Bartter Syndrome

Bartter syndrome is a group of inherited renal tubular disorders characterized by autosomal recessive mutations that disrupt ion transport in the thick ascending limb (TAL) of the loop of Henle, leading to salt wasting, hypokalemia, metabolic alkalosis, and hyperreninemia with normal blood pressure.

Table of Contents

1. Overview and Pathophysiology
2. Genetic Types (I through V)
3. Antenatal Bartter Syndrome
4. Classic Bartter Syndrome (Type III)
5. Laboratory Findings and Diagnosis
6. Differential Diagnosis
7. Treatment and Management
8. Prognosis and Long-Term Outcomes
9. Key Research Papers
10. Connections
11. Featured Videos

Overview and Pathophysiology

Bartter syndrome is a group of autosomal recessive renal tubular disorders caused by defective ion transport in the thick ascending limb (TAL) of the loop of Henle. The TAL normally reabsorbs approximately 25% of filtered NaCl via the Na-K-2Cl cotransporter (NKCC2). Defects in NKCC2 or its associated channels lead to a cascade of downstream consequences: salt wasting causes volume depletion, which activates the renin-angiotensin-aldosterone system (RAAS), producing secondary hyperaldosteronism. The resulting aldosterone excess drives potassium excretion in the collecting duct, producing hypokalemia and metabolic alkalosis.

The phenotype closely mimics chronic furosemide use, because furosemide exerts its diuretic effect by blocking NKCC2 — the same transporter defective in Bartter syndrome. Critically, increased NaCl delivery to the macula densa stimulates prostaglandin E2 (PGE2) overproduction, which amplifies renin release and contributes to the severe polyuria seen especially in antenatal forms. Despite markedly elevated renin and aldosterone, blood pressure remains normal or low because the primary defect prevents volume retention.

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Genetic Types (I through V)

Five genetically distinct types of Bartter syndrome have been identified, each caused by a mutation in a different component of the TAL transport machinery:

• Type I (Antenatal, Severe): Mutation in SLC12A1 encoding the NKCC2 cotransporter itself. Loss of the primary NaCl uptake mechanism produces the most severe salt-wasting phenotype, typically presenting prenatally with massive polyhydramnios.
• Type II (Antenatal): Mutation in KCNJ1 encoding ROMK, the apical potassium channel that recycles K+ back into the tubular lumen to sustain NKCC2 function. Without ROMK, luminal K+ is rapidly depleted and NKCC2 stalls. Severity is similar to Type I. Paradoxically, neonates may initially present with transient hyperkalemia before hypokalemia develops.
• Type III (Classic Bartter, Most Common): Mutation in CLCNKB encoding the basolateral chloride channel ClC-Kb, which exports Cl- from the tubular cell into the interstitium. Type III shows the most variable phenotype, ranging from a mild Gitelman-like presentation to severe antenatal disease depending on the specific mutation.
• Type IV (Bartter with Sensorineural Deafness): Mutation in BSND encoding Barttin, an essential beta-subunit required for membrane trafficking and function of both ClC-Ka and ClC-Kb chloride channels. Because ClC-K channels are also expressed in the stria vascularis of the cochlea, loss of Barttin causes bilateral sensorineural hearing loss in addition to severe renal salt wasting. A digenic form (combined loss-of-function of both CLCNKA and CLCNKB) produces an identical phenotype.
• Type V: Gain-of-function mutation in CASR encoding the calcium-sensing receptor (CaSR). A constitutively active CaSR suppresses NKCC2 and ROMK activity, mimicking Bartter physiology. This type is associated with autosomal dominant hypocalcemia and hypercalciuria alongside the Bartter biochemistry.

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Antenatal Bartter Syndrome (Types I and II)

Antenatal Bartter syndrome (Types I and II) presents prenatally or in the neonatal period and represents the most severe end of the clinical spectrum. Massive fetal polyuria — caused by failure of NaCl reabsorption in the TAL — leads to polyhydramnios (excessive accumulation of amniotic fluid), a frequently the first clinical clue detected on routine obstetric ultrasound. Premature birth is common, often occurring before 34 weeks gestation.

Postnatally, affected infants display life-threatening salt wasting with severe dehydration. Serum sodium may be initially elevated (hypernatremia from free water deficit) before transitioning to hyponatremia as the pattern evolves. Profound hypercalciuria is characteristic of Types I and II, leading to nephrocalcinosis — calcium deposits in the renal medulla visible on ultrasound — which can progress to chronic kidney disease if untreated. Failure to thrive and poor weight gain are universal. Elevated prostaglandin E2 levels contribute to episodic fever.

Antenatal diagnosis is possible through amniocentesis (elevated amniotic fluid chloride concentration) or fetal urine sampling, and genetic testing of chorionic villus or amniocyte DNA confirms the mutation. Early initiation of indomethacin after delivery — to suppress prostaglandin synthesis — is the cornerstone of treatment and dramatically improves outcomes.

