Finally, muscle samples from patients with RA compared to OA exhibited higher expression of Forkhead box protein O1 (FOXO1) and myostatin (MSTN), negative regulators of muscle growth (fold changes 2.35, p < 0.05 and 3.62, p < 0.05 respectively; Figure 1F,G). Here, MSTN is linked to rheumatoid arthritis.