What is Bartter syndrome?

What is Bartter Syndrome?

Bartter syndrome is a group of inherited salt-losing kidney disorders characterized by impaired salt reabsorption in the thick ascending limb of the loop of Henle, resulting in polyuria, hypokalemia, hypochloremic metabolic alkalosis, and normotensive hyperreninemic hyperaldosteronism 1.

Genetic Classification

Five distinct genetic subtypes exist, classified by the specific mutated gene 1:

• Type 1 (BS1): SLC12A1 gene mutation (NKCC2 protein) - autosomal recessive
• Type 2 (BS2): KCNJ1 gene mutation (ROMK/Kir1.1 channel) - autosomal recessive
• Type 3 (BS3): CLCNKB gene mutation (ClC-Kb chloride channel) - autosomal recessive
• Type 4a (BS4a): BSND gene mutation (Barttin protein) - autosomal recessive
• Type 4b (BS4b): Combined CLCNKA and CLCNKB mutations - autosomal recessive
• Type 5 (BS5): MAGED2 gene mutation - X-linked recessive (transient antenatal form)

All these proteins are directly involved in salt reabsorption in the thick ascending limb or regulate their expression 1, 2.

Pathophysiology

The fundamental defect involves impaired sodium chloride reabsorption in the thick ascending limb, which triggers a cascade of compensatory mechanisms 1:

1. Renal tubular salt wasting activates the renin-angiotensin-aldosterone system
2. Altered tubuloglomerular feedback at the macula densa senses low tubular chloride
3. Cyclooxygenase activation (primarily COX-2) produces excessive prostaglandins (especially PGE2)
4. This stimulates further renin secretion and aldosterone production
5. Results in hypokalemic hypochloremic metabolic alkalosis despite normal blood pressure

Two additional critical consequences occur 1:

• Reduced calcium reabsorption leading to hypercalciuria and nephrocalcinosis (except typically in BS3)
• Impaired urinary concentration ability (isosthenuria) due to loss of the medullary osmotic gradient

Clinical Presentation

Bartter syndrome is a potentially life-threatening condition requiring rapid diagnosis and treatment 1.

Typical Features:

• Polyuria and polydipsia (universal finding)
• Dehydration (often severe)
• Failure to thrive and growth retardation in children
• Polyhydramnios with premature birth (antenatal forms)
• Muscle weakness, cramps, or carpopedal spasms (from hypokalemia/hypocalcemia) 3
• Sensorineural deafness (specific to BS4a with BSND mutations)

Laboratory Hallmarks 1, 4:

• Hypokalemia (100% of cases)
• Hypochloremic metabolic alkalosis (>95% of cases)
• Hyperreninemia and hyperaldosteronism
• Normal to low blood pressure (distinguishes from primary hyperaldosteronism)
• Elevated urinary sodium, potassium, and chloride (renal wasting)
• Hypercalciuria (except BS3, which resembles Gitelman syndrome)
• Normal serum creatinine initially

Genotype-Phenotype Patterns

BS3 presents with milder features, often indistinguishable from Gitelman syndrome, without hypercalciuria and with partial urine concentration ability 1. BS4a uniquely includes sensorineural deafness due to Barttin's role in the inner ear 1. The antenatal forms (BS1, BS2, BS4) present with severe polyhydramnios and premature delivery, while classic BS (especially BS3) may present later in childhood or even adulthood 5, 6.

Management Principles

Treatment focuses on electrolyte replacement and reducing prostaglandin-mediated salt wasting 1:

Core Therapy:

• Sodium chloride supplementation (adjusted to severity)
• Potassium chloride supplementation (often high doses required)
• Liberal fluid intake to compensate for polyuria
• NSAIDs (indomethacin is mainstay) to block excessive prostaglandin production - particularly critical in early years

Adjunctive Options:

• Potassium-sparing diuretics (spironolactone, amiloride) 5
• ACE inhibitors or angiotensin receptor blockers (limited evidence)

Treatment must be individualized based on symptoms, tolerability, severity, age, and glomerular filtration rate 1. Early diagnosis and aggressive treatment prevent long-term complications including growth failure, nephrocalcinosis, and progression to end-stage renal disease 4, 7.

Important Clinical Pitfalls

Acquired Bartter-like syndrome (ABLS) can mimic genetic Bartter syndrome and is commonly caused by aminoglycosides (especially gentamicin), colistin, and amphoterin B 3. ABLS typically appears within 10 days of drug exposure and resolves within 14 days after discontinuation. Always exclude diuretic abuse, vomiting, and drug-induced causes before pursuing genetic testing 8, 5.

Adult-onset presentations are rare but occur, often misdiagnosed as they deviate from the classic pediatric presentation 5. Maintain high suspicion in adults with refractory hypokalemia and metabolic alkalosis after excluding common causes.