PTPN22 and autoimmune thyroid disease: The susceptibility to autoimmune thyroid disease depends mainly on the genetic determinants of HLA and non-HLA loci (CTLA4, CD40, PTPN22, TG, and TSH-R genes), and these genetic determinants may be affected by various environmental factors, such as iodine deficiency, stress, drugs, chemical contaminants, and infectious organisms [24].