Effect of vosoritide on genu varum in children with achondroplasia after 1 year in randomized placebo-controlled trials

Achondroplasia is a skeletal dysplasia associated with multisystem complications including genu varum, which causes pain and limits mobility. Vosoritide, a targeted treatment for achondroplasia, improves growth in children and has an established safety profile, but its effect on genu varum is unclear. Data were collected from 183 participants from randomized, double-blind, placebo-controlled phase 2 (CANOPY ACH-2I [111-206; NCT03583697]) and phase 3 (CANOPY ACH-3 [111-301; NCT03197766]) studies evaluating vosoritide (weight-based dose of 15 or 30 µg/kg/day) in children aged 0-5 and >5 years, respectively. Anterior/posterior lower limb radiographs were taken at baseline and 1 year to measure parameters associated with genu varum. Differences in least-squares mean (LSM) change from baseline were calculated for vosoritide vs placebo using an analysis of covariance model. In both studies, age at treatment initiation and sex distribution were generally balanced between vosoritide and placebo (except 58% males received vosoritide in CANOPY ACH-2I). After 1 year of vosoritide treatment vs placebo, tibial bowing decreased in children who initiated treatment aged <5 years (<i>n</i> = 40) and remained stable in those ≥5 years (<i>n</i> = 57). Vosoritide-treated participants with evidence of abnormal fibular growth at baseline had reduced overall and distal fibular overgrowth vs placebo. Children aged ≥5 years improved in ankle joint to distal fibula physis distance (difference in LSM change from baseline, -0.07, <i>P</i> = .010) and fibula/tibia ratio (-0.025, <i>P</i> < .0001), and children aged 2-5 years had improved fibula/tibia ratio (-0.033, <i>P</i> = .0032). Preliminary results suggest vosoritide may improve or limit genu varum in children with achondroplasia.