Inclusion Criteria: * Age greater than 6 months and less than 14 years * Confirmed duplication of exon 2 in the DMD gene using a clinically accepted technique that completely defines the mutation * Pre-ambulant (not yet walking) or ambulant (as defined by the ability to walk 10 meters without assistance) * Males of any ethnic group will be eligible * Ability to cooperate with muscle testing * In subjects age 4 and above, stable dose and regimen of corticosteroid therapy (prednisone, deflazacort, or their generic forms) for at least 12 weeks prior to gene transfer. Exclusion Criteria: * Active viral infection based on clinical observations * Symptoms or signs of cardiomyopathy, including: 1. Dyspnea on exertion, pedal edema, shortness of breath upon lying flat, or rales at the base of the lungs 2. Echocardiogram with ejection fraction below 40% * Serological evidence of HIV infection, or Hepatitis B or C infection * Diagnosis of (or ongoing treatment for) an autoimmune disease * Persistent leukopenia or leukocytosis (WBC ≤ 3.5 K/µL or ≥ 20.0 K/µL) or an absolute neutrophil count \< 1.5K/µL * Concomitant illness or requirement for chronic drug treatment that in the opinion of the SI creates unnecessary risks for gene transfer * AAV9 binding antibody titers ≥ 1:400 as determined by ELISA immunoassay * Abnormal laboratory values in the clinically significant range as listed in Table 7, based upon normal values in the Nationwide Children's Hospital Laboratory.