Muscular dystrophy

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Muscular dystrophy
MuscularDystrophy.png
In affected muscle (right), the tissue has become disorganized and the concentration of dystrophin (green) is greatly reduced, compared to normal muscle (left).
Specialty Neuromuscular medicine
Symptoms Increasing weakening, breakdown of skeletal muscles, trouble walking [1] [2]
DurationChronic [1]
Types> 30, including Duchenne muscular dystrophy, Becker muscular dystrophy, facioscapulohumeral muscular dystrophy, limb–girdle muscular dystrophy, myotonic dystrophy [1] [2]
Causes Genetic (X-linked recessive, autosomal recessive, or autosomal dominant) [2]
Diagnostic method Genetic testing [2]
Treatment Pharmacotherapy, physical therapy, braces, corrective surgery, assisted ventilation [1] [2]
Prognosis Depends on the particular disorder [1]

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. [1] The disorders differ as to which muscles are primarily affected, the degree of weakness, how fast they worsen, and when symptoms begin. [1] Some types are also associated with problems in other organs. [2]

Contents

Over 30 different disorders are classified as muscular dystrophies. [1] [2] Of those, Duchenne muscular dystrophy (DMD) accounts for approximately 50% of cases and affects males beginning around the age of four. [1] Other relatively common muscular dystrophies include Becker muscular dystrophy, facioscapulohumeral muscular dystrophy, and myotonic dystrophy, [1] whereas limb–girdle muscular dystrophy and congenital muscular dystrophy are themselves groups of several – usually ultrarare – genetic disorders.

Muscular dystrophies are caused by mutations in genes, usually those involved in making muscle proteins. [2] These mutations are either inherited from parents or may occur spontaneously during early development. [2] Muscular dystrophies may be X-linked recessive, autosomal recessive, or autosomal dominant. [2] Diagnosis often involves blood tests and genetic testing. [2]

There is no cure for any disorder from the muscular dystrophy group. [1] Several drugs designed to address the root cause are under development, including gene therapy (Microdystrophin), and antisense drugs (Ataluren, Eteplirsen etc.). [2] Other medications used include corticosteroids (Deflazacort), calcium channel blockers (Diltiazem) to slow skeletal and cardiac muscle degeneration, anticonvulsants to control seizures and some muscle activity, and immunosuppressants (Vamorolone) to delay damage to dying muscle cells. [1] Physical therapy, braces, and corrective surgery may help with some symptoms [1] while assisted ventilation may be required in those with weakness of breathing muscles. [2]

Outcomes depend on the specific type of disorder. [1] Many affected people will eventually become unable to walk [2] and Duchenne muscular dystrophy in particular is associated with shortened life expectancy.

Muscular dystrophy was first described in the 1830s by Charles Bell. [2] The word "dystrophy" comes from the Greek dys, meaning "no, un-" and troph- meaning "nourish". [2]

Signs and symptoms

The signs and symptoms consistent with muscular dystrophy are: [3]

Causes

The majority of muscular dystrophies are inherited; the different 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. [4] [5]

Diagnosis

The diagnosis of muscular dystrophy is based on the results of muscle biopsy, increased creatine phosphokinase (CpK3), electromyography, and genetic testing. 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. [6]

Classification

Disorder name OMIM GeneInheritance patternAge of onsetMuscles affectedDescription
Becker muscular dystrophy 300376 DMD XR ChildhoodDistal limbs progressing to generalised weaknessA less severe variant of Duchenne muscular dystrophy, [7] affects predominantly boys.
Congenital muscular dystrophy MultipleMultiple AD, AR At birthGeneralised weaknessSymptoms 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. 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. [8]

Several forms 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. [7]

Duchenne muscular dystrophy 310200 DMD XR ChildhoodDistal limbs progressing to generalised weakness, involving respiratory musclesThe most common childhood form of muscular dystrophy, affects predominantly boys (mild symptoms may occur in female carriers). Characterised by progressive muscle wasting. 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. [9] Typical lifespans range from 15 to 45. [9] Sporadic mutations in this gene occur frequently. [10]
Distal muscular dystrophy 254130 DYSF AD, AR 20–60 yearsDistal muscles in hands, forearms and lower legsProgress is slow and not life-threatening. [11]

