Growth Curves for Children with X-linked Hypophosphatemia

CONTEXT We characterized linear growth in infants and children with X-linked hypophosphatemia (XLH). OBJECTIVE Provide linear growth curves for children with XLH from birth to early adolescence. DESIGN Data from four prior studies of XLH were pooled to construct growth curves. UX023-CL002 was an observational, retrospective chart review. Pre-treatment data were collected from three interventional trials: two phase 2 trials (UX023CL201, UX023CL205) and a phase 3 trial (UX023-CL301). SETTING Medical centers with expertise in treating XLH. PATIENTS Children with XLH, 1-14 years of age. INTERVENTION None. MAIN OUTCOME MEASURE Height-for-age linear growth curves including values for the 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles for children with XLH compared to population norms. RESULTS 228 patients (132 girls, 96 boys) with 2,381 height measurements were included. Nearly all subjects (>99%) reported prior management with supplementation therapy. Compared to the CDC growth curves, boys at age 0.25, 0.50, 0.75, 1.0, and 2.0 years-old had median height percentiles of 46%, 37%, 26%, 18%, and 5%, respectively; for girls the median height percentiles were 52%, 37%, 25%, 18%, and 7%, respectively. Annual growth in children with XLH fell below that of healthy children near 1 year of age and progressively declined during early childhood, with all median height percentiles <8% between 2 and 12 years old. CONCLUSION Children with XLH show decreased height gain by 1 year of age and remain below population norms thereafter. These data will help evaluate therapeutic interventions on linear growth for pediatric XLH.