Nutrition and malnutrition: hereditary vitamin D-resistant rickets: 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: hereditary vitamin D-resistant rickets

Sample item

A 14-month-old has severe rickets and total scalp alopecia. Calcium and phosphate are low, PTH and alkaline phosphatase are high, and 1,25-dihydroxyvitamin D is markedly raised. Which is the defect?

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

The answer and the reasoning

B. End-organ resistance from vitamin D receptor mutation

In vitamin D-dependent rickets type 2 the receptor is defective, so the body cannot respond to a high circulating calcitriol. Alopecia is a marker of severe receptor defects, and high-dose calcium and vitamin D may be needed. In type 1 the 1-alpha-hydroxylase is deficient and calcitriol is low.

Option by option

  • A. Nutritional vitamin D deficiency

    Nutritional deficiency gives low 25-hydroxyvitamin D and does not cause alopecia.

  • B. End-organ resistance from vitamin D receptor mutation (correct)

    Correct. Vitamin D receptor defect gives rickets with high calcitriol and alopecia.

  • C. Renal phosphate wasting from PHEX mutation

    PHEX mutation gives hypophosphataemia with normal calcium and normal PTH.

  • D. Deficient renal 1-alpha-hydroxylase

    1-alpha-hydroxylase deficiency causes low calcitriol, not a raised level.

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 B, End-organ resistance from vitamin D receptor mutation. In vitamin D-dependent rickets type 2 the receptor is defective, so the body cannot respond to a high circulating calcitriol.

Why is "Nutritional vitamin D deficiency" not the answer?

Nutritional deficiency gives low 25-hydroxyvitamin D and does not cause alopecia.

Why is "Renal phosphate wasting from PHEX mutation" not the answer?

PHEX mutation gives hypophosphataemia with normal calcium and normal PTH.

Why is "Deficient renal 1-alpha-hydroxylase" not the answer?

1-alpha-hydroxylase deficiency causes low calcitriol, not a raised level.

What concept does this question test?

It tests Nutrition and malnutrition: hereditary vitamin D-resistant rickets in Pediatrics. Alopecia is a marker of severe receptor defects, and high-dose calcium and vitamin D may be needed. In type 1 the 1-alpha-hydroxylase is deficient and calcitriol is low.

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: hereditary vitamin D-resistant rickets?

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.