|Oculopharyngeal muscular dystrophy|
|Other names||Muscular dystrophy, oculopharyngeal|
|Autosomal dominant in majority of cases (autosomal recessive minority)|
|Causes||Mutations on the PABPN1 gene|
|Diagnostic method||Muscle biopsy|
|Treatment||Orthopedic devices for management|
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.
Autosomal dominant inheritance is the most common form of inheritance. Less commonly, OPMD can be inherited in an autosomal recessive pattern, which means that two copies of the mutated gene need to be present in each cell, both parents need to be carriers of the mutated gene, and usually show no signs or symptoms. The PABPN1 mutation contains a GCG trinucleotide repeatat the 5' end of the coding region, and expansion of this repeat which then leads to autosomal dominant oculopharyngeal muscular dystrophy (OPMD) disease.
In terms of the signs (and symptoms) of oculopharyngeal muscular dystrophy would be consistent with the following:
Though the aforementioned signs/symptoms are the most common, there have been cases though rare, where the peripheral nervous system has had involvement with significant reduction of myelinated fibers
In homozygous cases, this muscular dystrophy is severe and starts earlier in the affected individuals life.
The genetics of this type of muscular dystrophy revolve around the PABPN1 gene. This gene suffers mutations that cause the PABPN1 protein to have extra alanine (amino acids), this manifests itself physically in the symptoms of this MD.
The expansion caused by the mutations on the PABPN1 gene ultimately interrupts the cellular mechanics of poly(A) RNA. In most cases oculopharyngeal muscular dystrophy is inherited via autosomal dominance.
The alleles, which are a variant form of a geneinvolved in this form of MD are: PABPN1, (GCG)n EXPANSION, (GCG)8-13, PABPN1, (GCG)n EXPANSION, (GCG)7 and PABPN1, GLY12ALA.
The diagnosis of oculopharyngeal muscular dystrophy can be done via two methods, a muscle biopsy or a blood draw with genetic testing for GCG trinucleotide expansions in the PABPN1 gene. The genetic blood testing is more common. Additionally, a distinction between OPMD and myasthenia gravis or mitochondrial myopathy must be made, in regards to the differential diagnosis of this condition.
Currently no cure or specific treatment exists to eliminate the symptoms or stop the disease progression. A consistent diet planned with the help of a dietitian along with exercises taught by a speech therapist can assist with mild symptoms of dysphagia. Surgical intervention can also help temporarily manage symptoms related to the ptosis and dysphagia. Cutting one of the throat muscles internally, an operation called cricopharyngeal myotomy, can be one way to ease symptoms in more severe cases. However, for a majority of people, the benefits from such treatments are only temporary. There is currently no treatment available to address the proximal limb weakness. Many of those affected with the proximal limb weakness will eventually require assistive devices such as canes, braces or a wheelchair. As with all surgical procedures, they come with many risk factors.As the dysphagia becomes more severe, patients become malnourished, lose significant weight, become dehydrated and suffer from repeated incidents of aspiration pneumonia. These last two are often the cause of death.
The disease is found across 5 continents (30 countries) and is frequently seen in French Canadians, with a prevalence 1:1000. OPMD affects males and females equally, and affected individuals have been found in Europe (France), Jewish Ashkenazi, and Spanish Americans.
A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders are the most common, the term is mostly used when discussing disorders with a single genetic cause, either in a gene or chromosome. The mutation responsible can occur spontaneously before embryonic development, or it can be inherited from two parents who are carriers of a faulty gene or from a parent with the disorder. When the genetic disorder is inherited from one or both parents, it is also classified as a hereditary disease. Some disorders are caused by a mutation on the X chromosome and have X-linked inheritance. Very few disorders are inherited on the Y chromosome or mitochondrial DNA.
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.
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.
Malouf syndrome is a congenital disorder that causes one or more of the following symptoms: mental retardation, ovarian dysgenesis, congestive cardiomyopathy, broad nasal base, blepharoptosis, and bone abnormalities, and occasionally marfanoid habitus.
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.
Nemaline myopathy is a congenital, often hereditary neuromuscular disorder with many symptoms that can occur such as muscle weakness, hypoventilation, swallowing dysfunction, and impaired speech ability. The severity of these symptoms varies and can change throughout one's life to some extent. The prevalence is estimated at 1 in 50,000 live births. It is the most common non-dystrophic myopathy.
Hereditary inclusion body myopathies (HIBM) are a group of rare genetic disorders which have different symptoms. Generally, they are neuromuscular disorders characterized by muscle weakness developing in young adults. Hereditary inclusion body myopathies comprise both autosomal recessive and autosomal dominant muscle disorders that have a variable expression (phenotype) in individuals, but all share similar structural features in the muscles.
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. The overall incidence is unknown but a survey in North-eastern Italy has reported an incidence rate of 1.2 per 100,000 live births. It is the most severe form of congenital muscular dystrophy with most children dying before the age of three years.
Short-chain acyl-coenzyme A dehydrogenase deficiency (SCADD) is an autosomal recessive fatty acid oxidation disorder which affects enzymes required to break down a certain group of fats called short chain fatty acids.
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.
Fazio–Londe disease (FLD), also called progressive bulbar palsy of childhood, is a very rare inherited motor neuron disease of children and young adults and is characterized by progressive paralysis of muscles innervated by cranial nerves.
Bethlem myopathy is an autosomal dominant myopathy, classified as a congenital form of muscular dystrophy, that is caused by a mutation in one of the three genes coding for type VI collagen. These include COL6A1, COL6A2, and COL6A3. Gower's sign, tiptoe-walking and contractures of the joints are typical signs and symptoms of the disease. Bethlem myopathy could be diagnosed based on clinical examinations and laboratory tests may be recommended. Currently there is no cure for the disease and symptomatic treatment is used to relieve symptoms and improve quality of life. Bethlem myopathy affects about 1 in 200,000 people.
Poly(A)-binding protein is a RNA-binding protein which triggers the binding of eukaryotic initiation factor 4 complex (eIF4G) directly to the poly(A) tail of mRNA which is 200-250 nucleotides long. The poly(A) tail is located on the 3' end of mRNA and was discovered by Mary Edmonds, who also characterized the poly-A polymerase enzyme that generates the poly(a) tail. The binding protein is also involved in mRNA precursors by helping polyadenylate polymerase add the poly(A) nucleotide tail to the pre-mRNA before translation. The nuclear isoform selectively binds to around 50 nucleotides and stimulates the activity of polyadenylate polymerase by increasing its affinity towards RNA. Poly(A)-binding protein is also present during stages of mRNA metabolism including nonsense-mediated decay and nucleocytoplasmic trafficking. The poly(A)-binding protein may also protect the tail from degradation and regulate mRNA production. Without these two proteins in-tandem, then the poly(A) tail would not be added and the RNA would degrade quickly.
Polyadenylate-binding protein 2 (PABP-2) also known as polyadenylate-binding nuclear protein 1 (PABPN1) is a protein that in humans is encoded by the PABPN1 gene. PABN1 is a member of a larger family of poly(A)-binding proteins in the human genome.
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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.
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.
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.
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