A germline single nucleotide polymorphism at the intracellular domain of the human thyrotropin receptor does not have a major effect on the development of Graves' disease

The rs1991517 polymorphism is a genetic risk factor for congenital hypothyroidism

The objective of the current study is to explore the association of thyroid-stimulating hormone receptor (TSHR) rs1991517 polymorphism (c.2337 C > G, p.D727E) with congenital hypothyroidism (CH) through a case-control study followed by a meta-analysis. The case-control study was based on 45 CH subjects and 700 healthy controls. Meta-analysis comprised of seven published studies and our current findings (1044 CH cases and 1649 healthy controls). The allele contrast model showed that the presence of G- allele increased CH risk by 45% (OR: 1.45, 95% CI 1.20-1.76) and 41% (OR: 1.41, 95% CI 1.03-1.93) in fixed effect and random effect models, respectively. The GG- genotype is associated with 2.3-fold (95% CI 1.32-3.99) increased risk for CH in the fixed-effect model. I ² (0.58) and Cochran's Q test (Q: 16.72, p = 0.02) revealed evidence of heterogeneity in the association. No publication bias was observed by Egger's test (p = 0.70). Sensitivity analysis revealed that even after excluding any study this polymorphism is associated with risk for CH. The rs1991517 mutation alters the binding affinity to cAMP (ΔG of 727D vs.727E: - 7.27 vs. - 7.34 kcal/mol). In conclusion, rs1991517 is a genetic risk factor for CH and exerts its impact by altering cAMP-mediated signal transduction.

Genetics of Thyroid-Stimulating Hormone Receptor-Relevance for Autoimmune Thyroid Disease

Production of thyroid-stimulating hormone receptor (TSHR) antibodies represents the hallmark of Graves' disease (GD) pathogenesis. Thus, for more than two decades the TSHR gene has been at the center of studies intended to elucidate its contribution to disease pathology. The advent of genome-wide association technology allowed to establish a strong association of the TSHR gene with GD. Subsequent fine-mapping studies narrowed the disease-susceptibility region to a 40 kb sequence in intron 1, where at least five GD-associated SNPs in tight linkage disequilibrium were identified. The current challenge is to understand the functional mechanisms by which these polymorphisms modify physiological processes and trigger disease. The aim of this review is to summarize the current knowledge on the role of the TSHR gene in GD pathogenesis, which has been gained through linkage and association studies, as well as to discuss the emerging mechanisms underlying biological implications of TSHR variants in the development of GD.

Association of polymorphisms of rs179247 and rs12101255 in thyroid stimulating hormone receptor intron 1 with an increased risk of Graves' disease: A meta-analysis

The polymorphisms of thyroid stimulating hormone receptor (TSHR) intron 1 rs179247 and rs12101255 have been found to be associated with Graves' disease (GD) in genetic studies. In the present study, we conducted a meta-analysis to examine this association. Two reviewers systematically searched eligible studies in PubMed, Web of Science, Embase and China Biomedical Literature Database (CBM). A meta-analysis on the association between GD and TSHR intron 1 rs179247 or rs12101255 was performed. The odd ratios (OR) were estimated with 95% confidence interval (CI). Meta package in R was used for the analyses. Seven articles (13 studies) published between 2009 and 2014, involving 5754 GD patients and 5768 controls, were analyzed. The polymorphism of rs179247 was found to be associated with an increased GD risk in the allele analysis (A vs. G: OR=1.40, 95% CI=1.33-1.48) and all genetic models (AA vs. GG: OR=1.94, 95% CI=1.73-2.19; AA+AG vs. GG: OR=1.57, 95% CI=1.41-1.74; AA vs. AG+GG: OR=1.54, 95% CI=1.43-1.66). The site rs12101255 also conferred a risk of GD in the allele analysis (T vs. C: OR=1.50, 95% CI=1.40-1.60) and all genetic models (TT vs. CC: OR=2.22, 95% CI=1.92-2.57; TT+TC vs. CC: OR=1.66, 95% CI=1.50-1.83; TT vs. TC+CC: OR=1.74, 95% CI=1.53-1.98). Analysis of the relationship between rs179247 and Graves' ophthalmopathy (GO) showed no statistically significant correlation (A vs. G: OR=1.02, 95% CI=0.97-1.07). Publication bias was not significant. In conclusion, GD is associated with polymorphisms of TSHR intron 1 rs179247 and rs12101255. There is no association between rs179247 SNPs and GO.

