Duchenne Muscular Dystrophy (DMD) is a severe, progressive neuromuscular genetic disease that affects approximately one in every 3,500 – 6,000 males births worldwide. DMD occurs when a mutation in the dystrophin gene prevents the cell from making a functional dystrophin protein. The role of dystrophin is crucial to the structural and membrane stability of muscle fibers in the skeletal, diaphragm and heart muscle. Absence or low levels of dystrophin in boys and men with DMD causes excessive damage to muscle cells during the normal activity of contraction and stretching, and they are eventually replaced by connective tissue and fat, resulting in a progressive loss of function.

DMD is generally diagnosed between 2 and 5 years of age when symptoms such as motor developmental delay (including difficulty in walking, climbing stairs and the use of the Gower’s Maneuver to stand from the floor) and calf muscle pseudohypertrophy become apparent. Muscle degeneration leads to loss of ambulation at 8–14 years, and progressively affects higher limbs, neck muscle and other areas. Premature death occurs at 20–30 years due to respiratory and cardiac complications.

Bushby, K., R. Finkel, D. J. Birnkrant, L. E. Case, P. R. Clemens, L. Cripe, A. Kaul, K. Kinnett, C. McDonald, S. Pandya, J. Poysky, F. Shapiro, J. Tomezsko and C. Constantin (2010). "Diagnosis and management of Duchenne muscular dystrophy, part 1: diagnosis, and pharmacological and psychosocial management." The Lancet Neurology 9(1): 77-93. And "Diagnosis and management of Duchenne muscular dystrophy, part 2: implementation of multidisciplinary care." Lancet Neurol 9(2): 177-189.

Becker Muscular Dystrophy (BMD) is a generally milder and more variable form of dystrophinopathy, with an estimated incidence of 1/18,000 to 1/31,000 male births worldwide. While DMD genetic code mutations cause cells to make no functional dystrophin, in people with BMD cells make dystrophin that is partially functional. They make a shortened form of the protein, which protects the muscles of BMD patients from degenerating as completely or as quickly as those of people with DMD. Similar to DMD, boys with BMD present with progressive muscle weakness and calf hypertrophy. BMD's onset is usually in late childhood or adolescence, between the ages of 5 and 15 and the course is slower and less predictable than that of DMD. Generalized weakness first affects muscles of the hips, pelvic area, thighs and shoulders. In some cases, heart involvement (cardiomyopathy) is the first sign.

Becker muscular dystrophy generally leads to slow muscle fiber degeneration, but the progression of disease can vary among affected people. Some patients need a wheelchair, while others may only need walking aids such as canes or braces. The lifespan is often shorted due to heart disease and respiratory complications. Most people with BMD survive into mid - to late adulthood.

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Darras, B. T., Miller. D. T. & Urion, D. K. Dystrophinopathies in GeneReviews® (ed Pagon, R. A. et al.). Internet. Seattle (WA): University of Washington, 1993–2015. Available from http://www.ncbi.nlm.nih.gov/books/NBK1119/