Renal tubular acidosis (RTA) is characterized by metabolic acidosis, a severe disturbance of extracellular pH homeostasis, due to renal impaired acid excretion. Proximal RTA (type 2) is caused by an impairment of bicarbonate reabsorption in the proximal tubules, resulting in low renal bicarbonate threshold. Mutations in the gene SLC4A4, encoding Na+-HCO3- cotransporter (NBC-1), have been found in proximal RTA.