Genetic associations of the thyroid stimulating hormone receptor gene with Graves diseases and Graves ophthalmopathy: A meta-analysis

Graves' disease (GD) is a common thyroid disease, and Graves ophthalmopathy(GO) is the most common extra-thyroidal manifestation of GD. Genetic associations of the thyroid stimulating hormone receptor (TSHR) gene with GD and GO have been studied in different population groups for a long time. We aimed to obtain a more precise estimation of the effects of TSHR single nucleotide polymorphisms (SNPs) on GD/GO using a meta-analysis. Publications were searched on Pub Med and EMBASE up to December 30, 2015. Eight studies involving three SNPs (rs179247, rs12101255, and rs2268458), which included 4790 cases and 5350 controls, met the selection criteria. The pooled odds ratios (OR) and the 95% confidence intervals (CI) were estimated. SNPs rs179247 (dominant model [GG + GA vs. AA]: OR = 0.66, 95%CI: 0.61-0.73, P = 0.000, I(2) = 0%) and rs12101255 (dominant model [TT + TC vs. CC]: OR = 1.67, 95%CI: 1.53-1.83, P = 0.000, I(2) = 0%) were significantly associated with GD in all of the genetic models. TSHR rs12101255 and rs2268458 polymorphisms had no association between GO and GD (GD without GO). The results indicate that rs179247 and rs12101255 are likely to be genetic biomarkers for GD. Further studies with different population groups and larger sample sizes are needed to confirm the genetic associations of the TSHR gene with GD/GO.

Association between TSHR gene polymorphism and the risk of Graves' disease: a meta-analysis

Thyroid stimulating hormone receptor (TSHR) is thought to be a significant candidate for genetic susceptibility to Graves' disease (GD). However, the association between TSHR gene polymorphism and the risk of GD remains controversial. In this study, we investigated the relationship between the two conditions by meta-analysis. We searched all relevant case-control studies in PubMed, Web of Science, CNKI and Wanfang for literature available until May 2015, and chose studies on two single nucleotide polymorphisms (SNPs): rs179247 and rs12101255, within TSHR intron-1. Bias of heterogeneity test among studies was determined by the fixed or random effect pooled measure, and publication bias was examined by modified Begg's and Egger's test. Eight eligible studies with 15 outcomes were involved in this meta-analysis, including 6,976 GD cases and 7,089 controls from China, Japan, Poland, UK and Brazil. Pooled odds ratios (ORs) for allelic comparisons showed that both TSHR rs179247A/G and rs12101255T/C polymorphism had significant association with GD (OR=1.422, 95%CI=1.353–1.495, P<0.001, P_{heterogeneity}=0.448; OR=1.502, 95%CI: 1.410–1.600, P<0.001, P_{heterogeneity}=0.642), and the associations were the same under dominant, recessive and co-dominant models. In subgroup analyses, the conclusions are also consistent with all those in Asian, European and South America subgroups (P<0.001). Our meta-analysis revealed a significant association between TSHR rs179247A/G and rs12101255T/C polymorphism with GD in five different populations from Asia, Europe and South America. Further studies are needed in other ethnic backgrounds to independently confirm our findings.

TSHR intronic polymorphisms (rs179247 and rs12885526) and their role in the susceptibility of the Brazilian population to Graves' disease and Graves' ophthalmopathy

PURPOSE

Intronic thyroid-stimulating hormone receptor polymorphisms have been associated with the risk for both Graves' disease and Graves' ophthalmopathy, but results have been inconsistent among different populations. We aimed to investigate the influence of thyroid-stimulating hormone receptor intronic polymorphisms in a large well-characterized population of GD patients.

