Muscular dystrophy | |
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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] |
Duration | Chronic [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]
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 extremely rare – genetic disorders.
Muscular dystrophies are caused by mutations in genes, usually those involved in making muscle proteins. [2] The muscle protein, dystrophin, is in most muscle cells and works to strengthen the muscle fibers and protect them from injury as muscles contract and relax. [3] It links the muscle membrane to the thin muscular filaments within the cell. Dystrophin is an integral part of the muscular structure. An absence of dystrophin can cause impairments: healthy muscle tissue can be replaced by fibrous tissue and fat, causing an inability to generate force. [4] Respiratory and cardiac complications can occur as well. 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 currently available including gene therapy (Elevidys), and antisense drugs (Ataluren, Eteplirsen etc.). [2] Other medications used include glucocorticoids (Deflazacort, Vamorolone); calcium channel blockers (Diltiazem); to slow skeletal and cardiac muscle degeneration, anticonvulsants to control seizures and some muscle activity, and Histone deacetylase inhibitors (Givinostat) 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]
The signs and symptoms consistent with muscular dystrophy are: [5]
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. [9] [10]
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. [11]
An MRI can be used to assess the white matter of the nervous system and measure the merosin levels in young boys. An absence of merosin in young boys will result with neurological deficits and changes in the white matter. [12]
Disorder name | OMIM | Gene | Inheritance pattern | Age of onset | Muscles affected | Description |
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Becker muscular dystrophy | 300376 | DMD | XR | Childhood | Distal limbs progressing to generalised weakness | A less severe variant of Duchenne muscular dystrophy, [13] affects predominantly boys. |
Congenital muscular dystrophy | Multiple | Multiple | AD, AR | At birth | Generalised 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. 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. [14] 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. [13] |
Duchenne muscular dystrophy | 310200 | DMD | XR | Childhood | Distal limbs progressing to generalised weakness, involving respiratory muscles | The 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. [15] Typical lifespans range from 15 to 45. [15] Sporadic mutations in this gene occur frequently. [16] |
Distal muscular dystrophy | 254130 | DYSF | AD, AR | 20–60 years | Distal muscles in hands, forearms and lower legs | Progress is slow and not life-threatening. [17] 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. [13] |
Emery–Dreifuss muscular dystrophy | Multiple | Multiple | XR, AD, AR | Childhood, early teenage years | Distal limb muscles, limb-girdle, heart | 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. [18] [19] |
Facioscapulohumeral muscular dystrophy | 158900 | DUX4 | AD | Adolescence | Face, shoulders, upper arms, progressing to other muscles | Causes progressive weakness, initially in the muscles of the face, shoulders, and upper arms. Additional muscles are often affected. [20] Affected individuals can become severely disabled, with 20% requiring a wheelchair by age 50. [21] 30% of cases involve spontaneous mutations. [21] Penetrance and severity seem to be lower in females compared to males. [21] [22] |
Limb–girdle muscular dystrophy | Multiple | Multiple | AD, AR | Any | Upper arms and legs | The person normally leads a normal life with some assistance. Rare cardiopulmonary complications can be life-threatening. [23] |
Myotonic muscular dystrophy | 160900 602668 | DMPK CNBP | AD | Adulthood | Skeletal muscles, heart, other muscle groups | Presents with myotonia (delayed relaxation of muscles), as well as muscle wasting and weakness. [24] Varies in severity and manifestations and affects many body systems in addition to skeletal muscles, including the heart, endocrine organs, and eyes. [25] |
Oculopharyngeal muscular dystrophy | 164300 | PABPN1 | AD, rarely AR | 40–50 years | Eye muscles, face, throat, pelvis, shoulders |
Currently, there is no cure for muscular dystrophy. In terms of management, physical therapy, occupational therapy, orthotic intervention (e.g., ankle-foot orthosis), [26] [27] speech therapy, and respiratory therapy may be helpful. [26] Low intensity corticosteroids such as prednisone, and deflazacort may help to maintain muscle tone. [28] 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. [29] The myotonia (delayed relaxation of a muscle after a strong contraction) occurring in myotonic muscular dystrophy may be treated with medications such as quinine. [30]
Low-intensity, assisted exercises, dynamic exercise training, or assisted bicycle training of the arms and legs during a 24-week trial significantly delayed the functional loss of muscular dystrophy. It can be done in a safe and feasible manner, even with boys late in their ambulation stage. However, eccentric exercises, or intense exercises causing soreness should not be used as they can cause further damage. [31]
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. [32]
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]
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, [33] 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. [34]
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. [35]
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. [36] [37]
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.
