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Duchenne muscular dystrophy (DMD) is a recessive X-linked form of muscular dystrophy, affecting around 1 in 3,600 boys, which results in muscle degeneration and premature death. The disorder is caused by a mutation in the gene dystrophin, located on the human X chromosome, which codes for the protein dystrophin. Dystrophin is an important component within muscle tissue that provides structural stability to the dystroglycan complex (DGC) of the cell membrane. While both sexes can carry the mutation, females are rarely affected. Symptoms usually appear in boys between the ages of 2 and 3 and may be visible in early infancy.〔http://www.mayoclinic.org/diseases-conditions/muscular-dystrophy/basics/symptoms/con-20021240〕 Even though symptoms do not appear until early infancy, laboratory testing can identify children who carry the active mutation at birth. Progressive proximal muscle weakness of the legs and pelvis associated with loss of muscle mass is observed first. Eventually this weakness spreads to the arms, neck, and other areas. Early signs may include pseudohypertrophy (enlargement of calf and deltoid muscles), low endurance, and difficulties in standing without help or an inability to walk up stairs. As the condition progresses, muscle tissue experiences wasting and is eventually replaced by fat and fibrotic tissue (fibrosis). By age 10, braces may be required to aid in walking but most patients are wheelchair dependent by age 12. Later symptoms may include abnormal bone development that lead to skeletal deformities, including curvature of the spine. Due to progressive deterioration of muscle, loss of movement occurs, eventually leading to paralysis. Intellectual impairment may or may not be present but if present, does not progressively worsen as the child ages. The average life expectancy for individuals afflicted with DMD is around 25.〔 ==Signs and symptoms== The main symptom of Duchenne muscular dystrophy, a progressive neuromuscular disorder, is muscle weakness associated with muscle wasting with the voluntary muscles being first affected, especially those of the hips, pelvic area, thighs, shoulders, and calves. Muscle weakness also occurs later, in the arms, neck, and other areas. Calves are often enlarged. Symptoms usually appear before age 6 and may appear in early infancy. Other physical symptoms are: * Awkward manner of walking, stepping, or running – (patients tend to walk on their forefeet, because of an increased calf muscle tone. Also, toe walking is a compensatory adaptation to knee extensor weakness.) * Frequent falls * Fatigue * Difficulty with motor skills (running, hopping, jumping) * Lumbar hyperlordosis, possibly leading to shortening of the hip-flexor muscles. This has an effect on overall posture and a manner of walking, stepping, or running. * Muscle contractures of Achilles tendon and hamstrings impair functionality because the muscle fibers shorten and fibrose in connective tissue * Progressive difficulty walking * Muscle fiber deformities * Pseudohypertrophy (enlarging) of tongue and calf muscles. The muscle tissue is eventually replaced by fat and connective tissue, hence the term pseudohypertrophy. * Higher risk of neurobehavioral disorders (e.g., ADHD), learning disorders (dyslexia), and non-progressive weaknesses in specific cognitive skills (in particular short-term verbal memory), which are believed to be the result of absent or dysfunctional dystrophin in the brain. * Eventual loss of ability to walk (usually by the age of 12) * Skeletal deformities (including scoliosis in some cases) * Trouble getting up from lying or sitting position〔 According to Lewis P. Rowland, in the anthology ''Gene Expression In Muscle,'' if a boy is affected with Duchenne muscular dystrophy (DMD), the condition can be observed clinically from the moment he takes his first steps. It becomes harder and harder for the boy to walk; his ability to walk usually completely disintegrates between the time the boy is 9 to 12 years of age. Most men affected with DMD become essentially “paralyzed from the neck down” by the age of 21.〔Rowland, L. P. (1985). Clinical Perspective: Phenotypic Expression In Muscular Dhystrophy. In R. C. Strohman & S. Wolf (Eds.), Gene Expression in Muscle (pp. 3-5). New York, NY: Plenum Press.〕 Muscle wasting begins in the legs and pelvis, then progresses to the muscles of the shoulders and neck, followed by loss of arm muscles and respiratory muscles. Calf muscle enlargement (pseudohypertrophy) is quite obvious. Cardiomyopathy particularly (dilated cardiomyopathy) is common, but the development of congestive heart failure or arrhythmia (irregular heartbeat) is only occasional. * A positive Gowers' sign reflects the more severe impairment of the lower extremities muscles. The child helps himself to get up with upper extremities: first by rising to stand on his arms and knees, and then "walking" his hands up his legs to stand upright. * Affected children usually tire more easily and have less overall strength than their peers. * Creatine kinase (CPK-MM) levels in the bloodstream are extremely high. * An electromyography (EMG) shows that weakness is caused by destruction of muscle tissue rather than by damage to nerves. * Genetic testing can reveal genetic errors in the Xp21 gene. * A muscle biopsy (immunohistochemistry or immunoblotting) or genetic test (blood test) confirms the absence of dystrophin, although improvements in genetic testing often make this unnecessary. * Abnormal heart muscle (cardiomyopathy) * Congestive heart failure or irregular heart rhythm (arrhythmia) * Deformities of the chest and back (scoliosis) * Enlarged muscles of the calves, buttocks, and shoulders (around age 4 or 5). These muscles are eventually replaced by fat and connective tissue (pseudohypertrophy). * Loss of muscle mass (atrophy) * Muscle contractures in the heels, legs * Muscle deformities * Respiratory disorders, including pneumonia and swallowing with food or fluid passing into the lungs (in late stages of the disease)〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Duchenne muscular dystrophy」の詳細全文を読む スポンサード リンク
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