METHODS

We studied 279 Graves' disease patients (231 females and 48 males, 39.80 ± 11.69 years old), including 144 with Graves' ophthalmopathy, matched to 296 healthy control individuals. Thyroid-stimulating hormone receptor genotypes of rs179247 and rs12885526 were determined by Real Time PCR TaqMan(®) SNP Genotyping.

RESULTS

A multivariate analysis showed that the inheritance of the thyroid-stimulating hormone receptor AA genotype for rs179247 increased the risk for Graves' disease (OR = 2.821; 95 % CI 1.595-4.990; p = 0.0004), whereas the thyroid-stimulating hormone receptor GG genotype for rs12885526 increased the risk for Graves' ophthalmopathy (OR = 2.940; 95 % CI 1.320-6.548; p = 0.0083). Individuals with Graves' ophthalmopathy also presented lower mean thyrotropin receptor antibodies levels (96.3 ± 143.9 U/L) than individuals without Graves' ophthalmopathy (98.3 ± 201.9 U/L). We did not find any association between the investigated polymorphisms and patients clinical features or outcome.

CONCLUSION

We demonstrate that thyroid-stimulating hormone receptor intronic polymorphisms are associated with the susceptibility to Graves' disease and Graves' ophthalmopathy in the Brazilian population, but do not appear to influence the disease course.

Refined association of TSH receptor susceptibility locus to Graves' disease in the Chinese Han population

BACKGROUND

Convincing evidence has demonstrated the association of TSH receptor (TSHR) with Graves' disease (GD) in the Chinese Han population.

OBJECTIVE

The aim of this study was to identify the causal variants for GD in the region encompassing TSHR by a refining association study.

DESIGN AND METHODS

GD patients (1536) and 1516 sex-matched controls were recruited in the first stage, and an additional 3832 GD patients and 3426 sex-matched controls were recruited in the replication stage. Genotyping was performed using Illumina Human660-Quad BeadChips or TaqMan single nucleotide polymorphism (SNP) Genotyping Assays and the Fluidigm EP1 platform.

RESULTS

When the results of regression analysis for 74 genotyped SNPs and 922 imputed SNPs in the first-stage cohort were combined, rs179243 and rs3783949 were the probable susceptibility SNPs associated with GD in TSHR. Eleven SNPs, including rs179243 and rs3783949, were selected to further refine the association in the replication study. Finally, rs12101261 and rs179243 were confirmed as independent GD susceptibility variants in the replication and combined populations. Further, we also found that the rate of persistent TSHR autoantibody positivity (pTRAb+) was significantly higher in the GD patients with the susceptible genotypes rs12101261 or rs179243 than in the GD patients carrying the protective genotypes, after the GD patients had been treated for more than 1 year.

CONCLUSIONS

These findings indicate that rs12101261 and rs179243 are the possible causal SNPs for GD susceptibility in the TSHR gene and could serve as genetic markers to predict the outcome of pTRAb+ in GD patients.

The genetic basis of graves' disease

The presented comprehensive review of current knowledge about genetic factors predisposing to Graves’ disease (GD) put emphasis on functional significance of observed associations. In particular, we discuss recent efforts aimed at refining diseases associations found within the HLA complex and implicating HLA class I as well as HLA-DPB1 loci. We summarize data regarding non-HLA genes such as PTPN22, CTLA4, CD40, TSHR and TG which have been extensively studied in respect to their role in GD. We review recent findings implicating variants of FCRL3 (gene for FC receptor-like-3 protein), SCGB3A2 (gene for secretory uteroglobin-related protein 1- UGRP1) as well as other unverified possible candidate genes for GD selected through their documented association with type 1 diabetes mellitus: Tenr–IL2–IL21, CAPSL (encoding calcyphosine-like protein), IFIH1(gene for interferon-induced helicase C domain 1), AFF3, CD226 and PTPN2. We also review reports on association of skewed X chromosome inactivation and fetal microchimerism with GD. Finally we discuss issues of genotype-phenotype correlations in GD.