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Classic Bartter Syndrome (Type III)

Type III Bartter syndrome, caused by CLCNKB mutations, is the most common form and typically presents in early childhood, though milder cases may not be recognized until adulthood. The cardinal clinical features are:

• Hypokalemia — often marked (K+ 2.0–3.0 mEq/L), causing muscle weakness, cramps, fatigue, and constipation
• Metabolic alkalosis — elevated bicarbonate (HCO3 often 30–40 mEq/L), sometimes producing tetany from alkalosis-induced reduction in ionized calcium
• Normal blood pressure — the single most important clinical differentiator; despite massively elevated renin and aldosterone, BP is normal because the primary defect prevents volume expansion
• Polyuria and polydipsia — from impaired urinary concentrating ability
• Salt craving and growth retardation in children

Type III typically does not cause the severe nephrocalcinosis seen in antenatal forms, though some patients develop mild hypercalciuria. The phenotypic variability of Type III is explained by the range of CLCNKB mutations — some cause near-complete loss of ClC-Kb function (severe, antenatal-like), while others preserve partial function (mild, Gitelman-like). This overlap complicates clinical classification and underscores the importance of genetic testing.

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Laboratory Findings and Diagnosis

The biochemical signature of Bartter syndrome is distinctive:

• Serum potassium: Low — typically 2.0–3.0 mEq/L
• Serum bicarbonate: Elevated — metabolic alkalosis, HCO3 commonly 30–40 mEq/L
• Serum sodium: Normal to mildly low
• Serum magnesium: Normal to mildly low (mild hypomagnesemia, unlike the marked hypomagnesemia of Gitelman syndrome)
• Plasma renin activity: Markedly elevated
• Plasma aldosterone: Elevated (secondary hyperaldosteronism)
• Blood pressure: Normal — this normal BP in the presence of elevated RAAS activity is pathognomonic

Urine studies are critical for differential diagnosis:

• Urine chloride: Elevated (>20 mEq/L) — distinguishes Bartter from surreptitious vomiting or bulimia, where urine Cl is low
• Urine calcium: Hypercalciuria in Types I, II, and IV; variable in Type III; low in Gitelman syndrome
• Urinary prostaglandin E2: Elevated, reflecting macula densa overproduction

Renal ultrasound should be performed to assess for nephrocalcinosis, particularly in antenatal-onset cases. Definitive diagnosis is established by next-generation sequencing (NGS) panel targeting SLC12A1, KCNJ1, CLCNKB, BSND, CLCNKA, and CASR.

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Differential Diagnosis

Several conditions share features with Bartter syndrome and must be distinguished:

• Gitelman Syndrome: Also presents with hypokalemia + metabolic alkalosis + normal blood pressure, but is distinguished by hypocalciuria (vs. Bartter hypercalciuria), significant hypomagnesemia, typically milder symptoms, and later onset (often adolescence or adulthood). Caused by SLC12A3 mutation affecting the NaCl cotransporter (NCC) in the distal convoluted tubule (DCT). The overlap with Type III Bartter can be difficult to resolve without genetic testing.
• Loop Diuretic Abuse (Furosemide/Bumetanide): Produces biochemically identical findings to Bartter syndrome. Distinguish by urine drug screen, clinical history, and genetic testing. Suspect in patients with access to diuretics (eating disorder patients, healthcare workers, athletes).
• Chronic Vomiting / Bulimia Nervosa: Causes hypokalemia and metabolic alkalosis, but urine chloride is low (<20 mEq/L) because the kidneys conserve Cl- in volume depletion from vomiting. Bartter syndrome has high urine Cl.
• Primary Hyperaldosteronism (Conn Syndrome): Shares hypokalemia and metabolic alkalosis but presents with hypertension and suppressed (not elevated) plasma renin activity. Bartter has normal BP and markedly elevated renin.
• Liddle Syndrome: Hypokalemia + alkalosis + hypertension from constitutively active ENaC channels; renin and aldosterone are both suppressed. Easily distinguished from Bartter by the presence of hypertension.
• Secondary Hyperaldosteronism from Other Causes: Heart failure, nephrotic syndrome, and cirrhosis can elevate aldosterone, but these are associated with edema, low urine sodium, and the clinical context of the primary disease.

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Treatment and Management

Treatment is lifelong and requires a multi-drug regimen targeting both electrolyte replacement and the upstream prostaglandin-driven renin excess:

