While AD, FTD and VaD have both sporadic and genetic causes, HD is relatively rare in comparison, with a reported prevalence of 5.7 per 100,000,3 and is an autosomal dominant neurodegenerative condition caused by a trinucleotide CAG repeat expansion on chromosome 4, causing abnormal accumulation of the huntingtin protein (HTT).4 The gene discussed is HTT; the disease is Huntington disease.