recessive deficiency of phenylalanine hydroxylase, causing accumulation of phenylalanine and low tyrosine. Early dietary restriction, started in the first weeks, prevents intellectual disability. Newborn screening detects it.

Option by option

  • A. Homogentisate oxidase; vitamin C

    Homogentisate oxidase deficiency causes alkaptonuria.

  • B. Galactose-1-phosphate uridyltransferase; lactose-free diet

    GALT deficiency is galactosaemia.

  • C. Phenylalanine hydroxylase; phenylalanine-restricted diet (correct)

    Correct. PAH deficiency treated with a low-phenylalanine diet.

  • D. Tyrosinase; sun protection

    Tyrosinase deficiency causes albinism.

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 Pediatrics question

What is the answer to this Pediatrics question?

The best answer is C, Phenylalanine hydroxylase; phenylalanine-restricted diet. Classic PKU is an autosomal recessive deficiency of phenylalanine hydroxylase, causing accumulation of phenylalanine and low tyrosine.

Why is "Homogentisate oxidase; vitamin C" not the answer?

Homogentisate oxidase deficiency causes alkaptonuria.

Why is "Galactose-1-phosphate uridyltransferase; lactose-free diet" not the answer?

GALT deficiency is galactosaemia.

Why is "Tyrosinase; sun protection" not the answer?

Tyrosinase deficiency causes albinism.

What concept does this question test?

It tests Metabolic: phenylketonuria in Pediatrics. Early dietary restriction, started in the first weeks, prevents intellectual disability. Newborn screening detects it.

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 Metabolic: phenylketonuria?

Memorise milestones and the vaccine schedule as tables and revise them often. Then use the flashcards and the other Pediatrics 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.