Similar dose-dependent functional outcomes have been observed in two recent long-term studies of micro-dystrophin and myotubularin systemic gene therapy in canine models of Duchenne muscular dystrophy and X-linked myotubular myopathy, respectively.32, 33 The exact mechanisms leading to an accelerated decline in therapeutic benefits with low-dose viral gene therapy over time are not clear. The gene discussed is DMD; the disease is Duchenne muscular dystrophy.