Bartter syndrome

Bartter syndrome is a rare inherited defect in the thick ascending limb of the loop of Henle. It is characterized by low potassium levels (hypokalemia), increased blood pH (alkalosis), and normal to low blood pressure. There are two types of Bartter syndrome: neonatal and classic. A closely associated disorder, Gitelman syndrome, is milder than both subtypes of Bartter syndrome.

Features
In 90% of cases, neonatal Bartter syndrome is seen between 24 and 30 weeks of gestation with excess amniotic fluid (polyhydramnios). After birth, the infant is seen to urinate and drink excessively (polyuria, and polydipsia, respectively). Life-threatening dehydration may result if the infant does not receive adequate fluids. About 85% of infants dispose of excess amounts of calcium in the urine (hypercalciuria) and kidneys (nephrocalcinosis), which may lead to kidney stones. In rare occasions, the infant may progress to renal failure.

Patients with classic Bartter syndrome may have symptoms in the first two years of life, but they are usually diagnosed at school age or later. Like infants with the neonatal subtype, patients with classic Bartter syndrome also have polyuria, polydipsia, and a tendency to dehydration, but normal or just slightly increased urinary calcium excretion without the tendency to develop kidney stones. These patients also have vomiting and growth retardation. Kidney function is also normal if the disease is treated, but occasionally patients proceed to end-stage renal failure. Bartter's syndrome consists of hypokalaemia, alkalosis, normal to low blood pressures, and elevated plasma renin and aldosterone. Numerous causes of this syndrome probably exist. Diagnostic pointers include high urinary potassium and chloride despite low serum values, increased plasma renin, hyperplasia of the juxtaglomerular apparatus on renal biopsy, and careful exclusion of diuretic abuse. Excess production of renal prostaglandins is often found. Magnesium wasting may also occur.

Diagnosis
People suffering from Bartter syndrome present symptoms that are identical to those of patients who are on loop diuretics like furosemide.

The clinical findings characteristic of Bartter syndrome are hypokalemia, metabolic alkalosis, and normal to low blood pressure. These findings may also be caused by:
 * Chronic vomiting: These patients will have low urine chloride levels (Bartter's will have relatively higher urine chloride levels).
 * Abuse of diuretic medications (water pills): The physician must screen urine for multiple diuretics before diagnosis is made.
 * Magnesium deficiency and Calcium deficiency: These patients will also have low serum and urine magnesium and calcium

Patients with Bartter syndrome may also have elevated renin and aldosterone levels.

Prenatal Bartter syndrome can be associated with polyhydramnios.

Pathophysiology
Bartter syndrome is caused by mutations of genes encoding proteins that transport ions across renal cells in the thick ascending limb of the nephron.

Bartter and Gitelman syndromes can be divided into different subtypes based on the genes involved:

Treatment
While patients should be encouraged to include liberal amounts of sodium and potassium in their diet, potassium supplements are usually required, and spironolactone is also used to reduce potassium loss.

Nonsteroidal antiinflammatory drugs (NSAIDs) can be used as well, and are particularly helpful in patients with neonatal Bartter's syndrome.

Angiotensin-converting enzyme (ACE) inhibitors can also be used.

Prognosis
The limited prognostic information available suggests that early diagnosis and appropriate treatment of infants and young children with Classic Bartter Syndrome may improve growth and perhaps neurointellectual development. On the other hand, sustained hypokalemia and hyperreninemia can cause progressive tubulointerstitial nephritis, resulting in end-stage-renal disease (Kidney failure). With early treatment of the electrolyte imbalances the prognosis for patients with Classic Bartter Syndrome is good.

History
The condition is named after Dr. Frederic Bartter, who, along with Dr. Pacita Pronove, first described it in 1960 and in more patients in 1962.

Related conditions

 * Bartter and Gitelman syndromes are both characterized by hypokalemia, hypomagnesemia, normal to low blood pressure, and hypochloremic metabolic alkalosis.

However, Bartter syndrome is also characterized by high renin, high aldosterone, hypercalciuria, and an abnormal Na+-K+-2Cl- transporter in the thick ascending limb of the loop of Henle, Gitelman syndrome causes hypocalciuria and is due to an abnormal thiazide transporter in the distal segment.

Pseudo-Bartter’s syndrome is a syndrome of similar presentation as Bartter syndrome but without any of its characteristic genetic defects. Pseudo-Bartter’s syndrome has been seen in cystic fibrosis, as well as in excessive use of laxatives.