An 18-year-old man evaluated for muscle cramps and fatigue has serum potassium 2.7 mEq/L, magnesium 1.2 mg/dL, and metabolic alkalosis. Urine calcium-to-creatinine ratio is markedly low. Blood pressure is normal. His presentation is best classified as:

• A Gitelman syndrome ✓
• B Bartter syndrome type I
• C Liddle syndrome
• D Primary hyperaldosteronism

Explanation

Gitelman syndrome is caused by loss-of-function mutations in the distal tubule thiazide-sensitive NaCl cotransporter, producing hypokalaemic metabolic alkalosis with hypomagnesaemia and low urine calcium, mimicking chronic thiazide use. Bartter syndrome involves the thick ascending limb and features normal or high urine calcium with variable magnesium, resembling loop diuretic effect. Liddle syndrome and primary hyperaldosteronism both cause hypertension, which this normotensive patient lacks.

Reference: Williams Textbook of Endocrinology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.