The proposed clinical trial is a single-dose controlled trial using rAAVrh74.MHCK7.micro-dystrophin for DMD subjects. Cohort A will include six subjects ages 3 months to 3 years, and Cohort B will include six subjects ages 4 to 7 years old. All subjects will receive intravenous micro-dystrophin vector (2X10e14 vg/kg in 10mL/kg)