PTPN22 and Autoimmunity: Many susceptibility loci associated with autoimmunity (human leukocyte antigen [HLA], protein tyrosine phosphatase, non-receptor type 22 [PTPN22], cytotoxic T-lymphocyte associated protein 4 [CTLA4], and interleukin 2 receptor subunit alpha [IL2RA]) or thyroid-specific genes (thyroid-stimulating hormone receptor [TSHR] and forkhead box E1 [FOXE1]) have been identified to be associated with various thyroid diseases (5).