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Diseases

Genetic and Rare Diseases Information Center (GARD)

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Spinocerebellar ataxia 8


Other Names for this Disease
  • SCA8
  • Spinocerebellar ataxia type 8
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Inheritance


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How is spinocerebellar ataxia type 8 inherited?

Spinocerebellar ataxia 8 (SCA8) is more genetically complex than other SCAs.[1] Typically, a genetic disorder is considered autosomal dominant if only one copy of the defective gene needs to be inherited in order to develop the disease, and autosomal recessive if two copies of the defective gene (one from each parent) are required to develop the disease. SCA8 is a dominant condition because only one copy of the causative gene needs to be inherited, but quite often, family histories give the impression that the condition is sporadic (appearing without a family history) or inherited in an autosomal recessive manner.[1]

Genes are made up of substances known as nucleotides (identified by letters) linked together in chains. In SCA8, a change (mutation) in the ATXN8OS gene results in extra copies of a series of nucleotides identified by the letters CTG (this is called a trinucleotide repeat expansion). The ATXN8OS gene is genetically "unstable" which means that the number of repeats may expand or contract when the gene is passed on. Therefore, there are several potential outcomes for families in which the unstable gene is present: when a parent is unaffected, the number of CTG repeats can expand to cause the disease in a child; when a parent is affected, the number of repeats might contract (decrease) so that the child does not have the disease; an affected parent may have an affected child; or an unaffected parent may have an unaffected child. This unique aspect of SCA8 helps to explain why some family members can inherit the abnormal gene but not develop the disease, and why some family members develop the disease when neither parent is affected.[1][2]
Last updated: 1/2/2012

References
  1. Spinocerebellar Ataxia Type 8 (SCA8). National Ataxia Foundation. http://www.ataxia.org/pdf/NAF%20Web%20Content%20Publication%20SCA8.pdf. Accessed 1/2/2011.
  2. Yoshio Ikeda, Joline C Dalton, John W Day, Laura PW Ranum. Spinocerebellar Ataxia Type 8. GeneReviews. February 7, 2007; http://www.ncbi.nlm.nih.gov/books/NBK1268/. Accessed 1/2/2011.