Nephrocalcinosis in X-linked hypophosphataemic rickets: its relationship to treatment, kidney function, and growth

We studied 25 patients treated with oral phosphate and 1,25(OH)2 vitamin D for 0.5-15 y (mean, 7 y) to determine the incidence of nephrocalcinosis and its relationship to treatment, renal function, and growth. During the follow-up period, 3 hypercalcaemic and 13 random hypercalciuric episodes were documented. Creatinine clearances and urine concentration tests were normal in all patients. One patient's 24-h urine specimen indicated hypercalciuria. Kidney ultrasonography revealed nephrocalcinosis in 80% of the patients, but its severity was not significantly related to the dose of calcitriol or of phosphate, the duration of treatment, the age at which treatment was started, or growth. None of the 9 untreated affected family members had nephrocalcinosis. Longitudinal studies revealed that the greatest loss in height velocity occurred during the first 2 y of life. Our study shows that nephrocalcinosis is a common complication of phosphate and 1,25(OH)2D3 treatment, but it is not necessarily associated with impaired renal function. Although the treatment failed to prevent a decrease in height velocity during infancy, it effectively maintained height velocity after 2 y of age.