HTT and Huntington disease: We have previously reported the design and proof-of-concept, for short-term suppression of total human HTT using an AAV5 encoding a miRNA targeting exon 1 of human HTT (miHTT) in a humanized mouse model of HD, Hu128/21, which expresses two full length, human HTT transgenes heterozygous for the HD mutation on the Htt-/- background (60,61).