MSTN and rheumatoid arthritis: Further gender stratification analysis showed that female RA patients with myopenia had a lower level of serum myostatin than those without (2.855 ± 1.580 ng/ml vs. 3.335 ± 1.601 ng/ml, P=0.008, Figure 1H), but in male RA patients, there was no difference in serum myostatin between those with or without myopenia (3.839 ± 1.756 ng/ml vs. 3.895 ± 2.041 ng/ml, P=0.918, Figure 1I).