Spinocerebellar ataxia type 6

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Spinocerebellar ataxia type 6
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This condition is inherited in an autosomal dominant manner
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Spinocerebellar ataxia type 6 (SCA6) is a rare, late-onset, autosomal dominant disorder, which, like other types of SCA, is characterized by dysarthria, oculomotor disorders, peripheral neuropathy, and ataxia of the gait, stance, and limbs due to cerebellar dysfunction. Unlike other types, SCA 6 is not fatal. This cerebellar function is permanent and progressive, differentiating it from episodic ataxia type 2 (EA2) where said dysfunction is episodic. In some SCA6 families, some members show these classic signs of SCA6 while others show signs more similar to EA2, suggesting that there is some phenotypic overlap between the two disorders. SCA6 is caused by mutations in CACNA1A, a gene encoding a calcium channel α subunit. These mutations tend to be trinucleotide repeats of CAG, leading to the production of mutant proteins containing stretches of 20 or more consecutive glutamine residues; these proteins have an increased tendency to form intracellular agglomerations. Unlike many other polyglutamine expansion disorders expansion length is not a determining factor for the age that symptoms present.

Contents

Signs and symptoms

SCA6 is typified by progressive and permanent cerebellar dysfunction. These cerebellar signs include ataxia and dysarthria, likely caused by cerebellar atrophy. Prior to diagnosis and the onset of major symptoms, patients often report a feeling of "wooziness" and momentary imbalance when turning corners or making rapid movements. The age at which symptoms first occur varies widely, from age 19 to 71, but is typically between 43 and 52. Other major signs of SCA6 are the loss of vibratory and proprioceptive sensation and nystagmus. [1]

While most patients present with these severe progressive symptoms, others, sometimes within the same family, display episodic non-progressive symptoms more similar to episodic ataxia. Still others present with symptoms common to both SCA6 and familial hemiplegic migraine.[ citation needed ]

Pathophysiology

Most cases of SCA6 are a result of CAG repeat expansion beyond the normal range, i.e., more than 19 repeats, in the Cav2.1 calcium channel encoding gene CACNA1A. [1] This gene has two splice forms, "Q-type" and "P-type", and the polyglutamine coding CAG expansion occurs in the P-type splice form. This form is expressed heavily in the cerebellum where it is localized in Purkinje cells. In Purkinje cells from SCA6 patients, mutant Cav2.1 proteins form ovular intracellular inclusions, or aggregations, similar in many ways to those seen in other polyglutamine expansion disorders such as Huntington's disease. In cell culture models of the disease, this leads to early apoptotic cell death. [2]

Mutant channels that are able to traffic properly to the membrane have a negatively shifted voltage-dependence of inactivation. The result of this is that the channels are active for a shorter amount of time and, consequently, cell excitability is decreased. [3]

There are also a number of point mutations resulting in patients with phenotypes reminiscent of episodic ataxia and SCA6 (C271Y, G293R and R1664Q) or familial hemiplegic migraine and SCA6 (R583Q and I1710T). C287Y and G293R are both located in the pore region of domain 1 and are present in a single family each. Expression of these mutant channels results in cells with drastically decreased current density compared to wild-type expressing cells. In cell-based assays, it was found that these mutant channels aggregate in the endoplasmic reticulum, not dissimilar from that seen in the CAG expansion mutants above. [4] R1664Q is in the 4th transmembrane spanning segment of domain 4 and, presumably, affects the channel's voltage dependence of activation. [5] Little is known about the point mutations resulting in overlapping phenotypes of familial hemiplegic migraine and episodic ataxia. R583Q is present in the 4th transmembrane spanning region of domain 2 while the I1710T mutation is segment 5 of domain 4. [6] [7]

Diagnosis

Spinocerebellar Ataxia Diagnosis is done via genetic testing. Your Neurologist can administer the test. Spinocerebellar Ataxia is often misdiagnosed as other diseases such as ALC or Parkinson's Disease.[ citation needed ]

Screening

There is no known prevention of spinocerebellar ataxia. Those who are believed to be at risk can have genetic sequencing of known SCA loci performed to confirm inheritance of the disorder.[ citation needed ]

Treatment

There are no drug based treatments currently available for SCA Type 6, however, there are supportive treatments that may be useful in managing symptoms. Physical Therapy, Speech Pathology can help patients manage the symptoms.[ citation needed ]

Epidemiology

The prevalence of SCA6 varies by culture. In Germany, SCA6 accounts for 10-25% of all autosomal dominant cases of SCA (SCA itself having a prevalence of 1 in 100,000). [8] [9] This prevalence in lower in Japan, however, where SCA6 accounts for only ~6% of spinocerebellar ataxias. [10] In Australia, SCA6 accounts for 30% of spinocerebellar ataxia cases while 11% in the Dutch. [11] [12]

