A gain-of-function toxicity of the ataxin 1 protein was identified as the main causative agent in SCA1: In the ATXN1 gene on chromosome 6p23 a CAG-repeat expansion of variable length reaching between 39 and 83 repeats encodes for a prolonged polyglutamine chain in ataxin1 protein [2]. This evidence concerns the gene ATXN1 and spinocerebellar ataxia type 1.