Murillo-saich JD et al. found a lower SMI (P = 0.008) and a higher myostatin concentration in 84 RA patients compared to 127 controls (9.0 [1.2–140] ng/mL vs. 3.5 [1.0–89.9] ng/mL, P < 0.001)24. This evidence concerns the gene MSTN and rheumatoid arthritis.