Study to Assess the Efficacy and Safety of Garetosmab in Japanese Adult Patients With Fibrodysplasia Ossificans Progressiva (FOP)

Key Inclusion Criteria: * Clinical diagnosis of FOP (based on findings of congenital malformation of the great toes, episodic soft tissue swelling, and/or progressive HO) * Confirmation of FOP diagnosis with documentation of any Type I activin A receptor (ACVR1) mutation * FOP disease activity, as defined in the protocol, within 1 year of screening visit * Willing and able to undergo PET and CT imaging procedures and other procedures as defined in this study * Able to understand and complete study-related questionnaires and diaries (assistance from caregivers is allowed) Key Exclusion Criteria: * Patient has significant concomitant illness or history of significant illness such as but not limited to cardiac, renal, rheumatologic, neurologic, psychiatric, endocrine, metabolic, or lymphatic disease, that in the opinion of the study investigator might confound the results of the study or pose additional risk to the patient by their participation in the study * Previous history or diagnosis of cancer * Severely impaired renal function defined as estimated glomerular filtration rate \<30 mL/min/1.73 m2 calculated by the Modification of Diet in Renal Disease equation (1 retest is allowed) * Uncontrolled diabetes defined as hemoglobin A1C (HbA1c) \>9% at screening (1 retest allowed) * History of severe respiratory compromise, as defined in protocol * Concurrent participation in another interventional clinical study or a non-interventional study with radiographic measures or invas…