The following negative correlation values were found between myostatin and left hand grip strength (r = −0.370, p < 0.001) and myostatin and right hand grip strength (r = −0.318, p < 0.05), with a positive correlation found between myostatin and the Health Assessment Questionnaire (r = 0.494, p < 0.001); the higher myostatin levels were, the worse the physical functionality of patients with RA [59]. This evidence concerns the gene MSTN and rheumatoid arthritis.