UTRN and cardiomyopathy: These investigations have led us to suspect 2 potential causes of this microdystrophin-induced cardiomyopathy: (a) microdystrophin competes with and displaces endogenously expressed utrophin at the cardiomyocyte sarcolemma and (b) the long-term overexpression of microdystrophin protein contributes to overload of the ubiquitin-proteosomal system (UPS), resulting in impairments in cardiomyocyte protein quality control.