MSTN and rheumatoid arthritis: In the study performed by Gonzalez-Ponce et al., they determined a myostatin value of ≥17 ng/mL as an independent factor for muscle mass risk (OR = 3.04, 95% CI 1.14–8.10), with a sensitivity of 43%, indicating the possibility of positive myostatin results of ≥17 ng/mL in patients with myopenia, and a specificity of 77%, indicating the probability of negative myostatin results ≥17 ng/mL in RA patients without myopenia.