Bartter syndrome

Bartter syndrome is a group of kidney diseases that affect the renal tubules, characterized by impaired salt reabsorption in the thick ascending limb of Henle's loop.

Henle's loop is a U-shaped segment located into the nephrons. Each kidney has between 800,000 and 1 million nephrons. The nephron is the basic functional unit of the kidney, responsible of the blood filtration to regulate water and solutes in order to reabsorb what it is necessary and remove waste through the urine.

Each nephron contains:

• Glomerulus
• Proximal convoluted tubule
• Distal convoluted tubule
• Henle's loop.

Bartter syndrome is the consequence of a defect in sodium, potassium and chloride reabsorption at the level of Henle's loop.<7p>

It is characterized by hypokalemia, hypochloremic metabolic alkalosis, and hypercalciuria (elevated calcium in the urine).

Bartter syndrome is a genetic disease caused by the mutation in one or several genes. The following ones cause the different variants of the disease:

• Type I – mutation of gene SLC12A1 (15q15-21) placed on chromosome 15
• Type II – mutation of gene KCNJ1 (11q24) placed on chromosome 11
• Type III – mutation of gene CLCNKB (1p36) placed on chromosome 1
• Type IV – mutation of genes CLCNKA and CLCNKB (1p36) or gene BSND (1p32.3) placed on chromosome 1
• Type V – mutation of gene CASR (3q21-1) placed on chromosome 3

Types I and II are included in neonatal Bartter syndrome and type III is included in classic Bartter syndrome.

Bartter syndrome is inherited in autosomal recessive manner (except type V) so it is necessary to inherit both genes altered from both parents to suffer the disease.

Presents in early life, often in neonatal period, with an annual incidence estimated at 1/1,000,000.

The main symptom is the nephrocalcinosis (deposition of calcium in the kidney) that appears within weeks or months after birth.

Besides, other symptoms may be present such as:

• Dehydration
• Fatigue
• Kidney stones
• Irritability
• Constipation
• Needing to urinate more frequently
• Growth retardation

Clinically it is characterized by the following findings:

• Severe hypokalemia (low levels of potassium in the blood) that may induce insipid diabetes.
• Hypochloremia (low level of chloride in the blood)
• Metabolic alkalosis
• Hypomagnesemia (low level of magnesium in the blood)
• High renin (hyperreninemia) and high aldosterone (hyperaldosteronism) in the blood
• Sometimes, hypotension (low blood pressure)

In addition, there is an excessive loss of sodium, calcium, chloride, magnesium and potassium in the urine.

The excessive loss of calcium in the urine (hypercalciuria) may cause nephrocalcinosis.

A genetic test can confirm the diagnosis.

Bartter syndrome treatment consists of prostaglandin synthetase inhibitors such as indomethacin, to revert the hypercalciuria (and therefore nephrocalcinosis) and prevents the kidney deterioration.

Other treatments usually used are:

• Increase fluid intake
• Potassium-sparing diuretics to decrease potassium loss and avoid metabolic alkalosis
• Amiloride, spironolactone and triamterene and even las thiazides to prevent hypercalciuria and nephrocalcinosis
• Potassium, chloride and magnesium supplements