This RNA gain of function mechanism is best exemplified by the titration of the Muscleblind-like 1 and 2 (MBNL) RNA binding proteins into nuclear RNA foci constituted of CUG or CCUG RNA repeat expansions in myotonic dystrophy type 1 and 2 (DM1 and 2), as well as in Fuchs endothelial corneal dystrophy (FECD) (Miller et al., 2000; Fardaei et al., 2002; Wieben et al., 2017; Rong et al., 2019). The gene discussed is MBNL1; the disease is myotonic dystrophy type 1.