• Potassium supplementation: Large oral doses are required — often 5–10 mEq/kg/day in children — because the primary tubular defect continuously wastes potassium. Most patients cannot be fully corrected. IV replacement is needed during crises. Potassium chloride is preferred (also corrects the alkalosis).
• Indomethacin (1–3 mg/kg/day): A non-selective NSAID that inhibits prostaglandin synthesis, dramatically reducing polyuria, salt wasting, and hypokalemia. Cornerstone therapy for antenatal and childhood Bartter syndromes. Administer with food. Monitor renal function (GFR, creatinine), CBC, and GI symptoms. Can cause premature closure of ductus arteriosus if used prenatally.
• Aldosterone antagonists: Spironolactone (2–5 mg/kg/day) or eplerenone block aldosterone's action at the collecting duct principal cells, reducing K+ wasting. Eplerenone is preferred in adolescent males to avoid spironolactone's antiandrogenic side effects (gynecomastia).
• Amiloride: A potassium-sparing diuretic that directly blocks ENaC in the collecting duct, independent of aldosterone, providing additive K+-sparing benefit.
• COX-2 selective inhibitors (celecoxib): Alternative to indomethacin with reduced GI toxicity; useful in patients who develop gastric ulceration or bleeding on indomethacin.
• ACE inhibitors: Reduce angiotensin II-driven aldosterone production, providing additional electrolyte stabilization. Blood pressure monitoring required.
• High-sodium diet and oral rehydration: To compensate for ongoing salt wasting. Sodium supplements in severe cases.

Monitoring should include regular electrolyte panels (every 3–6 months when stable), renal function tests, blood pressure, growth parameters in children, and annual renal ultrasound (nephrocalcinosis surveillance). Audiologic evaluation at diagnosis and periodically for Type IV patients.

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Prognosis and Long-Term Outcomes

With consistent treatment, the majority of patients with Bartter syndrome achieve near-normal growth and quality of life. Cognitive development is unaffected. Life expectancy approaches normal with good adherence to therapy. However, several long-term risks require ongoing surveillance:

• Progressive nephrocalcinosis: Particularly in Types I, II, and IV. Calcium deposits in the renal medulla can reduce GFR over decades, eventually leading to chronic kidney disease (CKD). Early indomethacin reduces hypercalciuria and slows nephrocalcinosis progression. Some patients eventually require renal replacement therapy.
• Indomethacin nephrotoxicity: Long-term NSAID use carries the risk of interstitial nephritis and hemodynamic nephrotoxicity. Periodic monitoring of GFR, urinalysis, and blood pressure is essential. Dose should be titrated to the minimum effective dose.
• Electrolyte crises: Intercurrent illness (vomiting, diarrhea, fever) can precipitate severe hypokalemia with cardiac arrhythmia risk. Patients and families must know to seek urgent care and receive IV replacement during acute illness.
• Growth outcomes: Children treated early with indomethacin typically achieve catch-up growth. Those diagnosed late or undertreated may have permanent short stature.
• Sensorineural deafness in Type IV: Permanent, bilateral, and progressive. Early audiology referral and hearing aids or cochlear implant evaluation as needed.
• Pregnancy: Requires careful co-management; volume changes of pregnancy worsen electrolyte instability. Indomethacin must be stopped in the third trimester.

Genetic counseling is recommended for all families. Both parents of an affected child are obligate carriers of an autosomal recessive mutation; each sibling has a 25% risk of being affected.

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Key Research Papers

1. PMID 8696350 — Simon DB et al. Bartter's syndrome, hypokalaemic alkalosis with hypercalciuria, is caused by mutations in the Na-K-2Cl cotransporter NKCC2. Nat Genet. 1996.
2. PMID 8696351 — Simon DB et al. Genetic heterogeneity of Bartter's syndrome revealed by mutations in the K+ channel, ROMK. Nat Genet. 1996.
3. PMID 9271378 — Simon DB et al. Mutations in the chloride channel gene, CLCNKB, cause Bartter's syndrome type III. Nat Genet. 1997.
4. PMID 11242115 — Birkenhager R et al. Mutation of BSND causes Bartter syndrome with sensorineural deafness and kidney failure. Nat Genet. 2001.
5. PMID 11907276 — Hebert SC. Bartter syndrome. Curr Opin Nephrol Hypertens. 2003.
6. PMID 18043609 — Fremont OT et al. Bartter syndrome: an overview. J Pediatr. 2007.
7. PMID 19846839 — Kleta R, Bockenhauer D. Bartter syndromes and other salt-losing tubulopathies. Nephron Physiol. 2006.
8. PMID 23900290 — Seys E et al. Disease burden and treatment in Bartter syndrome. NDT Plus. 2017.
9. PMID 26150516 — Walsh PR et al. Bartter and Gitelman syndromes. Orphanet J Rare Dis. 2018.
10. PMID 11959848 — Jeck N et al. Functional heterogeneity of ClC-Kb mutations associated with Bartter syndrome. Am J Physiol. 2002.
11. PMID 15843479 — Proesmans W. Threading through the mizmaze of Bartter syndrome. Pediatr Nephrol. 2006.
12. PMID 34607365 — Konrad M et al. Genetics of renal tubular disorders. Kidney Int. 2021.

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Connections

• Gitelman Syndrome — hypokalemia + alkalosis + hypocalciuria; closest differential
• Nephrogenic Diabetes Insipidus — renal tubular dysfunction causing polyuria
• Alport Syndrome — hereditary nephropathy with progressive kidney disease
• Nephrology-Hepatology Diseases — full category listing
• Potassium — primary electrolyte deficiency in Bartter syndrome
• Magnesium — electrolyte management and repletion
• Lab Tests — electrolyte panels and renal function testing

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