Study of ACE-083 in Patients With Facioscapulohumeral Muscular Dystrophy (FSHD)

Part 1 (dose escalation, open-label) Part 1 will consist of up to 6 cohorts of patients and will evaluate multiple ascending dose levels of ACE-083 administered unilaterally or bilaterally to either the tibialis anterior (TA) or biceps brachii (BB) muscle(s). Patients in each cohort will be enrolled in a 4-week screening period before beginning treatment. A Safety Review Team (SRT) will meet to review data for each cohort when at least 4 patients within a cohort have completed their Day 43 visit prior to dose escalation of the next cohort. Study duration for Part 1 for each patient will be approximately 24 weeks, including a 4-week screening period, a 12-week treatment period, and an 8-week follow-up period after the last dose. Part 2 (randomized, double-blind, placebo-controlled, with open-label extension) Prior to the initiation of Part 2, a review of safety and efficacy data from Part 1 will be conducted to determine whether cohorts for one or both muscles will be pursued in Part 2, as well as the recommended dose level for each muscle. A total of up to 56 new patients (28 patients per muscle) may be enrolled and randomized (1:1) to receive either ACE-083 (n=14/muscle) or placebo (n=14/muscle) bilaterally to either the TA or BB muscles (but not both). Patients will receive blinded study drug once every three weeks for approximately 6 months (9 doses). Patients who complete the double-blind treatment period will immediately roll over to open-label treatment with ACE-083, receiving the same dose of active drug, bilaterally in either the TA or BB muscle, once every three weeks for approximately 6 months (8 doses). In Part 2, the SRT will periodically review blinded safety data for each muscle treated. Study duration for Part 2 for each patient will be approximately 15 months, including a 1-month screening period, a 12-month treatment period (6-month double-blind, placebo-controlled and a 6-month open-label extension), and a 2-month follow-up period after the last dose