Efficacy and Safety of Losmapimod in Subjects With Facioscapulohumeral Muscular Dystrophy (FSHD)

This study is a Phase 2, randomized, double-blind, placebo-controlled, parallel-group, multicenter study designed to evaluate the efficacy and safety of losmapimod in treating patients with Facioscapulohumeral Muscular Dystrophy (FSHD) over 48 weeks. Patients will participate in this study for approximately 53 weeks. This will include a 4-week screening period, a 48-week, placebo-controlled treatment period and a 7 day safety follow-up period. Patients must have a confirmed diagnosis of FSHD1 and genetic confirmation must be obtained prior to the screening MRI and baseline muscle biopsy. Patients will be randomized to receive 15 mg of losmapimod or placebo twice daily given as two 7.5 mg tablets per dose by mouth; for a total of 4 pills or 30 mg daily for 48 weeks. All patients will be asked to attend the study clinic for each scheduled visit. The primary endpoint of the study is to evaluate the efficacy of losmapimod in inhibiting or reducing expression of DUX4, as measured by a subset of DUX4-regulated gene transcripts in skeletal muscle biopsies of FSHD patients. Secondary endpoints include evaluation of the safety and tolerability of losmapimod, the plasma concentrations of losmapimod, levels of losmapimod in skeletal muscle and losmapimod target engagement in blood and skeletal muscle in FSHD patients. This study was conducted during the Coronavirus Disease-2019 (COVID-19) Pandemic. The pandemic restrictions limited some assessments in the FSHD1 population in the clinic, including collection of some data for Week 24.