What is muscular dystrophy?
Muscular dystrophy (MD) refers to a group of genetic diseases that cause progressive weakness and degeneration of skeletal muscles. These disorders (of which there are more than 30) vary in age of onset, severity, and the pattern of the affected muscles. All forms of MD grow worse over time as muscles progressively degenerate and weaken. Many people with MD eventually lose the ability to walk.
Some types of MD also affect the heart, lungs, gastrointestinal system, endocrine glands, spine, eyes, brain, or other organs. Some people with MD may develop a swallowing disorder. MD is not contagious and cannot be caused by injury or activity.
How Muscular Dystrophy Affects Muscles
Muscles are made up of thousands of fibers. Each fiber contains cells surrounded by an outer layer, or membrane. Muscle fibers that make up individual muscles are bound together by connective tissue.
Muscles are activated when an impulse, or signal, is sent from the brain through the spinal cord and peripheral nerves (nerves that connect the central nervous system to the body’s sensory organs and muscles) to the neuromuscular junction (the space between the nerve fiber and the muscle it activates). There, a chemical (acetylcholine) triggers a series of events that cause the muscle to contract.
The muscle fiber membrane contains a group of proteins, known as the dystrophin-glycoprotein complex, that prevent damage when muscle fibers contract and relax. When this protective membrane is damaged, muscle fibers begin to leak the protein creatine kinase and take on excess calcium. This damages the muscle fibers and eventually causes them to die, leading to progressive muscle degeneration. Some forms of MD are caused by defects in this dystrophin-glycoprotein complex. Others are caused by defects in the surrounding connective tissue. Still others are caused by expression of toxic gene products in muscle fibers.
Although MD can affect several body tissues and organs, its hallmark is damage to the integrity of muscle fibers. This damage can cause:
- Muscle degeneration
- Progressive weakness
- Fiber death and phagocytosis (wherein muscle fibers are broken down and destroyed by scavenger cells)
- Fiber branching and splitting
- Replacement of muscle tissue with fibrous tissue and fat
People with MD progressively lose muscle function, which can affect breathing. In many forms of MD, the heart muscle also is affected, which can lead to cardiac failure.
Conditions Similar to Muscular Dystrophy
There are many heritable diseases that affect muscles, nerves, and the neuromuscular junction. Diseases like inflammatory myopathy, progressive muscle weakness, and cardiomyopathy (heart muscle weakness that interferes with pumping ability) may produce symptoms that are similar to those found in some forms of MD, but they are caused by different genetic defects. Disorders with symptoms similar to MD include:
- Congenital myopathy
- Spinal muscular atrophy
- Congenital myasthenic syndromes
Because of these overlapping symptoms and the prevalence of MD with no known, genetic cause (sporadic MD) muscular dystrophycan be difficult to quickly diagnose. Some individuals may have signs and symptoms of MD but carry none of the currently recognized genetic mutations.
Who is more likely to get muscular dystrophy?
Muscular dystrophy occurs worldwide and affects people of all races. Its incidence varies as some forms are more common than others, and some types are more prevalent in certain countries and regions of the world. Many muscular dystrophies are familial, meaning there is some family history of the disease.
Most cases of MD are caused by gene changes that affect muscle proteins. The body's cells don't work properly when a protein is changed, or the body doesn’t produce enough (or any) of the protein. Many cases are caused by spontaneous gene mutations that are not present in either parent of the person with MD but can passed to the next generation.
MD can be inherited in three ways:
- Autosomal dominant inheritance occurs when a child receives a "normal" gene from one parent and a defective gene from the other parent.
- Autosomal recessive inheritance means that both parents carry and pass on the faulty gene.
- X-linked (or sex-linked) recessive inheritance occurs when the female parent carries the affected gene passes it to the male child.
How are the types of muscular dystrophy identified?
The types of muscular dystrophy are grouped by the:
- Extent and distribution of muscle weakness
- Age of onset
- Rate of progression
- Severity of symptoms
- Family history
Although some forms become apparent in infancy or childhood, others may not appear until middle age or later. Overall, incidence rates and severity vary, but each form causes progressive skeletal muscle deterioration.
What is Duchenne Muscular Dystrophy?
