The function of myostatin appears to have been conserved accross diverse species as indicated by the doubling of muscle mass in cattle, sheep, dog and human carrying natural mutations in the myostatin gene [1, 32-36]. In support of this, myostatin sequence is highly conserved through evolution, among species ranging from zebrafish to humans [1]. Thus, the discovery that myostatin acts as a negative regulator of muscle growth has led to intense scrutiny of the possibility that myostatin inhibition might be useful in treatment of muscle-wasting-related disorders. Accordingly, genetic inhibition of myostatin function or myostatin blockade by several agents (including myostatin antibodies, myostatin propeptide, follistatin-related proteins, soluble type II myostatin receptor) have been shown to be effective in increasing muscle mass and reducing disease severity in the mdx mouse model of Duchenne muscular dystrophy, in the caveolin 3 deficient model of limb-girdle muscular dystrophy 1C (LGMD1C) and in two rodent models of amyotrophic lateral sclerosis [19, 37-40]. Although myostatin does not correct the primary defects in muscle dystrophy, it can lessen the severity of the disease phenotype. In contrast, loss of myostatin activity in the dyw/dyw mouse model of laminin-deficient congenital muscular dystrophy, did not ameliorate the muscle pathology but increased postnatal lethality [41]. With respect to the therapeutic benefit of myostatin inhibition, Parsons et al. [42] reported that elimination of myostatin can improve the dystrophic phenotype in mice nullizygous for δ -sarcoglycan (scgd-/-) (a model of human limb-girdle muscular dystrophy referred as LGMD2F). However, this effect is obtained only in young dystrophic mice but not in older ones. In addition, their results also showed that the effectiveness of myostatin blockade could be dependent on specific muscle groups studied. Taken together these studies indicate that myostatin inhibition may not be beneficial in all dystrophic contexts. This is supported by data showing that AAV-mediated delivery of a mutated myostatin propeptide in the muscles of animal models of two limb-girdle muscular dystrophies (LGMD2A caused by mutations in the calpain gene and LGMD2D caused by mutations in the α -sarcoglycan gene) leads to different outcomes: it ameliorates calpain 3 but not α -sarcoglycan deficiency [43]. Therefore, it will be important for investigating the myopathies that are susceptible to myostatin antagonism, and, conversely, for identifying the stages of the disease at which the myostatin blockade is operative.