Renal tubular acidosis (RTA) is characterized by metabolic acidosis, a severe disturbance of extracellular pH homeostasis, due to renal impaired acid excretion. The distal type of RTA (dRTA) arises when the collecting duct fails to remove excess acid into the urine and is characterized by the inability to lower urine pH maximally (below 5.5) in the face of spontaneous acidemia or after acid loading. Autosomal-dominant and -recessive forms of dRTA are caused by mutations in ion transporters of the acid-secreting Type A intercalated cell of the renal collecting duct. These include the AE1 Cl-/HCO3- exchanger of the basolateral membrane and at least two subunits of the apical membrane vacuolar (v)H+-ATPase, the V1 subunit B1 (associated with deafness) and the V0 subunit a4.
