Efficacy and Safety of Losmapimod in Treating Participants With Facioscapulohumeral Muscular Dystrophy (FSHD) (REACH)

Key Inclusion Criteria: * Participants must be between 18 and 65 years of age, inclusive. * Genetically confirmed diagnosis of FSHD 1 or FSHD 2. * Clinical severity score of 2 to 4 (Ricci Score; Range 0-5), at screening. Participants who are wheelchair-dependent or dependent on walker or wheelchair for activities are not permitted to enroll in the study. * Screening total RSA (Q1-Q4) without weight in the dominant UE assessed by RWS ≥ 0.2 and ≤ 0.7. * No contraindications to MRI. Key Exclusion Criteria: * Previously diagnosed cancer that has not been in complete remission for at least 5 years. Localized carcinomas of the skin and carcinoma in situ of the cervix that have been resected or ablated for cure are not exclusionary. * Participants who are on drug(s) or supplements that may affect muscle function, as determined by the Investigator: participants must be on a stable dose of that drug(s) or supplement for at least 3 months prior to the first dose of study drug and remain on that stable dose for the duration of the study. * Known active opportunistic or life-threatening infections including Human Immunodeficiency virus (HIV) and hepatitis B or C. * Known active or inactive tuberculosis infection. * Acute or chronic history of liver disease. * Known severe renal impairment. * History of cardiac dysrhythmias requiring anti-arrhythmia treatment(s); or history or evidence of abnormal ECGs. * Use of another investigational product within 30 days or 5 half-lives (whichever …