HTT and juvenile Huntington disease: Huntington’s disease (HD) is an autosomal dominant, progressive, and devastating neurodegenerative disorder caused by a polyglutamine expansion in exon 1 of the huntingtin gene (Htt) with the primary site of neuron loss is at the striatal part of the basal ganglia (Agrawal and Fox, 2019; Lallani et al., 2019).