See also

Related Research Articles

<span class="mw-page-title-main">Spinocerebellar ataxia</span> Medical condition

Spinocerebellar ataxia (SCA) is a progressive, degenerative, genetic disease with multiple types, each of which could be considered a neurological condition in its own right. An estimated 150,000 people in the United States have a diagnosis of spinocerebellar ataxia at any given time. SCA is hereditary, progressive, degenerative, and often fatal. There is no known effective treatment or cure. SCA 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 a relevant gene until they have children who begin to show signs of having the disorder. Currently, research is being conducted at Universities, such as the University of Minnesota, to elucidate many of the unknown characteristics of the disease.

<span class="mw-page-title-main">Machado–Joseph disease</span> Genetic neurodegenerative disease

Machado–Joseph disease (MJD), also known as Machado–Joseph Azorean disease, Machado's disease, Joseph's disease or spinocerebellar ataxia type 3 (SCA3), is a rare autosomal dominantly inherited neurodegenerative disease that causes progressive cerebellar ataxia, which results in a lack of muscle control and coordination of the upper and lower extremities. The symptoms are caused by a genetic mutation that results in an expansion of abnormal "CAG" trinucleotide repeats in the ATXN3 gene that results in an abnormal form of the protein ataxin which causes degeneration of cells in the hindbrain. Some symptoms, such as clumsiness and rigidity, make MJD commonly mistaken for drunkenness or Parkinson's disease.

Familial hemiplegic migraine (FHM) is an autosomal dominant type of hemiplegic migraine that typically includes weakness of half the body which can last for hours, days, or weeks. It can be accompanied by other symptoms, such as ataxia, coma, and paralysis. Migraine attacks may be provoked by minor head trauma. Some cases of minor head trauma in patients with hemiplegic migraine can develop into delayed cerebral edema, a life-threatening medical emergency. Clinical overlap occurs in some FHM patients with episodic ataxia type 2 and spinocerebellar ataxia type 6, benign familial infantile epilepsy, and alternating hemiplegia of childhood.

<span class="mw-page-title-main">Ataxin 1</span> Protein-coding gene in the species Homo sapiens

Ataxin-1 is a DNA-binding protein which in humans is encoded by the ATXN1 gene.

Ataxin 7 (ATXN7) is a protein of the SCA7 gene, which contains 892 amino acids with an expandable poly(Q) region close to the N-terminus. The expandable poly(Q) motif region in the protein contributes crucially to spinocerebellar ataxia (SCA) pathogenesis by the induction of intranuclear inclusion bodies. ATXN7 is associated with both olivopontocerebellar atrophy type 3 (OPCA3) and spinocerebellar ataxia type 7 (SCA7).

<span class="mw-page-title-main">Hemiplegic migraine</span> Medical condition

Hemiplegic migraine is a type of migraine headache characterized by motor weakness affecting only one side of the body, accompanied by aura. There is often an impairment in vision, speech, or sensation. It can run in the family, called familial hemiplegic migraine, or in a single individual, called sporadic hemiplegic migraine. The symptoms can be similar to a stroke, and may be precipitated by minor head trauma. People with FHM are advised to avoid activities that may trigger their attacks.

<span class="mw-page-title-main">Sporadic hemiplegic migraine</span> Medical condition

Sporadic hemiplegic migraine (SHM) is a form of hemiplegic migraine headache isolated cases of which are observed. It is a rare disease. It is considered to be a separate type of migraine.

Episodic ataxia (EA) is an autosomal dominant disorder characterized by sporadic bouts of ataxia with or without myokymia. There are seven types recognized but the majority are due to two recognized entities. Ataxia can be provoked by psychological stress or startle, or heavy exertion, including exercise. Symptoms can first appear in infancy. There are at least six loci for EA, of which 4 are known genes. Some patients with EA also have migraine or progressive cerebellar degenerative disorders, symptomatic of either familial hemiplegic migraine or spinocerebellar ataxia. Some patients respond to acetazolamide though others do not.

<span class="mw-page-title-main">Spinocerebellar ataxia type-13</span> Medical condition

Spinocerebellar ataxia type 13 (SCA13) is a rare autosomal dominant disorder, which, like other types of SCA, is characterized by dysarthria, nystagmus, and ataxia of gait, stance and the limbs due to cerebellar dysfunction. Patients with SCA13 also tend to present with epilepsy, an inability to run, and increased reflexes. This cerebellar dysfunction is permanent and progressive. SCA13 is caused by mutations in KCNC3, a gene encoding a voltage-gated potassium channel KV3.3. There are two known mutations in this gene causative for SCA13. Unlike many other types of SCA, these are not polyglutamine expansions but, rather, point mutations resulting in channels with no current or altered kinetics.

