Huntington disease (HD) is an autosomal dominant neurodegenerative disease caused by a cytosine–adenine–guanine (CAG) expansion in the HTT gene that codes for an abnormal polyglutamine tract in the huntingtin protein (HTT).1 Polyglutamine-expanded mutant huntingtin (mHTT), the primary pathogenic cause of HD, leads to the progressive loss of neuronal populations in the striatum, as well as other structures of the basal ganglia and the cerebral cortex.2–7. Here, HTT is linked to juvenile Huntington disease.