To review progress in spinocerebellar ataxias (SCAs) and novel approaches to treatment.Results and conclusions:
Autosomal dominant ataxias are now referred to as SCAs, with polyglutamine expansion mutations constituting the most common cause of SCAs. Phenotypic variation in patients with SCA is remarkable even in patients with identical mutations. In patients with SCA2, cerebellar ataxia is typically associated with slowed saccadic eye movements. In addition to classic cerebellar and brainstem signs, however, SCA2 can also present as a parkinsonian syndrome or as amyotrophic lateral sclerosis. After identifying the SCA2 gene (gene symbol ATXN2) in 1996, we generated several mouse models that recapitulated salient features of the human disease. In these models, behavioral and physiologic changes preceded cell death. Modified antisense oligonucleotides (ASOs) provide a unique tool to target mRNA transcripts in vivo with extended stability of ASOs and better activation of RNAse H. We generated methoxyethyl group–gapmer ASOs that reduced ATXN2 expression >80% in vitro and then progressed the lead ASO to in vivo testing in an SCA2 mouse model. Compared to intraventricular injection of saline, treatment with ASO resulted in significant knockdown of endogenous mouse and human transgenic ATXN2. In addition, progression of the motor phenotype was slowed and Purkinje cell firing in the acute cerebellar slice normalized. ASO-based therapies are underway in humans providing hope that this approach will also be applicable to patients with cerebellar degenerations.