Huntington disease (HD) is an autosomal dominant, neurodegenerative disorder caused by an expanded trinucleotide (CAG) repeat sequence in the first exon of the HD (HTT) gene, leading to an enlarged polyglutamine tract in the encoded protein huntingtin.1 Unwanted choreiform movements, psychiatric and behavioural disturbances and cognitive impairment characterize the disease. The gene discussed is HTT; the disease is Huntington disease.