MSTN and Duchenne muscular dystrophy: It also acts as an inhibitor of excessive muscle growth.13 Indeed, creatine/creatinineratio levels were increased in patients with DMD, whereas serum myostatin was lower in BMD and DMD compared with healthy controls.14, -, 18 Although these cross-sectional studies provide evidence that creatine/creatinineratio (Cr/Crn) and myostatin may be suitable as biomarkers, their relation to functional performance over a longer period still has to be largely demonstrated.