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Spinocerebellar ataxia

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Spinocerebellar ataxia
ICD-10 G11
ICD-9 334
OMIM [1]
DiseasesDB 12339
MedlinePlus [2]
eMedicine /
MeSH {{{MeshNumber}}}

Spinocerebellar ataxia (SCA) is a genetic disease with multiple types, each of which could be considered a disease in its own right.

SymptomsEdit

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. [1]

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 the condition vary with the specific type (there are several), and with the individual patient. Generally, a person with ataxia retains full mental capacity but may progressively lose physical control.

Treatment and prognosisEdit

There is no known cure for spinocerebellar ataxia, which is a progressive disease (it gets worse with time), although not all types cause equally severe disability.

Treatments are generally limited to softening symptoms, not the disease itself. The condition can be irreversible. A person with this disease will usually end up needing to use a wheelchair, and eventually they may need assistance to perform daily tasks.

The treatment of incoordination or ataxia, then mostly involves the use of adaptive devices to allow the ataxia individual to maintain as much independence as possible. Such devices may include a cane, crutches, walker, or wheelchair for those with impaired gait; devices to assist with writing, feeding, and self cares if hand and arm coordination is impaired; and communication devices for 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 can be subject to variation. 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.

DiagnosisEdit

It can be easily misdiagnosed as another neurological condition, such as multiple sclerosis (MS).

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.

TypesEdit

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 29 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 amino acid 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[2] (ATXN1) 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 (Ataxin 1)
SCA2[3] (ATXN2) 3rd - 4th decade
(<10 to >60)
10 years
(1-30)
Diminished velocity saccades
areflexia (absence of neurologic reflexes)
Cuba CAG repeat, 12q
SCA3[4] (MJD) (ATXN3) 4th decade
(10-70)
10 years
(1-20)
Also called Machado-Joseph disease (MJD)[5]
Gaze-evoked nystagmus (a rapid, involuntary, oscillatory motion of the eyeball)
upper motor neuron
slow saccades
Azores
(Portugal)
CAG repeat, 14q
SCA4 (PLEKHG4) 4th - 7th decade
(19-72)
Decades areflexia (absence of neurologic reflexes)   Chromosome 16q
SCA5 (SPTBN2) 3rd - 4th decade
(10-68)
>25 years Pure cerebellar   Chromosome 11
SCA6[6] (CACNA1A) 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[7] (ATXN7) 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 (Ataxin 7)
SCA8[8] (IOSCA) 39 yrs
(18-65)
Normal lifespan Horizontal nystagmus (a rapid, involuntary, oscillatory motion of the eyeball)   CTG repeat, 13q
SCA10[9] (ATXN10) 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[10] (PPP2R2B) 33 yrs
(8-55)
  Head and hand tremor,
akinesia (loss of normal motor function, resulting in impaired muscle movement)
  CAG repeat, 5q
SCA13 Childhood or adulthood depending on mutation Depending on KCNC3 (a kind of gene) Mental retardation   19q
SCA14[11] (PRKCG) 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
SCA17 (TBP)         CAG repeat, 6q (TATA-binding protein)
SCA19, SCA22     Mild cerebellar syndrome, dysarthria    
SCA25 1.5-39 yrs Unknown ataxia with sensory neuropathy, vomiting and gastrointestinal pain.   2p

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).

InheritanceEdit

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.

  • 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." (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.

Notable casesEdit

Sufferers from the disease include:

ReferencesEdit

  1. Genes and Disease at nlm.nih.gov - Gives a concise description of SCA, along with a picture of shrunken degenerated cerebellum.
  2. GeneTests at NIH/UW sca1
  3. GeneTests at NIH/UW sca2
  4. GeneTests at NIH/UW sca3
  5. machado_joseph at NINDS
  6. GeneTests at NIH/UW sca6
  7. GeneTests at NIH/UW sca7
  8. GeneTests at NIH/UW sca8
  9. GeneTests at NIH/UW sca10
  10. GeneTests at NIH/UW sca12
  11. GeneTests at NIH/UW sca14

External linksEdit

  1. REDIRECT Template:CNS diseases of the nervous system

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