The objective is to determine the safety and tolerability of h5G1.1-mAb and to evaluate the pharmacokinetics and pharmacodynamics of this antibody as well as its efficacy in the target population. Safety will be assessed via the collection of adverse events and the evaluation of pre- and post-treatment laboratory data. Efficacy will be assessed by the change in the manual muscle testing score relative to placebo at 2.25 months (one week following the end of the active treatment period) (primary efficacy value), and the change in the muscle enzyme level, MRI findings, skin examination findings and biopsy, and SF-36 (secondary efficacy values).