A group of inherited, progressive muscle disorders, distinguished clinically by the selective distribution of weakness. The gene is located on chromosome 4q35 in most families, but the genetic defect has not been identified, and the pathogenesis is unknown. Difficulty in whistling, eye closure, and elevation of the arms due to weakness of the scapular stabilizer muscles occurs early. Anterior tibial and peroneal weakness develops in some patients. Although footdrop develops, ambulation is rarely lost.
Life expectancy is normal.
In limb-girdle muscular dystrophy, weakness develops in a limb girdle and proximal limb distribution. An X-linked recessive disorder characterized by progressive proximal muscle weakness with destruction and regeneration of muscle fibers and replacement by connective tissue. Duchenne dystrophy is caused by a mutation at the Xp21 locus, which results in the absence of dystrophin, a protein found inside the muscle cell membrane. It affects 1 in 3000 live male births. The pelvic girdle is affected before the shoulder girdle.