Indeed, while the Mecp2-null mice are characterized by a reduced skeletal muscle mass, the novel Mecp2flox/y;MyoDiCre transgenic line, in which Mecp2 has been deleted only in myoblasts and skeletal muscle fibers, does not show any of the RTT-like myopathy: in particular, weight and size of skeletal muscles do not differ from those of control littermates. The gene discussed is MECP2; the disease is myopathy.