Interaction of HLA-DRB1* alleles and CTLA4 (+49 AG) gene polymorphism in Autoimmune Thyroid Disease

Autoimmune Thyroid Diseases (AITDs), including Hashimoto's thyroiditis (HT) and Graves' disease (GD), arise by the complex interaction of genes and environmental factors. The aim of present study was to study the susceptible associations of HLA-DRB1* alleles and CTLA4 +49 AG polymorphism in AITD in south India. AITD patients (n=235; HT=180; GD=55) and age/sex matched healthy controls (n, 235) were enrolled to type HLA-DRB1* alleles and 'CTLA4 +49 AG' by PCR-SSP and PCR-RFLP methods respectively. Analysis revealed CTLA4 +49 'GG' genotype was increased significantly in patients (PL: p=8.7×10^-8; HT: p=9.3×10^-6; GD: p=0.006). Decreased frequencies of 'AA' genotype was observed in patients (PL: p=9.4×10^-6; HT: p=0.008; GD: p=9.0×10^-6). Increased frequencies were observed for HLA alleles DRB1*12 (PL: p=1.42×10^-10; HT: p=5.75×10^-8; GD: p=0.002) and DRB1*11 (PL: p=0.0025; HT: p=0.013) in patients. Decreased frequencies for alleles DRB1*10 (PL: p=0.00002; HT: p=0.018; GD: p=1.63×10^-5) and DRB1*03 (PL: p=0.003; HT: p=0.003) were observed, suggesting a protective association. Combinatorial/Synergistic analysis have revealed an increased frequencies for 'DRB1*11+AG' (PL: p=0.022), 'DRB1*12+AG' (PL: p=6.1×10^-5; HT: p=0.0001), 'DRB1*04+GG' (PL: p=0.003; HT: p=0.008), 'DRB1*07+GG' (PL: p=0.009; HT: p=0.014) and 'DRB1*12+GG' (PL: p=0.005; HT: p=0.005) in patients. However, the combinations such as 'DRB1*10+AA' (PL: p=1.8×10^-6; HT: p=0.003) and 'DRB1*15+AA' (PL: p=0.006; GD: p=0.011) were decreased in patients showing a protective association. The 'GG/G' of CTLA4 +49AG SNP, HLA-DRB1*11/-DRB1*12 (DR5) alleles and the combinations of DRB1*11/DRB1*12 alleles with AG/GG genotype and DRB1*04/07/12 alleles with GG genotype may act as synergistic manner to confer the strong susceptibility to AITD in south India.