tokens: Genotype - phenotype studies of mouse models for DMD show position - specific effects of the mutations upon the phenotype mice with 5 defects of dystrophin have normal ERGs , those with defects in the central region have a normal b - wave amplitude associated with prolonged implicit times for both the b - wave and oscillatory potentials , and mice with 3 defects have a phenotype similar to that seen in DMD / BMD patients .