Question

In Bartter syndrome, the genetic defect is located in the:

• A. Defect in PCT
• B. Defect in DCT
• C. Defect in thick ascending limb of loop of Henle
• D. None

Hint:

Bartter mimics a loop diuretic, so the defect sits where loop diuretics act - the TAL.

Answer 1

The Correct Option is C

Step 1: Bartter syndrome is an autosomal recessive salt-wasting tubulopathy. The lesion lies in the thick ascending limb (TAL) of the loop of Henle.
Step 2: The TAL normally reabsorbs sodium via the Na-K-2Cl (NKCC2) cotransporter, helped by the apical ROMK potassium channel and basolateral chloride channels. A loss-of-function mutation in any of these (NKCC2, ROMK or ClC-Kb) impairs salt reabsorption here, which mimics chronic loop-diuretic action.
Step 3: The result is salt wasting, hypokalaemic metabolic alkalosis, hypercalciuria and secondary hyperaldosteronism with normal-to-low blood pressure, plus loss of urinary concentrating ability.
Step 4: A DCT defect (option b) describes Gitelman syndrome (thiazide-sensitive NCC transporter), and the PCT is not the site, so option c, thick ascending limb, is the correct answer.