However, there is evidence from several mouse models of Huntington's disease that the level of huntingtin aggregates decrease within days of the levels of huntingtin protein being decreased either by turning off expression24 or by using siRNA to decrease expression.25 This suggests that in transgenic mouse models at least htt aggregates are not fixed but are being generated and either degraded or dispersed and that a decrease in htt levels is sufficient to decrease the aggregate levels. This evidence concerns the gene HTT and juvenile Huntington disease.