Nephrocalcinosis is associated with renal tubular acidosis in children with X-linked hypophosphatemia

Background. X-linked hypophosphatemia is characterized clinically by rickets and growth retardation. Therapy of this disorder with phosphate and vitamin D often produces nephrocalcinosis. The long-term effects of nephrocalcinosis on renal function in patients with X-linked hypophosphatemia are unknown. The purpose of this study was to evaluate the prevalence of glomerular and tubular disorders in patients with X-linked hypophosphatemia who developed nephrocalcinosis. Methods. The creatinine clearance and the prevalence of renal tubular acidosis were compared in 19 patients with X- linked hypophosphatemia and nephrocalcinosis with 15 patients with X-linked hypophosphatemia without nephrocalcinosis. Results. Sixteen of the 19 patients (84%) with nephrocalcinosis had a hyperchloremic metabolic acidosis compared with one of the 13 patients without nephrocalcinosis (P < .01). The serum bicarbonate of patients with nephrocalcinosis was 20.0 ± 0.7 as compared to 24.5 ± 0.6 mmol/L in patients without nephrocalcinosis (P < .01). The urinary anion gap was positive in all patients with acidosis (+62.1 ± 13.3 mmol/UL). The creatinine clearance was 125 ± 6 mL/min/1.73 m² in patients with nephrocalcinosis and 124 ± 7 mL/min/1.73 m² in those without nephrocalcinosis. Conclusion. Therapy of X-linked hypophosphatemia is often associated with nephrocalcinosis. Nephrocalcinosis is associated with renal tubular acidosis in patients with X-linked hypophosphatemia.