THE EFFECT OF PHOSPHATE SUPPLEMENTATION ON LINEAR GROWTH IN CHILDREN WITH X-LINKED HYPOPHOSPHATEMIA

Background. X-linked hypophosphatemia is the most common inherited cau se of rickets. Current therapy for this disorder includes vitamin D an d phosphate supplementation; however, phosphate therapy has been assoc iated with nephrocalcinosis. The purpose of this study is to evaluate the effect of oral phosphate therapy on growth in patients with X-link ed hypophosphatemia treated with either calcitriol or dihydrotachyster ol (vitamin D). Methods. We retrospectively evaluated the prepubertal growth of 36 children with X-linked hypophosphatemia. The height stand ard deviation score (Z-score) of patients initially treated with vitam in D alone and the Z-scores of patients treated with vitamin D and pho sphate therapy were compared. In addition, the growth of patients trea ted with vitamin D was compared with that of patients treated with vit amin D and phosphate from the outset of therapy. Results. Patients tre ated with vitamin D alone for 5.36 +/- 2.18 years had an improvement i n Z-score from -3.18 +/- 1.10 to -2.49 +/- 0.66 SDS, P < .05. Adding p hosphate therapy for patients initially treated with vitamin D alone f or 4.83 +/- 2.99 years did not further improve Z-score (-2.49 +/- 0.66 vs -2.35 +/- 0.83). Initial therapy with vitamin D and phosphate for 4.33 +/- 2.19 years also improved Z-score, (-2.84 +/- 1.02 vs -1.98 +/ - 0.82, P < .05). The change in Z-score was similar to the group treat ed with vitamin D alone compared with the group treated initially with vitamin D and phosphate (0.65 +/- 0.54 vs 0.85 +/- 0.65, respectively ). Conclusion. These data demonstrate that both vitamin D alone and in combination with phosphate improved lineal growth. Adding oral phosph ate for children initially treated with vitamin D alone did not improv e Z-score. Initial therapy with vitamin D and vitamin D plus phosphate produced similar changes in linear growth.