A 4-year-old boy presents with failure to thrive, polyuria, hypokalemic metabolic alkalosis, and hypercalciuria. Blood pressure is low-normal. Ultrasound shows nephrocalcinosis. Which inherited tubular defect best explains this picture?

• A Loss of function of the thiazide-sensitive NaCl cotransporter in the distal convoluted tubule
• B Loss of function of aquaporin-2 in the collecting duct
• C Gain of function of the epithelial sodium channel in the collecting duct
• D Loss of function of the Na-K-2Cl cotransporter in the thick ascending limb ✓

Explanation

Hypercalciuria with nephrocalcinosis points to Bartter syndrome, caused by defective salt reabsorption in the thick ascending limb, most commonly loss of function of NKCC2. Impaired NaCl reabsorption mimics a loop diuretic, producing hypokalemic metabolic alkalosis with elevated renin and aldosterone but no hypertension. The thiazide-sensitive cotransporter defect describes Gitelman syndrome, which features hypocalciuria and hypomagnesemia instead.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.