• Main Study - Treatment-Emergent Adverse Events [ Time Frame: Week 56 ]
  To evaluate the safety and tolerability of losmapimod based on the frequency of adverse events and clinically significant laboratory test results, electrocardiograms (ECGs), and vital signs.
• Extension Study - Efficacy of Treatment with Losmapimod [ Time Frame: Week 204 ]
  Change in skeletal muscle echogenicity will be evaluated by ultrasound of selected muscles.

• Target Engagement in Blood [ Time Frame: Week 52 ]
  Change from baseline in phospho-HSP27 and ratio of pHSP27/total HSP27 will be measured in peripheral whole blood.
• Target Engagement in Skeletal Muscle [ Time Frame: Weeks 40 ]
  Change from baseline in phospho-HSP27 and ratio of pHSP27/total HSP27 will be measured in muscle during the dosing period.
• Plasma Concentration of Losmapimod [ Time Frame: Week 52 ]
  Blood samples will be collected to measure the plasma concentration of losmapimod at specified timepoints.
• Muscle Concentration of Losmapimod [ Time Frame: Week 52 ]
  Muscle biopsies will be collected to measure the concentration of losmapimod at specified timepoints.

• Target Engagement in Blood [ Time Frame: Week 52 ]
  Change from baseline in phospho-HSP27 and ratio of pHSP27/total HSP27 will be measured in peripheral whole blood.
• Target Engagement in Skeletal Muscle [ Time Frame: Weeks 40 ]
  Change from baseline in phospho-HSP27 and ratio of pHSP27/total HSP27 will be measured in muscle.
• Plasma Concentration of Losmapimod [ Time Frame: Week 52 ]
  Blood samples will be collected to measure the plasma concentration of losmapidod at specified timepoints.

• Muscle Disease Transcripts [ Time Frame: Week 40 ]
  To evaluate the change from baseline in inflammatory, immune, apoptotic, and muscle disease transcripts in muscle biopsy and circulating proteins in plasma and serum.
• DUX4 Activity in Skeletal Muscle [ Time Frame: Week 40 ]
  Change from baseline in DUX4 activity by quantitative polymerase chain reaction (qPCR) of skeletal muscle using a subset of DUX4 regulated gene transcripts.
• Muscle Lean Tissue Volume [ Time Frame: Week 204 ]
  Change from baseline in skeletal muscle lean tissue volume as measured by whole body magnetic resonance imaging (MRI).
• Muscle Tissue Replacement by Fat [ Time Frame: Week 204 ]
  Change from baseline in skeletal muscle tissue replacement by fat as measured by whole body magnetic resonance imaging (MRI).
• Muscle Ultrasound [ Time Frame: Week 52 ]
  Ultrasound will be used to evaluate the echogenicity of specified muscles.
• Reachable Workspace (RWS) [ Time Frame: Week 204 ]
  Subjects are seated in front of a 3D camera and asked to perform a standardized upper extremity movement protocol under the supervision of a study clinical evaluator with and without weights to detect an individual's range of motion that reflects individual shoulder and proximal arm upper extremity function.
• Timed Up and Go (TUG) [ Time Frame: Week 204 ]
  Subjects are timed as they start from a seated or laying position, rise to a standing position, walk a total of 6 meters and then return to either a seated or laying position to determine ambulatory function.
• Motor Function Measure (MFM) Domain 1 [ Time Frame: Week 204 ]
  The MFM domain 1 is a validated evaluator administered functional measure for neuromuscular disorders, with 13 items related to standing and transfers and assesses the severity of the motor deficit.
• Quantitative Manual Dynamometry [ Time Frame: Week 204 ]
  Muscle strength will be assessed by quantitative dynamometry with hand-held devices (manual). Force will be measured on digital myometer, in KG-force.
• FSHD Rasch-built Overall Disability Scale (RODS) [ Time Frame: Week 204 ]
  The FSHD-RODS is a patient-reported, linearly weighted scale that precisely measures activities of daily living (ADLs) and participation in subjects with FSHD using 50 items based on the Rasch model.
• Real World Mobility Assessments [ Time Frame: Week 204 ]
  Each subject's activity will be monitored in the outpatient setting intermittently from the signing of the informed consent form (ICF) to the end of the study. Wearable activity monitoring devices will be provided to each subject at the start of the study. One device is placed on 1 arm, and 1 device goes on 1 leg.
• FSHD Health Index (FSHD-HI) [ Time Frame: Week 204 ]
  The FSHD-HI is a 15-domain questionnaire designed and based on patient interviews to measure total FSHD health-related quality-of-life, including both motor impairment and the social and emotional impact of FSHD. 116 questions are combined into a total score, the score is transformed onto a percentage scale, with 100 representing maximal disability, and lower scores representing decreasing disability.
• Patients' Global Impression of Change (PGIC) [ Time Frame: Week 204 ]
  The PGIC is a single question that assesses on a scale of 1-7 if there has been an improvement, decline or no change in clinical status.
• 6 Minute Walk Test (6-MWT) [ Time Frame: Week 204 ]
  Change from the pre-treatment period in the distance a subject is able to walk will be measured in time.
• Spirometry - Respiratory Function [ Time Frame: Week 204 ]
  Change in lung ventilatory function as measured by forced vital capacity and forced expiratory volume in 1 second using bedside spirometry.

