Muscular dystrophy
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Muscular dystrophy
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Muscular dystrophy
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Becker muscular dystrophy p. 59
presentation p. 714
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Transcript
Content Reviewers
Rishi Desai, MD, MPHContributors
Tanner Marshall, MS
With muscular dystrophy, “dys” means bad or difficult, and “troph” means nourish; so muscular dystrophy basically refers to the muscle appearing poorly nourished because of degeneration, which leads to muscle weakness.
Under a microscope, a biopsy of the tissue shows changes in the muscle itself but not in the nerve or neuromuscular junction; this distinguishes muscular dystrophy from other problems that cause muscle weakness as a result of nerve damage, like neuropathies.
Muscular dystrophy is actually a group of disorders, all of which are caused by genetic mutations.
Within that group, dystrophinopathies are the most common, which includes Duchenne muscular dystrophy, or DMD, and Becker muscular dystrophy, both of which result from mutations in the dystrophin gene.
In addition to those two, genetic mutations in other genes are responsible for several dozen other muscular dystrophies, some of which code for proteins that form a protein complex with dystrophin protein.
These other muscular dystrophies, therefore end up causing a lot of the same symptoms as the dystrophinopathies.
Now, the fact that both Duchenne and Becker muscular dystrophy result from mutations in the same dystrophin gene means that they are “allelic disorders,” and when a mutation occurs in dystrophin that’s severe enough to result in no protein at all, for example a nonsense or a frameshift mutation, the result is Duchenne muscular dystrophy, which ends up being the more severe of the two, with symptoms usually presenting by age 5.
On the other hand, mutations that allow for a misshapen protein to form, like missense mutations, lead to Becker muscular dystrophy which is basically a milder form of Duchenne muscular dystrophy that presents later on, usually between age 10 to 20.
Alright so the dystrophin gene is a huge gene on the X-chromosome, that has 79 exons and is over 2 million base pairs in length.
By comparison, most genes have only about 10 exons and are 50 thousand base pairs in length.
Summary
Muscular dystrophy is a group of inherited diseases that cause progressive weakness and degeneration of the skeletal muscles that control movement (e.g. Duchenne and Becker muscular dystrophy). Muscular dystrophy is caused by genetic defects that interfere with the production of proteins needed to form healthy muscle. There is currently no cure for muscular dystrophy, physical and occupational therapy, and medications can help manage the symptoms and slow the progression of the disease.
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