HTT and juvenile Huntington disease: Huntington’s disease (HD) is an autosomal dominant progressive neurodegenerative disorder with a distinct phenotype characterized by chorea, dystonia, incoordination, cognitive decline, and behavioral difficulties, which is caused by a heterozygous expanded trinucleotide repeat (CAG)n, encoding glutamine, in the gene encoding huntingtin (HTT) on chromosome 4p16 (Walker, 2007; Dayalu & Albin, 2015).