DMD and Duchenne muscular dystrophy: A number of studies using AONs in both mdx mice and DMD patients have shown restoration of dystrophin in a subset of muscle fibers.13, 17, 18 Most skeletal muscles are composed of a heterogeneous population of muscle fibers that differ in their metabolic properties as well as contractile speeds, a feature impacted by the type of myosin heavy chain (MHC) being expressed.