The effect of growth hormone treatment on biochemical indices in hypophosphatemic rickets

BACKGROUND: Growth hormone (GH) in combination with conventional therapy in hypophosphatemic rickets (HR) has been shown to promote renal phosphate (P) conservation and to result in a better metabolic control. This study aimed at investigating the acute biochemical effects of GH in 7 patients (5 female, 2 male) with HR aged between 2.16 and 16 years. METHODS: Each patient received the following in a sequential design: oral P plus 1,25-dihydroxyvitamin D(3) 1,25-(OH)(2)D(3)] therapy to determine the optimum doses for baseline requirement followed by GH-only therapy and GH +1,25-(OH)(2)D(3) therapy and GH + P +1,25-(OH)(2)D(3) therapy each for 2 weeks with 1 washout week off treatment in between. GH was given at a dose of 0.03 mg/kg/day s.c. on a daily basis. The dose of oral P used ranged between 500 and 2,000 mg/day, and the dose of 1,25-(OH)(2)D(3) ranged between 0.25 and 0.5 microg/day and was kept constant for each child throughout the study. RESULTS: Laboratory investigations repeated at the end of each treatment, and the first washout period showed that the serum P level was highest (2.9 ng/ml) during the GH + P + 1,25-(OH)(2)D(3) period with higher serum 1,25-(OH)(2)D(3) levels: 50.9 +/- (SD) 23.4 ng/l. Parathyroid hormone and alkaline phosphatase levels did not show a significant difference between the periods. The tubular P reabsorption rate showed an insignificant increase during GH therapy periods. CONCLUSION: Considering the fixed dose of P and calcitriol, it may be concluded that GH added to conventional treatment in HR resulted in a slight improvement in the biochemical parameters without any side effects at the short term.