These mice develop a progressive phenotype with many of the hallmarks of human HD, including motor and cognitive Smad inhibitor dysfunction, as well as brain atrophy (Hodgson et al., 1999). The HuASO, complementary to human huntingtin mRNA, was infused for 2 weeks into the right lateral ventricle of YAC128 mice beginning at 3 months of age, after which the osmotic pumps used to deliver the ASOs were removed and the animals were allowed to recover for 2 weeks prior to being assessed for motor coordination and anxiety (Figure 3A). As in BACHD mice, treatment with the human huntingtin specific ASO (HuASO) led to a significant reduction in huntingtin mRNA (p = 0.0012) and protein levels (to 16% ±

3% of vehicle [p < 0.001]) Small molecule library at 6 weeks after the termination of treatment (Figure 3C).

Motor deficits, which develop in the YAC128 animals as early as 2 months of age, improved within 1 month of initiating HuASO treatment (4 months of age), and were significantly different from saline (p = 0.024) and restored to nontransgenic control levels after two months (5 months of age) (Figure 3B). Behavioral assays directed at measuring anxiety (elevated plus maze; Figure S3A) and ambient motor activity (open-field; Figure S3B) revealed that deficits in ASO-treated mice were restored to nontransgenic performance levels within 2 months of ASO infusion, although improvements in these two behaviors failed to reach significance. Thus, transient ASO-mediated treatment after disease initiation leads to a sustained reduction in expanded huntingtin accumulation that in turn is reflected in a progressive restoration of initial motor deficits to normal over Carnitine dehydrogenase a 2 month period.

To test for a therapeutic benefit from reducing expanded huntingtin in older animals, the HuASO was infused for 2 weeks into 6-month-old (Figure 3D), more phenotypic YAC128 mice. This yielded a sustained reduction in mutant huntingtin mRNA and protein (which remained suppressed to 42% [p < 0.001] and 44% [p = 0.0057], respectively) when measured 2.5 months after discontinuing treatment (Figure 3E). Phenotypic reversal was again achieved. After a 2 month lag, motor function improved and treated animals were no longer significantly different from nontransgenic animals (Figure 3F). Some behavioral characteristics improved sufficiently to reach nearly normal levels by 9 months of age (Figures S3C and S3D), albeit these did not reach a p < 0.05 level of confidence. Thus, while mice transiently treated at this older age (6 months) never reached the improvement achieved in younger animals, therapy initiated in these more phenotypic mice provided sustained suppression of mutant huntingtin synthesis and partial reversal of disease characteristics 3 months after stopping treatment (Figures 3A–3C).