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Bartter syndrome and Gitelman syndrome are autosomal recessive renal disorders characterized by fluid, electrolyte, urinary, and hormonal abnormalities, including renal potassium, sodium, chloride, and hydrogen wasting; hypokalemia; hyperreninemia and hyperaldosteronism without hypertension; and metabolic alkalosis. Findings include electrolyte, growth, and sometimes neuromuscular abnormalities. Diagnosis is assisted by urine electrolyte measurements and hormone assays but is typically a diagnosis of exclusion. Treatment consists of nonsteroidal anti-inflammatory drugs, potassium-sparing diuretics, low-dose angiotensin-converting enzyme inhibitors, and electrolyte replacement.

Pathophysiology

Bartter syndrome and the more common Gitelman syndrome result from

Deranged sodium chloride reabsorption
In Bartter syndrome, the defect is in the ascending thick limb of the loop of Henle. In Gitelman syndrome, the defect is in the distal tubule.

In both syndromes, the impairment of sodium chloride reabsorption causes mild volume depletion, which leads to increases in renin and aldosterone release, resulting in potassium and hydrogen losses. In Bartter syndrome, there is increased prostaglandin secretion as well as a urinary concentrating defect due to impaired generation of the medullary concentration gradient. In Gitelman syndrome, hypomagnesemia and a low urinary calcium excretion are common. In both disorders, sodium wasting contributes to a chronic mild plasma volume contraction reflected by a normal to low blood pressure despite high renin and angiotensin levels.

Symptoms and Signs

Bartter syndrome tends to manifest prenatally or during infancy or early childhood. Gitelman syndrome tends to manifest during late childhood to adulthood. Bartter syndrome can manifest prenatally with intrauterine growth restriction and polyhydramnios. Different forms of Bartter syndrome can have specific manifestations, including hearing loss, hypocalcemia, and nephrocalcinosis, depending on the underlying genetic defect. Children with Bartter syndrome, more so than those with Gitelman syndrome, may be born prematurely and may have poor growth and development postnatally, and some children have intellectual disability.

Most patients have low or low-normal blood pressure and may have signs of volume depletion. Inability to retain potassium, calcium, or magnesium can lead to muscle weakness, cramping, spasms, tetany, or fatigue, particularly in Gitelman syndrome. Polydipsia, polyuria, and vomiting may be present.

In general, neither Bartter syndrome nor Gitelman syndrome typically leads to chronic renal insufficiency.

Diagnosis
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Serum and urine electrolyte levels
Exclusion of similar disorders
Bartter syndrome and Gitelman syndrome should be suspected in children with characteristic symptoms or incidentally noted laboratory abnormalities, such as metabolic alkalosis and hypokalemia. Measurement of urine electrolytes shows high levels of sodium, potassium, and chloride that are inappropriate for the euvolemic or hypovolemic state of the patient.

Primary and secondary aldosteronism can often be distinguished by the presence of hypertension and normal or low plasma levels of renin (see Table: Differential Diagnosis of Aldosteronism).
Surreptitious vomiting or laxative abuse can often be distinguished by low levels of urinary chloride (usually greater than 20 mmol/L).
Surreptitious diuretic abuse can often be distinguished by low levels of urinary chloride and by a urine assay for diuretics.
A 24-hour measurement of urinary calcium or the urine calcium/creatinine ratio may help distinguish the two syndromes; the levels are typically normal to increased in Bartter syndrome and low in Gitelman syndrome.

Treatment
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For Bartter syndrome, nonsteroidal anti-inflammatory drugs (NSAIDs)
Spironolactone or amiloride
Low-dose angiotensin-converting enzyme (ACE) inhibitors
Potassium and magnesium supplements
Because renal prostaglandin E2 secretion contributes to the pathogenesis in Bartter syndrome, NSAIDs (eg, oral indomethacin 1 to 5 mg/kg once a day) should be given (1); patients are also given oral potassium-sparing diuretics (eg, spironolactone 150 mg 2 times a day or amiloride 10 to 20 mg 2 times a day). Potassium-sparing diuretics alone are used in Gitelman syndrome. Low-dose ACE inhibitors can help limit the aldosterone-mediated electrolyte derangements. However, no therapy can completely eliminate potassium wasting, and oral potassium supplementation (potassium chloride 20 to 40 mEq one or 2 times a day) is often necessary. Magnesium supplements may also be needed.

Exogenous growth hormone can be considered to treat short stature.

#barttersyndrome #gitelmansyndrome #renaltubularacidosis #type1rta

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