This study indicates that non-oriental patients with dRTA caused by mutations in the SLC4A1 gene present later and have normokalemia or milder hypokalemia. Hypoacusia at diagnosis is characteristically associated with ATP6V1B1 gene mutations although it may also be present in infants with ATP6V0A4 defects. Other phenotypical manifestations do not allow predicting the involved gene.

Renal tubular acidosis (RTA) includes a group of diseases that manifest as normal anion gap hyperchloremic metabolic acidosis caused by disordered renal tubule function in the regulation of acid-base equilibrium, in the presence of normal or moderately impaired glomerular filtration rate. 1 Distal RTA (DRTA) is characterised by the inability of collecting duct to maximally acidify urine and by reduced urinary ammonium (NH4+) excretion despite coexisting metabolic acidosis. 2 In infants and children, most cases of DRTA result from loss-of-function mutations in either the ATP6VOA4 or the ATPV6V1B1 genes coding protein subunits of the H+-ATPase responsible for secreting hydrogen ions (H+) to the urine in the luminal side of type A intercalated cells of collecting duct. However, in adults, DRTA is usually acquired, secondary to systemic diseases, that is Sjögren syndrome, systemic lupus erythematosus. The term incomplete DRTA (iDRTA) is often used in the literature to describe adult patients having inability to acidify the urine but do not develop spontaneous metabolic acidosis. 3 The defect in urine acidification in iDRTA is less severe than in complete DRTA, and the glomerular filtration rate and the NH4+ excretion are greater in iDRTA than in complete DRTA patients. 4 These findings may explain

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