Spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD) is a progressive 
autosomal dominant neurodegenerative disease caused by abnormal CAG repeats in 
the exon 10 of ATXN3. The accumulation of the mutant ataxin-3 proteins carrying 
expanded polyglutamine (polyQ) leads to selective degeneration of neurons. Since 
the pathogenesis of SCA3 has not been fully elucidated, and no effective 
therapies have been identified, it is crucial to investigate the pathogenesis 
and seek new therapeutic strategies of SCA3. Induced pluripotent stem cells 
(iPSCs) can be used as the ideal cell model for the molecular pathogenesis of 
polyQ diseases. Abnormal CAG expansions mediated by CRISPR/Cas9 genome 
engineering technologies have shown promising potential for the treatment of 
polyQ diseases, including SCA3. In this study, SCA3-iPSCs can be corrected by 
the replacement of the abnormal CAG expansions (74 CAG) with normal repeats (17 
CAG) using CRISPR/Cas9-mediated homologous recombination (HR) strategy. Besides, 
corrected SCA3-iPSCs retained pluripotent and normal karyotype, which can be 
differentiated into a neural stem cell (NSCs) and neuronal cells, and maintained 
electrophysiological characteristics. The expression of differentiation markers 
and electrophysiological characteristics were similar among the neuronal 
differentiation from normal control iPSCs (Ctrl-iPSCs), SCA3-iPSCs, and isogenic 
control SCA3-iPSCs. Furthermore, this study proved that the phenotypic 
abnormalities in SCA3 neurons, including aggregated IC2-polyQ protein, decreased 
mitochondrial membrane potential (MMP) and glutathione expressions, increased 
reactive oxygen species (ROS), intracellular Ca2+ concentrations, and lipid 
peroxidase malondialdehyde (MDA) levels, all were rescued in the corrected 
SCA3-NCs. For the first time, this study demonstrated the feasibility of 
CRISPR/Cas9-mediated HR strategy to precisely repair SCA3-iPSCs, and reverse the 
corresponding abnormal disease phenotypes. In addition, the importance of 
genetic control using CRISPR/Cas9-mediated iPSCs for disease modeling. Our work 
may contribute to providing a potential ideal model for molecular mechanism 
research and autologous stem cell therapy of SCA3 or other polyQ diseases, and 
offer a good gene therapy strategy for future treatment.