A group of genetic diseases characterized by skeletal muscle weakness, muscle cell death and replacement of muscle cells by fibrosis in fat (Emery AE).
Muscular dystrophies (MD) are a genetically and clinically heterogeneous group of rare neuromuscular diseases that cause progressive weakness and breakdown of skeletal muscles over time.
Muscular dystrophies differ as to which muscles are primarily affected, the degree of weakness, how fast they worsen, and when symptoms begin.
Some types of muscular dystrophies are associated with problems in other organs.
Muscle degeneration may be mild or severe.
Problems may be restricted to skeletal muscle, or muscle degeneration may be paired with effects on the brain and other organ systems.
There are or than 30 different disorders are classified as muscular dystrophies.
Duchenne muscular dystrophy (DMD) accounts for approximately 50% of cases and affects males beginning around the age of four.
Other relatively common muscular dystrophies include Becker muscular dystrophy, facioscapulohumeral muscular dystrophy, and myotonic dystrophy.
Limb–girdle muscular dystrophy and congenital muscular dystrophy are ultrarare genetic disorders.
Muscular dystrophies are caused by mutations in genes, usually those involved in making muscle proteins.
These mutations are either inherited from parents or may occur spontaneously during early development.
Muscular dystrophies may be X-linked recessive, autosomal recessive, or autosomal dominant.
Dystroglycan, a transmembrane protein which is ultimately cleaved into a an alpha and beta component, is the link between the cytoskeleton and the extra cellular matrix that bear laminin globular domains, such as laminin, agrin, and neurexin (Barresi R et al).
Dystroglycan, a major extracellular matrix receptor in muscle and the CNS and requires extensive O-glycosylation to function.
The mucin the domain of aplha-dystroglycn is modified with the numerous O-linked oligosaccharides essential for normal functioning as an extra cellular matrix receptor in skeletal muscle and brain ( Mitchele DE et al).
Diagnosis often involves blood tests and genetic testing.
There is no cure for any disorder from the muscular dystrophy group.
Gene therapy and antisense drugs are being developed.
Other medications used include corticosteroids, calcium channel blockers to slow skeletal and cardiac muscle degeneration, anticonvulsants to control seizures and some muscle activity, and immunosuppressants to delay damage to dying muscle cells.
Physical therapy, braces, and corrective surgery may help with some symptoms while assisted ventilation may be required in those with weakness of breathing muscles.
Many affected people will eventually become unable to walk.
Duchenne muscular dystrophy in particular is associated with shortened life expectancy.
The signs and symptoms of muscular dystrophy are:
Progressive muscular wasting
Poor balance
Scoliosis
Progressive inability to walk
Waddling gait
Calf deformation
Limited range of movement
Respiratory difficulty
Cardiomyopathy
Muscle spasms
Gowers’ sign
The majority of muscular dystrophies are inherited.
Muscular dystrophies follow various inheritance patterns: X-linked, autosomal recessive or autosomal dominant.
In a small percentage of patients, the disorder may have been caused by a de novo spontaneous mutation.
Diagnosis
MD diagnosis based on the results of muscle biopsy, increased creatine phosphokinase (CpK3), electromyography, and genetic testing.
Specific muscle groups are affected by different types of muscular dystrophy, and help with diagnosis.
Congenital muscular dystrophy-
At birth generalized weakness.
Symptoms include general muscle weakness and possible joint deformities.
Disease progresses slowly, and lifespan is shortened.
Congenital muscular dystrophy includes several disorders with a range of symptoms.
There are several types of muscular dystrophy, each affecting different muscles and having varying degrees of severity.
Some of the most common types include:
1. Duchenne muscular dystrophy (DMD) – DMD is the most common type of muscular dystrophy and primarily affects boys. It usually starts to show symptoms in early childhood and progressively worsens over time.
2. Becker muscular dystrophy – Becker muscular dystrophy is similar to DMD but progresses more slowly and is less severe.
3. Limb-girdle muscular dystrophy – Limb-girdle muscular dystrophy is a group of diseases that affect the muscles in the hips and shoulders.
It can onset in childhood or adulthood, and the severity and rate of progression can vary.
4. Facioscapulohumeral muscular dystrophy (FSHD) – FSHD affects the muscles in the face, shoulders, and upper arms.
It usually starts to show symptoms in teenage years or early adulthood.
5. Myotonic dystrophy – Myotonic dystrophy affects the muscles in the face, neck, hands, and feet.
It can onset in childhood or adulthood, and symptoms can include muscle weakness, stiffness, and myotonia., or difficulty relaxing muscles after contraction
There are several other types of muscular dystrophy, each with its own unique set of symptoms, rate of progression, and prognosis.
