A systematic review of genetic studies of thyroid disorders in Taiwan

A systematic review of genetic studies of thyroid disorders in Taiwan identified studies of gene mutations involved in the synthesis and binding of thyroid hormone, as well as mutations of proto-oncogenes and tumor suppressor genes in thyroid cancer. Studies related to gene polymorphisms in patients with autoimmune thyroid disease (AITD) and thyroid cancer were also reviewed. The most prevalent mutations in the Han-Chinese population were c.2268insT in the thyroid peroxidase (TPO) gene and c.919-2A>G in the Pendred syndrome (PDS) gene. Additional mutations have also been revealed in the genes encoding TPO (n = 5), thyroglobulin (TG; n = 6), pendrin (n = 2), and thyroxine-binding globulin (TBG; n = 2), which were novel at the time they were reported. The prevalence of various somatic mutations in differentiated thyroid cancer was similar in Taiwan and Western countries, with the RAS kinase mutation and tyrosine receptor kinase (TRK) and rearranged during transfection (RET) proto-oncogenes being detected in lower frequencies and the B-type RAF kinase (BRAF) mutation accounting for the majority of cases. Recent microRNA analysis revealed an association between miR146b and the BRAF mutation, which was associated with poor prognosis of papillary thyroid carcinoma (PTC). Susceptibility to Graves' disease (GD) was linked to the human leukocyte antigen (HLA) region. The associated alleles were different in Han-Chinese and Caucasians; HLA-DPB1*0501, the major allele in Taiwan, has a low frequency in the West. By contrast, a high frequency of HLA-DRB1*0301 was detected in Caucasians but not Han-Chinese. In addition to the HLA region, cytotoxic T lymphocyte-associated molecule-4 (CTLA4) gene polymorphisms +49G>A and +6230G>A (CT60) were positively associated with GD. The GG genotype and G allele of single nucleotide polymorphism (SNP) +49G>A were also related to relapse of Graves' hyperthyroidism after antithyroid drug withdrawal. Differences in the genetic patterns between Han-Chinese and Caucasians for some thyroid disorders suggest the importance of variable genetic influences in different populations.