Dystrophin is a rod-shaped cytoplasmic protein, and a vital part of a protein complex that connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix through the cell membrane. This complex is variously known as the costamere or the dystrophin-associated protein complex (DAPC). Many muscle proteins, such as α-dystrobrevin, syncoilin, synemin, sarcoglycan, dystroglycan, and sarcospan, colocalize with dystrophin at the costamere. It has a molecular weight of 427 kDa
Duchenne muscular dystrophy (DMD) is a severe type of muscular dystrophy predominantly affecting boys. The onset of muscle weakness typically begins around age four, with rapid progression. Initially, muscle loss occurs in the thighs and pelvis, extending to the arms, which can lead to difficulties in standing up. By the age of 12, most individuals with Duchenne muscular dystrophy are unable to walk. Affected muscles may appear larger due to an increase in fat content, and scoliosis is common. Some individuals may experience intellectual disability, and females carrying a single copy of the mutated gene may show mild symptoms.
Becker muscular dystrophy (BMD) is an X-linked recessive inherited disorder characterized by slowly progressing muscle weakness of the legs and pelvis. It is a type of dystrophinopathy. The cause is mutations and deletions in any of the 79 exons encoding the large dystrophin protein, essential for maintaining the muscle fiber's cell membrane integrity. Becker muscular dystrophy is related to Duchenne muscular dystrophy in that both result from a mutation in the dystrophin gene, however the hallmark of Becker is milder in-frame deletions. and hence has a milder course, with patients maintaining ambulation till 50–60 years if detected early.
Fukuyama congenital muscular dystrophy (FCMD) is a rare, autosomal recessive form of muscular dystrophy (weakness and breakdown of muscular tissue) mainly described in Japan but also identified in Turkish and Ashkenazi Jewish patients; fifteen cases were first described on 1960 by Dr. Yukio Fukuyama.
Facioscapulohumeral muscular dystrophy (FSHD) is a type of muscular dystrophy, a group of heritable diseases that cause degeneration of muscle and progressive weakness. Per the name, FSHD tends to sequentially weaken the muscles of the face, those that position the scapula, and those overlying the humerus bone of the upper arm. These areas can be spared, and muscles of other areas usually are affected, especially those of the chest, abdomen, spine, and shin. Almost any skeletal muscle can be affected in advanced disease. Abnormally positioned, termed 'winged', scapulas are common, as is the inability to lift the foot, known as foot drop. The two sides of the body are often affected unequally. Weakness typically manifests at ages 15–30 years. FSHD can also cause hearing loss and blood vessel abnormalities at the back of the eye.
Mitochondrial myopathies are types of myopathies associated with mitochondrial disease. Adenosine triphosphate (ATP), the chemical used to provide energy for the cell, cannot be produced sufficiently by oxidative phosphorylation when the mitochondrion is either damaged or missing necessary enzymes or transport proteins. With ATP production deficient in mitochondria, there is an over-reliance on anaerobic glycolysis which leads to lactic acidosis either at rest or exercise-induced.
A neuromuscular disease is any disease affecting the peripheral nervous system (PNS), the neuromuscular junctions, or skeletal muscles, 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.
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.
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 (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 infertility. While myotonic dystrophy can occur at any age, onset is typically in the 20s and 30s.
Bethlem myopathy is predominantly an autosomal dominant myopathy, classified as a congenital form of limb-girdle muscular dystrophy. There are two types of Bethlem myopathy, based on which type of collagen is affected.
Ullrich congenital muscular dystrophy (UCMD) is a form of congenital muscular dystrophy. There are two forms: UCMD1 and UCMD2.
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.
Viltolarsen, sold under the brand name Viltepso, is a medication used for the treatment of Duchenne muscular dystrophy (DMD). Viltolarsen is a Morpholino antisense oligonucleotide.
Toshifumi (Toshi) Yokota is a biomedical scientist and professor of medical genetics at the University of Alberta, also holding the titles of the Friends of Garrett Cumming Research & Muscular Dystrophy Canada Endowed Research Chair and the Henri M. Toupin Chair in Neurological Science. Known for pioneering research in antisense therapy for muscular dystrophy that led to the development of an FDA-approved drug viltolarsen, research interests encompass precision medicine for muscular dystrophy and genetic diseases. Publications exceed 100 refereed papers and patents, with contributions as co-editor to three books in the Methods in Molecular Biology series from Humana Press, Springer-Nature, Roles include fellow of the Canadian Academy of Health Sciences, a member of the editorial boards for numerous journals, a member of the Medical and Scientific Advisory Committee of Muscular Dystrophy Canada, chief scientific officer of OligomicsTx, and a co-founder of the Canadian Neuromuscular Network (CAN-NMD).
An X-linked genetic disease is a disease inherited through a genetic defect on the X chromosome. In human cells, there is a pair of non-matching sex chromosomes, labelled X and Y. Females carry two X chromosomes, whereas males have one X and one Y chromosome. A disease or trait determined by a gene on the X chromosome demonstrates X-linked inheritance, which can be divided into dominant and recessive patterns.
Rigid spine syndrome, also known as congenital muscular dystrophy with rigidity of the spine (CMARS), is a rare and often debilitating neuromuscular disorder. It is characterized by progressive muscle stiffness and rigidity, particularly in the spine, which can severely limit mobility and impact quality of life. This condition is typically present from birth or early childhood and tends to worsen over time.
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