Clinical biochemistry: Bartter 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: Bartter syndrome

Sample item

An infant has polyuria, failure to thrive and normal blood pressure. Biochemistry shows hypokalaemia, metabolic alkalosis and hypercalciuria, and ultrasound shows nephrocalcinosis. Which transporter is defective in the classic form?

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

The answer and the reasoning

A. Sodium-potassium-2 chloride cotransporter of the thick ascending limb

Classic neonatal Bartter syndrome results from loss of the loop diuretic-sensitive NKCC2, mimicking chronic furosemide use. It causes salt wasting, hypokalaemic alkalosis and hypercalciuria with nephrocalcinosis. Gitelman syndrome has hypocalciuria instead.

Option by option

  • A. Sodium-potassium-2 chloride cotransporter of the thick ascending limb (correct)

    Correct. NKCC2 loss mimics a loop diuretic, with hypercalciuria and nephrocalcinosis.

  • B. Sodium-hydrogen exchanger of the proximal tubule

    Proximal exchanger defects do not produce this hypercalciuric salt-losing picture.

  • C. Sodium-chloride cotransporter of the distal tubule

    A defect of this transporter gives hypocalciuria and hypomagnesaemia, as in Gitelman syndrome.

  • D. Epithelial sodium channel of the collecting duct

    Overactivity of this channel gives hypertension with low renin.

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 A, Sodium-potassium-2 chloride cotransporter of the thick ascending limb. Classic neonatal Bartter syndrome results from loss of the loop diuretic-sensitive NKCC2, mimicking chronic furosemide use.

Why is "Sodium-hydrogen exchanger of the proximal tubule" not the answer?

Proximal exchanger defects do not produce this hypercalciuric salt-losing picture.

Why is "Sodium-chloride cotransporter of the distal tubule" not the answer?

A defect of this transporter gives hypocalciuria and hypomagnesaemia, as in Gitelman syndrome.

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

Overactivity of this channel gives hypertension with low renin.

What concept does this question test?

It tests Clinical biochemistry: Bartter syndrome in Biochemistry. It causes salt wasting, hypokalaemic alkalosis and hypercalciuria with nephrocalcinosis. Gitelman syndrome has hypocalciuria instead.

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 Clinical biochemistry: Bartter 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.