Metabolic control and growth during exclusive growth hormone treatment in X-linked hypophosphatemic rickets.

BACKGROUND: GH may improve phosphate balance and height in X-linked hypophosphatemic rickets (XLH). This study evaluated the impact of exclusive rhGH therapy on phosphate homeostasis and growth. METHODS: Ten children (median age 12.2 years) with XLH were included in a 12-month trial with GH. Conventional treatment was discontinued 1 month prior GH (0.033 mg/kg/day); 1alpha-hydroxyvitamin D was added at 6 months and oral phosphate at 12 months, when GH was discontinued. Patients were followed 1-3 monthly until 18 months for clinical, biochemical and radiographic parameters. RESULTS: Serum phosphate Z-score increased significantly from baseline at 6 months (p = 0.005) and 9 months (p = 0.009) but returned to baseline by 12 months. Serum 1,25-dihydroxyvitamin D also increased significantly. Parathyroid function normalized. The median height Z-score was -2.2 (-2.7 to +0.4) at GH onset and -1.7 (-2.3 to +0.3) at 12 months. One patient showed a significant increase in radiographic rickets activity and 3 patients aggravation of lower limb deformity; the others showed no changes or improvement in these parameters. CONCLUSIONS: GH treatment improved serum phosphate and 1,25-dihydroxyvitamin D, normalized parathyroid function and improved longitudinal growth in XLH. It may however aggravate pre-existing skeletal deformities.