Association between thyroid stimulating hormone receptor gene intron polymorphisms and autoimmune thyroid disease in a Chinese Han population

Autoimmune thyroid disease (AITD) is a multifactorial disease with a genetic susceptibility and environmental factors. The thyroid stimulating hormone receptor gene (TSHR) which is expressed on the surface of the thyroid epithelial cell is thought to be the main auto-antigen and a significant candidate for genetic susceptibility to AITD. This case-control study aimed at evaluating the association between single nucleotide polymorphisms (SNP) of TSHR and AITD in a Chinese Han population. We recruited 404 patients with Graves' disease (GD), 230 patients with Hashimoto's thyroiditis (HT) and 242 healthy controls. The Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometer (MALDI-TOF-MS) Platform was used to detect five SNPs (rs179247, rs12101255, rs2268475, rs1990595, and rs3783938) in TSHR gene. The frequencies of allele T and TT genotype of rs12101255 in GD patients were significantly increased compared with those of the controls (P=0.004/0.015, OR=1.408/1.446). The allele A frequency of rs3783938 was greater in HT patients than in the controls (P=0.025, OR=1.427). The AT haplotype (rs179247-rs12101255) was associated with an increased risk of GD (P=0.010, OR=1.368). The allele A of rs179247 was associated with ophthalmopathy in GD patients. These data suggest that the polymorphisms of rs12101255 and rs3783938 are associated with GD and HT, respectively.

Study on the relationship between TSHR gene and thyroid diseases

Thyroid stimulating hormone receptor (TSHR) is thought to play a critical role in the pathogenesis of certain thyroid diseases, including Graves' disease (GD), multinodular thyroid goiter (MTG), and Hashimoto's thyroiditis (HT). In order to understand whether single nucleotide polymorphisms in the TSHR gene contribute to thyroid diseases, we have conducted a case-control study in which, we examined 8 TSHR gene single-nucleotide polymorphisms in introns 1, 4, 5, 6 and exons 7 and 8, respectively, among patients with thyroid diseases. These included one family with GD (3 patients and 9 healthy members); 60 patients with familiar thyroid diseases (30 with GD, 20 with MTG, and 10 with HT patients), 48 sporadic patients with GD and 96 healthy control individuals. Direct sequencing of all 10 exons and part of introns of TSHR gene, in these patients as well as healthy controls revealed eight polymorphisms. A novel polymorphism in exon 8 AGA(Arg) → CGA(Arg). However, there were no significant differences between patients and controls in the incidence of these polymorphisms. These results suggest that the polymorphisms (polymorphism in intron 1 at 81 bp upstream of exon 2; polymorphism in intron 4 at 135 bp upstream of exon 5; polymorphism in intron 4 at 365 bp upstream of exon 5; polymorphism in intron 5 at 69 bp upstream of exon 6; means polymorphism in intron 6 at 13 bp downstream of exon 6; polymorphism in intron 6 at 187 bp upstream of exon 7; E7+16: polymorphism in 16 bp of exon 7; polymorphism in 40 bp of exon 8) of the TSHR gene may not contribute to the pathogenesis of thyroid diseases.

The R450H mutation and D727E polymorphism of the thyrotropin receptor gene in a Chinese child with congenital hypothyroidism

BACKGROUND

Congenital hypothyroidism (CH) is the most prevalent congenital endocrine disorder. The molecular cause of CH in the majority of newborns is unknown. The aim of this study was to investigate the mutation of thyrotropin receptor (TSHR) gene in Chinese children with congenital hypothyroidism (CH). and the hereditary characteristic.

METHODS

Eighteen Chinese children with CH were enrolled for molecular analysis of the TSHR gene and 105 normal controls were evaluated. The exons 1-9, and 10 of TSHR gene were detected by PCR-SSCP (single-stranded conformation polymorphism) and sequenced.

