The shared susceptibility genes involved in the pathogenesis of RA and thyroid disorders are HLA gene complex including HLA-DR-B1 (human leukocyte antigen DR B1), CTLA 4 (cytotoxic T-lymphocyte-associated antigen 4), PTPN22 (protein tyrosine phosphatase non-receptor type 22), FCRL3 (Fc receptor-like 3), and IL2RA (interleukin 2 receptor subunit alpha).[32] On the contrary, previous studies elucidated that the carriership of HLA gene complex is associated with anti-CCP positivity and therefore more aggressive disease. This evidence concerns the gene FCRL3 and rheumatoid arthritis.