CTLA4 and rheumatoid arthritis: Furthermore, multiple genes have been identified to be associated with susceptibility to RA and AITD, including the human leukocyte antigen DR B1 gene, the cluster of differentiation 226 gene, the protein tyrosine phosphatase non-receptor type 22, the Fc receptor-like 3 gene, the insulin-like growth factor 1 receptor gene, the cytotoxic T-lymphocyte-associated protein 4 gene, and the cluster of differentiation 40 gene, among others (37, 46).