HTT and juvenile Huntington disease: Splicing of the HTT huntingtin gene, which contains a CAG repeat, is altered at expanded repeats associated with Huntington’s Disease, resulting in the production of a transcript containing only exon 1 and the production of an exon 1 HTT protein (Gipson et al., 2013; Sathasivam et al., 2013; Neueder et al., 2017; Neueder et al., 2018; Franich et al., 2019).