Muscular dystrophy refers to a group of genetic diseases that cause progressive muscle weakness and loss. There are more than 30 types of muscular dystrophy, all with different causes and symptoms. While the most common types appear during childhood, other forms affect adults only.
Duchenne muscular dystrophy
Duchenne muscular dystrophy (DMD) is the disorder’s most common form. It is more common in males than females, affecting about one in every 3,500 male births. DMD is caused by mutations in the DMD gene, which provides instructions for making a protein called dystrophin that’s important for maintaining muscle health.
Signs of DMD can occur in early childhood, around ages 3 to 5. Weakness and wasting are usually first evident in the muscles of the upper legs and pelvis, with other muscles affected as the disease progresses. Many Duchenne children will lose an ability to walk around age 12. Historically, most people with DMD have not survived beyond their teens. Available treatments can now slow the disease’s progression, and today it is not uncommon for patients to live into their 30s.
Becker muscular dystrophy
Like DMD, Becker muscular dystrophy (BMD) is caused by a mutation in the DMD gene, and it, too, predominantly affects males. However, symptoms of BMD are milder than DMD, with an older age at onset and slower symptom progression, because the dystrophin protein is not affected as severely. Walking difficulties often develop in the teen years, and some patients will require a wheelchair by their 20s, while others are able to walk unassisted well into the later life. It is common for people with BMD to live to be in their 40s or older.
Facioscapulohumeral muscular dystrophy
Facioscapulohumeral muscular dystrophy (FSHD) usually affects muscles in the face, shoulders, and upper arms; the lower legs and hips may also be affected. FSHD is typically caused by abnormalities in a section of DNA called the D4Z4 region.
Age at onset is highly variable but most commonly in the teens; the majority of patients experience symptoms by the time they are 20. About 20% of FSHD patients eventually will need a wheelchair, and life expectancy is not shortened.
Limb-girdle muscular dystrophy
Limb-girdle muscular dystrophy refers to a group of muscular dystrophies characterized mainly by weakness and wasting in the muscles around the shoulders and hips. The disease’s severity and specific features vary substantially across different subtypes. Many patients exhibit an unusual walking stride, like waddling or walking on the balls of their feet, and patients may require a wheelchair as the disease progresses.
Oculopharyngeal muscular dystrophy
Oculopharyngeal muscular dystrophy is a type of muscular dystrophy characterized by weakening in the muscles that control the eyes and the throat. Symptoms usually appear later in life, as people reach their 40s or 50s; the first symptoms usually are difficulty swallowing and drooping eyelids. As the disease progresses, patients may have weakening in muscles elsewhere in the body, which can impact mobility.
Tibial muscular dystrophy
Tibial muscular dystrophy is characterized by weakness and wasting of the muscles of the lower leg, usually with symptoms appearing after age 35. This type of muscular dystrophy is prevalent in Finland, and is caused by mutations in the TTN gene.
Myotonic dystrophy is the most common form of adult-onset muscular dystrophy; affected individuals usually first experience symptoms around age 20 or 30. Myotonic dystrophy is characterized by myotonia, when muscles are unable to properly relax after they contract. It is caused by mutations in the genes DMPK or CNBP.
Emery-Dreifuss muscular dystrophy
Emery-Dreifuss muscular dystrophy is a slowly progressing form of muscular dystrophy characterized by muscle weakness, heart problems, and contractures (permanent muscle tightening). This type of muscular dystrophy may be caused by mutations in the EMD, FHL1, or LMNA genes, and affects males almost exclusively.
Congenital muscular dystrophies
Congenital muscular dystrophies (CMDs) are a group of muscular dystrophies characterized by symptoms of muscle weakness and wasting that are evident at or very near to birth.
Bethlem myopathy is a rare form of CMD caused by mutations that result in defects to a structural protein called type VI collagen. The symptoms of this type of CMD may be apparent in the womb, with the fetus showing decreased movement. Infants usually show hypotonia (low muscle tone) and torticollis (twisting of the neck), and children often have delayed motor development. Older people with Bethlem myopathy usually will have mobility problems due to muscle weakness and joint stiffness, and some may experience breathing difficulties.
Ullrich congenital muscular dystrophy
Ullrich congenital muscular dystrophy is another form of CMD caused by defects in type VI collagen, but is usually more severe than Bethlem myopathy. Severe muscle weakness is typically apparent soon after birth. Many patients are never able to walk, and others start walking but lose the ability as teenagers. Patients also may have unusually mobile joints.
Fukuyama congenital muscular dystrophy
Fukuyama congenital muscular dystrophy (FCMD) is a type of CMD found almost exclusively in Japan. Children with FCMD have weak muscles from early infancy and substantially impaired motor development; most are never able to stand or walk. FCMD can affect brain development and cause seizures. Children with the disease may have eye abnormalities, which can impair vision, and progressive heart problems.
Muscle-eye-brain disease is a form of CMD that occurs primarily in Finland. Children are born with muscle weakness, brain abnormalities, and profound nearsightedness. As they grow, affected individuals display developmental delays and intellectual disability.
Rigid spine muscular dystrophy
Rigid spine muscular dystrophy is characterized by muscle weakness at birth or shortly thereafter, primarily affecting muscles of the torso and neck (axial muscles). Over time, abnormalities in these muscles cause the spine and neck to become stiff and rigid, which can limit a person’s ability to move their head. Breathing problems and scoliosis, an abnormal curvature of the spine, are common.
Walker-Warburg syndrome (WWS) is characterized by muscle weakness, brain abnormalities, and eye problems that are present very early in life. WWS is the most severe form of CMD; most patients die in early childhood.
Last updated: Dec. 22, 2021, by Marisa Wexler MS
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