Duchenne muscular dystrophy (DMD) is the most common childhood form of MD. Because inheritance is caused by a mutation on the X chromosome, DMD primarily affects boys, although girls who carry the defective gene may show some symptoms. DMD results from an absence of the muscle protein dystrophin. DMD usually becomes apparent during the toddler years, sometimes soon after an affected child begins to walk. Progressive weakness and muscle wasting (a decrease in muscle strength and size) caused by degenerating muscle fibers begins in the upper legs and pelvis before spreading into the upper arms. Other symptoms include:
- Loss of some reflexes
- A waddling gait
- Frequent falls and clumsiness (especially when running)
- Difficulty when getting up from a sitting position or when climbing stairs
- Changes to overall posture
- Impaired breathing
- Heart problems (cardiomyopathy)
Many children with DMD are unable to run or jump. The calf muscles, and less commonly, muscles in the buttocks, shoulders, and arms, may be enlarged by an accumulation of fat and connective tissue, causing them to look larger and healthier than they actually are (called pseudohypertrophy). As the disease progresses, the muscles in the diaphragm that assist in breathing and coughing may weaken. Individuals may experience breathing difficulties, respiratory infections, and swallowing problems. Bone thinning and scoliosis (curving of the spine) are common. Some children have cognitive and behavioral impairments.
DMD Improvements in health care have extended the life expectancy and improved the quality of life significantly for children with DMD. Many people with DMD now survive into their 20s or 30s.
What is Becker Muscular Dystrophy?
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 they are in their mid-30s or later, while others are unable to walk past their teens. Muscle weakness is typically noticed first in the upper arms and shoulders, upper legs, and pelvis. Cognitive and behavioral impairments and heart problems are not as common or severe as in DMD, but they do occur. Early symptoms of Becker MD include:
- Walking on one's toes
- Frequent falls
- Difficulty rising from the floor
What is Congenital Muscular Dystrophy?
Congenital muscular dystrophy refers to a group of muscular dystrophies that are either present at birth or become evident before age 2. The degree and progression of muscle weakness and degeneration vary with the type of disorder. Weakness may be first noted when children do not meet developmental milestones related to motor function and muscle control. Muscle degeneration in congenital muscular dystrophy is restricted primarily to skeletal muscle. Most people with this type of MD are unable to sit or stand without support, and some may never learn to walk. There are many genetic forms of congenital MD including
- Merosin-negative disorders, in which the protein merosin (found in the connective tissue that surrounds muscle fibers) is missing
- Merosin-positive disorders, in which merosin is present but other necessary proteins are missing
People with congenital MD may develop:
- Contractures (shortening of muscles or tendons around joints)
- Scoliosis (curved spine)
- Breathing and swallowing difficulties
- Foot problems
The cognitive development of some children progresses as expected, while others are severely impaired. Weakness in the muscles of the diaphragm problems breathing and respiratory failure. Congenital MD may also affect the central nervous system, causing vision and speech problems, seizures, and structural changes in the brain.
What is Distal Muscular Dystrophy?
Distal muscular dystrophy (also known as distal myopathy) describes a group of muscle diseases that primarily affect the distal muscles (those farthest away from the shoulders and hips) in the forearms, hands, lower legs, and feet. Distal MDs are typically less severe, progress more slowly, and involve fewer muscles than other forms of MD, although they can spread to other muscles. Distal MD can affect the heart and respiratory muscles, and individuals with distal MD may eventually need a ventilator. They may not be able to perform fine hand movement and may have difficulty extending the fingers. Walking and climbing stairs may become difficult and some people may be unable to hop or stand on their heels.
Onset of distal MD is typically between the ages of 40 and 60. Although distal MD is primarily an autosomal dominant disorder, autosomal recessive forms have been reported in young adults. Symptoms are similar to those of DMD but with a different pattern of muscle damage. An infantile-onset form of autosomal recessive distal MD has also been reported. Slow but progressive weakness is often first noticed around age one, when the child begins to walk, and continues to progress very slowly throughout adult life.
What is Emery-Dreifuss Muscular Dystrophy?
Emery-Dreifuss muscular dystrophy primarily affects boys. The disorder has two forms: One is X-linked recessive and the other is autosomal dominant.
