Muscular dystrophy
| Muscular dystrophy | |
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| Specialty | Neurology, pediatrics, medical genetics  |
Muscular dystrophy (abbreviated MD) refers to a group of hereditary muscle diseases that weaken the muscles that move the human body.[1][2] Muscular dystrophies are characterized by progressive skeletal muscle weakness, defects in muscle proteins, and the death of muscle cells and tissue.[3] Nine diseases including Duchenne, Becker, limb girdle, congenital, facioscapulohumeral, myotonic, oculopharyngeal, distal, and Emery-Dreifuss are always classified as muscular dystrophy[4] but there are more than 100 diseases in total with similarities to muscular dystrophy. Most types of MD are multi-system disorders with manifestations in body systems including the heart, gastrointestinal and nervous systems, endocrine glands, skin, eyes and other organs.[4]
In the 1860s, 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 males of all ages.[citation needed]
Genetic cause
These conditions are inherited, and the different muscular dystrophies follow various inheritance patterns. The best-known type, Duchenne muscular dystrophy (DMD), is inherited in an X-linked recessive pattern, meaning that the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes, and is thus considered sex-linked. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a mutation must generally be present in both copies of the gene to cause the disorder (relatively rare exceptions, manifesting carriers, do occur due to dosage compensation/X-inactivation). Males are therefore affected by X-linked recessive disorders more often than females. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.
Symptoms
Main symptoms include:
- Progressive muscular wasting (weakness)
- Poor balance
- Frequent falls
- Walking difficulty
- Waddling gait
- Calf pain
- Limited range of movement
- Respiratory difficulty
- Drooping eyelids (ptosis)
- Gonadal atrophy
- Scoliosis (curvature of the spine)
- Inability to walk
Few or none of these symptoms may be present before diagnosis. Some types of muscular dystrophy can affect the heart, causing cardiomyopathy or arrhythmias.
Diagnosis
The diagnosis of muscular dystrophy is based on the results of a muscle biopsy. In some cases, a DNA blood test may be all that is needed.
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.
Prognosis
The prognosis for people with muscular dystrophy varies according to the type and progression of the disorder. Some cases may be mild and progress very slowly over a normal lifespan, while others produce severe muscle weakness, functional disability, and loss of the ability to walk. Some children with muscular dystrophy die in infancy while others live into adulthood with only moderate disability. The muscles affected vary, but can be around the pelvis, shoulder, face or elsewhere. Muscular dystrophy can affect adults, but the more severe forms tend to occur in early childhood.
Treatment
There is no known cure for muscular dystrophy. Inactivity (such as bed-rest and even sitting for long periods) can worsen the disease. Physical therapy, occupational therapy, orthotic intervention, speech therapy and orthopedic instruments (e.g., wheelchairs, standing frames) may be helpful.
There is no specific treatment for any of the forms of muscular dystrophy. Physical therapy to prevent contractures and maintain muscle tone, 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 adaptive equipment or the utilization of energy conservation techniques. Occupational therapy may 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.[5]69
Sam Kimmel
A grid computing-based research project called "Help Cure Muscular Dystrophy" was launched on December 19, 2006 by Décrypthon. The Jain Foundation is involved in research into Miyoshi myopathy, a form of distal muscular dystrophy and LGMD2B, a limb-girdle muscular dystrophy.[6]
MY0-029
MYO-029 is an experimental myostatin inhibiting drug developed by Wyeth Pharmaceuticals for the treatment of muscular dystrophy. Myostatin is a protein that inhibits the growth of muscle tissue, MYO-029 is a recombinant human antibody designed to bind and inhibit the activity of myostatin. A 2005/2006 trial was completed by Wyeth in Collegeville, PA. As of April 2007, the results of the study have not been made public. On 11 March 2008 it was announced that Wyeth would not develop the drug further for MD, but would continue to explore myostatin inhibition along with other strategies.[7]
National research and support in the USA
Within the United States, the three primary federally funded organizations that focus on Muscular Dystrophy include the National Institute of Neurological Disorders and Stroke (NINDS), National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), and National Institute of Child Health and Human Development (NICHD).[4]
In 1966, the Muscular Dystrophy Association began its annual Jerry Lewis MDA Telethon, which has arguably done more to raise awareness of muscular dystrophy than any other event or initiative.
