An Open-Label, Long-Term Extension Study to Evaluate the Safety and Tolerability Deflazacort

This is an open label, long-term extension study in approximately 24 male DMD subjects consisting of children (ages 4-12, inclusive) and adolescents (ages 13-16, inclusive) who participated in the MP-104-CL-005 PK study. Subjects may have received up to 8 (+2 days) doses of deflazacort during the MP-104-CL-005 PK study, at which point treatment will be continued at the same dose and frequency until such time that deflazacort becomes commercially available or the study is terminated. Concomitant corticosteroid therapy will be prohibited during the study while the subject is taking deflazacort. Subjects will be given medication to take at home for once-daily, morning dosing following the 8 hour PK sample on Day 8 (+2 days) of the MP-104-CL-005 PK study. Subjects will begin dosing at home the day following Day 8 (+2 days) of the MP-104-CL-005 PK study. Safety will be monitored throughout the study by repeated clinical and laboratory evaluations every 3 months for the first year, and then every 3 or 6 months, depending on subjects' disease status. Subjects will be contacted via telephone between study visits to determine if any adverse events (AE) have occurred since the last study visit. Subjects who terminate the study early will be contacted if the Principal Investigator (PI) deems necessary. Treatment will be continued for a maximum of three years or until such time that deflazacort becomes commercially available or the study is terminated.