The P-type calcium channel is a type of voltage-dependent calcium channel. Similar to many other high-voltage-gated calcium channels, the α1 subunit determines most of the channel's properties. The 'P' signifies cerebellar Purkinje cells, referring to the channel's initial site of discovery. P-type calcium channels play a similar role to the N-type calcium channel in neurotransmitter release at the presynaptic terminal and in neuronal integration in many neuronal types.

<span class="mw-page-title-main">Ataxin-2</span> Mammalian protein found in Homo sapiens

Ataxin-2 is a protein that in humans is encoded by the ATXN2 gene. Mutations in ATXN2 cause spinocerebellar ataxia type 2 (SCA2).

Ca<sub>v</sub>2.1 Protein found in humans

Cav2.1, also called the P/Q voltage-dependent calcium channel, is a calcium channel found mainly in the brain. Specifically, it is found on the presynaptic terminals of neurons in the brain and cerebellum. Cav2.1 plays an important role in controlling the release of neurotransmitters between neurons. It is composed of multiple subunits, including alpha-1, beta, alpha-2/delta, and gamma subunits. The alpha-1 subunit is the pore-forming subunit, meaning that the calcium ions flow through it. Different kinds of calcium channels have different isoforms (versions) of the alpha-1 subunit. Cav2.1 has the alpha-1A subunit, which is encoded by the CACNA1A gene. Mutations in CACNA1A have been associated with various neurologic disorders, including familial hemiplegic migraine, episodic ataxia type 2, and spinocerebellar ataxia type 6.

<span class="mw-page-title-main">Ataxin 3</span> Protein-coding gene in the species Homo sapiens

Ataxin-3 is a protein that in humans is encoded by the ATXN3 gene.

<span class="mw-page-title-main">PLEKHG4</span> Protein-coding gene in the species Homo sapiens

Puratrophin-1 is a protein that in humans is encoded by the PLEKHG4 gene.

Ataxin 8 opposite strand, also known as ATXN8OS, is a human gene.

<span class="mw-page-title-main">Dentatorubral–pallidoluysian atrophy</span> Congenital disorder of nervous system

Dentatorubral–pallidoluysian atrophy (DRPLA) is an autosomal dominant spinocerebellar degeneration caused by an expansion of a CAG repeat encoding a polyglutamine tract in the atrophin-1 protein. It is also known as Haw River syndrome and Naito–Oyanagi disease. Although this condition was perhaps first described by Smith et al. in 1958, and several sporadic cases have been reported from Western countries, this disorder seems to be very rare except in Japan.

<span class="mw-page-title-main">KCNC3</span> Protein-coding gene in the species Homo sapiens

Potassium voltage-gated channel, Shaw-related subfamily, member 3 also known as KCNC3 or Kv3.3 is a protein that in humans is encoded by the KCNC3.

<span class="mw-page-title-main">Autosomal dominant cerebellar ataxia</span> Medical condition

Autosomal dominant cerebellar ataxia (ADCA) is a form of spinocerebellar ataxia inherited in an autosomal dominant manner. ADCA is a genetically inherited condition that causes deterioration of the nervous system leading to disorder and a decrease or loss of function to regions of the body.

Huntington's disease-like syndromes are a family of inherited neurodegenerative diseases that closely resemble Huntington's disease (HD) in that they typically produce a combination of chorea, cognitive decline or dementia and behavioural or psychiatric problems.

<span class="mw-page-title-main">Spinocerebellar ataxia type 1</span> Rare neurodegenerative disorder

Spinocerebellar ataxia type 1 (SCA1) is a rare autosomal dominant disorder, which, like other spinocerebellar ataxias, is characterized by neurological symptoms including dysarthria, hypermetric saccades, and ataxia of gait and stance. This cerebellar dysfunction is progressive and permanent. First onset of symptoms is normally between 30 and 40 years of age, though juvenile onset can occur. Death typically occurs within 10 to 30 years from onset.