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.[8][9]
Types
Becker's muscular dystrophy
Becker muscular dystrophy (BMD) is a less severe variant of Duchenne muscular dystrophy and is caused by the production of a truncated, but partially functional form of dystrophin.[4] Survival is usually into old age.[10]
Congenital muscular dystrophy
Age at onset: birth; symptoms include general muscle weakness and possible joint deformities; disease progresses slowly; shortened life span.[citation needed]
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 paired 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.[4]
Duchenne muscular dystrophy
Duchenne muscular dystrophy (DMD) is the most common childhood form of muscular dystrophy, becoming clinically evident when a child begins walking. Patients typically require a wheelchair by age 10 to 12 and die in their late teens to early 30s, though some people with Duchenne muscular dystrophy are now living to age 40 and beyond.[11] In the early 1990s, researchers identified the gene for the protein dystrophin which, when absent, causes DMD. Since the gene is on the X-chromosome, this disorder affects primarily males and 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.[4]
Distal muscular dystrophy
Distal muscular dystrophies' age at onset: 20 to 60 years; symptoms include weakness and wasting of muscles of the hands, forearms, and lower legs; progress is slow and not life-threatening.[10]
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).[4]
Emery-Dreifuss muscular dystrophy
Age at onset, childhood to early teens. Symptoms include upper arm, and shin muscles; joint deformities are common; progress is slow; sudden death may occur from cardiac problems.[12]
Facioscapulohumeral muscular dystrophy
Facioscapulohumeral muscular dystrophy (FSHD) initially affects muscles of the face, shoulders, and upper arms with progressive weakness. Symptoms usually develop in the teenage years. Some affected individuals become severely disabled. The pattern of inheritance is autosomal dominant, but the underlying genetic defect is poorly understood. Most cases are associated with a deletion near the end of chromosome 4.[4]
Limb-girdle muscular dystrophy
Limb-girdle muscular dystrophy is also called LGMD. LGMDs all show a similar distribution of muscle weakness, affecting both upper arms and legs. Many forms of LGMD have been identified, showing different patterns of inheritance (autosomal recessive vs. autosomal dominant). In an autosomal recessive pattern of inheritance, an individual receives two copies of the defective gene, one from each parent. The recessive LGMDs are more frequent than the dominant forms, and usually have childhood or teenage onset. The dominant LGMDs usually show adult onset. Some of the recessive forms have been associated with defects in proteins that make up the dystrophin-glycoprotein complex.[4] Death from LGMD is usually due to cardiopulmonary complications.[citation needed]
Myotonic muscular dystrophy
Myotonic MD's age at onset: 20 to 40 years [citation needed] Myotonic muscular dystrophy is the most common adult form of muscular dystrophy. It is marked by myotonia as well as muscle wasting and weakness. Myotonic dystrophy varies in severity and manifestations and affects many body systems in addition to skeletal muscles, including the heart, endocrine organs, eyes, and gastrointestinal tract. Myotonic dystrophy follows an autosomal dominant pattern of inheritance. Myotonic dystrophy results from the expansion of a short repeat in the DNA sequence (CTG in one gene or CCTG in another gene). In other words, the gene defect is an abnormally long repetition of a three- or four-letter "word" in the genome. While the exact mechanism of action is not known, this molecular change may interfere with the production of important muscle proteins.[4]
Oculopharyngeal muscular dystrophy
Oculopharyngeal MD's age at onset: 40 to 70 years; symptoms affect muscles of eyelids, face, and throat followed by pelvic and shoulder muscle weakness, has been attributed to a short repeat expansion in the genome which regulates the translation of some genes into functional proteins.[4]
Additional Forms of Muscular Dystrophy
Spinal Muscular Atrophy
Spinal Muscular Atrophy (SMA) is a neuromuscular disease characterized by degeneration of motor neurons, resulting in progressive muscular atrophy (wasting away) and weakness. The clinical spectrum of SMA ranges from early infant death to normal adult life with only mild weakness. These patients often require comprehensive medical care involving multiple disciplines, including pediatric pulmonology, pediatric neurology, pediatric orthopaedic surgery, pediatric critical care, and physical medicine and rehabilitation; and physical therapy, occupational therapy, respiratory therapy, and clinical nutrition. Genetic counseling is also helpful for the parents and family members.
