Correct Answer: D. Liddle’s syndrome
Liddle's syndrome is an autosomal dominant pseudohyperaldosteronism caused by gain-of-function mutations in genes encoding epithelial sodium channel (ENaC) subunits in the collecting duct. This leads to constitutive sodium reabsorption independent of aldosterone, resulting in the classic triad: hypertension, hypokalemia, and metabolic alkalosis. The pathophysiology involves excessive sodium retention (causing hypertension), increased potassium and hydrogen ion secretion (causing hypokalemia and metabolic alkalosis). Critically, plasma renin and aldosterone levels are suppressed due to volume expansion and sodium retention—this distinguishes Liddle's from primary hyperaldosteronism. The diagnosis is clinical (triad + suppressed aldosterone/renin) and confirmed by genetic testing. Management includes ENaC blockers (amiloride or triamterene) and sodium restriction. In Indian clinical practice, this rare genetic disorder must be differentiated from acquired causes of hypokalemic hypertension, particularly when aldosterone levels are paradoxically low despite hypokalemia.
Why the other options are wrong
A. Fanconi's syndrome — Fanconi's syndrome causes proximal tubular dysfunction with renal wasting of glucose, amino acids, phosphate, and bicarbonate—leading to metabolic acidosis, not alkalosis. While hypokalemia may occur due to urinary losses, the metabolic derangement is opposite to the clinical presentation. Hypertension is not a feature of Fanconi's syndrome. B. Gitelman's syndrome — Gitelman's syndrome (thiazide-like tubulopathy) causes hypokalemia and metabolic alkalosis but presents with hypotension or normotension, not hypertension. It results from mutations in the thiazide-sensitive Na-Cl cotransporter (NCCT) in the distal convoluted tubule. The absence of hypertension is the key discriminator from Liddle's syndrome. C. Bartter syndrome — Bartter syndrome (loop of Henle dysfunction) presents with hypokalemia, metabolic alkalosis, and hypotension or normotension—not hypertension. Plasma renin and aldosterone are elevated (secondary hyperaldosteronism), contrasting sharply with Liddle's suppressed levels. The clinical triad of hypertension + hypokalemia + alkalosis with low aldosterone is pathognomonic for Liddle's.
High-Yield Facts
- Liddle's syndrome = ENaC gain-of-function → hypertension + hypokalemia + metabolic alkalosis + suppressed renin/aldosterone (key discriminator).
- Bartter/Gitelman = both cause hypokalemia + alkalosis but with hypotension and elevated renin/aldosterone (secondary hyperaldosteronism).
- Fanconi's syndrome = proximal tubular dysfunction → metabolic acidosis (not alkalosis), no hypertension.
- Liddle's syndrome is treated with ENaC blockers (amiloride, triamterene), not spironolactone (which blocks aldosterone, not the channel itself).
- The suppressed aldosterone level despite hypokalemia is the pathognomonic finding that separates Liddle's from primary hyperaldosteronism.
Mnemonics
LIDDLE = Low Aldosterone Despite Electrolyte abnormality Liddle's is the only condition where you see hypokalemia + alkalosis + hypertension with suppressed aldosterone. All other causes of this triad have elevated aldosterone. Use this to rule out Liddle's vs. primary hyperaldosteronism at the bedside. BBG (Bartter/Gitelman/Gitelman) = Hypotension, not Hypertension Bartter and Gitelman both cause the electrolyte triad but with low blood pressure. Liddle's is the hypertensive one. If you see HTN + hypokalemia + alkalosis, think Liddle's first.
NBE Trap
NBE often pairs Bartter/Gitelman with the electrolyte triad (hypokalemia + alkalosis) to trap students who forget that these conditions cause hypotension, not hypertension. The presence of hypertension is the key discriminator for Liddle's syndrome.
Clinical Pearl
In Indian clinical practice, when a young patient presents with resistant hypertension and unexplained hypokalemia, always check plasma renin and aldosterone levels. A suppressed aldosterone level (not elevated) in the setting of hypokalemia is the red flag for Liddle's syndrome and mandates genetic testing and ENaC blocker therapy rather than standard antihypertensive regimens.
_Reference: Harrison Ch. 277 (Disorders of Potassium and Acid-Base Metabolism); Robbins Ch. 20 (Kidney pathology); KD Tripathi Ch. 18 (Diuretics and Renal Pharmacology)_