Transcripts containing expanded copies of the CUG repeat accumulate as discrete nuclear RNA foci within tissue derived from individuals affected with FECD;15 similar to other repeat expansion-associated disorders, such as myotonic dystrophy type 1 (DM1 [MIM: 160900]), which is caused by an identical CTG repeat expansion located within the 3′ untranslated region (UTR) of DMPK (MIM: 605377).16, 17 DM1 pathogenesis has largely been attributed to these RNA aggregates sequestering RNA-splicing factors, including MBNL1 and MBNL2,18, 19, 20 leading to a functional deficiency of these proteins and subsequent global disruption of splicing.21, 22