Even though STAT4 has been linked to a variety of autoimmune disorders—neuromyelitis optica (NMO), systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) systemic sclerosis (SS), MS [11,23,24,25,26]—this is, as far as we know, the first study to investigate the relationship between the STAT4 (rs10181656, rs7574865, rs7601754, and rs10168266), STAT4 serum levels, and the occurrence of MS in the Lithuanian population. The gene discussed is STAT4; the disease is synovial sarcoma.