Many versions of micro-dystrophin have given different results in mice and dogs, with some offering protection from the disease, especially if treatment started early.16,18 New, optimized versions of micro-dystrophin, including functional domains are now available.19 In addition, four clinical trials have been started, which are also supported by spectacular efficacy and lack of toxicity of AAV systemically delivered to patients with spinal muscular atrophy. The gene discussed is DMD; the disease is spinal muscular atrophy.