Huntington's disease(HD)is an autosomal dominant neurodegenerative disorder caused by a CAG trinucleotide repeat expansion exceeding a threshold length(>35 repeats)in exon 1 of the huntingtin gene(HTT)[1].The age at onset is typically 40-50 years,except for a very low percentage(approximately 6%)of juvenile-onset HD patients carrying 75 or more CAG repeats;longer CAG repeats predict an earlier onset[1].The clinical features of HD vary among individuals but are typically characterized by progressive motor dysfunction,cognitive disorder,and psychiatric disturbance[1].HD patients are usually healthy before the onset,showing no diagnosable symptoms[1].