A Phase 2/?3 Study to Evaluate the Efficacy and Safety of BMN 333 Versus Vosoritide in Children With Achondroplasia (ASPEN)

INTERVENTION: Active Comparator Phase 2 Vosoritide Active Comparator Phase 3 Vosoritide Experimental Phase 2 High Dose Experimental Phase 2 Low Dose Experimental Phase 2 Medium Dose Experimental Phase 3 BMN 333 at selected dose after Phase 2 CONDITION: ; Musculoskeletal Diseases Musculoskeletal Diseases PRIMARY OUTCOME: Phase 2: Predicted Annualized Growth Velocity (AGV) at Week 52 (based on AGV at Weeks 26, 39, and 52 [available cumulative data] Phase 3: Annualized Growth Velocity (AGV) at Week 52 SECONDARY OUTCOME: Phase 2: AGV at Weeks 26 and 52 Phase 2: Change from Baseline in height Z‐score Phase 2: Change from Baseline in standing height Phase 2: Change from Baseline in upper to lower body segment ratio Phase 2: Incidence of adverse events (AEs) Phase 2: Incidence of events of interest (EOIs) Phase 2: Incidence of serious adverse events (SAEs) Phase 2: Lowest concentration (C trough) of BMN 333 in plasma Phase 2: Lowest concentration (C trough) of released vosoritide in plasma Phase 2: Maximum concentration (Cmax) of BMN 333 in plasma Phase 2: Maximum concentration (Cmax) of released vosoritide in plasma Phase 2: Time to reach maximum concentration (Tmax) for BMN 333 Phase 2: Time to reach maximum concentration (Tmax) for released vosoritide Phase 3: Change from Baseline in height Z‐score Phase 3: Change from Baseline in standing height Phase 3: Change from Baseline in upper to lower body segment ratio INCLUSION CRITERIA: 1. Participants must be aged = 2 to < 11 years (Phase 2) or = 2 to < 18 years (Phase 3), at the time of signing the informed consent 2. Participants must have ACH (confirmed by documented genetic testing) and open epiphyses 3. Are Tanner Stage I (Phase 2) or any Tanner stage (Phase 3) 4. Are ambulatory and able to stand without assistance