As the mdx mouse shows a compensatory over-expression of dystrophin-related proteins such as utrophin, thus resulting in a milder dystrophic phenotype compared to DMD patients, Gregorevic and colleagues selected the dystrophin/utrophin double-knockout (dko) mouse model to test the intravascular administration of micro-dystrophin packaged into an AAV-6 (86). The gene discussed is UTRN; the disease is Duchenne muscular dystrophy.