Onset of Emery-Dreifuss MD is usually apparent by age 10, but symptoms can appear as late as a person’s mid-20s. This disease causes slow yet progressive wasting of the upper arm and lower leg muscles and symmetric weakness. Contractures in the spine, ankles, knees, elbows, and back of the neck usually precede significant muscle weakness, which is less severe than in DMD. Contractures may cause elbows to become locked in a flexed position. The entire spine may become rigid as the disease progresses. Other symptoms include:
- Shoulder deterioration
- Walking on one's toes
- Mild facial weakness
Nearly all people with Emery-Dreifuss MD have some form of heart problem by age 30. Female carriers of the disorder often have cardiac complications without muscle weakness. In some cases, the cardiac symptoms may be the earliest and most significant symptom of the disease and may appear years before muscle weakness.
What is Facioscapulohumeral Muscular Dystrophy?
Facioscapulohumeral muscular dystrophy (FSHD) initially affects muscles of the face (facio), shoulders (scapulo), and upper arms (humera) with progressive weakness. Also known as Landouzy-Dejerine disease, this is a relatively common form of MD and is characterized as an autosomal dominant disorder. Most people with FSHD have a normal life span, but some become severely disabled.
Disease progression is typically very slow, with intermittent spurts of rapid muscle deterioration. Onset is usually in a person’s teens but may occur as early as childhood or as late as age 40. One hallmark of FSHD is that it causes asymmetric weakness. Muscles around the eyes and mouth are often affected first, followed by weakness around the shoulders, chest, and upper arms. A particular pattern of muscle wasting causes the shoulders to appear to be slanted and the shoulder blades to appear winged. Muscles in the lower extremities may also weaken. Reflexes are typically diminished in the same distribution as the weakness. People with FSHD may develop a crooked smile, a pouting look, flattened facial features, or a mask-like appearance. Some individuals cannot pucker their lips or whistle and may have difficulty swallowing, chewing, or speaking. Muscle weakness can also spread to the diaphragm, causing respiratory problems. Other symptoms may include hearing loss and an inward curve of the lumbar spine (called lordosis).
Contractures are rare. Some people with FSHD feel severe pain in the affected limb. Cardiac muscles are not usually affected, and significant weakness of the pelvis is less common than in other forms of MD. An infant-onset form of FSHD can cause retinal disease and some hearing loss.
What is Limb-girdle Muscular Dystrophy?
Limb-girdle muscular dystrophy (LGMD) refers to more than 20 inherited conditions marked by progressive loss of muscle and the symmetrical weakening of voluntary muscles, primarily those in the shoulders and around the hips. At least five forms of autosomal dominant limb-girdle MD (known as Type 1) and 17 forms of autosomal recessive limb-girdle MD (known as Type 2) have been identified. Some autosomal recessive forms of the disorder are caused by a deficiency of any of four dystrophin-glycoprotein complex proteins called the sarcoglycans. Deficiencies in dystroglycan, classically associated with congenital muscular dystrophies, may also cause LGMD.
The recessive LGMDs occur more frequently than the dominant forms and usually start in childhood or in a person’s teens. The dominant LGMDs usually begin in adulthood. In general, the earlier the symptoms appear, the more rapid the rate of disease progression. Limb-girdle MD affects both women and men. Some forms of the disease progress rapidly, resulting in serious muscle damage and loss of the ability to walk, while others advance very slowly over many years and cause minimal disability. In some cases, progression of the disorder appears to stop, but later resumes.
The pattern of muscle weakness is similar to that of DMD and Becker MD. Weakness is typically noticed first around the hips before spreading to the shoulders, legs, and neck. Individuals develop a waddling gait and have difficulty rising from chairs, climbing stairs, or carrying heavy objects. They fall frequently and are unable to run. Contractures at the elbows and knees are rare but individuals may develop contractures in the back muscles, which gives them the appearance of a rigid spine. Proximal reflexes (closest to the center of the body) are often impaired. Some individuals also experience heart and breathing problems.
What is Myotonic Dystrophy?
