In HD, the polyQ expansion encoded by an expanded CAG repeat (>36 CAGs) in exon 1 of the HD gene causes huntingtin (HTT) to misfold and aggregate in the patient brain, resulting in the preferential loss of the medium spiny neurons in the striatum and extended neurodegeneration in various brain regions as HD progresses (Bates et al., 2015). This evidence concerns the gene HTT and Huntington disease.