It functions by inhibiting the binding of myostatin and other members of the TGF-ß family to ActRIIB/IIA receptors, playing a crucial role in muscle fibre formation, growth, and hypertrophy.43,44 In our study, serum levels of follistatin were slightly elevated compared to controls, which is consistent with the previous anecdotal study involving four SMA cases,40 but the difference was not statistically significant. This evidence concerns the gene ACVR2B and proximal spinal muscular atrophy.