Oculopharyngeal muscular dystrophy
Other Names for this Disease
- Muscular dystrophy, oculopharyngeal
What are the signs and symptoms of oculopharyngeal muscular dystrophy?
What causes oculopharyngeal muscular dystrophy?
How is oculopharyngeal muscular dystrophy inherited?
Is genetic testing available for oculopharyngeal muscular dystrophy?
How might oculopharyngeal muscular dystrophy be treated?
There are many signs and symptoms of oculopharyngeal muscular dystrophy (OPMD), although the specific symptoms and age of onset varies among affected individuals. Most people show one or more symptoms by the age of 70. The most common symptoms of OPMD include:
- Muscle weakness (also known as myopathy)
- Droopy eyelids (also known as ptosis)
- Difficulty swallowing (also known as dysphagia)
- Double vision
- Tongue weakness
- Upper and/or lower body weakness
- Weakness of the muscles in the face
- Voice disorders (in about half of people with this condition)
Oculopharyngeal muscular dystrophy (OPMD) is caused by mutations in the PABPN1 gene. The PABPN1 gene provides instructions for making a protein that is active (expressed) throughout the body. In cells, the PABPN1 protein plays an important role in processing molecules called messenger RNAs (mRNAs), which serve as genetic blueprints for making proteins. The protein acts to protect the mRNA from being broken down and allows it to move within the cell.
Mutations in the PABPN1 gene that cause OPMD result in a PABPN1 protein that forms clumps within muscle cells, and hence they cannot be broken down. These clumps are thought to impair the normal function of muscle cells and eventually cause cells to die. The progressive loss of muscle cells most likely causes the muscle weakness seen in people with OPMD. It is not known why abnormal PABPN1 proteins seem to affect muscle cells in only certain parts of the body.
Most cases of oculopharyngeal muscular dystrophy (OPMD) are inherited in an autosomal dominant manner, which means one copy of the altered (mutated) gene in each cell is sufficient to cause the condition. Individuals have two copies of each gene; one copy having been inherited from each parent. An individual with the autosomal dominant form of OPMD may have inherited the condition from an affected parent, or less commonly, the condition may occur for the first time in the affected individual. Each child of an affected individual with this form of OPMD has a 50% (1 in 2) chance to be affected and a 50% chance to be unaffected.
Less commonly, OPMD is inherited in an autosomal recessive manner, which means that both copies of the disease-causing gene in each cell must have a mutation for an individual to be affected. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene (and are referred to as carriers), but they typically do not show signs and symptoms of the condition. When two carriers of an autosomal recessive condition have children, each child has a 25% (1 in 4) chance to be affected, a 50% (1 in 2) chance to be a carrier like each of the parents, and a 25% chance to be unaffected and not be a carrier. The children of an individual with autosomal recessive OPMD will always be carriers (obligate heterozygotes) for the disease-causing mutation. The risk of a child being affected if his/her parent has autosomal recessive OPMD is less than 1%.
- McLoon L, Lee M. Muscular Dystrophy, Oculopharyngeal. National Organization for Rare Disorders (NORD). 2007; http://www.rarediseases.org/search/rdbdetail_abstract.html?disname=Muscular%20Dystrophy%2C%20Oculopharyngeal. Accessed 12/7/2008.
- Oculopharyngeal muscular dystrophy. Genetics Home Reference (GHR). December 2008; http://ghr.nlm.nih.gov/condition=oculopharyngealmusculardystrophy. Accessed 12/8/2008.
- Facts About Rare Muscular Dystrophies. Muscular Dystrophy Association (MDA). June 2008; http://www.mda.org/publications/fa-rareMD.html. Accessed 12/7/2008.
- Braise B, Rouleau GA. Oculopharyngeal muscular dystrophy. Gene Reviews. 2006; http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=opmd#opmd. Accessed 2/4/2009.
- Urtizberea JA. Oculopharyngeal muscular dystrophy. Orphanet Encyclopedia. 2004; http://www.orpha.net/data/patho/GB/uk-OPMD.pdf. Accessed 2/4/2009.
- Bernard Brais, M Phil, and Guy A Rouleau. Oculopharyngeal Muscular Dystrophy. GeneReviews. June 22, 2006; http://www.ncbi.nlm.nih.gov/books/NBK1126/. Accessed 5/2/2012.
- Muscular Dystrophy, Oculopharyngeal. NORD. April 10, 2008; http://www.rarediseases.org/rare-disease-information/rare-diseases/byID/1182/viewAbstract. Accessed 5/2/2012.