Neurodegenerative Huntington's disease (HD) is caused by expansion of the trinucleotide CAG repeats in exon-1 of the HD gene, the mutation that encodes an extended polyglutamine (polyQ) tract within the N-terminal exon-1 of the Huntingtin protein (Htt) (Macdonald et al., 1993). This evidence concerns the gene HTT and juvenile Huntington disease.