Bartter syndrome is a rare inherited kidney disorder in which the kidneys cannot properly reabsorb salt. This leads to excessive loss of sodium, chloride, and potassium in the urine, triggering a cascade of electrolyte imbalances that affect growth, blood pressure, and overall health. The condition is present from birth, though some forms cause problems before delivery while others don’t become apparent until later in childhood.
How the Kidneys Normally Handle Salt
Your kidneys filter blood and then reclaim most of the water and salt before it reaches your bladder. A critical part of this recycling happens in a structure called the loop of Henle, where specialized transport proteins pull sodium, potassium, and chloride back into the body. In Bartter syndrome, genetic mutations disable one or more of these transport proteins. The result is similar to what happens when someone takes a powerful loop diuretic (a “water pill”): the body dumps salt and water into the urine at an abnormally high rate.
Because so much salt is lost, the body compensates by ramping up hormones like renin and aldosterone that try to retain sodium. A side effect of this hormonal overdrive is that even more potassium gets pushed out, deepening the potassium deficit. The kidneys also lose their ability to concentrate urine properly, so affected individuals produce large volumes of dilute urine and feel constantly thirsty.
The Five Subtypes
Bartter syndrome is classified into five types based on which gene is affected. Each gene encodes a different protein involved in salt transport in the loop of Henle:
- Type I involves the SLC12A1 gene, which produces the main sodium-potassium-chloride cotransporter in the loop of Henle.
- Type II involves the KCNJ1 gene, which produces a potassium channel that recycles potassium back into the kidney tubule to keep salt reabsorption running.
- Type III involves the CLCNKB gene, which produces a chloride channel that moves chloride out of kidney cells and into the bloodstream.
- Type IV can involve the BSND gene or a combination of mutations in both chloride channel genes (CLCNKA and CLCNKB). This form often causes sensorineural hearing loss because the same chloride channels operate in the inner ear.
- Type V involves the MAGED2 gene. This form is unique because it typically resolves on its own after birth, though it can cause severe problems during pregnancy.
All five types are inherited in an autosomal recessive pattern, meaning a child must receive a defective copy of the gene from both parents to develop the condition.
Signs Before and After Birth
Types I, II, IV, and V often announce themselves before delivery. Because the fetus cannot reabsorb salt normally, it produces excessive urine in the womb. This leads to polyhydramnios, an abnormal buildup of amniotic fluid that mothers typically notice between 24 and 30 weeks of gestation. Amniotic fluid testing in these cases shows normal sodium and potassium but consistently elevated chloride, a hallmark finding. The excess fluid frequently triggers premature delivery.
After birth, the neonatal (or “antenatal”) form presents with severe dehydration, excessive urination, poor feeding, and failure to gain weight. Infants may develop dangerous episodes of volume depletion that require emergency fluids.
Type III, sometimes called classic Bartter syndrome, tends to appear in early childhood rather than at birth. Children present with excessive thirst, frequent urination, growth retardation, and muscle weakness from low potassium. Blood pressure is typically normal or low despite the high levels of renin and aldosterone circulating in the blood, which is an important clue during diagnosis.
Key Symptoms and Complications
The core symptoms across all types reflect chronic electrolyte loss:
- Polyuria and polydipsia: producing large volumes of urine and feeling intensely thirsty.
- Muscle weakness and cramping: driven by persistently low potassium.
- Growth delay: common in childhood-onset forms, sometimes the first thing parents notice.
- Salt craving: the body’s attempt to replace what the kidneys are wasting.
Over the long term, excess calcium in the urine (particularly in Types I and II) can lead to nephrocalcinosis, a condition where calcium deposits accumulate in the kidney tissue. This can gradually impair kidney function if not managed. Type IV carries the additional burden of hearing loss, which may be present from birth.
How It’s Diagnosed
Diagnosis starts with blood tests showing low potassium, low chloride, and a blood pH that’s shifted toward alkaline (metabolic alkalosis). These findings alone aren’t unique to Bartter syndrome, so doctors look at urine values to narrow things down. A spot urine chloride above 35 meq/L points toward Bartter syndrome and helps rule out vomiting-related causes, which typically produce urine chloride below 25 meq/L.
Urinary calcium levels help distinguish Bartter syndrome from the closely related Gitelman syndrome. Bartter syndrome shows normal or elevated urinary calcium, while Gitelman syndrome features unusually low urinary calcium. Serum magnesium also differs: it’s consistently low in Gitelman syndrome but only occasionally low in classic Bartter syndrome. Genetic testing provides a definitive diagnosis by identifying the specific mutation involved.
Bartter Syndrome vs. Gitelman Syndrome
These two conditions look similar on basic blood work, both causing low potassium and metabolic alkalosis, but they affect different parts of the kidney and behave quite differently in practice. Bartter syndrome mimics the effect of a loop diuretic, while Gitelman syndrome mimics a thiazide diuretic acting further downstream in the kidney tubule.
Gitelman syndrome generally appears later in childhood or even adulthood, rarely causes dehydration or growth problems, and doesn’t produce excess urinary calcium. It does, however, cause more pronounced magnesium loss and is more likely to trigger muscle spasms called tetany. Bartter syndrome tends to be more severe in early life, with dehydration, growth retardation, and the potential for nephrocalcinosis. In ambiguous cases, doctors can use a diuretic challenge test: giving a thiazide or loop diuretic and measuring the chloride response in urine to see which part of the kidney is impaired.
Treatment and Daily Management
There is no cure for Bartter syndrome, but treatment can control symptoms and support normal growth. Management rests on two pillars: replacing lost electrolytes and reducing the kidney’s overproduction of prostaglandins, which amplify salt and water loss.
Electrolyte replacement is the foundation. Sodium chloride supplementation at relatively high doses is standard, though it’s spread throughout the day in small, frequent amounts rather than given in a few large doses. Large infrequent doses cause rapid swings in blood levels that can be counterproductive. Potassium is supplemented as potassium chloride specifically; other potassium salts like potassium citrate can worsen the alkalosis. Magnesium supplements are added when levels run low, with organic magnesium salts preferred for better absorption.
Anti-inflammatory medications (NSAIDs) play a central role, especially in early childhood. By blocking prostaglandin production, these drugs reduce the excessive urinary salt and water losses that drive the syndrome’s symptoms. Indomethacin is the most commonly used option, typically given in divided doses throughout the day. Ibuprofen and celecoxib are alternatives. Because NSAIDs can irritate the stomach, doctors generally pair them with a medication to reduce stomach acid. Adequate hydration is important before starting NSAID therapy, since these drugs can stress the kidneys if a patient is already dehydrated.
For children with Type IV Bartter syndrome, hearing aids or cochlear implants may be needed to address sensorineural hearing loss. Type V, linked to the MAGED2 gene, often improves spontaneously after birth as the affected protein becomes less critical to kidney function outside the womb.
Living With Bartter Syndrome
With consistent treatment, many people with Bartter syndrome lead relatively normal lives. Growth delay in children often improves once electrolyte levels are stabilized and NSAID therapy is started. Regular blood and urine monitoring is necessary to fine-tune supplement doses and watch for kidney complications like nephrocalcinosis.
Daily life requires some adaptation. Staying well-hydrated is essential, especially during hot weather, exercise, or illness, when extra salt and water losses can quickly tip the balance toward dehydration. People with Bartter syndrome typically need to carry supplements and water, and schools or workplaces may need to accommodate more frequent bathroom breaks and fluid intake. Episodes of vomiting or diarrhea can be particularly dangerous because they accelerate electrolyte losses on top of an already depleted baseline, so early medical attention during acute illness is important.