Hashimoto thyroiditis (HT) is a common form of chronic autoimmune thyroid disease (AITD), and is characterized by an inflammatory infiltrate of immunocytes that replace the parenchyma and induce thyroid enlargement, which eventually leads to gland fibrosis. Progressive thyrocyte depletion results in impaired thyroid hormone production and clinical hypothyroidism, a condition that involves a marked reduction of metabolic activity in various cells and tissues. AITDs are regarded as polygenic disorders resulting from the combination of a genetic predisposition in conjunction with an environmental trigger. Two main approaches have been employed to locate susceptibility loci for AITD, namely case control candidate gene studies and genome-wide linkage screens. Case control candidate gene studies have been employed to investigate numerous genes for association with AITD, but to date, only the human leucocyte region (HLA) on chromosome 6p21 and the cytotoxic T lymphocyte associated 4 (CTLA-4) gene on chromosome 2q33 have been consistently shown to be associated with disease.
