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.
Progression is steady, and limb flexion contractures and scoliosis develop.
Most patients are confined to a wheelchair by age 10 or 12 and die of respiratory complications by age 20 yr. One third have mild, nonprogressive intellectual impairment that affects verbal ability more than performance. Becker muscular dystrophy is a less severe variant, also due to a mutation at the Xp21 locus. Dystrophin is reduced in quantity or in molecular weight. Patients usually remain ambulatory, and most survive into their 30s and 40s.