The suspected sources of free radicals in dystrophin deficiency include damaged mitochondria, the activity of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) and xanthine oxidase (XO), expressed either in inflammatory cells or in muscle fibers, and the decoupling of neuronal nitric oxide synthase (nNOS) from the sarcolemma [79,80,81,82] (Figure 3); therefore, drugs acting at these levels have been tested in the treatment of DMD. The gene discussed is XDH; the disease is Duchenne muscular dystrophy.