A Study to Investigate the Safety, Pharmacokinetics (PK), and Efficacy of Garetosmab in Children and Adolescents With Fibrodysplasia Ossificans Progressiva (FOP)

Key Inclusion Criteria:

• For USA participants, age criteria are 4 to < 18 years old, at the time of the administration of the first dose of study intervention. Non-USA participants age criteria are 2 to < 18 years old
• Must have a confirmation of FOP diagnosis, as described in the protocol
• At the time of enrollment, participants must weight:

• Cohort 1 > 30 kg
• Cohort 2 > 30 kg
• Cohort 3 ≤ 30 kg

Key Exclusion Criteria:

• Cumulative Analog Joint Involvement Scale (CAJIS) score > 19 at the time of screening
• Participant has significant concomitant illness or history of significant illness, as described in the protocol
• Previous history or diagnosis of cancer
• Ongoing significant viral or bacterial illness, within 2 weeks of the first study drug administration
• History of severe respiratory compromise requiring oxygen, respiratory support
• Known history of cerebral vascular malformation
• Participants with a history of severe, non-traumatic bleeding requiring transfusion or hospitalization for hemodynamic compromise
• Participants with a known pre-existing medical history of a bleeding diathesis, as described in the protocol

NOTE: Other Protocol-defined Inclusion/Exclusion Criteria Apply