Huntington's disease (HD) is a neurodegenerative condition caused by a cytosine‐adenine‐guanine (CAG) repeat expansion in exon 1 of the huntingtin gene (HTT) (The Huntington's Disease Collaborative Research Group 1993) and is characterized by progressive motor, cognitive and psychiatric symptoms including involuntary movement disturbances, dementia and depression. This evidence concerns the gene HTT and dementia.