• Muscle Disease Transcripts [ Time Frame: Week 40 ]
  Change from baseline muscle disease transcripts related to immune function in muscle biopsy and in plasma and serum.
• DUX4 Activity [ Time Frame: Week 40 ]
  Change from baseline in DUX4 activity will be measured by quantitative polymerase chain reaction (qPCR) of skeletal muscle using a subset of DUX4-regulated gene transcripts.
• Muscle Lean Tissue Volume [ Time Frame: Week 52 ]
  Change from baseline in skeletal muscle lean tissue volume as measured by whole body magnetic resonance imaging (MRI).
• Muscle Tissue Replacement by Fat [ Time Frame: Week 52 ]
  Change from baseline in skeletal muscle tissue replacement by fat as measured by whole body magnetic resonance imaging (MRI).
• Muscle Ultrasound [ Time Frame: Week 52 ]
  Ultasound will be used to evaluate the echogenicity of specified muscles.
• Reachable Work Space (RWS) [ Time Frame: Week 52 ]
  Subjects are seated in front of a 3D camera and asked to perform a standardized upper extremity movement protocol under the supervision of a study clinical evaluator with and without weights.
• Timed Up and Go (TUG) [ Time Frame: Week 52 ]
  Subjects are timed as they start from a seated or laying position, rise to a standing position, walk a total of 6 meters and then return to either a seated or laying position.
• Motor Function Measure (MFM) Domain 1 [ Time Frame: Week 52 ]
  The MFM domain 1 is a validated evaluator administered functional measure for neuromuscular disorders, with 13 items related to standing and transfers.
• Muscle Strength [ Time Frame: Week 52 ]
  Muscle strength will be assessed by Hand-Held Quantitative Dynamometry.
• FSHD Rasch-built Overall Disability Scale (RODS) [ Time Frame: Week 52 ]
  The FSHD-RODS is a patient-reported, linearly weighted scale that precisely measures activities of daily living (ADLs) and participation in subjects with FSHD using 50 items based on the Rasch model.
• FSHD Health Index (FSHD-HI) [ Time Frame: Week 52 ]
  The HI is a 15 domain questionnaire designed and based on patient interviews to measure total FSHD health-related quality-of-life, including both motor impairment and the social and emotional impact of FSHD. 116 questions are combined into a total score, the score is transformed onto a percentage scale, with 100 representing maximal disability, and lower scores representing decreasing disability.
• Patients' Global Impression of Change (PGIC) [ Time Frame: Week 52 ]
  The PGIC is a single question that assesses on a scale of 1-7 if there has been an improvement, decline or no change in clinical status.
• Real World Mobility Assessments [ Time Frame: Week 52 ]
  Each subject's activity will be monitored in the outpatient setting intermittently from the signing of the informed consent form (ICF) to the end of the study. Wearable activity monitoring devices will be provided to each subject at the start of the study. One device is placed on 1 arm, and 1 device goes on 1 leg.
• Respiratory Function [ Time Frame: Week 52 ]
  Forced vital capacity and forced expiratory volume in 1 second using bedside spirometry.
• Quantitative Dynamometry [ Time Frame: Week 52 ]
  Force will be measured on digital myometer, in KG-force.