Myotonic dystrophy (DM1), also known as Steinert's disease or dystrophia myotonica, is another common form of MD. Myotonia, or the inability to relax muscles following a sudden contraction, is found only in this form of MD. People with DM1 can live a long life, with variable but slowly progressive disability. Typical disease onset is between ages 20 and 30, but childhood onset and congenital onset are well-documented. Muscles in the face and the front of the neck are usually first to show weakness and may produce a hallow temples, drooping facial skin, and a thin neck. Wasting and weakness noticeably affect forearm muscles. DM1 affects the central nervous system and other body systems, including the heart, adrenal glands and thyroid, eyes, and gastrointestinal tract.
Other symptoms include:
- Cardiac complications
- Difficulty swallowing
- Droopy eyelids (ptosis)
- Poor vision
- Early frontal baldness
- Weight loss
- Mild cognitive impairment
- Increased sweating
Individuals may feel drowsy and have an excessive need for sleep. A second form, known as myotonic dystrophy type 2 (DM2), is similar to the classic form, but usually affects proximal muscles more significantly.
This autosomal dominant disease affects both males and females. A woman with DM1 can give birth to an infant with a rare congental form of the disorder. Symptoms at birth may include:
- Difficulty swallowing or sucking
- Impaired breathing
- Absence of reflexes
- Skeletal deformities and contractures (club feet)
- Muscle weakness, especially in the face
A childhood-onset form of myotonic MD may become apparent between ages five and 10. Symptoms include:
- General muscle weakness (particularly in the face and muscles farthest away from center of the body)
- Lack of muscle tone
- Cognitive impairment
What is Oculopharyngeal Muscular Dystrophy?
Oculopharyngeal muscular dystrophy (OPMD) generally begins in a person’s 40s or 50s and affects both women and men. In the U.S., the disease is most common in families of French-Canadian descent as well as among Hispanic residents of northern New Mexico. People first report drooping eyelids, followed by weakness in the muscles of the face and throat that cause problems with swallowing. A person’s tongue may atrophy, their voice may change, and their eyelids may droop. People with OPMD also may have:
- Double vision
- Problems with looking up (upper gaze)
- Retina degeneration that affects night and peripheral vision (retinitis pigmentosa)
- Heart problems
Muscle weakness and wasting in the neck and shoulders is common. Limb muscles also may be affected. People with OPMD may find it difficult to walk, climb stairs, kneel, or bend. People who are severely affected by OPMD will eventually lose the ability to walk.
How is muscular dystrophy diagnosed and treated?
Doctors review an individual's medical and family history to determine if the muscle symptoms are caused by a disease that primarily affects other tissues or organs, and whether they can identify an inherited condition. The medical team will also take steps to rule out muscle weakness resulting from prior surgery, exposure to toxins, or current medications. Thorough clinical and neurological exams can help doctors do the following:
- Rule out disorders of the central and/or peripheral nervous systems
- Identify any patterns of muscle weakness and atrophy
- Test reflex responses and coordination
- Look for contractions
Various laboratory tests may be used to confirm the diagnosis of MD, including:
- Blood and urine tests.
- Exercise tests to detect elevated rates of certain chemicals during or after exercise. Genetic testing and genetic counseling. Genetic analysis is the standard method used to diagnose people who are expected to have MD and for characterizing the type. Participation in clinical trials usually requires a genetic diagnosis.
- Amniocentesis during pregnancy to test a sample of the amniotic fluid in the womb.
- Chorionic villus sampling (CVS) to test a very small sample of the placenta during early pregnancy.
- Diagnostic imaging including magnetic resonance imaging (MRI), phosphorus magnetic resonance spectroscopy, and sonography to examine muscle quality, atrophy, or other abnormalities.
- Muscle biopsies to monitor the course of disease and treatment effectiveness.
- Immunofluorescence testing to detect specific proteins within muscle fibers.
- Electron microscopy to identify changes in subcellular components of muscle fibers. Electron microscopy also can identify changes that characterize cell death, mutations in muscle cell mitochondria, and an increase in connective tissue.
- Neurophysiology studies to identify physical and/or chemical changes in the nervous system.
- Nerve conduction velocity to measure the speed and strength with which an electrical signal travels along a nerve. This can help determine whether nerve damage is present.
