HTT and Huntington disease: Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG trinucleotide repeat expansion in the huntingtin gene on chromosome 4 which leads to the production of a protein with an abnormally long polyglutamine stretch.1 The prevalence is 10.6 to 13.7 × 10−5 in Western countries and the age at onset ranges between 30 and 50 years.1,2 The cardinal symptoms consist of movement disorders, usually chorea, cognitive impairment, and psychiatric disturbances.1,2