Clinical biochemistry: Gitelman syndrome: 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 · Clinical biochemistry: Gitelman syndrome

Sample item

A 25-year-old has cramps and fatigue with normal blood pressure. Serum potassium is 2.8 mmol/L, magnesium is low, there is metabolic alkalosis, urinary calcium excretion is low, and renin and aldosterone are raised. Which transporter is defective?

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

The answer and the reasoning

B. Sodium-chloride cotransporter of the distal tubule

Gitelman syndrome is loss of function of the thiazide-sensitive NaCl cotransporter, mimicking chronic thiazide use. It gives hypokalaemic alkalosis, hypomagnesaemia and hypocalciuria. Thick-limb defects cause hypercalciuria instead.

Option by option

  • A. Renal outer medullary potassium channel

    A defect of this potassium channel causes antenatal Bartter syndrome with hypercalciuria.

  • B. Sodium-chloride cotransporter of the distal tubule (correct)

    Correct. The NCC defect reproduces the thiazide pattern with hypocalciuria and hypomagnesaemia.

  • C. Sodium-potassium-2 chloride cotransporter of the thick limb

    A thick-limb cotransporter defect causes Bartter syndrome with hypercalciuria.

  • D. Epithelial sodium channel of the collecting duct

    Gain of function of this channel causes hypertension with low renin and low aldosterone.

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, Sodium-chloride cotransporter of the distal tubule. Gitelman syndrome is loss of function of the thiazide-sensitive NaCl cotransporter, mimicking chronic thiazide use.

Why is "Renal outer medullary potassium channel" not the answer?

A defect of this potassium channel causes antenatal Bartter syndrome with hypercalciuria.

Why is "Sodium-potassium-2 chloride cotransporter of the thick limb" not the answer?

A thick-limb cotransporter defect causes Bartter syndrome with hypercalciuria.

Why is "Epithelial sodium channel of the collecting duct" not the answer?

Gain of function of this channel causes hypertension with low renin and low aldosterone.

What concept does this question test?

It tests Clinical biochemistry: Gitelman syndrome in Biochemistry. It gives hypokalaemic alkalosis, hypomagnesaemia and hypocalciuria. Thick-limb defects cause hypercalciuria instead.

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 Clinical biochemistry: Gitelman syndrome?

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.