- Repetitive stimulation to assess the function of the neuromuscular junction by electrically stimulating a motor nerve several times in a row.
- Electromyography (EMG) to record muscle fiber and motor unit activity. Results may reveal electrical activity characteristic of MD or other neuromuscular disorders.
Treating Muscular Dystrophy
Available treatments are aimed at keeping people independent for as long as possible and preventing complications that can arise from muscle weakness, reduced mobility, and heart and breathing difficulties. Treatment may involve a combination of approaches, including physical therapy, drug therapy, and surgery.
- Drug therapy may be prescribed to delay muscle degeneration in muscular dystrophies. There are several drugs approved by the U.S. Food and Drug Administration (FDA) to treat individuals with DMD (given orally or by injection). Steroids, such as prednisone and deflazacort, and immunosuppressive drugs can help slow the rate of muscle deterioration and damage to muscle cells, but some carry side effects that can be especially troubling in children. There are also drugs available to treat the symptoms of MD, including myotonia (muscle spasms and weakness). Breathing symptoms may be treated with antibiotics.
- Physical therapy can help improve movement and keep a person’s muscles as flexible and strong as possible. Passive stretching can also support join flexibility and prevent contractures.
- Occupational therapy can help people with MD perform everyday tasks at home and at work.
- Speech therapy can help people with weakened facial and throat muscles communicate.
- Regular, moderate exercise and/or physical activity can help people with MD maintain muscle function and mobility.
- Deep breathing and coughing exercises can help people with MD who are having breathing problems.
- Support aids such as wheelchairs, splints, braces, spinal supports, and posture correction devises can counter muscle weakness and help people with MD maintain mobility.
- No dietary supplements, specific foods, or specific diets have been shown to slow the progression of MD. People with MD should eat well as a way to support their overall health. People with MD who have trouble swallowing may need to use special techniques for feeding.
- Corrective surgery can ease complications from MD, including tendon or muscle release surgery for contractures, pacemakers for heart problems, surgery to reduce scoliosis-related pain or postural imbalance, and cataract surgery for eye problems.
- Assisted ventilation is often needed to treat respiratory muscle weakness that accompanies many forms of MD, especially in the later stages.
What are the latest updates on muscular dystrophy?
NIH supports a broad range of basic, translational, and clinical research on MD. While some genes that cause muscular dystrophy still remain to be identified, advances in gene sequencing has aided the identification of genes that may be involved for most types of muscular dystrophy. And new knowledge of specific disease mechanisms is identifying potential targets for therapy development in nearly all types of MD. For example, advances in targeted therapy have led to promising efforts in myotonic dystrophy and facioscapulohumeral muscular dystrophy.
NINDS, a part of NIH, is the leading supporter of MD research efforts conducted at NIH and at grantee institutions across the country.
Federal Commitment to MD
In response to the MD CARE Act of 2001 (Muscular Dystrophy Community Assistance, Research, and Education Amendments Act, Public Law 107-84), NIH formed the Muscular Dystrophy Coordinating Committee to help guide MD research. The Committee’s MDCC’s Action Plan for the Muscular Dystrophies contains specific research objectives and other goals for understanding the causes of MD and its impact on patients, families, and society, a path for accelerating diagnosis and treatment, and goals designed to improve the lives of individuals living with MD.
NIH also established The Wellstone Muscular Dystrophy Research Network in honor of the late Senator Paul D. Wellstone of Minnesota. Four NIH Institutes—NIAMS, NICHD, NINDS, and NHLBI—support a total of six Wellstone Centers, which promote collaborative research and provide important resources for the MD research community. Wellstone Centers projects include basic studies to better understand the mechanisms of these diseases, studies on the role of the immune response and inflammation, and research aimed at the development of new therapeutic approaches, including gene therapy and genomic editing.
NINDS Intramural Research Program
Several laboratories within the NINDS Intramural Research Program conduct research on MD. Projects focus on learning more about MD through neuroimaging and natural history studies and gaining a better understanding of the molecular mechanisms underlying early-onset nerve and muscle disorders.
Enabling New Therapies and Optimizing Existing Treatments
NINDS funds projects in DMD aimed at developing and testing novel therapies and advancing gene therapy delivery methods for DMD.
