MBNL1 and myotonic dystrophy type 1: Previous studies have shown that approximatelytwo 5′CUG/3′GUC motifs bind to one copy of MBNL1. Asthe average repeat length in DM1-affected patients is ∼500, MBNL1 accumulates in nuclear foci containinglong repeats in a pathogenic setting.,,, It was therefore hypothesizedthat two MBNL1 molecules brought into proximity by r­(CUG)exp could generate a BRET signal.