To test the hypothesis that CUGexp RNA induces pathogenic effects in muscle tissue that are independent of MBNL1 loss-of-function, we crossed the LR41 transgenic model with the Mbnl1−/− model to create the LR41;Mbnl1−/− double homozygous model of DM1 (Supplementary Fig. 1; see Methods). The gene discussed is MBNL1; the disease is myotonic dystrophy type 1.