Renal tubular acidosis (RTA) is characterized by metabolic acidosis, a severe disturbance of extracellular pH homeostasis, due to renal impaired acid excretion. RTA type 3 is a mixed type that shares the features of both proximal and distal lesions, with impaired proximal bicarbonate reabsorption coupled with an inability to acidify the urine maximally despite severe degrees of systemic acidemia. The condition is due to an inherited deficiency of carbonic anhydrase II (CAII) caused by a recessive mutation in the CA2 gene on chromosome 8q22.
