RT-qPCR analysis demonstrated the misregulation of Ldb3, Serca1, m-TTN, Tmem63b, Sorbs1 and Spag9 mRNA splicing, while the splicing efficiencies of Clcn1, Ryr1, Ryr2 and Tnnt3 mRNAs were normal (Supplementary information, Fig. S8; data not shown), reflecting the heterogeneity of mis-splicing in patients.62,63 A few mis-spliced genes observed in human patients appeared to be normal in our model, suggesting that other splicing factors such as MBNL264 and CUGBP159 might be involved in DM1. Here, SPAG9 is linked to myotonic dystrophy type 1.