Previous studies have demonstrated the involvement of DNA repair proteins in repeat instability in repeat expansion disorders, such as DM1.52 To examine whether the expression of these genes involved in DNA repair relates to the differences in repeat instability in each CNS cell lineage of DM1, we analyzed gene expression of mismatch repair genes (MSH2, MSH3 and MSH6) and FAN1. Here, MSH3 is linked to myotonic dystrophy type 1.