Balance and motor coordination abnormalities, as well as neuropathology, supporting the beneficial effects of this strategy as a therapeutic approach for MJD. In this study, we investigated whether allele-specific gene silencing initiated before onset of symptoms would alleviate MJD. For this purpose we used an experimental paradigm involving simultaneous injection of lentiviral vectors encoding for the mutant ataxin-3 and for the shRNA sequences in the mouse cerebella, in this way mimicking a gene silencing therapy initiated at a pre-symptomatic stage. We found that this strategy is able to suppress or drastically reduce the development of motor impairments and neuropathological abnormalities representative of MJD. The RNAi strategy has been proposed as potential therapy to down-regulate the expression of mutant genes and halt the progression of different autosomal dominant neurodegenerative diseases. To date its efficacy has been proved in several pre-clinical rodent trials for diseases such as Huntington’s disease, familial forms of amyotrophic lateral sclerosis and spinocerebellar ataxia type 1 as well as in familial forms of Alzheimer disease. Among the important concerns relative to RNAi therapy is the development of allele-specific approaches in order to selectively target the mutant allele without inhibiting the corresponding wild-type allele. This concern is of particular importance in diseases where the knockdown of wild-type allele has proved to be toxic; nevertheless even when an obvious toxicity is not present, given the potential unknown side effects of long-term silencing of wild-type proteins, selective strategies offer a better therapeutic solution. In previous work, we and others have shown that both allelespecific and undiscriminating silencing were effective strategies for alleviating striatal neuropathology of MJD. Here we show that early allele-specific silencing of mutant ataxin-3 is able not only to impede the development of mutant ataxin-3 aggregated and associated neuronal dysfunction within the cerebellum but also to robustly prevent the progression of balance and motor coordination deficits measured by the accelerated rotarod test as well as gait analysis of footprints. Despite the limitations of the experimental paradigm, as simultaneous injection of vectors encoding for mutant ataxin-3 and for the silencing sequences may prevent the levels of mutant ataxin-3 from reaching the levels found in controls, our data constitutes a proof-of-principle for initiation of therapy before onset of the disease. In MJD patients, as well as other SCAs patients, the gait ataxia is a clinical symptom always present. VE-822 1232416-25-9 Indeed, gait difficulty is reported as the initial symptom in 66% of the patients while for others, symptoms like cramps, sleep disturbances, neuropathic symptoms, restless legs syndrome among others appear first. In this study the allele-specific silencing was able to hamper the development and progression of gait ataxia, as measured by the specific test of footprint analysis. Furthermore, gene silencing mediated alleviation of the hyperactive phenotype observed in this mouse model. Hyperactivity had been already reported for a mouse model of Dentatorubral-Pallidoluysian Atrophy and MJD.