Nutrition and malnutrition: hypophosphatasia: 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 · Nutrition and malnutrition: hypophosphatasia

Sample item

An infant has rachitic-looking metaphyses, poor feeding and hypercalcaemia. Serum alkaline phosphatase is markedly low, and urine phosphoethanolamine is raised. Which gene defect explains this?

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

The answer and the reasoning

D. ALPL gene

Hypophosphatasia is caused by loss of tissue-nonspecific alkaline phosphatase, so ALP is low rather than high as in other forms of rickets. Phosphoethanolamine and pyridoxal phosphate accumulate, and premature tooth loss is a hallmark. Low ALP in a child with a rickets-like picture is the clue.

Option by option

  • A. PHEX gene

    PHEX mutation causes X-linked hypophosphataemic rickets with raised ALP and low phosphate.

  • B. CYP27B1 gene

    CYP27B1 defects give vitamin D-dependent rickets type 1 with high ALP and low calcitriol.

  • C. Vitamin D receptor gene

    Vitamin D receptor defects give rickets with high ALP and alopecia.

  • D. ALPL gene (correct)

    Correct. ALPL mutation lowers alkaline phosphatase and impairs mineralisation.

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 D, ALPL gene. Hypophosphatasia is caused by loss of tissue-nonspecific alkaline phosphatase, so ALP is low rather than high as in other forms of rickets.

Why is "PHEX gene" not the answer?

PHEX mutation causes X-linked hypophosphataemic rickets with raised ALP and low phosphate.

Why is "CYP27B1 gene" not the answer?

CYP27B1 defects give vitamin D-dependent rickets type 1 with high ALP and low calcitriol.

Why is "Vitamin D receptor gene" not the answer?

Vitamin D receptor defects give rickets with high ALP and alopecia.

What concept does this question test?

It tests Nutrition and malnutrition: hypophosphatasia in Pediatrics. Phosphoethanolamine and pyridoxal phosphate accumulate, and premature tooth loss is a hallmark. Low ALP in a child with a rickets-like picture is the clue.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Nutrition and malnutrition: hypophosphatasia?

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.