[Infantile transitory distal renal tubular acidosis with bicarbonate loss]

Apart from the classic distal renal tubular acidosis (RTA), the proximal RTA, and a few cases of distal RTA and renal bicarbonate wasting we know only 2 cases of infantile transient distal RTA with bicarbonate wasting. A 3 month-old male patient is admitted because of deficient suction, vomiting and dehydration. Despite a strong metabolic acidosis (pH 7,09, bicarbonate 8,6 mMol/l, chloride 110 meq/l) the urine is constantly alkaline; clinically the disease manifests itself in the form of an alkali-resistant RTA. Accompanying troubles such as inner ear deafness, G6PDH deficiency, hyperparathyroidism and vitamin D intoxication are to be excluded. A bicarbonate study carried out with care so as to prevent extracellular fluid expansion reveals the lack of excretion of titratable acid (-2.4 to +4.7 mueq/min/1.73 m2), an reduced excretion of ammonium (5 to 24.8 mueq/min/1.73 m2) with regard to GFR (42.4 ml/min/1.73 m2), and a constant loss of bicarbonate (FE HCO3- about 10%) covering most of the bicarbonate plasma concentration, which results in a constantly negative net acid excretion. Even with alkalosis there is no urine minus blood pCO2 increase. The renal excretion of gamma GT is significantly reduced. On substitution with high quantities of bicarbonate (10 meq/kg BW/day) the defect heals up at the age of 13 months. The pathogenesis of this disease is not quite clear, but is similar to that of the Lightwood infantile RTA. The acidification defect may be explained by a deficient hydrogen ions--secretion in the distal tubule; as for kinetics, it is not in the proximal tubule that the bicarbonate wasting occurs but it may be due to increased sodium delivery to the distal nephron.