Pathophysiology

Bartter syndrome and the more common Gitelman syndrome result from deranged NaCl 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 NaCl reabsorption causes mild volume depletion, which leads to increases in renin and aldosterone release, resulting in K and H 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 Ca excretion are common. In both disorders, Na wasting contributes to a chronic mild plasma volume contraction reflected by a normal to low BP despite high renin and angiotensin levels.

The features at clinical presentation vary (see Table 1: Some Differences Between Bartter Syndrome and Gitelman Syndrome).

Table 1
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Some Differences Between Bartter Syndrome and Gitelman Syndrome Feature Bartter Syndrome Gitelman Syndrome Location of kidney defect Ascending loop of Henle (mimics effects of loop diuretics) Distal tubule (mimics effects of thiazides) Urinary Ca excretion Normal or increased, commonly with nephrocalcinosis Decreased Serum Mg level Normal or decreased Decreased, sometimes greatly Renal prostaglandin E2 production Increased Normal Usual age at presentation Before birth to early childhood, often with intellectual disability and growth disturbance Late childhood to adulthood Neuromuscular symptoms (eg, muscle spasms, weakness) Uncommon or mild Common

Etiology

Both syndromes are usually autosomal recessive, although sporadic cases and other types of familial patterns can occur. There are several genotypes of both syndromes; different genotypes can have different manifestations.

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 BP and may have signs of volume depletion. Inability to retain K, Ca, or Mg 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

• 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 Na, K, and Cl that are inappropriate for the euvolemic or hypovolemic state of the patient. Diagnosis is by exclusion of other disorders:

• Primary and secondary aldosteronism can often be distinguished by the presence of hypertension and normal or low plasma levels of renin (see Table 3: Differential Diagnosis of Aldosteronism).
• Surreptitious vomiting or laxative abuse can often be distinguished by low levels of urinary Cl (usually < 20 mmol/L).
• Surreptitious diuretic abuse can often be distinguished by low levels of urinary Cl and by a urine assay for diuretics.

Definitive diagnosis is through genetic testing, which is rarely done because of factors such as the large number of known mutations, large gene size, and prohibitive cost.

A 24-h measurement of urinary Ca or the urine Ca/creatinine ratio may help distinguish the two syndromes; the levels are typically normal to increased in Bartter syndrome and low in Gitelman syndrome.

Treatment

• NSAIDs (for Bartter syndrome)
• Spironolactone
  
  
  or amiloride
  
  
  
• Low-dose ACE inhibitors
• K, Mg, and Ca supplements

Because renal prostaglandin E2 secretion contributes to the pathogenesis in Bartter syndrome, NSAIDs (eg, indomethacin


1 to 2 mg/kg po once/day) are helpful; patients are also given K-sparing diuretics (eg, spironolactone


150 mg po bid or amiloride


10 to 20 mg po bid). K-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 K wasting, and K supplementation (KCl 20 to 40 mEq po once/day or bid) is often necessary. Mg and Ca supplements may also be needed.

Exogenous growth hormone can be considered to treat short stature.

Key Points

• Both syndromes have impaired NaCl reabsorption, which causes mild volume depletion, leading to increases in renin and aldosterone release, resulting in urinary K and H losses.
• Manifestations vary depending on genotype, but growth and development may be affected and electrolyte abnormalities may cause muscle weakness, cramping, spasms, tetany, or fatigue.
• Diagnosis involves serum and urinary electrolyte measurement; genetic testing is rarely done.
• Treatment involves K and sometimes Mg replacement. K-sparing diuretics and low-dose ACE inhibitors may be used; for Bartter syndrome, NSAIDs may be added.