Physical Effects of Muscular Dystrophy:
FORMS AND SYMPTOMS
The lack of dystrophin, a necessary enzyme, causes the breakdown of muscle fibers that lead to a specific clinical pattern that is called Duchenne Muscular Dystrophy. Duchenne is the most common form of muscular dystrophy; it occurs in one of every 3,300 male births. Because inheritance of this form of MD is by an X-linked recessive mechanism, virtually all patients are boys. When a child is born with Duchenne, is it not immediately noticeable. However, when the child begins to walk, a slight waddle or walking on the toes is apparent. Death may result from respiratory weakness or from involvement of the heart muscle. Most patients die before the age of twenty.
(The photoes to the right represent the stages of Duchenne in muscle tissue. The first is unaffected muscle, the second is moderatly affected, and the third is severly affected tissue).
Facioscapulohumeral affects both sexes equally and results in weakness and wasting of the shoulder girdle and upper arms. The specific cause of FSHD is unknown, but it most often has been associated with a DNA mutation toward the terminal end of the DNA strand of chromosome 4. FSHD occurs in one out of every 20,000 births. It is usually noted around the onset of puberty. The first symptom may be difficulty in raising the arms. It also usually affects the face. The affected person may be mildly affected or may be totally disabled. Generally, the heart is not affected, nor is the level of intelligence. Most patients remain ambulatory until an advanced age. It is more slowly progressive than Duchenne's muscular dystrophy, and most patients have a normal life span. DNA-based testing detects about 95% of cases and is available in a limited number of clinical laboratories.
Limb Girdle affects both sexes equally. It is usually autosomal recessive. This is means that both parents must donate the affected gene for expression of the disease. It is the least common of the MDs. Muscles of either the shoulder or the hip girdle, or both are affected. People with only one abnormal gene in the gene pair are called carriers, but since the gene is recessive they do not exhibit the disease. The disease may begin either early, or late in life. The first symptoms are manifest in the pelvic region, starting in late childhood. Frequent falls, difficulty in climbing, and waddling is common. The range of severity in limb girdle dystrophy is wide with some cases having an early onset and rapid progression much like that of Duchenne MD. It is for this reason that females may be seen to have the clinical symptoms of what is essentially presenting as DMD.
In myotonic muscular dystrophy, delayed relaxation of the muscles accompanies wasting and weakness. 13.5 out of every 100,000 people in the West are born with Myotonic MD. Myotonic MD causes muscle weakness and affects the central nervous system, heart, gastrointestinal tract, eyes, and endocrine glands. Peculiar emotional and mental indifferences have also been found to accompany Myotonic MD in some patients. The age of onset of symptoms is variable. However, the disease tends to occur earlier in life. Myotonic muscular dystrophy affects both sexes, but children of affected mothers are more likely to inherit a severe form of the disease than children of affected fathers.
Muscular dystrophy has its origin in genetic mutation. However, the biochemical steps by which this genetic defect manifests itself in the degenerative process are unknown. Specific treatment is not available, therefore, general measures, such as physical and occupational therapy, are used. It is recommended to participate many activities; being restless can cause the disease to worsen. Medications, such as phenytoin or quinine can be used to delay relaxation of a muscle after a strong contraction. Genetic tests for muscular dystrophy provide an accurate diagnosis for patients. Most of the knowledge about muscular dystrophy has been gained in the past fifty years. Since then, testing and medication has been improved.