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Spinocerebellar ataxia (SCA) is a genetic disease with multiple types, each of which could be considered a disease in its own right. 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.
It can be easily misdiagnosed as another neurological condition, such as multiple sclerosis (MS). There is no known cure for this degenerative condition, which lasts for the remainder of the sufferer's life. Treatments are generally limited to softening symptoms, not the disease itself. The condition is irreversible. A person with this disease will usually end up needing to use a wheelchair, and eventually they will need assistance to perform daily tasks. The symptoms of the condition vary with the specific type (there are several), and with the individual patient. Generally, a sufferer retains full mental capacity while they progressively lose physical control over their body until their death.
One means of identifying the disease is with an MRI to view the brain. Once the disease has progressed sufficiently, the cerebellum (a part of the brain) can be seen to have visibly shrunk. The most precise means of identifying SCA, including the specific type, is through DNA analysis. Some, but far from all, types of SCA may be inherited, so a DNA test may be done on the children of a sufferer, to see if they are at risk of developing the condition.
SCA is related to olivopontocerebellar atrophy (OPCA); SCA types 1, 2, and 7 are also types of OPCA. However, not all types of OPCA are types of SCA, and vice versa. This overlapping classification system is both confusing and controversial to some in this field.
Types
The following is a list of some, not all, types of Spinocerebellar ataxia. The first ataxia gene was identified in 1993 for a dominantly inherited type. It was called “Spinocerebellar ataxia type 1" (SCA1). Subsequently, as additional dominant genes were found they 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 22 different gene mutations which have been found (not all listed).
Identifying the different types of SCA now requires knowledge of the normal genetic code, and faults in this code, which are contained in a person's DNA (Deoxyribonucleic acid). The "CAG" mentioned below is one of many three-letter sequences that makes up the genetic code, this specific one coding the aminoacid glutamine. Thus, those ataxias with poly CAG expansions, along with several other neurodegenerative diseases resulting from a poly CAG expansion, are referred to as polyglutamine diseases.
| SCA Type | Average Onset (Range in Years) | Average Duration (Range in Years) | What the patient experiences | Common origin | Problems with DNA |
|---|---|---|---|---|---|
| SCA1 | 4th decade (<10 to >60) | 15 years (10-28) | Hypermetric saccades, slow saccades, upper motor neuron (note: saccades relates to eye movement) | CAG repeat, 6p | |
| SCA2 | 3rd - 4th decade (<10 to >60) | 10 years (1-30) | Diminished velocity saccades areflexia (absence of neurologic reflexes) | Cuba | CAG repeat, 12q |
| SCA3 (MJD) | 4th decade (10-70) | 10 years (1-20) | Also called Machado-Joseph disease (MJD) Gaze-evoked nystagmus (a rapid, involuntary, oscillatory motion of the eyeball) upper motor neuron slow saccades | Azores (Portugal) | CAG repeat, 14q |
| SCA4 | 4th - 7th decade (19-72) | Decades | areflexia (absence of neurologic reflexes) | Chromosome 16q | |
| SCA5 | 3rd - 4th decade (10-68) | >25 years | Pure cerebellar | Chromosome 11 | |
| SCA6 | 5th - 6th decade (19-71) | >25 years | Downbeating nystagmus, positional vertigo Symptoms can appear for the first time as late as 65 years old. | CAG repeat, 19p Calcium channel gene | |
| SCA7 | 3rd - 4th decade (0.5 - 60) | 20 years (1-45; early onset correlates with shorter duration) | Macular degeneration, upper motor neuron, slow saccades | CAG repeat, 3p | |
| SCA8 | 39 yrs (18-65) | Normal lifespan | Horizontal nystagmus (a rapid, involuntary, oscillatory motion of the eyeball) | CTG repeat, 13q | |
| SCA10 | 36 years | 9 years | ataxia, seizures | Mexico | Chromosome 22q linked pentanucleotide repeat |
| SCA11 | 30 yrs (15-70) | Normal lifespan | Mild, remain ambulatory (able to walk about on one's own) | 15q | |
| SCA12 | 33 yrs (8-55) | Head and hand tremor, akinesia (loss of normal motor function, resulting in impaired muscle movement) | CAG repeat, 5q | ||
| SCA13 | Childhood | Unknown | Mental retardation | 19q | |
| SCA14 | 28 yrs (12-42) | Decades (1-30) | Myoclonus (a sudden twitching of muscles or parts of muscles, without any rhythm or pattern, occurring in various brain disorders) | 19q | |
| SCA16 | 39 yrs (20-66) | 1-40 years | Head and hand tremor | 8q | |
| SCA19, SCA22? | Mild cerebellar syndrome, dysarthria | ||||
| SCA25 | 1.5-39 yrs | Unknown | ataxia with sensory neuropathy, vomiting and gastrointestinal pain. | 2p |
Notes
Both onset of initial symptoms and duration of disease can be subject to variation. If the disease is caused by a polyglutamine trinucleotide repeat CAG expansion, a longer expansion will lead to an earlier onset and a more radical progression of clinical symptoms, resulting in earlier death.
Technical description
Spinocerebellar ataxia 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.
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 (such as Friedreich's ataxia and ataxia-telangiectasia), or X-linked manner.
- Numerous 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."
- 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, spastic ataxia. Disorder Subdivisions: Friedreich's ataxia, Marie's ataxia, Ataxia telangiectasia, Vasomotor ataxia, Vestibulocerebellar, Ataxiadynamia, Ataxiophemia, Olivopontocerebellar atrophy, and Charcot-Marie-Tooth disease.
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.
External links
Medical
- Genes and Disease - Gives a concise description of SCA, along with a picture of shrunken degenerated cerebellum.
- Rehab Network web site - Detailed description of SCA.
- Cerebellar Degenerations
- Hereditary ataxia overview
- Spinocerebellar ataxia type 1, 2, 3, 6, 7, 8, 10, 12, 14, 17
- Machado-Joseph Disease (MJD) - SCA type 3 (SCA3) can also be called MJD. This page is provided by the National Institute of Neurological Disorders and Stroke.
- DRPLA - Dentatorubropallidoluysian atrophy (DRPLA) is an autosomal dominant neurodegenerative disorder characterised by myoclonus, epilepsy, cerebellar ataxia, choreoathetosis and dementia.
Other
- Ichi Rittoru no Namida (One Litre of Tears) - A japanese drama based on a true story and experiences of a victim who suffered from Spinocerebellar ataxia.
"Spinocerebellar ataxia"