Although no lower threshold requirement for dystrophin expression has been firmly established, very low levels have been reported to be associated with some functional benefit in mouse models and human DMD/BMD.22, 23, 24 Some BMD patients have been reported to express as low as 3% of wild-type levels of internally deleted dystrophin.22, 23 Although these patients present with “severe BMD,” they are less severe than typical DMD. Here, DMD is linked to Duchenne muscular dystrophy.