TPO Gene Expression in Relation with Promoter SNPs in Iraqi Patients with Hyperthyroidism

Abstract

Background: Thyroid peroxidase (TPO) gene mutations are one of the most common causes of thyroid disorders. Objective: To investigate the effect of genetic polymorphisms in the TPO promoter region on gene expression in early-diagnosed hyperthyroid patients. Methods: Genomic DNA was extracted from 100 blood samples (75 hyperthyroid patients and 25 healthy controls), then the TPO promoter region was amplified and sequenced for genotyping rs2071399, rs2071400, and rs2071403 SNPs. Total RNA was also isolated, and cDNA synthesis was performed to determine quantitatively the expression of TPO by using qPCR. The level of TPO antibodies in serum was determined by using an enzyme-linked immunosorbent assay (ELISA). Results: The prevalence of hyperthyroidism in women was significantly higher than in men, as were serum levels of TPO-Abs. There was a significant increase in serum TPO-Abs in hyperthyroid patients (235.29 IU/ml) compared with healthy controls. Genotypes of three SNPs (rs2071399 G/A, rs2071400 C/T, and rs2071403 A/G) in the TPO promoter region were TPO rs2071399 AG and GG, and rs2071400 CT and TT genotypes were more frequent in hyperthyroid patients. There are no significant differences between rs2071403 polymorphic and non-polymorphic genotypes among hyperthyroid patients and healthy controls. The rs2071399 G/A and rs2071400 C/T gene promoter polymorphism significantly down-regulated constitutive TPO gene expression in hyperthyroid patients, but rs2071403 A/G has no major effect on gene expression. Conclusion: There was an association between the mutation in the promoter region of TPO and the incidence of hyperthyroidism.