Muscular dystrophy refers to a group of diseases that cause muscle weakness and wasting that gets progressively worse over time.
Causes
Muscular dystrophies are caused by mutations in the genetic code. Mutations in dozens of different genes have been linked with the various types of muscular dystrophy; in general, these disease-causing mutations disrupt the activity of genes that are important for muscle health. For example, Duchenne and Becker muscular dystrophies are caused by mutations in the DMD gene that codes for dystrophin, a protein that helps to protect muscle cells from being damaged during movements.
Mutations that cause muscular dystrophies usually are inherited from a person’s biological parents; the exact pattern of inheritance depends on the specific gene and mutation. More rarely, mutations can occur spontaneously (de novo mutations).
Types
There are more than 30 different types of muscular dystrophy. The most common are Duchenne muscular dystrophy (DMD) and the milder and rarer Becker muscular dystrophy (BMD).
The onset age for symptoms, and the severity of symptoms, varies a great deal from type to type. DMD usually manifests in childhood, while symptoms of BMD usually aren’t apparent until adolescence. Congenital muscular dystrophies are usually apparent from birth, whereas myotonic dystrophy and oculopharyngeal muscular dystrophy do not typically cause problems until adulthood.Â
Symptoms
The primary indicator of muscular dystrophy is the progressive weakening and atrophy (wasting) of muscles. The specific muscles that are affected, and the severity of the resultant symptoms, vary widely depending on the type of disease.
Many forms of muscular dystrophy cause weakness in muscles needed for movement, which can cause fatigue and impair mobility. Many patients rely on wheelchairs or other mobility aids to get around. Contractures, when muscles permanently tighten up, are common in many types.
In some forms, cardiac muscles are affected, which can lead to heart problems. Breathing problems may also result due to weakness in muscles needed to inhale and exhale. Weakness in the trunk muscles can lead to abnormal curvature of the spine (called scoliosis), which also may contribute to breathing problems.
Some types affect the muscles around the eyes, which can cause vision problems. Neurological abnormalities and intellectual disability are common in some types of muscular dystrophy.
Diagnosis
In addition to reviewing a patient’s symptoms, medical history, and family history, tools are available to aid in the diagnosis of muscular dystrophies. Blood tests can be used to detect markers of muscle damage, and muscle biopsies may be taken to look for specific abnormalities in the tissue. Magnetic resonance imaging (MRI) and other imaging technologies may be helpful for identifying and monitoring muscle wasting.
Genetic testing — analyzing a person’s DNA to look for disease-causing mutation(s) — may be useful to confirm a diagnosis. Genetic tests may be recommended for an affected person’s family members, so they can know whether they might also carry a disease-causing mutation, even if they themselves don’t have symptoms. A genetic counselor may help interpret the results of genetic testing and recommend next steps and resources.
Treatment
Although muscular dystrophy cannot be cured, several treatments and nonpharmacological interventions can help slow progression of the disease and minimize its symptoms.
Physiotherapy (physical therapy) can help to improve muscle strength, and occupational therapy can be helpful for finding strategies to navigate life while living with muscular dystrophy. Speech therapy may benefit patients with difficulty talking.
For patients who are having problems breathing, ventilation may be helpful. Some patients may benefit from surgeries to address specific problems associated with muscular dystrophy, like correcting scoliosis or elongating shortened tendons.
Anti-inflammatory medications called corticosteroids can help preserve muscle strength, though since these medications cause weight gain and osteoporosis — weak and brittle bones — doctors usually don’t recommend their extended use.
In recent years, a class of medicines called exon-skipping therapies has become available for people with Duchenne muscular dystrophy caused by specific mutations in the DMD gene. These medications allow cellular protein-making machinery to “skip over” the mutated section of genetic code while “reading” the DMD gene, allowing for the production of a shortened but still functional dystrophin protein.
Last updated: Dec. 23, 2021, by Marisa Wexler MS
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