HTT and Huntington disease: Sequence differences between mouse host and human genes allowed allele-specific silencing of the pathogenic human Htt transcripts in the setting of preserved expression of endogenous Htt. Intraventricular infusions of lipid-encapsulated [69] or intrastriatal injections of cholesterol-conjugated [70] siRNAs effectively silenced mutant huntingtin transcripts by ≈70% leading to a 56–66% reduction in HD protein levels.