Stimulation of growth hormone secretion in children with X-linked hypophosphatemia.

X-linked hypophosphatemia is characterized by low serum phosphorus, relative vitamin D deficiency and rickets. Despite adequate metabolic control with oral phosphate and vitamin D therapy, patients with X-linked hypophosphatemia have short stature. Whether growth hormone (GH) deficiency plays a role in short stature in patients with X-linked hypophosphatemia is not known. The purpose of this report was to investigate the response of GH to sequential paired pharmacological stimulation in patients with X-linked hypophosphatemia. Basal GH was 3.8 +/- 0.7 ng/ml, insulin-like growth factor-I (IGF-I) was 225 +/- 38 ng/ml and IGF binding protein-3 was 3.0 +/- 0.2 mg/l in 16 children studied with X-linked hypophosphatemia. In response to L-dopa and arginine hydrochloride stimulation, serum GH rose to above 7 mg/ml in all patients. Thus, the short stature in patients with X-linked hypophosphatemia is not due to a GH/IGF-I secretory defect.