The spinocerebellar ataxias (SCA) are a clinically and genetically heterogeneous group of neurodegenerative disorders characterized by limb and gait ataxia. More than 25 different types of SCA have been described, although the causative genes have not yet been identified for all types. To date, SCA type 10 (SCA10) has only been found in populations of Amerindian origin (specifically, Mexican, Brazilian, and Argentinean). It is often a predominantly cerebellar syndrome, with prominent limb and gait ataxia, eye movement disorders, and dysarthria (slow, distorted speech). However, a subset of SCA10 patients, particularly those of Mexican descent, also experience epilepsy with generalized motor and/or partial complex seizures. Additional features of SCA10 include hyperreflexia, spasticity, peripheral neuropathy, cognitive impairment, and mood disturbances. The onset of symptoms in SCA10 patients is variable, but tends to occur in the second to fifth decade. SCA10 is caused by extreme expansions of a pentanucleatide repeat, ATTCT, in intron 9 of the ataxin-10 gene (ATXN10) located on chromosome 22 at band q13. The repeat tract in SCA10 patients may contain pure stretches of ATTCT pentanucleotides, or it may be interrupted with other penta- or septa-nucleotide sequences.