muscular dystrophy
-
What is muscular dystrophy?
Muscular dystrophy refers to a group of hereditary conditions marked by the degeneration and progressive weakening of skeletal muscles. It arises from mutations in genes encoding proteins responsible for muscle structure and function. Muscle fibers initially degenerate and regenerate, growing larger than normal. Eventually, fibrous scar tissue and fat replace the muscles, resulting in a loss of strength and function.
Several types exist, including Duchenne, Becker, and limb-girdle muscular dystrophy, varying in severity, onset, and affected muscles. Diagnosis involves genetic testing, muscle biopsy, electromyography, and creatine kinase testing. While there is no cure, treatments such as physical therapy, medication, and surgery can help manage symptoms.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How does muscular dystrophy affect the muscles?
Muscular dystrophy is a group of hereditary conditions marked by progressive weakening and degeneration of skeletal muscles. This degeneration arises from mutations in genes responsible for muscle structure and function.
Initially, some muscle fibers degenerate and then regenerate, growing larger than normal. Over time, the muscles are totally replaced by fibrous scar tissue and fat, which leads to a loss of muscle strength and function. In Duchenne muscular dystrophy, muscle degeneration results from a lack of the protein dystrophin, disrupting the muscle fiber membrane, causing excess calcium ions to enter the cell and lead to cell degeneration.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What causes muscles to become weak in muscular dystrophy?
In muscular dystrophy, muscle weakness results from the degeneration and regeneration of muscle fibers due to genetic mutations affecting muscle structure and function. Over time, muscles are replaced by fibrous scar tissue and fat, which leads to a loss of strength and function. For example, Duchenne muscular dystrophy is caused by a lack of the protein dystrophin, which disrupts muscle fiber membranes, causing excess calcium to enter cells and resulting in cell degeneration.
3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What is the role of proteins like dystrophin in healthy muscles?
In healthy muscles, dystrophin is a protein associated with a transmembrane complex of skeletal muscle cells. Dystrophin's presence is essential for maintaining muscle mass and function, enabling muscles to regenerate after damage and adapt to loads. In Duchenne muscular dystrophy, a defective gene on the X chromosome causes the body to not produce functional dystrophin, which leads to the disruption of the membrane covering the muscle fiber, the entry of excess amounts of calcium ions into the cell, and cell degeneration.
3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How do damaged muscle fibers change over time in muscular dystrophy?
In muscular dystrophy, muscle fibers undergo degeneration and regeneration due to gene mutations affecting muscle structure and function. Regenerated fibers become larger than normal (hypertrophy). Over time, muscles are replaced by fibrous scar tissue and fat, leading to loss of strength and function. A muscle biopsy from an individual with muscular dystrophy is likely to show cellular changes associated with damage, regeneration, and growth.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are some common signs and symptoms seen in the pathology of muscular dystrophy?
In muscular dystrophy, muscle biopsies often show cellular changes associated with damage, regeneration, and growth. There is degeneration and attempted regeneration of muscle fibers. In more severe forms of muscle disease, lost muscle fibers are replaced with fat cells. With Duchenne muscular dystrophy, a defect of a gene on the X chromosome causes muscle degeneration because of the lack of a protein called dystrophin. This leads to excess amounts of calcium ions entering the cell, causing cell degeneration. Genetic testing and muscle biopsy can detect abnormalities or alterations in dystrophin levels.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
muscular dystrophy, any of a group of hereditary conditions that are characterized by progressive weakness and degeneration of the skeletal muscles. There are several types of muscular dystrophy, all of which arise from mutations in genes that encode proteins with roles in muscle structure and function. There often is early evidence of degeneration and then regeneration of some muscle fibers; fibers that regenerate become larger than normal, and eventually the muscles are totally replaced by fibrous scar tissue and fat, resulting in loss of muscle strength and function.
