Association of DRB1*04-DQB1*0301 Haplotype and Lack of Association of Two Polymorphic Sites at CTLA-4 Gene with Hashimoto's Thyroiditis in an Italian Population

Abstract

Hashimoto's thyroiditis (HT) is an autoimmune disease resulting from a complex interaction between genetic and environmental factors. The genetic loci conferring susceptibility need to be still defined. The aim of the present study was to determine whether Cytotoxic T-Lymphocyte-Associated Antigen-4 (CTLA-4), HLA DRB1, and DQB1 genes were associated to HT in an Italian population. We evaluated the allele distribution of the following loci: CTLA-4 exon 1 A49G dimorphism, which resulted in an amino acidic exchange (Thr/Ala) in the leader peptide, CTLA-4 3′ microsatellite, HLA DRB1 and DQB1 in 126 patients with HT and in 301 control subjects from an Italian population (Lazio region). CTLA-4 exon 1 A49G dimorphism was typed by Polymerase Chain Reaction and Restriction Fragment Length Polymorphism (PCR-RFLP); CTLA-4 3′ microsatellite alleles were defined using a fluorescence-based method. HLA DRB1 and DQB1 alleles were typed using a SSO reverse line blot method and a probeless procedure based on allele group-specific amplification followed by DNA heteroduplex analysis, respectively. Data were initially analyzed by χ² test or Fisher's exact test. Multiple logistic regression analysis was then applied on factors with significant crude odds ratios and on CTLA-4 exon 1 A49G dimorphism to investigate their independent effects. The two polymorphic sites at CTLA-4 gene did not increase the risk for HT. The distribution of HLA DRB1 and DQB1 alleles did not show any significant difference between patients and controls, however, the DRB1*04-DQB1*0301 haplotype was significantly increased in patients. Other factors that increase the risk of disease were gender and age. Females showed approximately 18 times more risk than males; subjects older than 50 years had an odds ratio of 6.6. These data suggest that these two polymorphic sites at CTLA-4 do not play a major role in the susceptibility of the disease in an Italian population while female gender, age over 50 years, HLA DRB1*04-DQB1*0301 haplotype increase the risk of developing HT.