Renal Tubular Acidosis, Proximal

Proximal RTA is distinct from classic, or distal, RTA (see 179800), which is characterized by an inability of the distal tubule to generate a sufficiently large hydrogen ion gradient between blood and tubular fluid. Thus, excretion of ammonium ions and titratable acid are reduced, and urinary pH is usually above 6.5 despite overt acidosis. In the proximal, or bicarbonate-wasting, type of RTA, excretion of acid in the distal tubule is normal, and the urine is normally acidic, with a pH down to 5 during acidosis. In this type of RTA, an inability to reabsorb bicarbonate in the proximal tubules causes hyperchloremic acidosis. Type II RTA is a feature of the Fanconi syndrome (see 134600). As an isolated defect, it is a transitory condition in male infants, with growth retardation as the main clinical feature (Nash et al., 1972). Also see proximal renal tubular acidosis with ocular abnormalities and mental retardation (604278).

Brenes et al. (1977) studied a family in which 9 members had hyperchloremic acidosis with normal plasma creatinine and good ability to acidify urine. Renal functions, other than bicarbonate wasting, were normal. The acidosis persisted into adult life. All affected persons were asymptomatic but showed diminished stature. No hypercalciuria, rickets or osteomalacia was found. The authors suggested autosomal dominant inheritance. However, because of no male-to-male transmission, failure of expression in at least 3 persons who by the dominant hypothesis must have had the affected genotype, and the possibility (not excluded by the report) of consanguinity leading to a pseudodominant pedigree pattern, the mode of inheritance cannot be considered certain.

Fry and Karet (2007) reviewed the clinical features and molecular genetics of the inherited renal acidoses.