HTT and juvenile Huntington disease: Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG triplet repeat expansion in exon 1 of the HTT gene that is translated into polyglutamine (polyQ) sequences in the huntingtin (HTT) protein which leads to progressive deterioration of cognitive and motor functions (The Huntington’s Disease [MACDONALD, 1993; Ross and Tabrizi, 2011; Vonsattel and DiFiglia, 1998]).