PPP2R2B and spinocerebellar ataxia type 12: We have used this method to modify the length of the CAG repeat contained in exon 7 of PPP2R2B. When longer than 43 triplets, this repeat causes the neurodegenerative disorder spinocerebellar ataxia type 12 (SCA12); our goal was to seamlessly introduce the SCA12 mutation into a human control iPSC line.