Distal renal tubular acidosis is characterized by an elevation in urinary pH despite the presence of serum acidosis. Prevalence is unknown. Complete distal tubular renal acidosis is responsible for delayed growth, plasma acidosis with hyperchloremia, hypokalemia, and hypercalciuria with nephrocalcinosis and hypocitruria. Deafness may be associated. Distal renal tubular acidosis is caused by defective secretion of H+ ions by the collecting tubule cells. Autosomal recessive and dominant patterns of transmission have been observed. In distal renal tubular acidosis type I, transmission is autosomal recessive and mutations have been described in the ATP6B1 gene, coding for the ATP6V1B1 protein, a subunit of the H+ ATPase ion pump. Distal renal tubular acidosis type I is associated with progressive hearing loss. Distal renal tubular acidosis type II is also autosomal recessive. Mutations have been described in the ATP6N1B gene, encoding the ATP6VOA4 protein, another subunit of the H+ ATPase ion pump. Hearing loss may be a late feature of this form of the disease but is not constant. Mutations in the SLC4A1 gene (encoding AE1, an anion exchange protein) are responsible for autosomal dominant forms and, less often, for autosomal recessive forms of distal renal tubular acidosis. These two forms are associated with progressive hearing loss. As the defect in urine acidification can be partial, formal diagnosis needs to be made by a urine acidifying test with ammonium chloride. This test reveals failure of the distal tubule to lower the urinary pH to below 5.5, even when the level of bicarbonates in the plasma is below 18 mmol/L. Treatment aims at bringing the levels of bicarbonate, potassium, and calcium to within acceptable limits and includes administration of potassium and sodium bicarbonate supplements. This treatment also boosts growth and helps to reduce the calciuria.
Last update: February 2007