Huntington's disease (HD) is a relentlessly degenerative disorder of the central nervous system, affecting the striatum most prominently, but also the cerebral cortex and other subcortical structures. It is characterized by progressive dementia with chorea (brief, irregular movements that are not rhythmic but appear to flow from one muscle to the next), athetosis (slow, writhing movements), impaired coordination, abnormal speech, swallowing difficulties and neuropsychiatric symptoms, such as depression. Although HD has been around since at least the Middle Ages, early definitive descriptions were made during the mid-19th century by Charles O. Waters and, later, by Johan C. Lund. A comprehensive and influential description of HD was subsequently made by George Huntington in 1872, and the disease has since borne his name. By examining the medical histories of several generations of a family exhibiting similar symptoms, Huntington recognized that their diseases were linked. Later, William Osler's interest in HD brought increased attention throughout the medical community. Smith Ely Jelliffe and Charles Davenport made major contributions to the understanding of the genealogy of the disease during the early 20th century, establishing that it was autosomal dominant and documenting several key features of its inheritance, such as anticipation, whereby age of symptom onset, severity, or both worsen in succeeding generations [1].

Research into HD continued steadily throughout the 20th century, with several pathogenic themes emphasized, particularly excitotoxicity, beginning during the mid 1970s [2]. A major breakthrough occurred in 1983 when the US–Venezuela Huntington's Disease Collaborative Research Project identified the approximate location of a causal gene. In 1993, the research group isolated the disease gene at chromosome 4p16. 3, marking this as the first autosomal disease gene identified using genetic linkage analysis [3]. The genetic change was a triplet nucleotide repeat (CAG) expansion, giving rise to a long polyglutamine stretch in the huntingtin (Htt) protein.