Descriptive cohort study of transient isolated tubular acidosis in early childhood: experience from a rare kidney disease expert center.

UNLABELLED: Growth faltering and/or failure to thrive in children often prompts metabolic assessment, sometimes revealing metabolic acidosis and leading to referral to pediatric nephrology. Renal tubular acidosis (RTA), causing hyperchloremic metabolic acidosis due to impaired renal acidification, includes transient isolated RTA, a relatively frequent but poorly described condition. We reviewed pediatric patients referred to the Lyon Rare Kidney Disease Center (MAREGE) between March 2023 and March 2024 for linear growth faltering and/or failure to thrive associated with isolated metabolic acidosis, after excluding systemic, endocrine, and gastrointestinal causes. Patients with suspected secondary, genetic forms, or distal RTA were excluded. Follow-up was analyzed from the initial nephrology consultation to the last visit before March 2025. Data are presented as medians [IQR] and compared using non-parametric tests. Thirty-five patients were included. At diagnosis, age was 15.3 [13.1-25.6] months, with weight and height standard deviation (SD) scores of - 1.5 [- 2.5; - 1.0] and - 1.0 [- 2.0; 0.0], respectively. Tubular assessments showed low plasma bicarbonate (19 [18-20] mmol/L), non-adapted bicarbonaturia (8.0 [2.8-18.6] mmol/L), and elevated urinary pH (7.0 [6.4-7.4]). After a follow-up of 2.2 [1.4-3.1] years at an of age 3.4 [1.9-4.1] years, weight SD scores increased significantly (- 1.0 [- 1.9; - 0.4], p = 0.04). Height SD scores also increased (- 0.5 [- 1.5; 0.0]), though not significantly (p = 0.41). Catch-up growth in weight, height, or both was achieved in 77% of patients. Bicarbonate supplementation, initiated at 1.2 [0.7-1.6] mmol/kg/day, was discontinued in 54% of cases; for others, dosing remained stable (1.3 [0.9-2.0] mmol/kg/day, p = 0.16).

CONCLUSION

Transient isolated RTA is observed in infants and young children with mild metabolic acidosis, isolated bicarbonaturia, and moderate failure to thrive and/or growth faltering. It resolves spontaneously within a few years, usually requiring only low-dose alkalizing therapy.

WHAT IS KNOWN: • Renal tubular acidosis (RTA) is a hyperchloremic, normal anion gap metabolic acidosis due to impaired renal acidification. In children, it is a recognized cause of growth faltering or failure to thrive and is usually a genetic disease (either proximal or distal acidosis).

WHAT IS NEW: • In cases of mild metabolic acidosis associated with moderate growth delay, without other tubular or extrarenal abnormalities, the possibility of transient isolated renal tubular acidosis should be considered. This condition warrants parental reassurance, as most patients show catch-up growth with minimal bicarbonate supplementation, which can usually be discontinued over time.