CD40 and autoimmune thyroid disease: In several families with recurrent autoimmune thyroiditis, there has been described a positive linkage between GD and various genes that can be divided among immune system regulators (human leukocyte antigen—antigen D regulated, HLA‐DR; cytotoxic T‐lymphocyte‐associated protein4, CTLA4–OMIM #123890; cluster of differentiation 40, CD40—OMIM #109535; and protein tyrosine phosphatase non‐receptor type 22, PTPN22—OMIM #600716) and thyroid specific (thyroglobulin, TG—OMIM #188450; and thyroid‐stimulating hormone receptor, TSHR–OMIM #603372) had been established, showing reduced penetrance 31.