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 4 prior studies of XLH were pooled to construct growth curves. UX023-CL002 was an observational, retrospective chart review. Pretreatment data were collected from 3 interventional trials: two phase 2 trials (UX023-CL201, UX023-CL205) 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 5(th), 10(th), 25(th), 50(th), 75(th), 90(th), and 95(th) percentiles for children with XLH compared to population norms. RESULTS: A total of 228 patients (132 girls, 96 boys) with 2381 height measurements were included. Nearly all subjects (> 99%) reported prior management with supplementation therapy. Compared to the Center for Disease Control and Prevention growth curves, boys at age 3 months, 6 months, 9 months, 1 year, and 2 years 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.