Clinical biochemistry: Liddle 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: Liddle syndrome

Sample item

A 20-year-old has early-onset hypertension, hypokalaemia and metabolic alkalosis with low renin and low aldosterone. Spironolactone does not correct the hypokalaemia but amiloride does. What is the defect?

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

The answer and the reasoning

D. Overactive epithelial sodium channel

Liddle syndrome is a gain-of-function mutation of the collecting duct epithelial sodium channel, so sodium is reabsorbed and potassium lost despite low aldosterone. Amiloride blocks the channel and corrects the abnormalities. Spironolactone works through the mineralocorticoid receptor and is ineffective.

Option by option

  • A. Aldosterone-secreting adrenal adenoma

    An adenoma would raise aldosterone and respond to spironolactone.

  • B. Loss of the thiazide-sensitive cotransporter

    Loss of this cotransporter causes Gitelman syndrome with normal or low blood pressure.

  • C. Deficient 21-hydroxylase activity

    A 21-hydroxylase defect causes salt wasting or virilisation, not hypertension with low aldosterone.

  • D. Overactive epithelial sodium channel (correct)

    Correct. A constitutively active channel mimics hyperaldosteronism 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 D, Overactive epithelial sodium channel. Liddle syndrome is a gain-of-function mutation of the collecting duct epithelial sodium channel, so sodium is reabsorbed and potassium lost despite low aldosterone.

Why is "Aldosterone-secreting adrenal adenoma" not the answer?

An adenoma would raise aldosterone and respond to spironolactone.

Why is "Loss of the thiazide-sensitive cotransporter" not the answer?

Loss of this cotransporter causes Gitelman syndrome with normal or low blood pressure.

Why is "Deficient 21-hydroxylase activity" not the answer?

A 21-hydroxylase defect causes salt wasting or virilisation, not hypertension with low aldosterone.

What concept does this question test?

It tests Clinical biochemistry: Liddle syndrome in Biochemistry. Amiloride blocks the channel and corrects the abnormalities. Spironolactone works through the mineralocorticoid receptor and is ineffective.

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: Liddle 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.