The most common form of muscular dystrophy, Duchenne, was first described by the French physician Guillaume Benjamin Amand Duchenne in 1861. Most cases are caused by a recessive sex-linked gene located on the X chromosome and carried only by females. Each son of a carrier has a 50% chance of inheriting the gene and developing the disease. Each daughter has a 50% chance of inheriting the gene and becoming a carrier. In small number of "sporadic" cases there is no family history. The disease begins with leg weakness before age 3 and progresses rapidly, with death often occurring before age 30, often because of involvement of lung or heart muscle. Research has shown that the abnormal gene fails to produce an essential skeletal muscle protein called dystrophin. Becker's muscular dystrophy is similar to the Duchenne form, but appears somewhat later in life and progresses more slowly.
Fascioscapulohumeral muscular dystrophy primarily involves facial and shoulder muscles and affects both sexes. Symptoms can begin from adolescence to around age 40. It is caused by an autosomal dominant trait (at least one parent will have the disease). Progression is usually slow and severe disability is unusual.
Myotonic muscular dystrophy is another autosomally dominant disease affecting both sexes. It appears to be caused by the repetition of a section of DNA on chromosome 4. In a surprising development, researchers found that the number of repetitions on the chromosome increase and the disease becomes more severe with each generation. It is characterized by an inability of the muscles to relax properly after contraction and primarily affects the muscles of the hands and feet. It usually begins in adulthood and is often accompanied by cataracts, baldness, and abnormal endocrine function.
The limb-girdle form of the disease first affects the muscles of the hip and shoulder areas. Symptoms usually become apparent in late adolescence or early adulthood. Caused by an autosomal recessive trait (carried by a gene passed on by both asymptomatic parents), it can affect males and females alike. This form usually progresses slowly.
There is no known cure for muscular dystrophy. Corticosteriods may slow the destruction of muscle tissue in persons with Duchenne muscular dystrophy, and phenytoin, procainamide, or quinine is used to treat delayed muscle relaxation in myotonic muscular dystrophy. Supportive measures and exercises can improve the quality of life and preserve mobility for as long as possible. Scientists have begun to identify the genetic abnormalities responsible for multiple dystrophy and hope that further understanding will lead to treatment. Genetic screening is recommended for all family members who might be carriers. Prenatal tests such as chorionic villus sampling and amniocentesis can detect some forms of muscular dystrophy early in a pregnancy.
See A. E. H. Emery, Muscular Dystrophy: The Facts (1994).
In the 1850s, descriptions of boys who grew progressively weaker, lost the ability to walk, and died at an early age became more prominent in medical journals. In the following decade, French neurologist Guillaume Duchenne gave a comprehensive account of 13 boys with the most common and severe form of the disease (which now carries his name — Duchenne muscular dystrophy). It soon became evident that the disease had more than one form, and that these diseases affected people of either gender and of all ages.
In about two thirds of DMD cases, an affected male inherits the mutation from a mother who carries one altered copy of the DMD gene. The other one third of cases probably result from new mutations in the gene. Females who carry one copy of a DMD mutation may have some signs and symptoms related to the condition (such as muscle weakness and cramping), but these are typically milder than the signs and symptoms seen in affected males. Duchenne muscular dystrophy and Becker's muscular dystrophy are caused by mutations of the gene for the dystrophin protein and lead to an overabundance of the enzyme creatine kinase. The dystrophin gene is the largest gene in humans.
A physical examination and the patient's medical history will help the doctor determine the type of muscular dystrophy. Specific muscle groups are affected by different types of muscular dystrophy.
Often, there is a loss of muscle mass (wasting), which may be hard to see because some types of muscular dystrophy cause a build up of fat and connective tissue that makes the muscle appear larger. This is called pseudohypertrophy.
There is no specific treatment for any of the forms of muscular dystrophy. Physical therapy to prevent contractures (a condition when an individual with a muscular dystrophy grows and the muscles don't move with the bones and can easily be slowed down and/or make the individual's body straighter by daily physical therapy), orthoses (orthopedic appliances used for support) and corrective orthopedic surgery may be needed to improve the quality of life in some cases. The cardiac problems that occur with Emery-Dreifuss muscular dystrophy and myotonic muscular dystrophy may require a pacemaker. The myotonia (delayed relaxation of a muscle after a strong contraction) occurring in myotonic muscular dystrophy may be treated with medications such as quinine, phenytoin, or mexiletine but no actual long term treatment has been found.
Occupational therapy assists the individual with MD in engaging in his/her activities of daily living (self-feeding, self-care activities, etc) and leisure activities at the most independent level possible. This may be achieved with use of adapted equipment or the utilization of energy conservation techniques. Occupational therapy may also implement changes to a person's environment, both at home or work, to increase the individual's function and accessibility. Occupational therapists also address psychosocial changes and cognitive decline which may accompany MD as well as provide support and education about the disease to the family and individual.
On December 18, 2001 the MD CARE Act was signed into law and amends the Public Health Service Act to provide research for the various muscular dystrophies. This law also established the Muscular Dystrophy Coordinating Committee to help focus research efforts through a coherent research strategy.
Congenital muscular dystrophy includes several disorders with a range of symptoms. Muscle degeneration may be mild or severe. Problems may be restricted to skeletal muscle, or muscle degeneration may be pair with effects on the brain and other organ systems. A number of the forms of the congenital muscular dystrophies are caused by defects in proteins that are 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 (DMD) is the most common childhood form of muscular dystrophy. DMD usually becomes clinically evident when a child begins walking. Patients typically require a wheelchair by age 10 to 12 and die in their late teens or early 20s. In the early 1990s, researchers identified the gene for the protein dystrophin which, when absent, causes DMD. The dystrophin gene is the largest known gene in humans. Since the gene is on the X-chromosome, this disorder affects primarily males. Females who are carriers have milder symptoms. Sporadic mutations in this gene occur frequently, accounting for a third of cases. The remaining two-thirds of cases are inherited in a recessive pattern.
Dystrophin is part of a complex structure involving several other protein components. The "dystrophin-glycoprotein complex" helps anchor the structural skeleton within the muscle cells, through the outer membrane of each cell, to the tissue framework that surrounds each cell. Due to defects in this assembly, contraction of the muscle leads to disruption of the outer membrane of the muscle cells and eventual weakening and wasting of the muscle.
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 [[LGMD] (Limb Girdle Muscular Dystrophy)].