The Influence of the Exon 1 Polymorphism of the Cytotoxic T Lymphocyte Antigen 4 Gene on Thyroid Antibody Production in Patients with Newly Diagnosed Graves' Disease

Abstract

Increasing evidence supports the genetic susceptibility for thyroid antibody (TAb) production in patients with autoimmune thyroid disease, and recently, it has been shown that the cytotoxic T lymphocyte antigen 4 (CTLA-4) gene is most likely a major TAb susceptibility gene. To assess the relationship between exon 1 CTLA-4 gene polymorphism and TAb production, we genotyped 67 patients with newly diagnosed Graves' disease. Free thyroid hormones and TAb were measured, including thyroglobulin antibodies (TgAb), thyroid peroxidase antibodies (TPOAb), and thyroid-stimulating antibodies (TSAb). AA genotype was found in 25 patients, AG genotype in 34 patients, and GG genotype in 8 patients. G allele carrying genotypes showed significantly higher frequency of positive TPOAb (p < 0.005) and TgAb (p< 0.05) compared to AA genotype. Furthermore, the median values of TPOAb were significantly higher in the group with G allele (p < 0.002). However, the median values of TgAb and TSAb did not differ significantly between both groups and similarly, CTLA-4 genotype showed no association with serum free thyroxine (T₄) and Graves' ophthalmopathy. In conclusion, our findings suggest that G allele carrying genotype of the CTLA-4 gene influences higher production of TPOAb and TgAb, and therefore, support the hypothesis that CTLA-4 gene plays a major role in TAb production.