Polyglutamine diseases are a group of nine hereditary neurodegenerative disorders and include Huntington disease (HD), the most prevalent spinocerebellar ataxias (SCAs type 1, 2, 3, 6, 7 and 17), dentatorubral-pallidoluysian atrophy and spinal and bulbar muscular atrophy (also known as Kennedy disease). Apart from the latter, these disorders are characterized by a range of movement disorders, especially chorea and ataxia. They are caused by a trinucleotide (cytosine-adenine-guanine (CAG)) repeat expansion in the translated regions of otherwise unrelated genes, resulting in proteins with expanded polyglutamine domains. This article is protected by copyright. All rights reserved.