A Study to Assess the Effectiveness and Safety of 2 Dosage Regimens of Oral Fidrisertib (IPN60130) for the Treatment of Fibrodysplasia Ossificans Progressiva (FOP).

Key Inclusion Criteria:

• Participants must be at least 5 years of age, to be confirmed (entry for youngerpaediatric participants <15 years of age will only be once safety in adult and olderpaediatric participants ≥15 years of age has been established) at the time ofsigning the informed participant/parent consent and, for participants who areminors, age-appropriate assent.

• Participants must be at least 15 years of age at the time of signing the informedparticipant/parent consent for the main study and, for participants who are minors,age-appropriate assent

• Participants must be clinically diagnosed with FOP, with the R206H ACVR1 mutation orother FOP variants associated with progressive HO.

• Participants must have disease progression in the preceding year of the screeningvisit.

• Participants who have participated in a prior clinical study using anotherinvestigational product for the treatment of FOP may be enrolled after a washout ofat least 5 half-lives of the other investigational product. Participants with priortreatment such as, but not limited to, imatinib, isotretinoin, garetosmab, orpalovarotene may be enrolled 30 days after discontinuation or after washout of atleast 5 half-lives, whichever is longer.

1. Washout period for palovarotene is 30 days

2. Washout period for garetosmab is 4 months

• Participants must be able to perform pulmonary function tests adequately andreliably.

• Participants must be able to have an adequate echocardiography assessment atscreening for evaluation of left ventricular structure and function as defined bythe protocol.

• Participants must be accessible for treatment and follow-up and be able to undergoall study procedures. Participants living at distant locations from theinvestigational site must be able and willing to travel to a site for the initialand all on-site follow-up visits. Participants must be able to undergo low-dose WBCT (excluding head) without sedation.

• Body weight ≥10 kg.

• Abstinent or using two highly effective forms of birth control. Females must alsohave a negative blood or urine pregnancy test prior to administration of study drug.

• Participants must be capable of giving written, signed, and dated informedparticipant/parent consent; and for participants who are minors, age-appropriateassent and/or legal guardian consent (performed according to local regulations)

Key Exclusion Criteria:

• Participants with complete heart block and left bundle branch block on screeningelectrocardiogram.

• Participants with screening echocardiography showing septal or left ventricular freewall thickness >12 mm for adult participants or a z-score >3 compared withpopulation norms for children and adolescent participants or left ventricularejection fraction (LVEF) <50%.

• Participants with severe mitral or tricuspid regurgitation on echocardiography atscreening.

• Participants with significant underlying lung disease requiring supplementary oxygenor forced vital capacity <35% of predicted at screening.

• Participants with uncontrolled cardiovascular, hepatic, pulmonary, gastrointestinal,endocrine, metabolic, ophthalmologic, immunologic, psychiatric, or anothersignificant disease as judged by the investigator.

• Participants with severe hepatic impairment.

• Concomitant medications that are strong inhibitors (including grapefruit juice) orinducers (including St John's Wort) of cytochrome P450 (CYP) 3A4 activity; or kinaseinhibitors such as imatinib.

• Prior use in the past year and concomitant use of bisphosphonates for participantsin the PET-CT sub study.

• Concurrent participation in another interventional clinical study, or anoninterventional study with radiographic measures or invasive procedures (e.g.collection of blood or tissue samples).

• Amylase or lipase >2× the upper limit of normal (ULN) or with a history of chronicpancreatitis.

• Elevated aspartate aminotransferase (AST) or alanine aminotransferase (ALT) >5×ULN.

• Participants with hematologic abnormalities:

• Hgb<10g/dL

• Platelets<75,000/mm3

• WBC<2000/mm3

• Participants with coagulation test measurements outside of the normal range atscreening.