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Dystonia

Dystonia (literally, "abnormal muscle tone") is a generic term used to describe a neurological movement disorder involving involuntary, sustained muscle contractions. Dystonia may affect muscles throughout the body (generalised), in certain parts of the body (segmental), or may be confined to particular muscles or muscle groups (focal). more...

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Causes

Primary dystonia is caused by a pathology of the central nervous system, likely originating in those parts of the brain concerned with motor function, such as the basal ganglia. The precise cause of primary dystonia is unknown. In many cases it probably involves some genetic predisposition towards the disorder combined with environmental conditions.

Secondary dystonia refers to dystonia brought on by some identified cause, usually involving brain damage or chemical imbalance. Some cases of (particularly focal) dystonia are brought on after trauma, are induced by certain drugs (tardive dystonia), or may be the result of diseases of the nervous system such as Wilson's disease.

Symptoms

Symptoms vary according to the kind of dystonia involved. In all cases, dystonia tends to lead to abnormal posturing, particularly on movement. For many sufferers, pain is also a feature of the condition.

Types of Dystonia

  • Generalised
  • Segmental
  • intermediate

The Focal Dystonias

These are the most common dystonias and tend to be classified as follows:

  • Cervical dystonia (spasmodic torticollis). This affects the muscles of the neck, causing the head to rotate to one side, to pull down towards the chest, or back, or a combination of these postures.
  • Blepharospasm. This affects the muscles around the eyes. The sufferer experiences rapid blinking of the eyes or even their forced closure causing effective blindness.
  • Oromandibular dystonia. This affects the muscles of the jaw and tongue, causes distortions of the mouth and tongue.
  • Spasmodic dysphonia. This affects the muscles of the larynx, causing the voice to sound broken or reducing it to a whisper.

The combination of blepharospasmodic contractions and oromandibular dystonia is called Meige's syndrome.

Treatment

Drugs, such as anticholinergics which act as an inhibitor of the neurotransmitter acetylcholine, may provide some relief. However, for most sufferers their effects are limited. Botulinum toxin injections into affected muscles have proved quite successful in providing some relief for around 3-6 months, depending on the kind of dystonia. The injections have to be repeated and around 15% of recipients develop immunity to the toxin. Surgery, such as the denervation of selected muscles, may also provide some relief. Recently, the procedure of deep brain stimulation has proved successful in a number of cases of severe generalised dystonia.

One type of Dystonia, Dopa-Responsive Dystonia can be completely treated with regular doses of Levadopa/Carbidopa (Simnet). Although this doesn't remove the condition, it does alleviate the symptoms most of the time.

Read more at Wikipedia.org


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Gene defect for muscle disorder identified - torsion dystonia - Brief Article
From Science News, 9/13/97 by Nathan Seppa

Since 1982, a small cadre of scientists has gathered family histories of people with early-onset torsion dystonia, a crippling disorder that causes the muscles to contract, twist, or sometimes jerk involuntarily. The researchers also took blood samples from the families and painstakingly probed their DNA for genetic clues that might reveal dystonia's origin.

There were few other options. Unlike neuromuscular diseases such as Parkinson's or Huntington's, dystonia is difficult to track in the body. "There is no part of the brain that degenerates [in dystonia], so there is no easy way to see what's going on," says Laurie J. Ozelius, a geneticist at Harvard University Medical School in Boston.

Their efforts have now paid off. Ozelius and her colleagues report in the September Nature Genetics the discovery of a mutation that underlies the disease. It's in a gene named DYT1.

The researchers examined blood samples from 267 unrelated people with no history of severe dystonia and from members of 68 families with clear symptoms of the disorder. The mutation appears in none of the control group and in all of the dystonia patients' families.

Ozelius and her collaborators also identified a mysterious protein, torsinA, which the DYT1 gene encodes. A defective version of torsinA predisposes a person to dystonia.

If one parent has the disease, which is genetically dominant, each child should have a 50-50 chance of inheriting it. Yet researchers were puzzled for years because fewer than half of the children showed symptoms of dystonia. Indeed, recent work reveals that only 30 to 40 percent of people with a mutated DYT1 ever show its effects.

This oddity led researchers to suspect that environmental factors combine with the mutation to trigger the disease. The answer may lie in the role of torsinA. While the protein's function is unclear, scientists see links between it and known actors in the cell. For example, torsinA resembles compounds called heat-shock proteins, which are expressed when a cell faces fever or injury.

Researchers now plan to reexamine family data from carriers of the mutated gene. Many such families report incidents of trauma or high fever in a youngster who later developed severe dystonia, says study coauthor Susan B. Bressman, a neurologist at Columbia University. However, since virtually all young children encounter such stresses, the researchers don't know whether a connection will emerge.

An age-related decline in the risk of symptoms also poses a puzzle. "Once you reach the age of 22, you're generally home free," Bressman says.

The fact that dystonia doesn't strike in later adulthood raises biological questions, she says. Does the body do something to block the mutation in later years, or does the mutation have a time-dependent shutoff switch?

"It's a fascinating discovery. It will whet the appetite of neuroscientists," says Giovanna Spinella of the National Institute of Neurological Disorders and Stroke in Bethesda, Md.

The DYT1 mutation is rare, occurring in no more than I in 5,000 people in the United States. Among Jews of European descent, it occurs in as many as 1 in 1,000 people, Bressman says.

The discovery of the mutation opens the way for a simple test to distinguish a child with severe dystonia from one with cerebral palsy or one of several milder types of dystonia. Severe dystonia is seldom fatal, but it can render an individual wheelchair-bound.

Future research will involve rodents with and without mutated DYT1, Ozelius says. Researchers in the laboratory will also be able to expose tissue cultures with and without the mutated gene to hot temperatures and stress to determine whether torsinA behaves like a heat-shock protein.

COPYRIGHT 1997 Science Service, Inc.
COPYRIGHT 2004 Gale Group

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