Bartter syndrome

Bartter syndrome is an AR hereditary tubulopathy with a combination of impaired water and electrolyte metabolism. The syndrome arises as a consequence of a complex disorder of tubular transport and 'excretion of ions.

Etiology
Diseases are caused by abnormalities' of three different transport systems': Na+/K+/2Cl-- cotransporter, potassium channel and chloride channel.

Pathogenesis
Na+/K+/2Cl--cotransporter defect (NKCC2, an ATP-independent ion channel) in the ascending part of the loop of Henle of the nephron leads to insufficient absorption of sodium, and its reduced level in the macula densa will increase the activity of the RAAS, which leads to an increase in the level of aldosteroneu and to secondary hyperaldosteronism with all clinical symptoms (blood pressure is normal).

Clinical picture
The main symptoms include:
 * hypokalemia (significant muscle weakness)
 * alkalosis
 * hypercalciuria
 * polyuria
 * hyperrenin hyperaldosteronism
 * growth disorders.

According to the type of defective transport system, we recognize 6 types of Bartter syndrome.

Type I - Na+/K+/2Cl--cotransporter defect (NKCC2, gene "SLC12A" ); manifests already in infancy, mostly in children born prematurely to mothers with polyhydramnios.

Type II − ATP-dependent apical potassium channel defect (ROMK1, gene KCNJ1); phenotypically it is the same as type I.

Type III - basolateral chloride channel defect (ClC-Kb, gene CLCNKB); hypomagnesemia is observed in 30% of patients (types I and II do not have it).

Type IVa' − β-subunit defect of the basolateral chloride channel (Barttin, gene BSND); characteristic trias: Bartter's syndrome, renal insufficiency, hearing impairment.

Type IVb - combined dysfunction of two chloride channels ClC-Ka and ClC-Kb (genes "CLCNKA" and "CLCNKB"), prenatal manifestation, polyhydramnios

Type V - transient form (defect in the MAGED2 gene), polyhydramnios, excessive salt loss with secondary metabolic alkalosis, disappears spontaneously in the first months of life

Therapy
The therapy is only symptomatic, its basis is diet adjustment and ion substitution.

Prognosis
The prognosis of the disease is uncertain, some patients develop mental retardation or kidney failure.