This study is a single-centre, open-label pilot study that will investigate the safety, tolerability, pharmacokinetics (PK), and target engagement during long-term dosing with losmapimod tablets in adult subjects with FSHD1. Subjects will be evaluated during an 8- week pre-treatment period (Visits 1 through 3) to establish pre-treatment baseline assessments. Subjects will then be treated with losmapimod for approximately 1 year (Visits 4 through 9) and assessed at relatively regular intervals for change from pre-treatment assessments. All subjects will undergo two muscle biopsies; one at baseline, pre-treatment (Visit 4, Week 8 ± 1 week) and the second on-treatment muscle biopsy approximately 4 or 8 weeks later (Visit 5, Week 14 ± 2 weeks). Up to 8 subjects will have an on-treatment biopsy at 4 weeks and up to 8 subjects will have the on-treatment biopsy at 8 weeks.

Only subjects who participated in and competed all study procedures in the OLS Study treatment period (Week 60) will be eligible to participate in the open-label extension study.

The extension of this study will enable continued investigation of the efficacy of long-term dosing with losmapimod tablets in adult subjects with FSHD1. During the extension study, subjects will receive 15 mg of losmapimod by mouth twice daily for a total of 30 mg by mouth daily. All subjects will attend clinic visits approximately every 12 weeks and 7 days after the last dose of study drug for safety follow-up assessment. Participation in the open-label extension study will continue until losmapimod is approved, the patient withdraws from the study, or the Sponsor terminates the study.

The primary endpoint of the main study is to evaluate the safety and tolerability of long-term dosing of losmapimod tablets in subjects with FSHD1. Secondary endpoints include assessment of target engagement of losmapimod in blood and skeletal muscle and repeated dose pharmacokinetics in subjects with FSHD1 over long-term dosing.

The extension will continue investigation of efficacy with assessment of skeletal muscle by ultrasound as well as the safety, tolerability, pharmacokinetics (PK), and exploration of efficacy measures including whole body skeletal muscle MRI and selected clinical outcome assessments during long- term dosing with losmapimod tablets in adult subjects with FSHD1. Secondary endpoints include assessment of efficacy as evaluated by whole body skeletal muscle MRI parameters, safety and tolerability of long-term dosing, target engagement of losmapimod in blood and skeletal muscle and repeated dose pharmacokinetics in subjects with FSHD1 over long-term dosing.

• Barbour AM, Sarov-Blat L, Cai G, Fossler MJ, Sprecher DL, Graggaber J, McGeoch AT, Maison J, Cheriyan J. Safety, tolerability, pharmacokinetics and pharmacodynamics of losmapimod following a single intravenous or oral dose in healthy volunteers. Br J Clin Pharmacol. 2013 Jul;76(1):99-106. doi: 10.1111/bcp.12063.
• Cheriyan J, Webb AJ, Sarov-Blat L, Elkhawad M, Wallace SM, Mäki-Petäjä KM, Collier DJ, Morgan J, Fang Z, Willette RN, Lepore JJ, Cockcroft JR, Sprecher DL, Wilkinson IB. Inhibition of p38 mitogen-activated protein kinase improves nitric oxide-mediated vasodilatation and reduces inflammation in hypercholesterolemia. Circulation. 2011 Feb 8;123(5):515-23. doi: 10.1161/CIRCULATIONAHA.110.971986. Epub 2011 Jan 24.
• de Greef JC, Frants RR, van der Maarel SM. Epigenetic mechanisms of facioscapulohumeral muscular dystrophy. Mutat Res. 2008 Dec 1;647(1-2):94-102. doi: 10.1016/j.mrfmmm.2008.07.011. Epub 2008 Aug 3. Review.
• Han JJ, Kurillo G, Abresch RT, de Bie E, Nicorici A, Bajcsy R. Reachable workspace in facioscapulohumeral muscular dystrophy (FSHD) by Kinect. Muscle Nerve. 2015 Feb;51(2):168-75. doi: 10.1002/mus.24287. Epub 2014 Nov 19.
• Statland JM, Tawil R. Risk of functional impairment in Facioscapulohumeral muscular dystrophy. Muscle Nerve. 2014 Apr;49(4):520-7. doi: 10.1002/mus.23949. Epub 2014 Feb 10.

