Evaluation of Safety, Tolerability, and Changes in Biomarker and Clinical Outcome Assessments of Losmapimod for FSHD1 With Extension

Inclusion Criteria: * FSHD1 subjects age 18-65 years. * Subject will sign and date an informed consent form (ICF). * Confirmed diagnosis of FSHD1 with 1 to 9 repeats via assessment of the size of the D4Z4 array on chromosome 4. Genetic confirmation must be obtained prior to the screening MRI and baseline muscle biopsy; genetic confirmation can come from previous testing if verified with appropriate documentation. * Must be willing and able to comply with scheduled visits, treatment plan, study restrictions, laboratory tests, contraceptive guidelines, scheduled needle muscle biopsies, and other study procedures. * Both male and female subjects must be willing to practice an approved method of birth control. * Clinical Severity Score between 2 and 4 on Ricci's Scale (scale range is from 0 to 5). Subjects that use a wheelchair or walker for any activity are not permitted to enroll in the study. * Commitment to complete the 2 visits for skeletal muscle needle biopsy and all visits for whole-body MRI. * Able to complete the RWS, TUG, and FSHD PROs (FSHD-RODS and FSHD-HI) at the screening visit. * Must have an MRI-eligible muscle for biopsy as determined by the central reader. * Subject must complete the main study through the Week 60 visit in order to participate in the open-label extension study. Exclusion Criteria: * History of any illness or any clinical condition that, in the opinion of the investigator, might confound the results of the study or pose an additional risk in …