Long-term growth hormone treatment in children with renal hypophosphatemic rickets: effects on growth, mineral metabolism, and bone density.

OBJECTIVE

To evaluate the effects of treatment with recombinant human growth hormone (rhGH) on growth, mineral metabolism, and bone density in children with renal hypophosphatemic rickets (RHR).

DESIGN

Long-term rhGH treatment combined with conventional therapy with 1,25-dihydroxyvitamin D3 plus inorganic phosphate salts.

SETTING

Endocrine unit, department of pediatrics, university hospital.

SUBJECTS

Twelve patients (5 boys; age range 4.6 to 12.5 years, median 7.0 years) were subdivided into two groups of six patients on the basis of the median of height z score (-2.41) and the median bone age/statural age (BA/SA) ratio (1.23). Group A included patients with a severe degree of short stature (height z score -3.4 +/- 0.5) (mean +/- SD) and altered BA/SA ratio (1.26 +/- 0.08); group B included patients with a lesser degree of short stature (height z score -2.1 +/- 0.6, p < 0.001 vs group A) and more normal BA/SA ratio (1.04 +/- 0.15, p < 0.01 vs group A).

INTERVENTION

Group A received rhGH treatment (0.6 IU/kg per week subcutaneously) combined with conventional therapy; group B received conventional therapy alone.

MEASUREMENTS

Height, growth velocity, predicted adult height, serum values of calcium, phosphate, bone alkaline phosphatase isoenzyme, osteocalcin, propeptides of type I and type III procollagen, intact parathyroid hormone, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and urinary calcium/urinary creatinine ratio and tubular maximum for phosphate reabsorption normalized to the glomerular filtration rate (TmP/GFR), as well as radial bone density, were measured at baseline and for 3 years.

RESULTS

Height z score, growth velocity z score, predicted adult height, serum values of phosphate, bone alkaline phosphatase isoenzyme, osteocalcin, propeptides of type I and type III procollagen, intact parathyroid hormone 1,25-dihydroxyvitamin D, and TmP/GFR, as well as radial bone density, improved significantly only in group A. Serum calcium and 25-hydroxyvitamin D, and urinary calcium/urinary creatinine ratio did not change in either group.

CONCLUSIONS

Long-term rhGH administration may benefit growth, phosphate retention, and bone density in patients with RHR, without evidence of side effects.