HTT and Huntington disease: An earlier study suggested that the expression of another striatally enriched gene, CalDAG-GEF1, might account for the brain regional selectivity of mutant htt toxicity [13], by demonstrating that the CalDAG-GEF1 is downregulated in HD human caudate and in R6/2 mice striatum and that silencing of this gene protects neurons from toxicity induced by mutant htt in an organotypic cortico-striatal slice model of HD.