The importance of genetic susceptibility to these diseases was demonstrated by studies on twin cohorts that observed a concordance rate for Graves’ disease [127], and linkage studies that identified polymorphisms in several loci including genes for human leukocyte antigen, cytotoxic T lymphocyte antigen-4, protein tyrosine phosphatase nonreceptor-type 22, thyroglobulin, vitamin D receptor, and cytokines immune-modifying genes [128]. Here, TG is linked to Graves disease.