Comprehensive Genotyping in Two Homogeneous Graves' Disease Samples Reveals Major and Novel HLA Association Alleles

BACKGROUND: Graves' disease (GD) is the leading cause of hyperthyroidism and thyroid eye disease inherited as a complex trait. Although geoepidemiology studies showed relatively higher prevalence of GD in Asians than in Caucasians, previous genetic studies were contradictory concerning whether and/or which human leukocyte antigen (HLA) alleles are associated with GD in Asians. METHODOLOGY/PRINCIPAL FINDINGS: We conducted a case-control association study (499 unrelated GD cases and 504 controls) and a replication in an independent family sample (419 GD individuals and their 282 relatives in 165 families). To minimize genetic and phenotypic heterogeneity, we included only ethnic Chinese Han population in Taiwan and excluded subjects with hypothyroidism. We performed direct and comprehensive genotyping of six classical HLA loci (HLA-A, -B, -C, -DPB1, -DQB1 and -DRB1) to 4-digit resolution. Combining the data of two sample populations, we found that B*46:01 (odds ratio under dominant model [OR]  = 1.33, Bonferroni corrected combined P [P(Bc)]  = 1.17 x 10⁻²), DPB1*05:01 (OR  = 2.34, P(Bc) = 2.58 x 10⁻¹⁰), DQB1*03:02 (OR  = 0.62, P(Bc)  = 1.97 x 10⁻²), DRB1*15:01 (OR  = 1.68, P(Bc) = 1.22 x 10⁻²) and DRB1*16:02 (OR  = 2.63, P(Bc)  = 1.46 x 10⁻⁵) were associated with GD. HLA-DPB1*05:01 is the major gene of GD in our population and singly accounts for 48.4% of population-attributable risk. CONCLUSIONS/SIGNIFICANCE: These GD-associated alleles we identified in ethnic Chinese Hans, and those identified in other Asian studies, are totally distinct from the known associated alleles in Caucasians. Identification of population-specific association alleles is the critical first step for individualized medicine. Furthermore, comparison between different susceptibility/protective alleles across populations could facilitate generation of novel hypothesis about GD pathophysiology and indicate a new direction for future investigation

A Study on the Level of T3, T4, TSH and the Association of A/G Polymorphism with CTLA-4 Gene in Graves’ Hyperthyroidism among South Indian Population

Graves’ disease (GD) is an organ-specific heterogenous autoimmune disorder associated with T-lymphocyte abnormality affecting the thyroid, eyes and skin. GD is a multifactorial disease that develops as a result of complex interaction between genetic susceptibility genes and environmental factors. It has been suggested that the Cytotoxic T lymphocytes associated molecule-4 (CTLA-4) is a genetic susceptibility candidate for GD. The present study was focused on A/G polymorphism at position 49 in exon-1 of the CTLA-4 gene in 80 GD patients (GP) and 80 sex and age matched healthy individuals among South Indian (Madurai) population. Serum concentrations of thyroid hormone (T4, T3 and TSH) were determined by using automated analyzer. The genomic DNA was isolated from the patient and control groups and genotyping was performed using the polymerase chain reaction followed by restriction enzyme analysis using Bbv1. Significant difference (P < 0.001) was observed in the level of T3, T4 and TSH in GD patients and healthy individuals. The results revealed the CTLA-4 gene G/G genotype to be 32 (40%) in patients and 26 (32.50%) in healthy individuals, A/G genotype to be 37 (46.25%) in patients and 25 (31.25%) in healthy individuals and A/A genotype to be 11 (13.75%) in patients and 29 (36.25%) in healthy individuals. The calculated odds ratio (OR) in individuals with mutant genotype (GG/AG) reveal 3.6 fold risk for GD (95% confidence interval = 1.6–7.8). The mutant “G” allele frequency was observed to be 0.63 in GD patients and 0.48 in healthy individuals. Thus the present study demonstrates an association between the CTLA-4 gene polymorphism and Graves’ disease