Duchenne muscular dystrophy

Duchenne muscular dystrophy: The best-known form of muscular dystrophy, due to mutation in a gene on the X chromosome that prevents the production of dystrophin, a normal protein in muscle. DMD affects boys and, very rarely, girls. DMD typically appears between the ages of two with weakness in the pelvis and upper limbs, resulting in clumsiness, frequent falling, an unusual gait and general weakness. Some patients also have mild mental retardation. As DMD progresses, a wheelchair may be needed. Most patients with Duchenne MD die in their early twenties because of muscle-based breathing and heart problems. There is no cure for DMD. Current treatment is directed toward symptoms, such as assisting with mobility, preventing scoliosis, and providing pulmonary therapy (respiratory toilet). Gene replacement with dystrophin minigenes is being investigated but no cure appears around the corner.

The DMD gene: The muscular dystrophies associated with defects in dystrophin range greatly from the very severe Duchenne muscular dystrophy (DMD) to the far milder Becker muscular dystrophy (BMD). DMD and BMD result from different mutations in the gigantic gene that encodes dystrophin. The DMD gene contains 79 exons spanning at least 2,300 kb. Deletions cause deficiencies in 1 or more of these, which may explain why mental retardation and cardiomyopathy sometimes accompany DMD, for there are clearcut differences in clinical presentation depending on what the deletions remove from the dystrophin gene. The DMD gene encodes a 3,685-amino acid protein product. From its amino acid sequence, dystrophin is similar to spectrin and other cytoskeletal proteins. It is rather like an I-beam with globular domains at each end, joined by a rod-like segment in the middle.

History: The disease is named for the pioneering 19th century French neurologist Guillaume Benjamin Amand Duchenne. After graduating in medicine, he practiced in the provinces but returned to Paris in 1842 to pursue medical research where he became known under the name of Duchenne de Boulogne to avoid confusion with edouard Adolphe Duchesne, a fashionable society physician. Duchenne was a diligent clinical investigator, meticulous in recording the patient’s history. He followed his patients from hospital to hospital to complete his studies. In this way he developed an exceptionally rich resource of clinical research material, far superior to that available to a single physician or hospital. Duchenne described a boy with the form of muscular dystrophy that now bears his name in the 1861 edition of his book “Paraplegie hypertrophique de l’enfance de cause cerebrale.” A keen photographer, he depicted his patient a year later in his “Album de photographies pathologiques.” In 1868 he gave an account of 13 affected children under the designation “paralysie musculaire pseudohypertrophique.” The term “pseudohypertrophic” stuck to this form of muscular dystrophy. Duchenne was the first to do a biopsy to obtain tissue from a living patient for microscopic examination. This aroused a deal of controversy in the lay press concerning the morality of examining living tissues. Duchenne used his biopsy needle on boys with DMD and concluded correctly that the disease was one of muscle.

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