Spinocerebellar ataxia (SCA) or also known as Spinocerebellar atrophy or Spinocerebellar degeneration, is a progressive, degenerative,[1]genetic disease with multiple types, each of which could be considered a disease in its own right. An estimated 150,000 people in the United States are diagnosed with Spinocerebellar Ataxia. SCA's are the largest group of this hereditary, progressive, degenerative and often fatal neurodegenerative disorder. There is no known effective treatment or cure. Spinocerebellar Ataxia can affect anyone of any age. The disease is caused by either a recessive or dominant gene. In many cases people are not aware that they carry the ataxia gene until they have children who begin to show signs of having the disorder.[2]
Most of the 60 different types of SCA that have been identified are diagnosed via autopsy, as there is no definitive test that can tell what type of SCA a living individual or if they have it at all. In 2008, a genetic ataxia blood test developed to test for 12 types of SCA, Friedreich's ataxia, and several others. However, in the SCA group, with so many different types most go with a diagnosis of SCA unidentified or unknown. Usually the diagnosis comes after examination by a neurologist, which includes a physical exam, family history, MRI scanning of the brain and spine, and spinal tap.[3]
Many SCAs below fall under the category of polyglutamine diseases, which are caused when a disease-associated protein (i.e., ataxin-1, ataxin-3, etc.) contains a large number of repeats of glutamine residues, termed a polyQ sequence or a "CAG triplet repeat disease" for either the one-letter designation or codon for glutamine respectively. The threshold for symptoms in most forms of SCA is around 35, though for SCA3 it extends beyond 50. Most polyglutamine diseases are dominant due to the interactions of resulting polyQ tail.[citation needed]
The first ataxia gene was identified in 1993 and called Spinocerebellar ataxia type 1" (SCA1); later genes were called SCA2, SCA3, etc. Usually, the "type" number of "SCA" refers to the order in which the gene was found. At this time, there are at least 29 different gene mutations that have been found.[citation needed]
The following is a list of some of the many types of Spinocerebellar ataxia.
Others include SCA18, SCA20, SCA21, SCA23, SCA26, SCA28, and SCA29.
Four X-linked types have been described (302500, 302600, 301790, 301840), but only the first of these has so far been tied to a gene (SCAX1).
Spinocerebellar ataxia (SCA) is one of a group of genetic disorders characterized by slowly progressive incoordination of gait and is often associated with poor coordination of hands, speech, and eye movements. A review of different clinical features among SCA subtypes was recently published describing frequent hand movements in patients, causing intentional tremor.[16] As with other forms of ataxia, SCA frequently results in atrophy of the cerebellum,[17] loss of fine coordination of muscle movements leading to unsteady and clumsy motion, and other symptoms.
The symptoms of an ataxia vary with the specific type and with the individual patient. In general, a person with ataxia retains full mental capacity but progressively loses physical control.
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.
There is no known cure for spinocerebellar ataxia, which is considered to be a progressive and irreversible disease, although not all types cause equally severe disability. In general, treatments are directed towards alleviating symptoms, not the disease itself. 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. Typically, a person afflicted with this disease will eventually be unable to perform daily tasks (ADLs). However, rehabilitation therapists can help patients to maximize their ability of self-care and delay deterioration to certain extent. Stem cell research has been sought for a future treatment.[citation needed]
Physical therapists can assist patients in maintaining their level of independence through therapeutic exercise programs. In general, physical therapy emphasizes postural balance and gait training for ataxia patients.[18] General conditioning such as range-of-motion exercises and muscle strengthening would also be included in therapeutic exercise programs. Research showed that spinocerebellar ataxia 2 (SCA2) patients [19] with a mild stage of the disease gained significant improvement in static balance and neurological indices after six months of a physical therapy exercise training program.[20]Occupational therapists may assist patients with incoordination or ataxia issues through the use of adaptive devices. 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. A randomized clinical trial revealed that an intensive rehabilitation program with physical and occupational therapies for patients with degenerative cerebellar diseases can significantly improve functional gains in ataxia, gait, and activities of daily living. Some level of improvement was shown to be maintained 24 weeks post-treatment.[21] Speech language pathologists may use augmentative and alternative communication devices to help patients with impaired speech.
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