HTT and Huntington disease: The inherent limitation of RNAi is partial suppression of gene expression, which might be advantageous in HD treatment because of the gain of function of mHTT and the loss of function of normal HTT potentially acting concomitantly in HD etiology.56 By knocking down the expression of HTT, which includes both mHTT and normal HTT, we showed the amelioration of the disease phenotype.