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Muscular dystrophy (MD) is a group of more than 30 genetic disorders that cause progressive muscle weakness and degeneration of skeletal muscles. The symptoms vary depending on the type of MD and can manifest at any age, though MD is most frequently diagnosed during childhood. The disorders differ in which muscles are primarily affected, the degree of weakness, how fast they worsen, and when symptoms begin. MD is caused by changes in the genes responsible for muscle structure and function, resulting in progressive degeneration and loss of muscle fibres. This causes the muscle cells to become vulnerable to injury and leads to symptoms such as muscle pain, stiffness, and weakness, as well as difficulties with movement.
| Characteristics | Values |
|---|---|
| Cause | Mutations in genes responsible for muscle structure and function |
| Mechanism | Progressive weakness and degeneration of skeletal muscles |
| Age of Onset | Variable, can be present at birth, develop in childhood or adulthood |
| Severity | Variable, some forms are more common than others |
| Pattern of Muscle Involvement | Variable, different muscle groups are affected by different types of MD |
| Treatments | Physical therapy, corrective surgery, orthoses, drug therapy, gene therapy, antisense drugs |
| Prognosis | Variable, some forms cause severe disability and reduced life expectancy, others cause mild impairment |
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What You'll Learn
Gene mutations
Muscular dystrophy is a group of more than 30 genetic conditions that cause muscle weakness and other muscle-related symptoms. The symptoms of muscular dystrophy get worse over time. It can be present at birth, develop in childhood, or develop in adulthood depending on the type.
The majority of muscular dystrophy cases are caused by inherited gene mutations that affect muscle proteins. These mutations mean that the cells that would normally maintain muscles can no longer do so, leading to progressive muscle weakness. There are several genes and possible genetic mutations that play a role in muscle function, which is why there are so many different forms of muscular dystrophy.
In 1986, researchers identified a gene on the X chromosome that, when mutated, causes Duchenne, Becker, and intermediate forms of muscular dystrophy. The DMD gene provides instructions for making a protein called dystrophin, which is located primarily in skeletal and cardiac muscle. Dystrophin helps stabilize and protect muscle fibres and may also play a role in chemical signalling within cells. Mutations in the DMD gene alter the structure or function of dystrophin or prevent any functional dystrophin from being produced. Without enough of this protein, muscle cells become damaged as muscles contract and relax. The damaged fibres weaken and die over time, leading to the muscle weakness and heart problems characteristic of Duchenne and Becker muscular dystrophies.
Duchenne and Becker muscular dystrophies are caused by different mutations in the same gene. The two conditions differ in their severity, age of onset, and rate of progression. In boys with Duchenne muscular dystrophy, muscle weakness tends to appear in early childhood and worsen rapidly. Affected children may have delayed motor skills, such as sitting, standing, and walking. They are usually wheelchair-dependent by adolescence. The signs and symptoms of Becker muscular dystrophy are usually milder and more varied.
In addition to Duchenne and Becker muscular dystrophies, there are several other types of muscular dystrophy caused by gene mutations. These include Emery-Dreifuss muscular dystrophy, which causes muscle weakness in the shoulders, upper arms, and shins, and facioscapulohumeral muscular dystrophy, which affects the muscles in the face, shoulders, and upper arms. Limb-girdle muscular dystrophy affects the muscles in the upper arms, upper legs, shoulders, and hips, while oculopharyngeal muscular dystrophy weakens the muscles in the eyelids and throat.
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Progressive muscle weakness
Muscular dystrophy (MD) is a group of over 30 genetic disorders characterised by progressive muscle weakness and wasting. The disorders vary in age of onset, severity, and the pattern of affected muscles. The root cause of muscular dystrophy lies in mutations affecting genes responsible for muscle structure and function, leading to the gradual degeneration and loss of muscle fibres.
The main symptom of muscular dystrophy is progressive muscle weakness, which makes everyday tasks harder to do. Muscles involved in breathing can become weaker, leading to poor breathing, especially during sleep. Many people with MD eventually lose the ability to walk. The symptoms of the most common type of muscular dystrophy start in childhood, mostly in boys. Other types sometimes don't start until adulthood.
Duchenne muscular dystrophy (DMD) is the most common childhood form of MD. DMD results from an absence of the muscle protein dystrophin. Progressive weakness and muscle wasting caused by degenerating muscle fibres begin in the upper legs and pelvis before spreading into the upper arms. Other symptoms include muscle cramps, stiffness, and enlarged calf muscles. Many children with DMD are unable to run or jump.
Becker muscular dystrophy is less severe than but closely related to DMD. The disorder usually appears around age 11 but may occur as late as age 25, and people with Becker MD usually live into middle age or later. The rate of muscle atrophy and weakness varies greatly. Many people maintain their ability to walk until their mid-30s or later, while others are unable to walk past their teens.
Emery-Dreifuss muscular dystrophy (EDMD) mainly affects male children and young adults. It tends to cause muscle weakness in the shoulders, upper arms, and shins. EDMD also affects the heart and usually progresses slowly. Facioscapulohumeral muscular dystrophy (FSHD) most commonly affects muscles in the face, shoulders, and upper arms. Limb-girdle muscular dystrophy (LGMD) affects the muscles in the upper arms, upper legs, shoulders, and hips.
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Muscle degeneration
The process of muscle degeneration in muscular dystrophy involves a cascade of events that lead to muscle fibre damage and loss. Firstly, the lack of dystrophin causes increased membrane permeability in muscle fibres, allowing calcium ions to enter the cell. These calcium ions activate enzymes that degrade the muscle fibre structure, leading to inflammation and degeneration. This initiates a regeneration process by satellite cells, but over time, this regeneration becomes less efficient, contributing to progressive muscle fibre loss and the development of fibrosis.
