CTLA4 and Hashimoto thyroiditis: Candidate gene studies have also suggested links between autoimmune hypothyroidism and PTPN22 (protein tyrosine phosphatase, non-receptor type 22 (lymphoid)), as well as the HLA (human leukocyte antigen) class II region, CTLA4 (cytotoxic T lymphocyte antigen 4), and 8q23-24 [5]–[13].