Muscular dystrophy refers to a group of inherited diseases that are characterized by a progressive weakness and degeneration of the skeletal muscles. The skeletal muscles control movement. As the muscle fibers weaken, fibrous and fatty tissues replace them. The disease is caused by a gene mutation that is transmitted genetically.
There are at least six different muscular dystrophy disorders. The modes of inheritance differ among the six. The most common, Duchenne dystrophy is inherited in the X-linked recessive manner by a gene mutation on the X chromosome. Males have an XY chromosomal pattern, and females have an XX pattern. Therefore, a male with Duchenne dystrophy inherits the illness through his mother who contributes the X chromosome to the XY male genotype. Emery-Dreifuss dystrophy is also inherited through the X chromosome, so only males will be affected with this type of dystrophy. Other patterns of inheritance for the muscular dystrophies include autosomal dominant through chromosome 13 or 17 for the limb girdle dystrophy, and autosomal recessive through chromosome 6 or 9 for congenital dystrophy. Chromosome 4 is involved in facioscapulohumeral dystrophy, which is inherited in an autosomal dominant manner. In this case, fifty percent of offspring would inherit the illness. Myotonic dystrophy is reviewed under musculoskeletal disorders.
Who is likely to develop muscular dystrophy?
Duchenne dystrophy is the most common type of muscular dystrophy in childhood. It occurs in approximately 1 out of 3,500 male births. About one third of the males born with Duchenne dystrophy have a spontaneous mutation that accounts for the disorder rather than inheriting it through the X chromosome. A daughter born to a male with Duchenne dystrophy will have a fifty percent chance of carrying the affected gene. The mothers of affected children, who also have a family history of Duchenne dystrophy, are carriers of the mutated gene. The mother and sisters of a patient who has a spontaneous gene mutation leading to Duchenne dystrophy are not at risk for being carriers.
What are the symptoms of muscular dystrophy?
All types of muscular dystrophy are characterized by a progressive weakness of skeletal muscles. The rate of progression and the distribution of the weakness vary between the types of muscular dystrophy. In Duchenne muscular dystrophy, early gross motor skills in the affected males are usually normal. Around age two or three years, some signs of limb girdle weakness may occur. The child may have frequent falls or show difficulty in running, jumping and getting up from a sitting or lying down position. There may be weakness in the buttock muscles and the toddler may assume a lordotic or sway back position.
The progression of muscle weakness is relentless. Some patients are confined to a wheelchair by seven years, but by ten years most patients need bracing, physiotherapy or surgery in order to continue walking. The teen is usually able to use his hands and fingers well so eating, writing and keyboarding abilities continue into adolescence. However, respiratory muscles may become progressively weaker so that a teen’s cough may become ineffective and he could be prone to aspiration of food that may lead to pneumonia. Scoliosis is common due to the muscle weakness.
Other skeletal problems can also occur. Due to muscular weakness and fibrosis, stiffness of the joints, termed contractures, can occur in the ankles, knees, elbows and hips. The heart muscle may become involved, and this could lead to heart failure. Intellectual impairment occurs in all patients and this is characterized by learning disabilities. Most patients, however, function in a regular classroom setting with remedial help. In Duchenne dystrophy, most males die around eighteen years due to respiratory or heart failure or lung infection.
In Duchenne dystrophy, since it is inherited through the X chromosome, only males are affected since they have only one X-chromosome. However, females may carry the defective gene on one of their X chromosomes. The female carrier usually shows neither muscle weakness nor any clinical signs of disease. Rarely, a female carrier of Duchenne dystrophy will present with some signs of a very mild muscle weakness. This is explained by the Lyon hypothesis where the normal X chromosome is inactivated, and the chromosome with the defective gene is active. An adolescent girl with Turner Syndrome, who has only one X chromosome, could also demonstrate the full clinical picture of Duchenne dystrophy.
The other muscular dystrophies can present in different ways. Emery-Dreifuss dystrophy is less severe than Duchenne dystrophy. It is slowly progressive, begins in the middle of childhood and muscle weakness occurs in the shoulder girdle. Although the patients are intellectually normal, involvement of the heart is severe and often the cause of death. Myotonic dystrophy, which can be seen in girls and boys, is characterized by facial weakness as well as weakness of the fingers. Eventually there is difficulty with walking up stairs as well as standing from a lying position. Since the muscles of the face are involved, speech is often poorly articulated and slurred. Limb-girdle dystrophy affects the hip and shoulder girdles. The symptoms may be delayed until late adolescence or young adulthood. Weakness of the neck muscles may occur as well as other parts of the body including the hands.
How is muscular dystrophy evaluated?
The history and physical examination usually are the basis for diagnosing muscular dystrophy. Laboratory evaluations are supportive. An enzyme called creatine phosphokinase, produced by skeletal or cardiac muscle death is often elevated in the blood of patients with muscular dystrophy. Another enzyme called aspartate aminotransferase may be elevated in muscle death. It can also be elevated in liver problems. The diagnosis of muscular dystrophy can be confirmed with a muscle biopsy. An examination of the patient’s DNA looking for specific gene deletions may be helpful in diagnosing Duchenne dystrophy. This also may be valuable for identifying carrier status and establishing a prenatal diagnosis. Usually a cardiac assessment is performed including echocardiography and an electrocardiogram.
How is muscular dystrophy treated?
There is no definitive cure for muscular dystrophy, nor is there any way of slowing the progression of the disease. The management of muscular dystrophy depends on the type of dystrophy and the affected muscles. Supportive therapies include daily passive stretching of joint contractures, night splints, bracing when ambulation is lost, orthopedic surgery and respiratory support. Good primary medical care is important including preventive immunizations as well as an annual influenza vaccination. Preservation of a good nutritional state is also important. There is some evidence that steroids in the form of prednisone for Duchenne dystrophy may be helpful. Muscle strength appears to be improved. The value of steroids for other types of muscular dystrophy is unproven.
There may be a place for alternative or complementary treatments. These include regular massage for reducing muscle spasm and contractures. Some practitioners advocate herbal remedies to offer relief from symptoms.
Adolescents with this chronic disease need family and professional support. Adolescent growth and development, athletics, self esteem, social life and academics as just a few of the life issues that may be affected by muscular dystrophy.
How is muscular dystrophy prevented?
Since muscular dystrophy is inherited on a genetic basis, there is no prevention at this time. Prenatal examinations may identify those babies at high risk for the disease.
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Academics, body image, chronic illness, dating, deaths, depression, disabilities, genetic disease, growth and development, heart disease, learning disorders, musculoskeletal disorders, Turner syndrome
