spinocerebellar ataxia

Definition
The spinocerebellar ataxias (SCAs) are a group of inherited conditions that affect the brain and spinal cord causing progressive difficulty with coordination.
Description
The SCAs are named for the parts of the nervous system that are affected in this condition. Spino refers to the spinal cord and cerebellar refers to the cerebellum or back part of the brain. The cerebellum is the area of the brain that controls coordination. In people with SCA, the cerebellum often becomes atrophied or smaller. Symptoms of SCA usually begin in the 30s or 40s, but onset can be at any age. Onset from childhood through the 70s has been reported.
As of early 2001, at least 13 different types of SCA have been described. This group is numbered 1-14 and each is caused by mutations or changes in a different gene. Although the category of SCA9 has been reserved, there is no described condition for SCA9 and no gene has been found. Spinocerebellar ataxia has also been called olivopontocerebellar atrophy, Marie's ataxia, and cerebellar degeneration. SCA3 is sometimes called Machado-Joseph disease named after two of the first families described with this condition. All affected people in a family have the same type of SCA.


Signs and symptoms
Spinocerebellar ataxia (SCA) is one of a group of genetic disorders characterized by slowly progressive incoordination of gait and often associated with poor coordination of hands, speech, and eye movements. Frequently, atrophy of the cerebellum occurs, and different ataxias are known to affect different regions within the cerebellum.[14]
As with other forms of ataxia, SCA results in unsteady and clumsy motion of the body due to a failure of the fine coordination of muscle movements, along with other symptoms.
The symptoms of an ataxia vary with the specific type and with the individual patient. Generally, a person with ataxia retains full mental capacity but may progressively lose physical control.
[edit] Cause
The hereditary ataxias are categorized by mode of inheritance and causative gene or chromosomal locus. The hereditary ataxias can be inherited in an autosomal dominant, autosomal recessive, or X-linked manner.
• Many types of autosomal dominant cerebellar ataxias are now known for which specific genetic information is available. Synonyms for autosomal dominant cerebellar ataxias (ADCA) used prior to the current understanding of the molecular genetics were Marie's ataxia, inherited olivopontocerebellar atrophy, cerebello-olivary atrophy, or the more generic term "spinocerebellar degeneration." (Spinocerebellar degeneration is a rare inherited neurological disorder of the central nervous system characterized by the slow degeneration of certain areas of the brain. There are three forms of spinocerebellar degeneration: Types 1, 2, 3. Symptoms begin during adulthood.)
• There are five typical autosomal recessive disorders in which ataxia is a prominent feature: Friedreich ataxia, ataxia-telangiectasia, ataxia with vitamin E deficiency, ataxia with oculomotor apraxia (AOA), spastic ataxia. Disorder Subdivisions: Friedreich's ataxia, Spinocerebellar ataxia, Ataxia telangiectasia, Vasomotor ataxia, Vestibulocerebellar, Ataxiadynamia, Ataxiophemia, Olivopontocerebellar atrophy, and Charcot-Marie-Tooth disease.
• There have been reported cases where a polyglutamine expansion may lengthen when passed down, which often can result in an earlier age-of-onset and a more severe disease phenotype for individuals who inherit the disease allele. This falls under the category of genetic anticipation.
Treatment
There is no currently known cure for spinocerebellar ataxia, which is considered to be a progressive and irreversible disease, although not all types cause equally severe disability. Treatments are generally directed towards alleviating symptoms, not the disease itself. Typically, a person afflicted with this disease will eventually be unable to perform daily tasks.
The treatment of incoordination or ataxia mostly involves the use of adaptive devices to allow the individual to maintain the greatest degree of independence for as long as possible. Such devices may include a cane, crutches, walker, or wheelchair for those with impaired gait. Other devices are available to assist with writing, feeding, and self care if hand and arm coordination are impaired; and communication devices exist to help those with impaired speech. Many patients with hereditary or idiopathic forms of ataxia have other symptoms in addition to ataxia. Medications or other therapies might be appropriate for some of these symptoms, which could include tremor, stiffness, depression, spasticity, and sleep disorders, among others. Both onset of initial symptoms and duration of disease are variable. If the disease is caused by a polyglutamine trinucleotide repeat CAG expansion, a longer expansion may lead to an earlier onset and a more radical progression of clinical symptoms.