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Renal tubular acidosis (RTA) refers to kidney tubulopathies that present metabolic acidosis with a normal anion gap due to diminished tubular reabsorption of bicarbonate (HCO3-) and/or reduced urinary excretion of hydrogen ions (H+). Distal renal tubular acidosis (dRTA), also known as type 1 RTA, is caused by the inability of the distal tubule to secrete H+ and to reduce urinary pH, even in presence of systemic metabolic acidosis. dRTA can be primary or secondary. The primary form, predominant in pediatric patients, arises from genetic mutations affecting key proteins in distal tubule cells. Secondary dRTA can be caused by autoimmune diseases, medications, or urological obstructions.This study aims to analyze a cohort of 19 patients with primary dRTA followed-up in the Pediatric Nephrology Unit of Universidade Federal de Minas Gerais (UFMG) from 1984 to 2023. The study's relevance relies on the rarity of dRTA and the long-term follow-up.
A retrospective cohort study analyzed data of dRTA patients of the Pediatric Nephrology Unit-UFMG between 1984 and 2023. Patients with defined clinical diagnosis of primary dRTA were included, based on genetic testing or clinical and laboratory findings. Patients with type 2, 3, 4, or secondary dRTA were excluded. The Ethics Committee of UFMG approved the study.
The study included 19 patients with primary dRTA, with an average follow-up of 157.89±86.31 months. The mean age at diagnosis was 34.74±38.4 months. The average venous gasometry pH levels at diagnosis were 7.31±0.08, significantly increasing to 7.35±0.05 at the end of the follow-up period. Mean bicarbonate concentrations also increased from 16.38±6.95 mEq/L at diagnosis to 22.62±3.40 mEq/L at the end of follow-up. The initial mean base excess was -8.68±7.15 mmol/L, decreasing to -2.24±3.78 mmol/L at the end of the follow-up period.
Regarding renal function, the mean creatinine levels at diagnosis were 0.41±0.18 mg/dL, with an average glomerular filtration rate (GFR) of 138.69±36.0 mL/min/1.73 m², while the final creatinine was 0.66±0.16 mg/dL, with a final GFR of 109.02±29.67 mL/min/1.73 m². It is noteworthy that 45% of patients had nephrocalcinosis at the time of diagnosis. There was also a significant improvement in hypercalciuria from diagnosis to the end of the follow-up (4.22±2.56 vs. 3.08±0.94, p=0.006). The growth rate of the patients increased during follow-up and was positively correlated with blood potassium levels at the beginning (r = 0.575, p = 0.010) and at the end of treatment (r = 0.786, p < 0.001), emphasizing the importance of controlling hydroelectrolytic disorders for the appropriate growth of dRTA patients.
During the follow-up, the 19 patients with primary dRTA significantly improved clinical and biochemical parameters. The acid-base equilibrium was obtained in all patients. Renal function remained stable and urinary calcium excretion normalized. Growth rate also significantly improved and positively correlated with plasma levels of potassium, highlighting the importance of rigorous hydroelectrolyte control for patients with primary dRTA. Therefore, the approach of dRTA includes the correction of metabolic disorders, the evaluation and promotion of growth rate and the preservation of renal function by the strict control of hypercalciuria and nephrocalcinosis.