Serum myostatin levels were significantly lower in subjects with SMA, with a median of 98 pg/mL (5–157 pg/mL), compared to controls who had a median of 412 pg/mL (299–730 pg/mL; P < 0.001 corrected for weight or BMI; Fig. 2A). This evidence concerns the gene MSTN and proximal spinal muscular atrophy.