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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.
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.
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.
Walker–Warburg syndrome (WWS), also called Warburg syndrome, Chemke syndrome, HARD syndrome, Pagon syndrome, cerebroocular dysgenesis (COD) or cerebroocular dysplasia-muscular dystrophy syndrome (COD-MD), is a rare form of autosomal recessive congenital muscular dystrophy. It is associated with brain and eye abnormalities. This condition has a worldwide distribution. Walker-Warburg syndrome is estimated to affect 1 in 60,500 newborns worldwide.
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.
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:
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.
Fukutin is a eukaryotic protein necessary for the maintenance of muscle integrity, cortical histogenesis, and normal ocular development. Mutations in the fukutin gene have been shown to result in Fukuyama congenital muscular dystrophy (FCMD) characterised by brain malformation - one of the most common autosomal-recessive disorders in Japan. In humans this protein is encoded by the FCMD gene, located on chromosome 9q31. Human fukutin exhibits a length of 461 amino acids and a predicted molecular mass of 53.7 kDa.
Fukutin-related protein (FKRP) is also known as FKRP_HUMAN, LGMD2I, MDC1C, MDDGA5, MDDGB5, and MDDGC5. FKRP can be located in the brain, cardiac muscle and skeletal muscle, and in cells it is found in the Golgi apparatus. Fukutin is expressed in the mammalian retina and is located in the Golgi complex of retinal neurons.
Laminin subunit alpha-2 is a protein that in humans is encoded by the LAMA2 gene.
Protein O-linked-mannose beta-1,2-N-acetylglucosaminyltransferase 1 is an enzyme that in humans is encoded by the POMGNT1 gene.
Selenoprotein N is a protein that in humans is encoded by the SEPN1 gene.
Protein O-mannosyl-transferase 1 is an enzyme that in humans is encoded by the POMT1 gene. It is a member of the dolichyl-phosphate-mannose-protein mannosyltransferases.
Collagen VI (ColVI) is a type of collagen primarily associated with the extracellular matrix of skeletal muscle. ColVI maintains regularity in muscle function and stabilizes the cell membrane. It is synthesized by a complex, multistep pathway that leads to the formation of a unique network of linked microfilaments located in the extracellular matrix (ECM). ColVI plays a vital role in numerous cell types, including chondrocytes, neurons, myocytes, fibroblasts, and cardiomyocytes. ColVI molecules are made up of three alpha chains: α1(VI), α2(VI), and α3(VI). It is encoded by 6 genes: COL6A1, COL6A2, COL6A3, COL6A4, COL6A5, and COL6A6. The chain lengths of α1(VI) and α2(VI) are about 1,000 amino acids. The chain length of α3(VI) is roughly a third larger than those of α1(VI) and α2(VI), and it consists of several spliced variants within the range of 2,500 to 3,100 amino acids.
Spinal muscular atrophy with lower extremity predominance 1 (SMALED1) is an extremely rare neuromuscular disorder of infants characterised by severe progressive muscle atrophy which is especially prominent in legs.
Congenital distal spinal muscular atrophy (cDSMA), also known as distal hereditary motor neuropathytype VIII (dHMN8), is a hereditary medical condition characterized by muscle wasting (atrophy), particularly of distal muscles in legs and hands, and by early-onset contractures of the hip, knee, and ankle. Affected individuals often have shorter lower limbs relative to the trunk and upper limbs. The condition is a result of a loss of anterior horn cells localized to lumbar and cervical regions of the spinal cord early in infancy, which in turn is caused by a mutation of the TRPV4 gene. The disorder is inherited in an autosomal dominant manner. Arm muscle and function, as well as cardiac and respiratory functions are typically well preserved.
Muscle–eye–brain (MEB) disease, also known as muscular dystrophy-dystroglycanopathy congenital with brain and eye anomalies A3 (MDDGA3), is a kind of rare congenital muscular dystrophy (CMD), largely characterized by hypotonia at birth. Patients have muscular dystrophy, central nervous system abnormalities and ocular abnormalities. The condition is degenerative.
References
- ↑ Dorland's Illustrated Medical Dictionary Merck Archived 2007-10-11 at the Wayback Machine .
- ↑ Murakami T, Hayashi YK, Noguchi S, et al. (November 2006). "Fukutin gene mutations cause dilated cardiomyopathy with minimal muscle weakness". Ann. Neurol. 60 (5): 597–602. doi: 10.1002/ana.20973 . PMID 17036286.
- ↑ Brockington M, Blake DJ, Prandini P, et al. (December 2001). "Mutations in the fukutin-related protein gene (FKRP) cause a form of congenital muscular dystrophy with secondary laminin alpha2 deficiency and abnormal glycosylation of alpha-dystroglycan". Am. J. Hum. Genet. 69 (6): 1198–209. doi:10.1086/324412. PMC 1235559 . PMID 11592034.
