Two-year recombinant human growth hormone (rhGH) treatment is more effective in pre-pubertal compared to pubertal short children with X-linked hypophosphatemic rickets (XLHR).

Context: Twenty-five to 40% of patients with well-controlled X-linked hypophosphatemic rickets (XLHR) have a final height under -2 SDS. Previous studies have shown that recombinant human growth hormone (rhGH) treatment improves linear growth in short children with XLHR.

Objective: We studied the effectiveness of rhGH treatment in children with XLHR in a larger cohort.

Design: Monocentric, prospective, non-randomized trial.

Setting: University hospital in France.

Patients: 19 patients with XLHR and a mutation in the PHEX gene. Six male and 6 female Tanner stage 1 patients (age 6.1±2.4years) and 4 male and 3 female Tanner stage 2 patients (age 13.1±1years). At inclusion, height SDS was -2.35±0.8 SDS and growth velocity was -1.12±1.2 SDS.

Intervention: 2years of treatment with 67mcg/kg/day of rhGH at initiation. Every three months rhGH dosage was adjusted using an IGF-1 dosing protocol.

Main Outcome Measures: Comparison in change from baseline to year 2 in height and growth velocity.

Results: Height SDS improved from -2.35±0.8 SDS at baseline, to -1.62±0.8 SDS (p=0.01) after one and to -1.2±1 SDS (p=0.04) after two years of rhGH treatment. There was a strong correlation (r=0.6104, p<0.0001) between the age of onset of rhGH treatment and the number of cm gained over the study period. Pre-pubertal patients height SDS improved compared to baseline height SDS after one (-1.5±0.7, p<0.03) and two (-0.96±1, p<0.03) years of rhGH treatment. In pubertal patients there was no significant improvement in height SDS after one year (-1.75±1) and after two years (-1.7±0.8) of rhGH treatment.

Conclusion: Two-year rhGH treatment is effective to treat short stature in XLHR children. Pre-pubertal children responded better to rhGH.

Clinical Trial Registration Number: NCT02720770.