For more information on other types of ataxia, go to www.ataxia.org (The US National Ataxia Foundation)
About Ataxia
Spinocerebellar ataxias
Spinocerebellar ataxias (SCAs) are a group of ataxias which result from damage to an area of the brain called the cerebellum (Dueñas et al, 2006). The cerebellum controls balance and coordination. Therefore individuals affected by SCA often experience a loss of balance and co-ordination and often first present with changes in movement or manner of walking (gait) (Zoghbi, 2000).
SCAs are genetically inherited, ie they are passed on from parents to their children. For a child to inherit SCA, only one of their parents need carry the abnormal gene and therefore each child has a 50% chance of inheriting the condition (Zoghbi, 2000). Although there are over 30 known types of SCA, genetic tests are not available for all of them, so you would only be able to have routine diagnostic tests for some of them.
There are currently 31 known types of SCA. These are known as SCA 1-8 and SCA 10-32 (there is currently no condition associated with SCA9 but the name has been reserved). SCAs can be categorized into three main groups, according to the type of mutation in the gene. The first of these is the expanded polyglutamine ataxias (SCA 1, 2, 3, 6, 7 and 17). The second is the noncoding repeat ataxias (SCA 8, 10 and 12). The third is the ataxias caused by other gene mutations (SCA 5, 13, 14 and 27) (Soong & Paulson, 2007). More details about these categories can be found below.
There is currently no cure or preventative treatment for any of the SCAs, however there are several therapies available to treat the symptoms associated with each condition. Research is ongoing in terms of finding treatments as well as looking at what causes each SCA in the hope of one day developing a cure.
Read about SCA research currently being funded by Ataxia UK
Expanded polyglutamine spinocerebellar ataxias
This category includes SCA 1, 2, 3, 6, 7 and 17. In these conditions, the abnormality in the faulty gene has been identified precisely.
Proteins in the human body are formed from many different amino acids. The order of amino acids in each protein is coded for by each gene in an individual’s DNA. The genes are codes made up of different sequences of the four nucleotide bases found in DNA: cytosine, adenine, guanine and thymine, (abbreviated to C, A, G and T, respectively).
The sequence CAG codes for an amino acid known as glutamine. In normal genes, CAG can be repeated from 6-35 times, however in SCA, these repeats are expanded to include 40-100 repeats (Zoghbi, 2000). These repeats are found in the coding parts of the genes and therefore when the protein is made, long stretches of the amino acid glutamine are found in these proteins. These conditions are known as polyglutamine disorders (literally meaning ‘many glutamine’).
Research has shown that an individual with a high number of CAG repeats will have a more severe SCA and will display symptoms at an earlier stage than someone with fewer CAG repeats (Soong & Paulson, 2007).
This expansion in CAG repeats is thought to produce abnormal proteins which have a ‘toxic effect’ (Zoghbi, 2000). Research is currently being undertaken to look at the ways in which these ‘toxic’ proteins cause damage and how this might be prevented.
Read more about expanded polyglutamine repeat SCAs
Non-coding repeat spinocerebellar ataxias
This category includes SCA 8, 10 and 12. In these conditions, the abnormality is less clear.
In the same way as the previous category, it includes abnormal repeats of nucleotide bases in DNA. However, these repeats are found in parts of the genes that do not code for the amino acids in the affected protein (Dueñas et al, 2006).
It remains unclear how these abnormalities cause SCA but there are several different theories and research is being undertaken into these.
Read more about non-coding SCAs
Spinocerebellar ataxias caused by other gene mutations
This category includes SCA 5, 13, 14 and 27. In these conditions, the abnormality is caused by what are known as conventional gene mutations. These include things such as a deletion or insertion of a nucleotide base or the exchange of one nucleotide base for another which results in the production of the wrong amino acid for a specific protein (Soong & Paulson, 2007).
Little is known as to how these mutations are linked to the damage seen in SCAs but research is being undertaken to look at possibilities for this.
Read more about SCAs caused by other gene mutations
REFERENCES
Dueñas et al. Brain 2006; 129:1357-1370
Soong & Paulson. Current opinion in Neurology 2007; 20: 438-446
Zoghbi. Neurobiology of Disease 2000; 7: 523-527
Page created February 2012
