Huntington’s disease (OMIM #143100) is the most prevalent autosomal dominant polyglutamine (polyQ) disorder (5–10 cases per 100,000 inhabitants worldwide), and it is caused by an aberrant expansion of polymorphic trinucleotide CAG repeats (>36) in exon 1 of the huntingtin (HTT) gene1. This evidence concerns the gene HTT and juvenile Huntington disease.