Gitelman Syndrome

Gitelman syndrome (GS; OMIM #263800) is the most common inherited renal tubular disorder, with a prevalence of ~25 per million (heterozygous carrier rate ~1% of the general population). It is an autosomal recessive salt-losing tubulopathy affecting the distal convoluted tubule (DCT).

Genetics and Molecular Basis

Gene	Protein	Location	Notes
SLC12A3	Thiazide-sensitive Na⁺-Cl⁻ cotransporter (NCC/NCCT)	Apical membrane, DCT	Responsible for the vast majority of cases
CLCNKB	Basolateral chloride channel CLC-Kb	Basolateral membrane, DCT/TAL	Rare; phenotype overlaps with Bartter type 3

Loss-of-function mutations in SLC12A3 abolish NCC activity. Many mutations cause a defect in cellular trafficking (the mutant protein is retained in the endoplasmic reticulum and never reaches the apical membrane). Commercial genetic panels now test the full complement of relevant genes rather than single genes.

Pathophysiology

The mechanisms mirror those of chronic thiazide diuretic use:

Loss of NCC function → Na⁺ and Cl⁻ wasting from the DCT → volume depletion
Volume depletion → activates the renin–angiotensin–aldosterone system (RAAS)
Increased aldosterone → upregulates ENaC in the cortical collecting tubule (CNT) → increased Na⁺ reabsorption, offset by K⁺ and H⁺ secretion → hypokalemia + metabolic alkalosis
Hypomagnesemia: NCC deficiency leads to DCT cell apoptosis and downregulation of the epithelial Mg²⁺ channel TRPM6 in the DCT → renal Mg²⁺ wasting
Hypocalciuria: Volume contraction enhances proximal tubular Ca²⁺ reabsorption (passive, secondary to increased Na⁺ reabsorption); the late DCT remains morphologically intact with preserved TRPV5 expression

DCT transport mechanisms showing NCC site of thiazide and Gitelman syndrome action

Clinical Features

GS presents in childhood or adolescence (contrast with Bartter syndrome, which presents neonatally). Many patients are discovered incidentally on routine electrolyte testing.

Symptoms (variable severity):

Muscle weakness, cramps, fatigue (most common)
Salt craving (nearly universal; sometimes extreme)
Nocturia
Polyuria and polydipsia (rare — distinguishes GS from Bartter)
Paresthesias, tetany (exceptional)
QT interval prolongation (increased arrhythmia risk; rare events of presyncope/ventricular tachycardia reported)
Chondrocalcinosis (calcium pyrophosphate dihydrate deposition in joint cartilage — a distinctive late complication, linked to hypomagnesemia)
Sclerochoroidal calcifications (ocular choroidal calcification)
Women: symptom exacerbation with menses; complicated pregnancies possible

Blood pressure: Normal to low (no hypertension)

Laboratory Findings

Parameter	Finding
Serum K⁺	Low (hypokalemia)
Serum Mg²⁺	Low (hypomagnesemia)
Serum HCO₃⁻/pH	High (metabolic alkalosis)
Serum Cl⁻	Low (hypochloremia)
Serum Ca²⁺	Normal
Urine Ca²⁺	Low (hypocalciuria) — key distinguishing feature
Urine Cl⁻, K⁺, Mg²⁺	Elevated (renal wasting)
Renin/Aldosterone	Elevated (secondary hyperreninemic hyperaldosteronism)
Urinary prostaglandin E₂	Normal (unlike Bartter syndrome)
Blood pressure	Normal to low

Distinguishing Gitelman from Bartter Syndrome

Feature	Gitelman	Bartter
Defect site	DCT (NCC)	TAL (NKCC2, ROMK, CLC-Kb, Barttin)
Age of onset	Childhood/adolescence	Neonatal
Urinary calcium	Low	Elevated
Serum magnesium	Low	Normal
Nephrocalcinosis	Absent	Present
Polyhydramnios	Absent	Common
Polyuria/polydipsia	Rare	Marked
Urinary PGE₂	Normal	Elevated
Response to NSAIDs	Poor	Good

Differential Diagnosis

Bartter syndrome (especially type 3, which can overlap)
EAST/SeSAME syndrome (KCNJ10 mutation: hypokalemic alkalosis + epilepsy, ataxia, sensorineural deafness, mental retardation)
Thiazide diuretic abuse (identical biochemical picture — check urine diuretic screen)
Laxative abuse, chronic vomiting (urine Cl⁻ helps distinguish: low in vomiting, elevated in GS)
Sjögren syndrome (acquired GS phenotype: hypokalemia + hypomagnesemia + hypocalciuria with normal NCC coding sequence)
HNF1B-related disease
Cisplatin nephrotoxicity (can cause an acquired GS-like picture)

Treatment

Targets: Serum K⁺ ≥ 3.0 mEq/L; Serum Mg²⁺ ≥ 0.6 mmol/L (1.46 mg/dL)

Dietary salt liberalization — counteracts volume depletion
Oral magnesium supplementation (lifelong): Organic magnesium salts (e.g., magnesium citrate, glycinate) preferred over MgCl₂, Mg(OH)₂, or MgO (better tolerated, less diarrhea)
Potassium supplementation: Oral KCl or potassium-rich diet
Amiloride — often preferred over spironolactone; blocks ENaC, reduces kaliuresis; doses up to 10 mg twice daily; can be combined with spironolactone or eplerenone
Spironolactone / eplerenone — adjunct to amiloride for refractory hypokalemia
RAAS inhibitors (ACE inhibitors) — in selected patients where hypotension is not a concern
NSAIDs — generally not useful (prostaglandin levels are normal, unlike Bartter syndrome)
Dietary caution: Identify and limit excessive salt-loading foods — salt loading increases distal NaCl delivery, amplifying K⁺ secretion by the CCT

Bone Effects

An interesting paradox: homozygous GS patients show higher bone mineral density than unaffected wild-type family members, while heterozygotes have intermediate values. This mirrors the bone-protective effect of thiazide diuretics. The hypocalciuria and enhanced proximal Ca²⁺ reabsorption are presumed responsible.

Acquired (Secondary) Gitelman-Like Syndromes

Conditions that mimic GS biochemically without NCC mutations:

Sjögren syndrome with tubulointerstitial nephritis
Cisplatin chemotherapy
Autoimmune tubulointerstitial nephritis

Sources: Brenner and Rector's The Kidney (2-Volume Set); National Kidney Foundation Primer on Kidney Diseases, 8e; Comprehensive Clinical Nephrology, 7th Edition; Harrison's Principles of Internal Medicine, 22e

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