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 administering study drug to the subject. This may include, but is not limited to, history of relevant drug or food allergies; history of cardiovascular or central nervous system disease; history or presence of clinically significant pathology; clinically significant history of mental disease; and history of cancer, except for squamous cell skin cancer, basal cell skin cancer, and Stage 0 cervical carcinoma in situ (all 3 with no recurrence for the last 5 years).
• Subject has a known or clinically suspected infection with human immunodeficiency virus or hepatitis B or C viruses.
• Subject has current clinically significant liver (alanine aminotransferase > 2X upper limit of normal or total bilirubin >1.5 X upper limit of normal) or kidney (GFR < 30 mL/min/1.73m2) dysfunction.
• Subject screens positive for hepatitis B surface antigen, hepatitis C virus (HCV) antibody, or antibodies against human immunodeficiency viruses 1 and 2 (HIV 1/HIV 2 antibodies).
• Subject has any condition possibly affecting drug absorption (eg, gastrectomy, cholecystectomy, or other gastrointestinal tract surgery, except appendectomy).
• Subject has a standard 12-lead ECG demonstrating QT interval by Fredericia (QTcF) >450 msec for male subjects and QTcF >470 msec for female subjects at Screening. If QTcF exceeds 450 msec for males or 470 msec for females, the ECG will be repeated 2 more times, and the average of the 3 QTcF values will be used to determine the subject's eligibility.
• Subject has a history of cardiac dysrhythmias requiring anti-arrhythmia treatment(s); or history or evidence of abnormal ECGs that, in the opinion of the investigator or Medical Monitor, would preclude the subject's participation in the study.
• Male subject has a female partner who is planning to become pregnant during the study or within 90 days after the last study drug dose.
• Subject has donated blood (of approximately 1 pint [500 mL] or more) or has had any significant loss of blood within 90 days before the first study drug dose, as determined by the investigator.
• Vaccination with a live attenuated vaccine within 6 weeks of randomisation.
• Subject has a history of alcohol, analgesic/opioid, and/or illicit drug abuse as defined by the American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, in the last 6 months before screening, or a positive test for drugs of abuse at screening.
• Subject has participated in a clinical trial in which they have received an investigational product within the following time period prior to enrolment in the current study: 30 days, 5 half-lives or twice the duration of the biological effect of the investigational product (whichever was longer).
• For subjects that are on drug(s) or supplements that may affect muscle function as determined by the treating physician or included in the list of drugs presented in Section 15: subjects must be on a stable dose of that drug(s) or supplement for at least 3 months prior to enrollment in the study and remain on that stable dose for the duration of the study (list of drugs presented in Section 15). Changes to the dose or treatment discontinuation during the study can only be done for strict medical reasons by the treating physician with clear documentation and notification to the Sponsor.
• Subject has a history of sensitivity to any of the study medications or components thereof, or a history of drug or other allergy that, in the opinion of the investigator or Medical Monitor, contraindicated their participation.
• Female subject is pregnant as determined by positive urine Human Chorionic Gonadotropin (HCG) test at Screening or prior to dosing.
• Female subject is lactating.
• Subject is unwilling or unable to follow the procedures outlined in the protocol.
• Subject has any contraindication for MRI (including severe claustrophobia and any shrapnel or metal implants in the body that are not MRI compatible).
• Subject was mentally or legally incapacitated up to 2 years prior to enrollment.
• Subject has abnormal laboratory results indicative of any significant medical disease that, in the opinion of the investigator or the medical monitor, would preclude the subject's participation in the study.
• Subject, or close relative of the subject, is the investigator or a subinvestigator, research assistant, pharmacist, study coordinator, or other staff directly involved with the conduct of the study at that site.
• Subject has taken any anticoagulants for at least 1 month and anti-platelet agents for at least 1 week before each muscle biopsy.