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. [7]

Emery–Dreifuss muscular dystrophy MultipleMultiple XR, AD, AR Childhood, early teenage yearsDistal limb muscles, limb-girdle, heartSymptoms 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. [12] [13]
Facioscapulohumeral muscular dystrophy 158900 DUX4 AD AdolescenceFace, shoulders, upper arms, progressing to other musclesCauses progressive weakness, initially in the muscles of the face, shoulders, and upper arms. Additional muscles are often affected. [14] Affected individuals can become severely disabled, with 20% requiring a wheelchair by age 50. [15] 30% of cases involve spontaneous mutations. [15] Penetrance and severity seem to be lower in females compared to males. [15] [16]
Limb–girdle muscular dystrophy MultipleMultiple AD, AR AnyUpper arms and legsThe person normally leads a normal life with some assistance. Rare cardiopulmonary complications can be life-threatening. [17]
Myotonic muscular dystrophy 160900
602668
DMPK
CNBP
AD AdulthoodSkeletal muscles, heart, other muscle groupsPresents with myotonia (delayed relaxation of muscles), as well as muscle wasting and weakness. [18] Varies in severity and manifestations and affects many body systems in addition to skeletal muscles, including the heart, endocrine organs, and eyes. [19]
Oculopharyngeal muscular dystrophy 164300 PABPN1 AD, rarely AR 40–50 yearsEye muscles, face, throat, pelvis, shoulders

Management

Ankle foot orthosis Ankle Foot Orthosis leg brace worn on the left foot with ankle hinge.jpg
Ankle foot orthosis

Currently, there is no cure for muscular dystrophy. In terms of management, physical therapy, occupational therapy, orthotic intervention (e.g., ankle-foot orthosis), [20] [21] speech therapy, and respiratory therapy may be helpful. [20] Low intensity corticosteroids such as prednisone, and deflazacort may help to maintain muscle tone. [22] Orthoses (orthopedic appliances used for support) and corrective orthopedic surgery may be needed to improve the quality of life in some cases. [2] The cardiac problems that occur with Emery–Dreifuss muscular dystrophy (EDMD) and myotonic muscular dystrophy may require a pacemaker. [23] The myotonia (delayed relaxation of a muscle after a strong contraction) occurring in myotonic muscular dystrophy may be treated with medications such as quinine. [24]

Occupational therapy assists the individual with MD to engage in activities of daily living (such as self-feeding and self-care activities) and leisure activities at the most independent level possible. This may be achieved with use of adaptive equipment or the use 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; 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. [25]

Prognosis

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. [2]

History

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, [26] French neurologist Guillaume Duchenne gave a comprehensive account of the most common and severe form of the disease, which now carries his name – Duchenne MD. [27]

Society and culture

In 1966 in the US and Canada, Jerry Lewis and the Muscular Dystrophy Association (MDA) began the annual Labor Day telecast The Jerry Lewis Telethon , significant in raising awareness of muscular dystrophy in North America. Disability rights advocates, however, have criticized the telethon for portraying those living with the disease as deserving pity rather than respect. [28]

On December 18, 2001, the MD CARE Act was signed into law in the US; it 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. [29] [30]

See also

Related Research Articles

Limb–girdle muscular dystrophy Medical condition

Limb–girdle muscular dystrophy (LGMD) is a genetically heterogeneous group of rare muscular dystrophies that share a set of clinical characteristics. It is characterised by progressive muscle wasting which affects predominantly hip and shoulder muscles. LGMD usually has an autosomal pattern of inheritance. It currently has no known cure or treatment.

