At the beginning in literature, there were only a few studies that addressed BTLA gene polymorphisms, and majority of them have investigated its role in susceptibility to autoimmune diseases, such as rheumatoid arthritis (RA) (55, 210), systemic lupus erythematosus (SLE) and type 1 diabetes mellitus (211). The gene discussed is BTLA; the disease is rheumatoid arthritis.