Fine mapping of thyroglobulin gene identifies two independent risk loci for Graves' disease in Chinese Han population

Abstract

Background: This study aimed to determine independent risk loci of Graves' disease (GD) in the thyroglobulin (TG) region.

Methods: In this two-staged association study, a total of 9,757 patients with GD and 10,626 sex-matched controls were recruited from Chinese Han population. Illumina Human660-Quad BeadChips in the discovery stage and TaqMan SNP Genotyping Assays in the replication stage were used for genotyping. Trend test and logistic regression analysis were performed in this association study.

Results: In the discovery stage, rs2294025 and rs7005834 were the most highly associated susceptibility loci with GD in TG. In the replication phase, 7 SNPs, including rs2294025 and rs7005834, were selected for fine-mapping. Finally, we confirmed that rs2294025 and rs7005834 were the independent risk loci of GD in the combined populations. At the same time, there was no significant difference between the risk allele frequencies of rs2294025 and rs7005834 in different clinical phenotypes of GD.

Conclusions: The fine mapping study of thyroglobulin identified two independent SNPs (rs2294025 and rs7005834) for GD susceptibility. However, no significant differences for rs2294025 and rs7005834 were observed, between the different clinical phenotypes of GD, including gender, Graves' ophthalmopathy (GO), and serum levels of thyrotropin receptor antibody, thyroid peroxidase antibody, and thyroglobulin antibody. These results provide a deeper understanding of the association mechanism of thyroglobulin and GD risk.

Keywords: Graves’ disease (GD); Thyroglobulin; single nucleotide polymorphism (SNP).

Figure 1

Results of association analysis for SNPs in 8q24.22 in the discovery stage. (A) In the discovery stage the regional plots of susceptibility loci associated with Graves’ disease (GD) in 8q24.22. The -log10 P values of each SNP at 8q24.22 are plotted against chromosomal position. The top SNP at 8q24.22 is rs2294025 shown as a big purple diamond. The color of each SNP spot reflects its r² value with rs2294025 and decreasing values of r² demonstrates with various colors from red, orange, green to sky-blue and blue. One thousand genomes from Asian samples were used to compute genetic recombination rates. Physical positions are based on GRCh37; (B) Haploview analysis results of 85 SNPs of Block 1 and 13 SNPs of Block 2, two highly linked independent susceptible blocks. The number in each small square represents the interlocking unbalance r² value seen in two SNPS. The big red represents the complete interlocking r²=1. The higher the interlocking degree is, the closer the color is to the big red and the completely non-interlocking color is white; (C) in the replication stage, Haploview analysis of the 7 TagSNPs. The number in each small square case represents the Linkage disequilibrium r² value between the two SNPs, and red represents the complete Linkage disequilibrium r²=1. The higher the Linkage disequilibrium is, the closer the color is to black, while the completely non-Linkage disequilibrium value is white.

Figure 2

Logistic regression results of 98 SNPs with P<0.01 at 8q24.22 in the discovery stage. (A,B) Two-locus conditional logistic regression for rs2294025 (A) or rs7005834 (B) with the other 97 SNPs with P<0.01. Conditioning on rs2294025 (A) or rs7005834 (B), the P values of each of the other 97 SNPs are shown in blue triangles. And conditioning on each of the other 97 SNPs, the P values of rs2294025 or rs7005834 are shown in red circles; (C) after conditioning on rs2294025 and rs7005834 at the same time, the P values of other SNPs in the GD susceptibility locus on 8q24.22 are shown in blue triangle. None of the other 96 SNPs on 8q24.22 improved the model with rs2294025 and rs7005834 at the level of P<0.01. The P levels of trend analysis for each of 98 SNPs are shown in red square and the top SNP rs2294025 is shown in red diamond. Estimated recombination rates (based on the eastern Asian samples from the HapMap project) plotted in cyan reflect the local linkage disequilibrium structure around the associated SNPs.