The Muscular Dystrophy Association (MDA) is an American 501(c)(3) umbrella organization that works to support people with neuromuscular diseases. Founded in 1950 by Paul Cohen, who lived with muscular dystrophy, it works to combat neuromuscular disorders by funding research, providing medical and community services and educating health professionals and the general public and contributed more than $1 billion toward researching therapies and cures, helping to fund the identification of the dystrophin gene responsible for Duchenne muscular dystrophy as well as prospective treatments.

<span class="mw-page-title-main">Duchenne muscular dystrophy</span> Type of muscular dystrophy

Duchenne muscular dystrophy (DMD) is a severe type of muscular dystrophy that primarily affects boys. Muscle weakness usually begins around the age of four, and worsens quickly. Muscle loss typically occurs first in the thighs and pelvis followed by the arms. This can result in trouble standing up. Most are unable to walk by the age of 12. Affected muscles may look larger due to increased fat content. Scoliosis is also common. Some may have intellectual disability. Females with a single copy of the defective gene may show mild symptoms.

Hypotonia is a state of low muscle tone, often involving reduced muscle strength. Hypotonia is not a specific medical disorder, but a potential manifestation of many different diseases and disorders that affect motor nerve control by the brain or muscle strength. Hypotonia is a lack of resistance to passive movement, whereas muscle weakness results in impaired active movement. Central hypotonia originates from the central nervous system, while peripheral hypotonia is related to problems within the spinal cord, peripheral nerves and/or skeletal muscles. Severe hypotonia in infancy is commonly known as floppy baby syndrome. Recognizing hypotonia, even in early infancy, is usually relatively straightforward, but diagnosing the underlying cause can be difficult and often unsuccessful. The long-term effects of hypotonia on a child's development and later life depend primarily on the severity of the muscle weakness and the nature of the cause. Some disorders have a specific treatment but the principal treatment for most hypotonia of idiopathic or neurologic cause is physical therapy and/or occupational therapy for remediation.

<span class="mw-page-title-main">Becker muscular dystrophy</span> Genetic muscle disorder

Becker muscular dystrophy is an X-linked recessive inherited disorder characterized by slowly progressing muscle weakness of the legs and pelvis. It is a type of dystrophinopathy. This is caused by mutations in the dystrophin gene, which encodes the protein dystrophin. Becker muscular dystrophy is related to Duchenne muscular dystrophy in that both result from a mutation in the dystrophin gene, but has a milder course.

Oculopharyngeal muscular dystrophy Medical condition

Oculopharyngeal muscular dystrophy (OPMD) is a rare form of muscular dystrophy with symptoms generally starting when an individual is 40 to 50 years old. It can be autosomal dominant neuromuscular disease or autosomal recessive. The most common inheritance of OPMD is autosomal dominant, which means only one copy of the mutated gene needs to be present in each cell. Children of an affected parent have a 50% chance of inheriting the mutant gene.

<span class="mw-page-title-main">Fukuyama congenital muscular dystrophy</span> Medical condition

Fukuyama congenital muscular dystrophy (FCMD) is a rare, autosomal recessive form of muscular dystrophy mainly described in Japan but also identified in Turkish and Ashkenazi Jewish patients; fifteen cases were first described on 1960 by Dr. Yukio Fukuyama.

Neuromuscular disease Medical condition

A neuromuscular disease is any disease affecting the peripheral nervous system (PNS), the neuromuscular junction, or skeletal muscle, all of which are components of the motor unit. Damage to any of these structures can cause muscle atrophy and weakness. Issues with sensation can also occur.

<span class="mw-page-title-main">Congenital muscular dystrophy</span> Medical condition

Congenital muscular dystrophies are autosomal recessively-inherited muscle diseases. They are a group of heterogeneous disorders characterized by muscle weakness which is present at birth and the different changes on muscle biopsy that ranges from myopathic to overtly dystrophic due to the age at which the biopsy takes place.

