CELF1 and myotonic dystrophy type 1: Moreover, an increase in fetal splicing shifts of representative muscle DM1 targets was not observed in AAV/Hhnrph1-transduced myofibers (SI Appendix, Fig. S4C), and MBNL1 levels were not markedly perturbed in DM1 biopsies or HNRNPA1/CELF1-overexpressed myofibers (SI Appendix, Fig. S4 A, B, and D).