Moreover, mutations in genes encoding for dystroglycan, such as DAG1 or Fukutin-related protein (FKRP), cause various forms of MD, including muscular dystrophy–dystroglycanopathy type A9 (MDDGA9) or limb–girdle muscular dystrophy (LGMD) type 2I [20,21,22]. This evidence concerns the gene DAG1 and Menkes disease.