4.3.1　Muscular Dystrophies

The muscular dystrophies（MDs）are a group of genetic diseases characterized by progressive weakness and degeneration of the skeletal muscles that control movement.The disorders differ in terms of the distribution and extent of muscle weakness，age of onset，rate of progression，and pattern of inheritance.

There are several types of muscular dystrophy.Duchenne MD is the most common form of MD that primarily affects boys.It is caused by the absence of dystrophin，a protein involved in maintaining the integrity of muscle.The onset peaks between 3 and 5 years of age and the disorder progresses rapidly.Most boys are unable to walk by age 12，and later need a respirator to breathe.Girls in these families have a 50 percent chance of inheriting and passing the defective gene to their children.Boys with Becker MD（very similar to but less severe than Duchenne MD）have faulty or not enough dystrophin.Facioscapulohumeral MD usually begins in the teenage years.It causes progressive weakness in muscles of the face，arms，legs，and around the shoulders and chest.Myotonic MD 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 necks.

Treatment of MD may include physical therapy，respiratory therapy，speech therapy，orthopedic appliances used for support，and corrective orthopedic surgery.Drug therapy for MD includes corticosteroids to slow muscle degeneration，anticonvulsants to control seizures and some muscle activity，immunosuppressants to delay some damage to dying muscle cells，and antibiotics to treat respiratory infections.(https://www.daowen.com)

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Task 3　Define the meaning of each medical term given below.