Endocrine: familial hypocalciuric hypercalcaemia: practice question

A Physiology 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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Physiology · Endocrine: familial hypocalciuric hypercalcaemia

Sample item

A 30-year-old woman has asymptomatic mild hypercalcaemia with normal PTH, and her father has the same. Her 24-hour urinary calcium is low, with a calcium-to-creatinine clearance ratio under 0.01. What is the defect?

AInactivating mutation of the calcium-sensing receptor, shifting the set point upwardBParathyroid adenoma with autonomous PTH secretionCSecretion of PTH-related peptide by a tumourDExcess vitamin D from granulomatous disease

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

The answer and the reasoning

A. Inactivating mutation of the calcium-sensing receptor, shifting the set point upward

In familial hypocalciuric hypercalcaemia, loss of function of CaSR in parathyroid and kidney makes the set point for calcium higher, so PTH is inappropriately normal and the kidney avidly reabsorbs calcium, producing hypocalciuria. It is benign and surgery is not helpful. Primary hyperparathyroidism has normal or high urinary calcium.

Option by option

A. Inactivating mutation of the calcium-sensing receptor, shifting the set point upward (correct)
Correct. A raised set point and avid renal calcium reabsorption produce this pattern.
B. Parathyroid adenoma with autonomous PTH secretion
An adenoma usually causes hypercalciuria and a clearance ratio above 0.01.
C. Secretion of PTH-related peptide by a tumour
PTH-related peptide causes marked hypercalcaemia with suppressed PTH.
D. Excess vitamin D from granulomatous disease
Vitamin D excess suppresses PTH and increases urinary calcium.

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.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is A, Inactivating mutation of the calcium-sensing receptor, shifting the set point upward. In familial hypocalciuric hypercalcaemia, loss of function of CaSR in parathyroid and kidney makes the set point for calcium higher, so PTH is inappropriately normal and the kidney avidly reabsorbs calcium, producing hypocalciuria.

Why is "Parathyroid adenoma with autonomous PTH secretion" not the answer?

An adenoma usually causes hypercalciuria and a clearance ratio above 0.01.

Why is "Secretion of PTH-related peptide by a tumour" not the answer?

PTH-related peptide causes marked hypercalcaemia with suppressed PTH.

Why is "Excess vitamin D from granulomatous disease" not the answer?

Vitamin D excess suppresses PTH and increases urinary calcium.

What concept does this question test?

It tests Endocrine: familial hypocalciuric hypercalcaemia in Physiology. It is benign and surgery is not helpful. Primary hyperparathyroidism has normal or high urinary calcium.

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 Endocrine: familial hypocalciuric hypercalcaemia?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.