Graves disease is a common form of chronic autoimmune thyroid disease (AITD), and is characterized by overstimulation of the thyroid gland with agonistic anti-thyrotropin (TSH) receptor autoantibodies. This overstimulation leads to follicular hypertrophy and hyperplasia, causing thyroid enlargement, as well as increases in thyroid hormone production and the fraction of triiodothyronine (T3) relative to thyroxine (T4) in thyroid secretion. Thyroid autoimmune diseases 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.
