A recent study on myostatin pathways in neuromuscular diseases has demonstrated the extremely low baseline level of myostatin in patients with muscle wasting or atrophic diseases and in particular in DMD and SMA.25 In keeping with the data reported in SMA patients, we confirm in this study that the Mstn mRNA transcripts was downregulated by ~80% in skeletal muscles in the severe SMA mice compared with that of the unaffected littermate controls. This evidence concerns the gene MSTN and proximal spinal muscular atrophy.