ACUTE BIOCHEMICAL EFFECTS OF GROWTH-HORMONE TREATMENT COMPARED WITH CONVENTIONAL TREATMENT IN FAMILIAL HYPOPHOSPHATEMIC RICKETS

OBJECTIVE Conventional treatment of familial hypophosphataemic rickets with oral phosphate and 1 alpha-hydroxycholecalciferol (1 alpha HCC) does not satisfactorily correct the metabolic or physical defects of t he disease and can have adverse effects, such as nephrocalcinosis. Hyp eroxaluria from increased oral phosphate intake may contribute to neph rocalcinosis. Growth hormone enhances renal tubular phosphate reabsorp tion and 1,25-dihydroxycholecalciferol production in normal and in GH deficient individuals, and may thus be of benefit to patients with fam ilial hypophosphataemic rickets. PATIENTS We have assessed the acute e ffects of GH on phosphate and calcium metabolism in 6 children (age 4- 14 years) with familiar hypophosphataemic rickets. DESIGN Each patient served as his/her own control and received the following In a sequent ial non-randomized design: conventional treatment with oral phosphate 1 . 0-3 . 4 mmol/kg/day in 3-6 divided doses and 1 alpha HCC 18-31 ng/ kg/day-no treatment-GH 0 . 05 mg/kg daily-GH and 1 alpha HCC-and GH wi th phosphate and 1 alpha HCC. Each treatment was given for 7 days with 7 day periods of no treatment in between. MEASUREMENTS AND RESULTS Gl omerular filtration rate, tubular maximum rate of phosphate reabsorpti on per litre of glomerular filtrate (TmP/GFR) and serum 1,25-dihydroxy cholecalciferol increased with GH. Mean 24-hour plasma phosphate conce ntrations did not increase with GH but were higher in the treatment ph ases which included phosphate and 1 alpha HCC (P = 0 . 002). Serum PTH was higher when GH was given in combination with phosphate and 1 alph a HCC compared to other phases. Urine oxalate excretion did not differ between the treatment phases. CONCLUSIONS GH seemed to partially corr ect the defects in renal tubular phosphate transport and 1 alpha-hydro xylation of 25-hydroxycholecalciferol. We speculate that the net effec t of GH treatment was an increase in body phosphate, although this was not reflected in a change in plasma phosphate. Therefore, GH in combi nation with 1 alpha HCC may act as a phosphate sparing agent, permitti ng treatment with lower and less frequent doses of oral phosphate and reducing adverse effects such as nephrocalcinosis.