Common types
- Duchenne muscular dystrophy
- Becker muscular dystrophy
- Limb-girdle muscular dystrophy
- Myotonic dystrophy
- Facioscapulohumeral muscular dystrophy
- Congenital muscular dystrophy
- Emery-Dreifuss muscular dystrophy
The different types of muscular dystrophy vary in onset, muscles affected, and severity. Examples of common types of the condition include Duchenne muscular dystrophy, Becker muscular dystrophy, limb-girdle muscular dystrophy, facioscapulohumeral muscular dystrophy, and myotonic dystrophy.
Duchenne muscular dystrophy
Duchenne muscular dystrophy is the most common childhood form of the disease; it occurs in one of every 3,300 male births. It is a sex-linked disorder, meaning that it strikes males almost exclusively. The disease is caused by a defective gene on the 23rd, or X, chromosome that results in the failure of the body to produce a functional muscle protein known as dystrophin. Most females who carry the genetic alteration are unaffected, but they have a 50 percent probability of passing the condition to each of their sons.
" height="20" alt="HEW Logo">
Early symptoms, which usually occur between ages two and six, include a waddling gait, frequent falling, difficulty in getting up from a lying or sitting position, enlargement of the calf muscles, inability to raise the knees, and disappearance of a normal knee or ankle jerk; symptoms become more obvious as the child ages. Stairs eventually become impossible to climb, and by early adolescence the child is unable to walk. Muscle wasting progresses upward from the legs, and the arms are eventually affected. Ultimately, muscle wasting affects the muscles of the diaphragm, and breathing becomes shallow. Life-threatening pulmonary infections or respiratory failure usually occurs before age 20.
Becker muscular dystrophy
Becker muscular dystrophy has symptoms similar to Duchenne but begins in later childhood or adolescence and progresses more slowly. It is also a sex-linked disorder that is caused by a defective gene on the X chromosome; however, some functional dystrophin is produced. Individuals with this form of muscular dystrophy may function well into adult life, with certain limitations.
Limb-girdle and facioscapulohumeral dystrophies
Limb-girdle dystrophy (dystrophy of the pelvic or shoulder muscles) affects males and females. The first symptoms arise in the pelvic region, becoming evident in late childhood. Muscular weakness eventually progresses to the arms and legs. Symptoms include frequent falling, difficulty in climbing, and a waddling gait.
Facioscapulohumeral dystrophy (dystrophy related to the face, the shoulder blade, and the upper arm) is caused by a mutation on chromosome 4. It typically emerges in adolescence and affects males and females. The first symptom may be difficulty in raising the arms. Later symptoms may include weakness of the legs and pelvic girdle, forward sloping of the shoulders, and difficulty in closing the eyes. This form of muscular dystrophy can range in severity; individuals with facioscapulohumeral dystrophy may be mildly affected or totally disabled.
The trusted destination for professionals, college students, and lifelong learners.
SUBSCRIBE
Myotonic dystrophy
Myotonic muscular dystrophy is the most common form of the disease affecting adults. The primary symptom is myotonia, a stiffening of the muscles after use. Myotonic dystrophy may also affect the central nervous system, heart, gastrointestinal tract, eyes, and endocrine glands. Because of the possibility of serious cardiac complications, individuals with this form of muscular dystrophy may require a pacemaker. Myotonic dystrophy type 1 and myotonic dystrophy type 2 are both caused by a genetic mutation in the DMPK and CNBP genes, respectively.
Diagnosis and treatment
Genetic testing can reliably detect mutations that cause the different forms of muscular dystrophy. Muscle biopsy is performed to analyze muscle tissue for structural abnormalities or alterations in dystrophin levels. Other tests include electromyography, which measures electrical activity in muscles, and creatine kinase testing to assess muscle tissue damage.
There is no cure for muscular dystrophy. Physical therapy, exercises, splints, braces, and corrective surgery may help relieve some of the symptoms. Corticosteroid medications may slow the progression of the disease. In the case of Duchenne muscular dystrophy, the drug givinostat may facilitate the production of larger muscle fibers, thereby enhancing muscle regeneration, and lower inflammation and fibrosis in muscle tissue. These combined effects can help slow the advance of muscle weakness.