A 12-year-old boy has hypokalaemic metabolic alkalosis with normal blood pressure and elevated plasma renin and aldosterone. Urine calcium is high. The primary biochemical defect lies in which transporter?

• A Na+-K+-2Cl- cotransporter of the thick ascending limb ✓
• B Na+-Cl- cotransporter of the distal convoluted tubule
• C Epithelial sodium channel of the collecting duct
• D Na+/H+ exchanger of the proximal tubule

Explanation

Bartter syndrome results from defective salt reabsorption in the thick ascending limb, most commonly mutation of the furosemide-sensitive NKCC2 cotransporter, mimicking chronic loop diuretic effect. Salt wasting activates the renin-angiotensin-aldosterone axis without hypertension, and impaired paracellular calcium reabsorption causes hypercalciuria. Defective NCC in the distal convoluted tubule defines Gitelman syndrome, which features hypocalciuria instead.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.