This study is designed to explore the efficacy, safety and pharmacokinetics of two doses of GSK2402968 given over 24 weeks. The two doses to be assessed are 6mg/kg/week and 3mg/kg/week. Based on pharmacokinetic and pharmacodynamic modeling, it is predicted at steady-state that the 6 mg/kg/week dose will induce dystrophin expression greater than 30% of control. The 3 mg/kg/week dose was chosen as modeling predicts 3 mg/kg/week of GSK2402968 will produce dystrophin expression in the range of 18-22%. Potential variability between subjects could theoretically produce higher expression and lead to a dystrophin level correlated with clinical improvement.