FST and proximal spinal muscular atrophy: Myostatin expression is impaired in serum and muscle biopsies of SMA patients (Mariot et al., 2017), and its inhibition with intramuscular injection of AAV1-follistatin or muSRK-015P monoclonal antibody ameliorated muscle mass functions in different models of SMA mice (Feng et al., 2016; Long et al., 2019).