UTRN and Becker muscular dystrophy: Next, we compared sarcolemmal utrophin levels between mature and regenerating muscle fibres (determined by the presence of developmental and fetal myosin) in sections from 3 BMD patients from 4 to10 years of age (P5, P6 and P7) and 6 DMD patients from 4 to 8 years of age (P9, P10, P11, P12, P14 and P15) by co-immunostaining utrophin with a cocktail of fetal and developmental myosin antibodies.