Muscular Dystrophies

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Muscular Dystrophies
The muscular dystrophies (MD) are a group of more than 30 genetic diseases characterized by progressive weakness and degeneration of the skeletal muscles that control movement. Some forms of MD are seen in infancy or childhood, while others may not appear until middle age or later. The disorders differ in terms of the distribution and extent of muscle weakness (some forms of MD also affect cardiac muscle), age of onset, rate of progression, and pattern of inheritance.
X-Linked Recessive Genetic Defect
X-Linked recessive genetic defects are inherited through a genetic defect on an X chromosome. A female has 2 X chromosomes, one she inherited from her mother and one she got from her father. A male has an X chromosome from his mother and a Y chromosome from his father. If a woman has the defect on one of her X chromosomes, and the father's X chromosome is normal, there is a 25% chance for each pregnancy to produce: an unaffected girl; a girl who carries the defect; an unaffected boy; or a boy with the disorder.
Duchenne MD
Becker MD
Facioscapulohumeral MD
Myotonic MD
the most common form of MD and primarily affects boys. It is caused by the absence of dystrophin, a protein involved in maintaining the integrity of muscle. Onset is between 3 and 5 years and the disorder progresses rapidly.
Girls in these families have a 50 percent chance of inheriting and passing the defective gene to their children.
Very similar to but less severe than Duchenne MD. Boys with Becker MD have faulty or not enough dystrophin.
MD usually begins in the teenage years. It causes progressive weakness in muscles of the face, arms, legs, and around the shoulders and chest. It progresses slowly and can vary in symptoms
the disorder's most common adult form and is typified by prolonged muscle spasms, cataracts, cardiac abnormalities, and endocrine disturbances. Individuals with myotonic MD have long, thin faces, drooping eyelids, and a swan-like neck.
Source: U.S. Department of Health and Human Services, National Institutes of Health, National Institute of Neurological Disorders and Stroke.