A 30-year-old woman presents with profound hypokalaemia (K 2.1 mEq/L), metabolic alkalosis, low-normal blood pressure, elevated plasma renin, and elevated aldosterone. Urinary chloride is low. Which diagnosis fits this picture?

• A Gitelman syndrome (SLC12A3 mutation) ✓
• B Liddle syndrome (pseudohyperaldosteronism)
• C Bartter syndrome type III (CLCNKB mutation)
• D Primary hyperaldosteronism

Explanation

Gitelman syndrome is caused by loss-of-function mutations in SLC12A3 (NCC thiazide-sensitive cotransporter in distal convoluted tubule), presenting with hypomagnesaemia, hypocalciuria, hypokalaemia, metabolic alkalosis, low-normal BP, elevated renin, and elevated aldosterone (secondary). Bartter syndrome presents similarly but with hypercalciuria and normal magnesium. Liddle syndrome has low renin and low aldosterone (gain-of-function ENaC). Primary hyperaldosteronism has hypertension with suppressed renin.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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