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Summary

Duchenne and Becker muscular dystrophies (DMD and BMD) are neuromuscular diseases characterized by progressive muscle wasting and weakness due to degeneration of skeletal, smooth and cardiac muscle. DMD is more frequent, occurs earlier and is more severe than BMD. DMD and BMD primarily affect males. The incidence of DMD is 1/3,300 male births. The incidence of BMD varies from 1/18,000 to 1/31,000 male births. In DMD, walking is often delayed. Cognitive functions can be altered. Diagnosis is generally made at the age of 5 when children present with a waddling gait and talipes equines with calf hypertrophy (positive Gower's sign). Inability to walk appears by 10 to 12 years of age. Scoliosis, cardiomyopathy and restrictive respiratory failure progressively appear. BMD appears later, between the ages of 5 and 15 years with a proximal motor deficiency of variable progression. Heart involvement can be the initial sign. Other clinical forms also exist (isolated cardiomyopathy, exercise intolerance, and symptomatic forms of muscular dystrophy of Duchenne and Becker in female carriers; see this term). Both X-linked recessive diseases are caused by dystrophin deficiency in skeletal and heart muscles, leading to progressive necrotizing lesions. The dystrophin gene (DMD) is located at Xp21.2 and encodes several isoforms. Genotype-phenotype correlations are currently being investigated. The clinical diagnosis can be confirmed by several methods. Creatine phosphokinase levels are 50- to 200-fold (DMD) or 10- to 35-fold (BMD) higher than standard values. Muscular biopsy shows dystrophic features (necrotic and regenerative fibers). Immunohistochemical studies show a total absence of dystrophin (DMD) or altered quantity and/or quality (BMD). Molecular analysis most frequently shows deletions of the DMD gene. The differential diagnosis should include the sarcoglycanopathies (see this term). The screening of women carriers in the family is essential. Prenatal diagnosisrequires the most precise molecular diagnosis possible in the index case. Treatment is symptomatic and multidisciplinary: orthopedic (prevention and treatment of retractions, physiotherapy, fitting with prosthesis, spinal arthrodesis (at 12-15 years of age), and technical support), respiratory (prevention and treatment of infections, respiratory physiotherapy, and ventilation), and cardiac (ACE inhibitors and heart protection). Corticotherapy helps to stabilize motor abilities. School and social integration is essential (role of patient associations). Progression is severe with end-stage cardiorespiratory failure in the young adult with DMD; it is slower and life span is subnormal to normal for BMD. Several research avenues are being explored: cellular therapy trials, genetic therapy studies (including exon-skipping) and studies on glutamine effects.

Expert reviewer(s):   Chritophe BOULAY - Pr Brigitte CHABROL - Last update: August 2007