The term "juvenile spinal muscular atrophy" refers to Kugelberg-Welander syndrome.
Brown-Vialetto-Van Laere syndrome (BVVL)
The Brown-Vialetto-Van Laere syndrome (BVVL), sometimes better known as Brown's Syndrome, is an exceptionally rare neurological disorder of unknown cause, characterized primarily by deafness and paralysis of the muscles of the face, neck, shoulders and limbs. The neurological manifestations develop insidiously: they usually begin with sensorineural deafness, progress inexorably to paralysis, and often culminate in respiratory failure. The syndrome affects children, adolescents, and younger adults; the age at onset of symptoms in the reported cases has ranged from infancy to the third decade of life. The prognosis is poor — most patients diagnosed with the syndrome die within 10 years. There is no cure.
To date, there is no test of confirmation for BVVL, although researchers are currently searching to isolate the responsible gene and are enlisting BVVL and Fazio-Londe patients and their families to contribute DNA to the BVVL BioBank (http://www.bvvl.org). It has been proposed that Fazio-Londe disease and Brown-Vialetto-Van-Laere syndrome are a phenotypically associated condition.
The syndrome was first described by Charles Brown in 1894; further accounts by Vialetto and Van Laere followed in 1936 and 1966, respectively. There are fewer than 60 cases reported in the medical literature over the 100 odd years since its first description.
Official web site: http://www.bvvlinternational.org
Fazio-Londe (FL) syndrome
It produces rapidly progressive weakness of tongue, face and pharyngeal muscles in a clinical pattern similar to myasthenia bulbar palsy. Neuromuscular transmission may be abnormal in these muscles because of rapid denervation and immature reinervation, and strength may improve with administration of cholinesterase inhibitors. Paralysis occurs secondary to degeneration of the motor neurons of the brain stem. It causes progressive bulbar paralysis due to involvement of motor neurons of the cranial nerve nuclei. The most frequent symptoms at onset of progressive bulbar paralysis of childhood has been a unilateral facial paralysis. It is followed in frequency by dysarthria due to facial weakness or by dysphagia. Palatal weakness and palpebral ptosis also have been reported in few patients. Both sexes can be affected.
It has been proposed that Fazio-Londe disease and Brown-Vialetto-Van-Laere syndrome are a phenotypically associated condition.[3]
See also
- Muscular Dystrophy Association (USA)
- Muscular Dystrophy Campaign (UK)
- Facioscapulohumeral muscular dystrophy
- Muscle hypertrophy
- Myostatin
References
- ^ Harrison's Principle's of Internal Medicine. 2005. p. 2527. doi:10.1036/0071402357.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Muscular Dystrophy Campaign Retrieved 9 April 2007.
- ^ Emery AE (2002). "The muscular dystrophies". Lancet. 359 (9307): 687–695. doi:10.1016/S0140-6736(02)07815-7. PMID 11879882.
- ^ a b c d e f g h i j k May 2006 report to Congress on Implementation of the MD CARE Act, as submitted by Department of Health and Human Service's National Institutes of Health
- ^ R.M. Lehman & G.L. McCormack, 2001. Neurogenic and Myopathic Dysfunction pp. 802-803. In L. Pedretti and M Early Occupational Therapy Skills for Physical Dysfunction 5th ED St Louis MO: Mosby
- ^ Jain Foundation Inc: Research into Miyoshi/LGMD2B
- ^ Wyeth Won't Develop MYO-029 for MD
- ^ H.R. 717--107th Congress (2001): MD-CARE Act, GovTrack.us (database of federal legislation), (accessed Jul 29, 2007)
- ^ Public Law 107-84, PDF as retrieved from NIH website
- ^ a b [1]: MD USA Website (accessed 03SEP2007)
- ^ Muscular Dystrophy Association
- ^ Emedicine re EDMD Retrieved 30 July 2007.
External links
- Muscular Dystrophy Association
- Template:DMOZ
- dbmd at NIH/UW GeneTests
- MedlinePlus Encyclopedia: 001190
- Muscular dystrophy, Duchenne and Becker types at NLM Genetics Home Reference
- National Institute of Neurological Disoders and Stroke
- physorg.com | Genetic source of muscular dystrophy neutralized
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