The main purpose of this study is to evaluate the effects of BMN 333 on growth compared with vosoritide in participants with achondroplasia who have not received any growth-promoting treatments. The study includes 2 parts: the Phase 2 part will select the optimal BMN 333 dose to be used in Phase 3 and determine study continuation into Phase 3; the Phase 3 part will compare the effects of the selected dose of BMN 333 with vosoritide. Study details for either Phase 2 or Phase 3 include the following:
* Study duration: up to 61 weeks (from screening to Safety Follow-up visit)
* Treatment duration: 52 weeks. Treatment frequency: BMN 333, once weekly; vosoritide, once daily
