Provided herein are compositions and methods related to treating repeat expansion diseases that feature the sequestration of Muscleblind-like (MBNL) proteins by the toxic repeat RNA transcripts within distinct nuclear foci that are expressed from the expanded repeat tracts. Certain compositions of synthetic MBLN proteins can be used to displace endogenous MBNL from the toxic RNAs or replace endogenous MBNL within the cell for normal function.
