When applying RNA fluorescence in situ hybridization (RNA-FISH) on the fibroblast and corneal endothelium of FECD cases and controls, they detected RNA foci containing misspliced poly(CUG)n TCF4 transcripts and the associated protein muscleblind-like splicing regulator 1 (MBNL1) in the corneal endothelium of the FECD cohort with an intronic TNR expansion in TCF4. The gene discussed is MBNL1; the disease is Fuchs endothelial corneal dystrophy.