Growth Hormone Secretion and Serum Insulin-like Growth Factor-I Concentration in X-linked Hypophosphatemic Rickets Before and After Treatment

SUMMARY The aetiology of growth retardation in children with X-linked hypophosphatemic rickets (HPR) has not been totally defined. We evaluated growth hormone (GH)/insulin-like growth factor-I (IGF-I) changes in relation to linear growth and biochemical parameters in seven children with X-linked hypophosphatemic rickets before and after treatment with 1,25-dihydroxyvitamlnD3 and phosphate therapy for a year or more. Moreover, we compared patients' growth data and GH/IGF-I changes with those for 20 age-matched children with normal variant short stature (NVSS) [with normal GH secretion and height standard deviation score (HtSDS) before −2]. Before treatment, all children with HPR secreted normal GH in response to clonidine provocation (>10μg/l) and their IGF-I concentration was significantly lower than those with NVSS. The HtSDS and growth velocity (GV) of children with HPR improved significantly after (−3.05, 8.9 cm/year, respectively) v. before (−3.9 and 4.1 cm/year, respectively) therapy. Their serum IGF-I concentration increased significantly from 76.7 ng/ml before to 99.6 ng/ml after treatment In summary children with HPR had no abnormality of GH secretion but improvement of their linear growth was associated with significant increase of circulating IGF-I concentration after treatment.