<span class="mw-page-title-main">Emery–Dreifuss muscular dystrophy</span> Medical condition

Emery–Dreifuss muscular dystrophy (EDMD) is a type of muscular dystrophy, a group of heritable diseases that cause progressive impairment of muscles. EDMD affects muscles used for movement, causing atrophy, weakness and contractures. It almost always affects the heart, causing abnormal rhythms, heart failure, or sudden cardiac death. It is rare, affecting 0.39 per 100,000 people. It is named after Alan Eglin H. Emery and Fritz E. Dreifuss.

The dystrophin-associated protein complex, also known as the dystrophin-associated glycoprotein complex is a multiprotein complex that includes dystrophin and the dystrophin-associated proteins. It is one of the two protein complexes that make up the costamere in striated muscle cells. The other complex is the integrin-vinculin-talin complex.

Myotonic dystrophy Genetic disorder that impairs muscle function

Myotonic dystrophy (DM) is a type of muscular dystrophy, a group of genetic disorders that cause progressive muscle loss and weakness. In DM, muscles are often unable to relax after contraction. Other manifestations may include cataracts, intellectual disability and heart conduction problems. In men, there may be early balding and an inability to have children. While myotonic dystrophy can occur at any age, onset is typically in the 20s and 30s.

Stamulumab (MYO-029) is an experimental myostatin inhibiting drug developed by Wyeth Pharmaceuticals for the treatment of muscular dystrophy (MD). Stamulumab was formulated and tested by Wyeth in Collegeville, Pennsylvania. Myostatin is a protein that inhibits the growth of muscle tissue, stamulumab is a recombinant human antibody designed to bind to and inhibit the activity of myostatin.

The Muscular Dystrophy Community Assistance Research and Education Amendments of 2001 amended the Public Health Service Act to provide for research with respect to various forms of muscular dystrophy, including Duchenne, Becker, limb girdle, congenital, facioscapulohumeral, myotonic, oculopharyngeal, distal, and Emery–Dreifuss muscular dystrophies.

Ullrich congenital muscular dystrophy Medical condition

Ullrich congenital muscular dystrophy is a form of congenital muscular dystrophy. It is associated with variants of type VI collagen, it is commonly associated with muscle weakness and respiratory problems, though cardiac issues are not associated with this type of CMD. It is named after Otto Ullrich, who is also known for the Ullrich-Turner syndrome.

Paul D. Wellstone Muscular Dystrophy Community Assistance, Research and Education Amendments of 2013 US law

The Paul D. Wellstone Muscular Dystrophy Community Assistance, Research and Education Amendments of 2013 is a United States public law that amends the Public Health Service Act to revise the muscular dystrophy research program of the National Institutes of Health (NIH).

Sunil Pradhan is an Indian neurologist, medical researcher and writer, known for the invention of two electrophysiological techniques. He has also described five medical signs, of which one related to Duchenne muscular dystrophy is known as Pradhan Sign, and the others associated with facioscapulohumeral muscular dystrophy (FSHD) and similar neuro diseases. The Government of India awarded him the Padma Shri, the fourth highest civilian award, in 2014 for his contributions to the field of neuroscience.

Toshifumi (Toshi) Yokota is a medical scientist and professor of medical genetics at the University of Alberta, where he also holds the titles of the Friends of Garrett Cumming Research & Muscular Dystrophy Canada Endowed Research Chair and the Henri M. Toupin Chair in Neurological Science. He is best known for his studies of antisense oligonucleotide-based therapeutics for muscular dystrophy that led to the development of an FDA-approved drug viltolarsen. His research interests include precision medicine for muscular dystrophy and genetic diseases. He has co-edited two books both published in the Methods in Molecular Biology series from Humana Press, Springer-Nature, and has published more than 100 refereed papers and patents. He is a member of the editorial boards for the International Journal of Molecular Sciences, Genes, Frontiers in Genome Editing, Frontiers in Physiology, and Nucleic Acid Therapeutics, a member of the Medical and Scientific Advisory Committee of Muscular Dystrophy Canada, and a co-founder of the Canadian Neuromuscular Network (CAN-NMD).

References

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Further reading