Knowledge about some of the rarer causes of dementia is now quite advanced (Lautenschlager and Martins, 2005), which can in turn inform other more common causes of dementia. Such is the case with the monogenic disorder of Huntington's disease (HD) when compared to, say, Alzheimer's disease (AD). HD is an autosomal dominant hereditary neurodegenerative disease, which involves the basal ganglia, its connections to the frontal lobe and related neural circuits. The onset of HD is typically in mid-life (but onset can range from childhood to old age), with motor, cognitive and neuropsychiatric symptoms. There is currently no cure for this devastating and inevitably fatal neurodegenerative disease, with current treatment approaches being solely symptomatic. The highest frequencies of HD are found in Europe and in those countries whose populations are of predominately European origin such as the USA and Australia (approximately 1 case per 10,000 people).