HTT and Huntington disease: The phenotype exhibited by each animal model of HD needs to be considered in the context of the different approaches used to generate the respective model.42 Key distinguishing factors are the genetic approach and transgene construct used, for example, the use of full‐length or only a fragment of mutant huntingtin (HTT), the length of the CAG repeat incorporated into the genome, the expression of the HD mutation from a transgene versus knock‐in of the mutation into the endogenous HTT locus.