NINDS–funded researchers are identifying biomarkers—measures of what’s happening in the body—for myotonic dystrophy and DMD, including imaging techniques to detect muscle composition, structure, and function.
NINDS funded the FOR-DMD (Finding the Optimum Regimen of Corticosteroids for DMD) trial to compare and optimize the most widely used corticosteroid regimens used to treat DMD. Corticosteroids may slow the progression of DMD.
Gene replacement therapy
Gene therapy has the potential to address the primary cause of MD by providing for the production of the missing or underproduced protein. Researchers are developing and fine-tuning the way we deliver genetic materials to cells (known as gene therapy vectors) that can cross the protective blood-brain barrier. Refining viral vector types can improve our ability to target muscles and avoid other tissues that may decrease efficiency or lead to adverse reactions to the therapy.
Clinical trials of gene therapy for DMD, delivered through the bloodstream throughout the body have been conducted by several groups. The first such gene therapy was approved by the FDA in 2023. Additional trials are ongoing to further understand the efficacy and durability of such treatments.
Several other therapies for DMD have been approved in the past few years, including gene fragments called antisense oligonucleotides that allow for muscle cells to produce shortened but functional forms of dystrophin.
Utrophin is a protein that is closely related to dystrophin and is not affected in the gene mutations that cause Duchenne MD. Increasing expression of utrophin may prove a useful approach in treating Duchenne MD. NIH supports both gene therapy and small molecule drug development programs to increase the muscle production of utrophin.
Additionally, modifier genes—genes with activities that act to reduce the severity of MD—have been discovered by NIH-funded teams and represent new therapeutic targets to potentially reduce the severity of several types of muscular dystrophy.
Most individuals with Duchenne have mutations in the dystrophin gene that cause it to function improperly and stop producing the dystrophin protein. By manipulating the protein synthesis process, production of a gene that either "reads through" or “skips” the genetic mutation can result in at least partial functional dystrophin. Several products using this approach are approved by the FDA for the treatment of DMD caused by certain mutations.
Clinical trials are underway for myotonic, facioscapulohumeral, and other forms of MD.
Moving Towards Clinical Trial Readiness
NINDS-funded scientists are improving clinical research tools such as biomarkers, clinical outcome measures, and inclusion criteria needed for future trials, so that clinical trials are feasible when a candidate therapeutic reaches that stage. Patient registries, natural history studies, biomarker identification, development of clinical trial endpoint measures, and the emergence of standards of care are all essential in supporting clinical trials and are being advanced in several types of muscular dystrophy with the support of both public and private sector partners.
NINDS also has developed Common Data Elements (CDEs) for DMD, the congenital muscular dystrophies, myotonic dystrophy and FSHD. CDEs are critical to ensure that data is collected and reported in a consistent way. NIH has recently undertaken several new initiatives in training, career development, and research that are targeted toward MD. These advances, along with NINDS’s focus on translational and clinical research, will lead to the growth of clinical trials and promising treatment strategies.
How can I or my loved one help improve care for people with muscular dystrophy?
Consider participating in a clinical trial so clinicians and scientists can learn more about MD and related disorders. Clinical research uses human volunteers to help researchers learn more about a disorder and perhaps find better ways to safely detect, treat, or prevent disease.
All types of volunteers are needed—those who are healthy or may have an illness or disease—of all different ages, sexes, races, and ethnicities to ensure that study results apply to as many people as possible, and that treatments will be safe and effective for everyone who will use them.
Where can I find more information about muscular dystrophy?
Information may be available from the following organizations and resources:
Centers for Disease Control and Prevention (CDC)
Phone: 800-311-3435 or 404-639-3311
Coalition to Cure Calpain 3
Facioscapulohumeral Muscular Dystrophy (FSH) Society
Muscular Dystrophy Association
Myotonic Dystrophy Foundation
Phone: 866-968-6642; 415-800-7777
National Heart, Lung, and Blood Institute (NHLBI)
Phone: 301-592-8573 or 240-629-3255 (TTY)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Phone: 301-496-8190 or 877-226-4267
National Institute of Child Health and Human Development (NICHD)
Parent Project Muscular Dystrophy (PPMD)