Publisher Summary The term “myopathy” covers the entire spectrum of diseases of muscle and implies that the disorder is a disease of muscle and does not involve the central nervous system, anterior horn cell, peripheral nerve, or neuromuscular junction. In 1982 a linkage between a polymorphic DNA marker (known as RC8) and the Duchenne muscular dystrophy gene was found. As the DNA marker was in the middle of the short arm of the X chromosome in the position Xp21, the gene for Duchenne muscular dystrophy was mapped in that area. The Becker muscular dystrophy gene was also mapped to the same locus, suggesting that Duchenne–Becker dystrophies were either closely linked to each other or possibly allelic. Patients with classic Duchenne or Becker muscular dystrophy (DMD or BMD) do not need an electromyographic (EMG) for diagnostic purposes. Some recommend an EMG for atypical phenotypes. In the mid-1980s electromyography (EMG) was one of the main tools used in the diagnostic work-up of suspected myopathy. In Emery–Dreifuss muscular dystrophy of the X-linked variety, there is now availability of DNA testing for emerin gene mutations on the X chromosome and, therefore, EMG is not needed. EMG is useful for differentiating facioscapulohumeral (FSH) from some forms of non-chromosome 5 spinal muscular atrophy with scapuloperoneal distribution of the weakness. After childbirth, if the EMG is normal in the infant and the mother has suspicious signs of myotonic dystrophy, an EMG in the mother can quickly support the diagnosis and the necessity for a DNA test.