References

  1. 1 2 Zhuchenko O, Bailey J, Bonnen P, Ashizawa T, Stockton D, Amos C, Dobyns W, Subramony S, Zoghbi H, Lee C (1997). "Autosomal dominant cerebellar ataxia (SCA6) associated with small polyglutamine expansions in the alpha 1A-voltage-dependent calcium channel". Nat Genet. 15 (1): 62–9. doi:10.1038/ng0197-62. PMID   8988170. S2CID   9116828.
  2. ↑ Ishikawa K, Fujigasaki H, Saegusa H, Ohwada K, Fujita T, Iwamoto H, Komatsuzaki Y, Toru S, Toriyama H, Watanabe M, Ohkoshi N, Shoji S, Kanazawa I, Tanabe T, Mizusawa H (1999). "Abundant expression and cytoplasmic aggregations of [alpha]1A voltage-dependent calcium channel protein associated with neurodegeneration in spinocerebellar ataxia type 6". Hum Mol Genet. 8 (7): 1185–93. doi: 10.1093/hmg/8.7.1185 . PMID   10369863.
  3. ↑ Toru S, Murakoshi T, Ishikawa K, Saegusa H, Fujigasaki H, Uchihara T, Nagayama S, Osanai M, Mizusawa H, Tanabe T (2000). "Spinocerebellar ataxia type 6 mutation alters P-type calcium channel function". J Biol Chem. 275 (15): 10893–8. doi: 10.1074/jbc.275.15.10893 . PMID   10753886.
  4. ↑ Wan J, Khanna R, Sandusky M, Papazian D, Jen J, Baloh R (2005). "CACNA1A mutations causing episodic and progressive ataxia alter channel trafficking and kinetics". Neurology. 64 (12): 2090–7. doi:10.1212/01.WNL.0000167409.59089.C0. PMID   15985579. S2CID   5679518.
  5. ↑ Tonelli A, D'Angelo M, Salati R, Villa L, Germinasi C, Frattini T, Meola G, Turconi A, Bresolin N, Bassi M (2006). "Early onset, non fluctuating spinocerebellar ataxia and a novel missense mutation in CACNA1A gene". J Neurol Sci. 241 (1–2): 13–7. doi:10.1016/j.jns.2005.10.007. PMID   16325861. S2CID   36806418.
  6. ↑ Alonso I, Barros J, Tuna A, Coelho J, Sequeiros J, Silveira I, Coutinho P (2003). "Phenotypes of spinocerebellar ataxia type 6 and familial hemiplegic migraine caused by a unique CACNA1A missense mutation in patients from a large family". Arch Neurol. 60 (4): 610–4. doi: 10.1001/archneur.60.4.610 . hdl: 10400.16/349 . PMID   12707077.
  7. ↑ Kors E, Vanmolkot K, Haan J, Kheradmand Kia S, Stroink H, Laan L, Gill D, Pascual J, van den Maagdenberg A, Frants R, Ferrari M (2004). "Alternating hemiplegia of childhood: no mutations in the second familial hemiplegic migraine gene ATP1A2". Neuropediatrics. 35 (5): 293–6. doi:10.1055/s-2004-821082. PMID   15534763.
  8. ↑ Riess O, Schöls L, Bottger H, Nolte D, Vieira-Saecker A, Schimming C, Kreuz F, Macek M, Krebsová A, Klockgether T, Zühlke C, Laccone F (1997). "SCA6 is caused by moderate CAG expansion in the alpha1A-voltage-dependent calcium channel gene". Hum Mol Genet. 6 (8): 1289–93. doi: 10.1093/hmg/6.8.1289 . PMID   9259275.
  9. ↑ Schöls L, Amoiridis G, Büttner T, Przuntek H, Epplen J, Riess O (1997). "Autosomal dominant cerebellar ataxia: phenotypic differences in genetically defined subtypes?". Ann Neurol. 42 (6): 924–32. doi:10.1002/ana.410420615. PMID   9403486. S2CID   32742844.
  10. ↑ Watanabe H, Tanaka F, Matsumoto M, Doyu M, Ando T, Mitsuma T, Sobue G (1998). "Frequency analysis of autosomal dominant cerebellar ataxias in Japanese patients and clinical characterization of spinocerebellar ataxia type 6". Clin Genet. 53 (1): 13–9. doi:10.1034/j.1399-0004.1998.531530104.x (inactive 22 December 2024). PMID   9550356.{{cite journal}}: CS1 maint: DOI inactive as of December 2024 (link)
  11. ↑ Storey E, du Sart D, Shaw J, Lorentzos P, Kelly L, McKinley Gardner R, Forrest S, Biros I, Nicholson G (2000). "Frequency of spinocerebellar ataxia types 1, 2, 3, 6, and 7 in Australian patients with spinocerebellar ataxia". Am J Med Genet. 95 (4): 351–7. doi:10.1002/1096-8628(20001211)95:4<351::AID-AJMG10>3.0.CO;2-R. PMID   11186889.
  12. ↑ Sinke R, Ippel E, Diepstraten C, Beemer F, Wokke J, van Hilten B, Knoers N, van Amstel H, Kremer H (2001). "Clinical and molecular correlations in spinocerebellar ataxia type 6: a study of 24 Dutch families". Arch Neurol. 58 (11): 1839–44. doi:10.1001/archneur.58.11.1839. PMID   11708993.
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