The impact of CTLA-4 gene polymorphism on the content of organ-specific antibodies in patients with autoimmune thyroiditis among the population of Azerbaijan

Abstract

BACKGROUND: The risk of developing immune tolerance to self-antigens in autoimmune thyroiditis is largely associated with a mutation in the CTLA-4 gene, the product of which negatively regulates T-cell activity. AIM: To study the A49G (rs231775) CTLA-4 polymorphism in patients with autoimmune thyroiditis in a sample of Azerbaijani residents and the effect of the frequency of identified alleles and genotypes on the level of antibodies to thyroid peroxidase and thyroglobulin. MATERIAL AND METHODS: A study was conducted in 2021–2023 involving 170 patients with autoimmune thyroiditis and 65 individuals without thyroid pathology or other autoimmune diseases, who formed a comparison group. The groups were matched by gender and age. Based on the patient history, thyroid status study results, thyroid ultrasound data, and organ-specific antibody assessment, the patients were diagnosed with autoimmune thyroiditis. The routine thyroid status study results in the comparison group were within normal limits. Genotyping of the A49G (rs231775) polymorphism was performed using polymerase chain reaction followed by digestion of the reaction product with PspEI restriction endonuclease. The results of the quantitative studies were presented as the median (Me) and interquartile range (25th quartile; 75th quartile). The correspondence of genotype frequencies to the Hardy–Weinberg equilibrium was assessed using the χ2 criterion. RESULTS: The results revealed a statistically significant increase in the frequency of the G allele (48%) compared to the control group [33.8%; p=0.039, χ2=4.27, odds ratio (OR) 1.865, 95% confidence interval (CI) 1.028–3.382] and a decrease in the frequency of the A allele (51.2%) relative to the control group (66.1%; p=0.0389, χ2=4.27, OR=0.536, CI=0.296–0.973). In 22.4% of patients with the GG genotype (p=0.005, χ2=7.86, OR=0.237, 95% CI=0.088–0.635) and 55.6% of patients with the G allele (p=0.0012, χ2=10.43, OR=0.360, 95%, CI=0.192–0.674), thyroglobulin antibody titers were more than 100 IU/ml. Thyroid peroxidase antibody levels of 100 IU/ml or more were recorded in 22.7% of study participants with the GG genotype (p=0.030) and 50.0% with the G allele (p=0.048). CONCLUSION: Elevated titers of antibodies to thyroid peroxidase and thyroglobulin were detected in patients from the population of Azerbaijan with the G allele and homozygous genotype GG of the +49A/G polymorphism of the CTLA-4 gene.