As it was increasingly studied, it was shown that Huntington’s disease represents an autosomal dominant progressive neurodegenerative disorder, consisting of a repetitive set of (CAG)n trinucleotide sequences in a gene found on the chromosome 4p16.3, between D4S10 and D4S98 [115] (Gusella et al., 1983), called huntingtin (HTT), leading to a polyglutamine expansion. The gene discussed is HTT; the disease is juvenile Huntington disease.