Several types of the congenital muscular dystrophies are caused by defects in proteins thought to have some relationship to the dystrophin-glycoprotein complex and to the connections between muscle cells and their surrounding cellular structure.
Some forms of congenital muscular dystrophy show severe brain malformations, such as lissencephaly and hydrocephalus.
Duchenne muscular dystrophy is characterized by distal limb weakness that progresses to generalised weakness, involving respiratory muscles.
The most common childhood form of muscular dystrophy, affects predominantly boys.
Mild symptoms may occur in female carriers.
Clinical symptoms become evident when the child begins walking.
By age 10, the child may need braces and by age 12, most patients are unable to walk.
Typical lifespans range from 15 to 45.
Sporadic mutations in this gene occur frequently.
Distal muscular dystrophy
Affects individuals 20–60 years.
Distal muscles in hands, forearms and lower legs are affected.
Progress is slow and not life-threatening.
Miyoshi myopathy, one of the distal muscular dystrophies, causes initial weakness in the calf muscles, and is caused by defects in the same gene responsible for one form of limb–girdle muscular dystrophy.
Emery–Dreifuss muscular dystrophy
Childhood, early teenage years.
Distal limb muscles, limb-girdle, heart involvement
Symptoms include muscle weakness and wasting, starting in the distal limb muscles and progressing to involve the limb–girdle muscles.
Most patients also have cardiac conduction defects and arrhythmias.
Emery-Dreifuss muscular dystrophy (EDMD) is a rare genetic disorder that primarily affects the skeletal muscles and heart.
Common symptoms include joint contractures, weakness in the upper arms and lower legs, and heart problems such as arrhythmias.
Emery-Dreifuss muscular dystrophy is caused by mutations in several different genes that encode proteins that are important for maintaining the structure and function of the skeletal muscles and heart.
Facioscapulohumeral muscular dystrophy
Adolescence
Face, shoulders, upper arms, progressing to other muscles.
Causes progressive weakness, initially in the muscles of the face, shoulders, and upper arms.
Affected individuals can become severely disabled, with 20% requiring a wheelchair by age 50.
30% of cases involve spontaneous mutations.
Penetrance and severity lower in females compared to males.
Limb–girdle muscular dystrophy
Involves upper arms and legs.
The person normally leads a normal life with some assistance.
Rare cardiopulmonary complications can be life-threatening.
Limb-girdle muscular dystrophy (LGMD) is a group of inherited genetic disorders that affect the muscles of the hip and shoulder girdles.
LGMD typically causes progressive muscle weakness and wasting, and the age of onset can vary.
Symptoms may appear in childhood or adulthood depending on the specific type of LGMD.
LGMD is believed to be caused by mutations in genes responsible for producing proteins necessary for healthy muscle function.
There are over 30 genetic subtypes of LGMD that have been identified, each caused by different mutations of different genes.
Symptoms of LGMD may include difficulty walking, running, or climbing stairs, progressive weakness and loss of muscle mass in the limbs, and difficulty raising the arms above the head.
There is currently no cure for LGMD, but treatments can help manage symptoms, including physical therapy, braces or orthotics, and medication to help manage symptoms.
Myotonic muscular dystrophy
Adulthood
Skeletal muscles, heart, other muscle groups
Present with myotonia or delayed relaxation of muscles, as well as muscle wasting and weakness.
Varies in severity and manifestations and affects many body systems in addition to skeletal muscles, including the heart, endocrine organs, and eyes.
Oculopharyngeal muscular dystrophy
40–50 years
Eye muscles, face, throat, pelvis, shoulders
Management:
No cure for muscular dystrophy presently exists.
Physical therapy, occupational therapy, orthotic intervention, speech therapy, and respiratory therapy may be helpful.
Low intensity corticosteroids may help to maintain muscle tone.
Orthoses and corrective orthopedic surgery may be needed in some cases.
The cardiac problems that occur with Emery–Dreifuss muscular dystrophy (EDMD) and myotonic muscular dystrophy may require a pacemaker.
The myotonia, which is the delayed relaxation of a muscle after a strong contraction, occurring in myotonic muscular dystrophy may be treated with medications such as quinine.
Occupational therapy may implemented to increase the individual’s function and accessibility; furthermore, it addresses psychosocial changes and cognitive decline which may accompany MD, and provides support and education about the disease to the family and individual.
Prognosis depends on the individual form of muscular dystrophy.
Some dystrophies cause progressive weakness and loss of muscle function, which may result in severe physical disability and a life-threatening deterioration of respiratory muscles or heart.
Other dystrophies do not affect life expectancy and only cause relatively mild impairment.