source: Medical Home Portal (University of Utah)
Duchenne (DMD), Becker (BMD), and intermediate (IMD) muscular dystrophies represent varying clinical presentations of an X-linked, progressive symmetric muscle weakness caused by a relative or absolute absence of dystrophin, a muscle protein. The weakness, greater proximally than distally, occurs because muscles are gradually replaced by fatty, fibrotic connective tissue. DMD refers to the earliest, most common, and most severe form of the disease. It occurs primarily in males, although occasionally, female carriers demonstrate increasingly recognized manifestations, such as cardiac and motor issues, especially later in adulthood. Boys with DMD will present in the preschool years with muscle weakness, difficulty walking, and large calves.