The symptoms of muscular dystrophy are varied and depend on the specific type and the affected muscle groups. However, common symptoms include muscle weakness, wasting, and stiffness, as well as challenges with movement such as walking, running, jumping, and climbing stairs. In some cases, muscular dystrophy can also affect the heart, lungs, endocrine system, spine, eyes, brain, and other organs, leading to cardiac problems, breathing difficulties, endocrine issues, scoliosis, eye problems, and more.
The progression of muscle degeneration in muscular dystrophy can be slowed through various treatments. Drug therapy, for example, can delay muscle degeneration and reduce damage to muscle cells. Steroids and immunosuppressive drugs may be used, but they can have side effects, especially in children. Other medications are available to treat specific symptoms, such as myotonia (muscle spasms and weakness). Physical therapy, braces, and corrective surgery can also help improve movement, flexibility, and quality of life.
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Loss of muscle function
Muscular dystrophy refers to a group of more than 30 genetic conditions that cause muscle weakness and other muscle-related symptoms. The symptoms of muscular dystrophy get worse over time. It can be present at birth, develop in childhood, or develop in adulthood depending on the type. The condition is caused by changes in the genes that make proteins needed to form healthy muscles. These mutations mean that the cells that would normally maintain your muscles can no longer fulfil this role, leading to progressive muscle weakness.
The symptoms of muscular dystrophy vary depending on the type but often include challenges with movement, such as late walking, frequent falls, trouble rising from the floor, and trouble running, jumping, or climbing stairs. Many people with MD eventually lose the ability to walk. Some people with MD may also develop a swallowing disorder.
The muscles involved in breathing can also become weaker, leading to poor breathing, especially during sleep. Facioscapulohumeral muscular dystrophy (FSHD) is a type of MD that causes muscle weakness in the face, shoulders, and upper arms. The weakness often affects one side of the body more than the other. When muscles around the eyes are affected, it can cause trouble fully closing the eyelids, leading to dryness of the eye. When the shoulders are affected, the shoulder blades might stick out like wings when the arms are raised.
Another type of MD is Emery-Dreifuss muscular dystrophy (EDMD), which mainly affects male children and young adults. It causes muscle weakness in the shoulders, upper arms, and shins. EDMD also affects the heart and usually progresses slowly.
Congenital muscular dystrophies (CMD) are a group of muscular dystrophies that are either present at birth or become evident in early childhood. They cause overall muscle weakness with possible joint stiffness or looseness. Depending on the type, CMD may also involve spinal curvature (scoliosis), breathing issues, intellectual disabilities, learning disabilities, eye issues, or seizures.
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Cardiomyopathy
Muscular dystrophy is a group of more than 30 genetic conditions that cause muscle weakness and other muscle-related symptoms. The symptoms of muscular dystrophy get worse over time, and in many forms of MD, the heart muscle is affected, which can lead to cardiac failure. Cardiomyopathy, or heart muscle weakness, is a common symptom of muscular dystrophy.
Duchenne muscular dystrophy (DMD) is a rare, X-linked condition with progressive muscle weakness and accompanying cardiomyopathy. DMD cardiomyopathy (DCM) is characterised by a hypokinetic, dilated phenotype that progressively increases with age. It is typically the most severe form of muscular dystrophy. Becker muscular dystrophy (BMD) is the more benign form, with less severe symptoms. Both DMD and BMD affect the synthesis of dystrophin, a large sarcolemmal protein that is absent in DMD and reduced or abnormal in BMD. Dystrophin has an important role in stabilising the cell membrane of both skeletal and cardiac myocytes. Its absence produces sarcolemmal fragility and muscle cell degeneration.
Emery-Dreifuss muscular dystrophy (EDMD) is an X-linked or autosomal dominant condition that causes muscle weakness in the shoulders, upper arms, and shins. EDMD also affects the heart, causing cardiac conduction defects and cardiomyopathy. Facioscapulohumeral muscular dystrophy (FSHD) affects muscles in the face, shoulders, and upper arms. Limb-girdle muscular dystrophy (LGMD) affects the muscles in the upper arms, upper legs, shoulders, and hips. Both FSHD and LGMD can also cause heart conditions.
Myotonic dystrophy is the most common type of muscular dystrophy diagnosed in adulthood, affecting men and women equally. It causes difficulty relaxing muscles after use and can also affect the heart and lungs. Cardiomyopathy is a significant cause of death in patients with muscular dystrophy, and early detection is important to slow adverse cardiac remodelling and attenuate heart failure symptoms.
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Frequently asked questions
Muscular dystrophy is a group of more than 30 genetic disorders that cause progressive muscle weakness and degeneration of skeletal muscles.
Muscular dystrophy is caused by changes or mutations in the genes responsible for making muscle proteins. These mutations affect the functioning of the muscle cells, making them vulnerable to injury and leading to progressive muscle degeneration and weakness.
The symptoms of muscular dystrophy vary depending on the specific type but generally include progressive muscle weakness, wasting, and loss of function. Some types of muscular dystrophy also affect the heart, lungs, and other organs. Common symptoms include challenges with movement, muscle pain and stiffness, and breathing difficulties.
The age of onset for muscular dystrophy varies depending on the specific type, but it can manifest at any age. Some types, such as Duchenne muscular dystrophy, typically appear in early childhood, while others like facioscapulohumeral muscular dystrophy may have a later onset in the teenage or adult years.
Currently, there is no cure for any disorder in the muscular dystrophy group. However, various treatments are available to manage symptoms and slow the progression of the disease. These include drug therapy, physical therapy, braces, corrective surgery, and assisted ventilation for breathing support.
