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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. The disorders differ as to which muscles are primarily affected, the degree of weakness, how fast they worsen, and when symptoms begin. Some types are also associated with problems in other organs.
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.
Myotonia is a symptom of a small handful of certain neuromuscular disorders characterized by delayed relaxation of the skeletal muscles after voluntary contraction or electrical stimulation.
Weakness is a symptom of a number of different conditions. The causes are many and can be divided into conditions that have true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, including muscular dystrophy and inflammatory myopathy. It occurs in neuromuscular junction disorders, such as myasthenia gravis.
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.
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.
Facioscapulohumeral muscular dystrophy (FSHD) is a type of muscular dystrophy, a group of heritable diseases that cause progressive impairment of muscles. FSHD preferentially weakens the skeletal muscles of the face, those that position the scapula (scapulo), and those in the upper arm, overlying the humerus bone (humeral). These areas can be spared, and others usually are affected, especially the chest, the trunk, and around the shin. Abnormally positioned scapulas and inability to lift the foot are common. 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 in the back of the eye.
Beevor's sign is medical sign in which the navel moves towards the head upon flexing the neck, indicating selective weakness of the lower abdominal muscles. Causes include spinal cord injury, amyotrophic lateral sclerosis (ALS), and facioscapulohumeral muscular dystrophy (FSHD).
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.
Distal myopathy is a group of rare genetic disorders that cause muscle damage and weakness, predominantly in the hands and/or feet. Mutation of many different genes can be causative. Many types involve dysferlin.
p38 mitogen-activated protein kinases are a class of mitogen-activated protein kinases (MAPKs) that are responsive to stress stimuli, such as cytokines, ultraviolet irradiation, heat shock, and osmotic shock, and are involved in cell differentiation, apoptosis and autophagy. Persistent activation of the p38 MAPK pathway in muscle satellite cells due to ageing, impairs muscle regeneration.
A winged scapula is a skeletal medical condition in which the shoulder blade protrudes from a person's back in an abnormal position.
Congenital myopathy is a very broad term for any muscle disorder present at birth. This defect primarily affects skeletal muscle fibres and causes muscular weakness and/or hypotonia. Congenital myopathies account for one of the top neuromuscular disorders in the world today, comprising approximately 6 in 100,000 live births every year. As a whole, congenital myopathies can be broadly classified as follows:
Gamma-sarcoglycan is a protein that in humans is encoded by the SGCG gene. The α to δ-sarcoglycans are expressed predominantly (β) or exclusively in striated muscle. A mutation in any of the sarcoglycan genes may lead to a secondary deficiency of the other sarcoglycan proteins, presumably due to destabilisation of the sarcoglycan complex. The disease-causing mutations in the α to δ genes cause disruptions within the dystrophin-associated protein (DAP) complex in the muscle cell membrane. The transmembrane components of the DAP complex link the cytoskeleton to the extracellular matrix in adult muscle fibres, and are essential for the preservation of the integrity of the muscle cell membrane.
Protein FRG1 is an actin-bundling protein that in humans is encoded by the FRG1 gene.
Double homeobox, 4 also known as DUX4 is a protein which in humans is encoded by the DUX4 gene. Its misexpression is the cause of facioscapulohumeral muscular dystrophy (FSHD).
Electrical impedance myography, or EIM, is a non-invasive technique for the assessment of muscle health that is based on the measurement of the electrical impedance characteristics of individual muscles or groups of muscles. The technique has been used for the purpose of evaluating neuromuscular diseases both for their diagnosis and for their ongoing assessment of progression or with therapeutic intervention. Muscle composition and microscopic structure change with disease, and EIM measures alterations in impedance that occur as a result of disease pathology. EIM has been specifically recognized for its potential as an ALS biomarker by Prize4Life, a 501(c)(3) nonprofit organization dedicated to accelerating the discovery of treatments and cures for ALS. The $1M ALS Biomarker Challenge focused on identifying a biomarker precise and reliable enough to cut Phase II drug trials in half. The prize was awarded to Dr. Seward Rutkove, chief, Division of Neuromuscular Disease, in the Department of Neurology at Beth Israel Deaconess Medical Center and Professor of Neurology at Harvard Medical School, for his work in developing the technique of EIM and its specific application to ALS. It is hoped that EIM as a biomarker will result in the more rapid and efficient identification of new treatments for ALS. EIM has shown sensitivity to disease status in a variety of neuromuscular conditions, including radiculopathy, inflammatory myopathy, Duchenne muscular dystrophy, and spinal muscular atrophy.
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.
Calpainopathy is the most common type of autosomal recessive limb-girdle muscular dystrophy (LGMD). It preferentially affects the muscles of the hip girdle and shoulder girdle.
References
- 1 2 3 Han, JJ; Kurillo, G; Abresch, RT; De Bie, E; Nicorici, A; Bajcsy, R (September 2015). "Upper extremity 3-dimensional reachable workspace analysis in dystrophinopathy using Kinect". Muscle & Nerve. 52 (3): 344–55. doi:10.1002/mus.24567. PMC 4506893 . PMID 25597487.
- ↑ Bortolani, S; Brusa, C; Rolle, E; Monforte, M; De Arcangelis, V; Ricci, E; Mongini, TE; Tasca, G (28 December 2021). "Technology outcome measures in neuromuscular disorders: A systematic review". European Journal of Neurology. 29 (4): 1266–1278. doi:10.1111/ene.15235. PMID 34962693. S2CID 245544808.
- ↑ Han, JJ; Kurillo, G; Abresch, RT; de Bie, E; Nicorici, A; Bajcsy, R (February 2015). "Reachable workspace in facioscapulohumeral muscular dystrophy (FSHD) by Kinect". Muscle & Nerve. 51 (2): 168–75. doi:10.1002/mus.24287. PMC 4233016 . PMID 24828906.