Definition:

Renal tubular acidosis (RTA) is characterized by metabolic acidosis, a severe disturbance of extracellular pH homeostasis, due to renal impaired acid excretion. Type 4 RTA is a heterogeneous group of disorders associated with hyperkalemia due to aldosterone deficiency or impairment in aldosterone molecular signaling. Primary pseudohypoaldosteronism type 1 (PHA1) is characterized by salt-wasting, hyperkalemia, and metabolic acidosis in the presence of markedly elevated plasma renin activity and aldosterone concentration. In the autosomal dominant form, aldosterone resistance is due to heterozygous mutations in the mineralocorticoid receptor gene. In the autosomal recessive form, aldosterone resistance is caused by loss-of-function homozygous mutations in the genes encoding one of the three constitutive subunits (alpha, beta, and gamma) of the epithelial Na+ channel (SCNN1A, SCNN1B, and SCNN1G). Other inherited cause of type 4 RTA includes hyperkalaemia associated with hypertension and low or normal levels of plasma aldosterone. This syndrome is called pseudohypoaldosteronism type 2 (PHA2), or Gordon's syndrome, which results in a renal aldosterone resistance. Mutations in the genes encoding WNK1 and WNK4 kinases (WNK1 and WNK4), which regulate ion-transporters on renal tubules, were identified in patients with PHA2. Acquired hyperkalemic RTA is observed in the context of mineralocorticoid deficiency, systemic lupus erythematosus, and AIDS nephropathy. It is also often seen in a number of tubulointerstitial renal diseases. Finally, a great number of drugs may induce hyperkalemic RTA.