FST and proximal spinal muscular atrophy: There was no significant difference in serum follistatin levels between SMA cases and controls (cases: 573.5 pg/mL, controls: 790.8 pg/mL, P = 0.288—P = 0.438 corrected for weight and P = 0.760 corrected for BMI, Supplementary Fig. 1A in Supplementary material).