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Gitelman SLC12A3 Mechanism — ESENeph MCQ

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ModerateTubular DisordersGitelman SLC12A3 MechanismESENeph

A 34-year-old man presents with episodic muscle weakness. Bloods: K+ 2.4 mmol/L, Mg2+ 0.5 mmol/L, Na+ 140 mmol/L, bicarbonate 30 mmol/L, calcium 2.35 mmol/L. BP 108/68 mmHg. Urine calcium:creatinine ratio is low. Urine potassium is elevated. Genetic testing reveals a pathogenic variant in SLC12A3. What is the underlying channel defect?

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Correct answer: E — Sodium-chloride cotransporter in the distal convoluted tubule

SLC12A3 encodes the thiazide-sensitive sodium-chloride cotransporter (NCC) in the distal convoluted tubule. Loss-of-function mutations cause Gitelman syndrome, characterised by hypokalaemic metabolic alkalosis, hypomagnesaemia, hypocalciuria, and low-to-normal BP. This is distinct from Bartter syndrome, which involves defects in the thick ascending limb (NKCC2, ROMK, ClC-Kb). The low urine calcium:creatinine ratio is a key distinguishing feature from Bartter syndrome.

Reference: https://guidelines.ukkidney.org