HTT and Atrophy: With medium dose AAV5-miHTT, which resulted in ∼75% lowering of mHTT and ∼80% lowering of wtHTT in the striatum as well as ∼40% lowering of mHTT and ∼50% lowering of wtHTT in the cortex at 7 months post-injection, this level of HTT suppression led to improvement of striatal atrophy but also resulted in a trend towards preventing the onset of spatial learning deficits in Hu128/21 mice.