The role of IGF-I in phosphate therapy for the short stature of patients with hypophosphatemic vitamin D-resistant rickets

The role of phosphate in short-statured patients with X-linked hypophosphatemic rickets (XLH) was investigated. Plasma insulin-like growth factor (IGF)-I levels were within the normal range in XLH patients. After oral phosphate loading, plasma IGF-I levels increased clearly in XLH patients, while there were no changes in normal controls. Plasma IGF-I levels significantly correlated with the maximal serum parathyroid hormone (PTH) concentrations in XLH patients. Plasma PTH concentrations and nephrogenic cyclic AMP values were increased significantly in XLH patients compared with normal controls. The former values correlated significantly with the increments of serum phosphate concentrations. The increase of serum PTH concentrations did not correlate either with the decrease of serum calcium concentrations or with the serum 1,25-dihydroxyvitamin D concentrations in either XLH patients or the normal controls. A 1-34 human PTH loading test revealed a clear increase of the plasma IGF-I levels in two XLH patients, while there was no change in the normal controls. The height SD scores of XLH patients significantly correlated with the maximal increase of plasma IGF-I concentrations. These data suggest that the increased IGF-I levels via PTH were in part supposed to restore the IGF action resulting in improved growth in XLH patients due to phosphate therapy.