RESULTS

A slower and a faster mobility SSCP shift showed in a 12-year old child with hypoplasic gland. Sequencing of TSHR gene revealed a homozygous mutation (CGC --> CAC, Arg450His) and a polymorphism (GAC --> GAG, Asp727Glu). The controls revealed no variants. The 12 relatives of the proband were enrolled and investigated. Six relatives, including his mother and father, were heterozygous for R450H mutation and D727E polymorphism of the TSHR gene. Thyroid hormone levels were normal except for circulating TSH (5.96-6.92 mU/L) level slightly elevated in six heterozygous family members.

CONCLUSIONS

Homozygous mutation R450H of the TSHR gene led to CH. Heterozygous mutation R450H was the cause of subclinical hypothyroidism.

Thyroid stimulating hormone receptor (TSHR) intron 1 variants are major risk factors for Graves' disease in three European Caucasian cohorts

BACKGROUND

The thyroid stimulating hormone receptor (TSHR) gene is an established susceptibility locus for Graves' disease (GD), with recent studies refining association to two single nucleotide polymorphisms (SNPs), rs179247 and rs12101255, within TSHR intron 1.

METHODOLOGY AND PRINCIPAL FINDINGS

We aimed to validate association of rs179247 and rs12101255 in Polish and UK Caucasian GD case-control subjects, determine the mode of inheritance and to see if association correlates with specific GD clinical manifestations. We investigated three case-control populations; 558 GD patients and 520 controls from Warsaw, Poland, 196 GD patients and 198 controls from Gliwice, Poland and 2504 GD patients from the UK National collection and 2784 controls from the 1958 British Birth cohort. Both rs179247 (P = 1.2×10(-2)-6.2×10(-15), OR = 1.38-1.45) and rs12101255 (P = 1.0×10(-4)-3.68×10(-21), OR = 1.47-1.87) exhibited strong association with GD in all three cohorts. Logistic regression suggested association of rs179247 is secondary to rs12101255 in all cohorts. Inheritance modeling suggested a co-dominant mode of inheritance in all cohorts. Genotype-phenotype correlations provided no clear evidence of association with any specific clinical characteristics.

CONCLUSIONS

We have validated association of TSHR intron 1 SNPs with GD in three independent European cohorts and have demonstrated that the aetiological variant within the TSHR is likely to be in strong linkage disequilibrium with rs12101255. Fine mapping is now required to determine the exact location of the aetiological DNA variants within the TSHR.

The genetics of the thyroid stimulating hormone receptor: history and relevance

BACKGROUND

The thyroid stimulating hormone receptor (TSHR) is the key regulator of thyrocyte function. The gene for the TSHR on chromosome 14q31 has been implicated as coding for the major autoantigen in the autoimmune hyperthyroidism of Graves' disease (GD) to which T cells and autoantibodies are directed.

SUMMARY

The TSHR is a seven-transmembrane domain receptor that undergoes complex posttranslational processing. In this brief review, we look at the genetics of this important autoantigen and its influence on a variety of tissue functions in addition to its role in the induction of GD.

CONCLUSIONS

There is convincing evidence that the TSH receptor gene confers increased susceptibility for GD, but not Hashimoto's thyroiditis. GD is associated with polymorphisms in the intron 1 gene region. How such noncoding nucleotide changes influence disease susceptibility remains uncertain, but is likely to involve TSHR splicing variants and/or microRNAs arising from this gene region. Whether such influences are confined to the thyroid gland or whether they influence cell function in the many extrathyroidal sites of TSHR expression remains unknown.

Analysis of thyroglobulin gene polymorphisms in patients with autoimmune thyroiditis

The autoimmune thyroid disease is a complex disorder caused by a combination of genetic susceptibility and environmental factors, which are believed to initiate the autoimmune response to thyroid antigens. Identification of the susceptibility genes has found that unique and diverse genetic factors are in association with Graves' disease and autoimmune thyroiditis. The thyroglobulin gene is an identified thyroid-specific gene associated to autoimmune thyroid disease and, principally, with autoimmune thyroiditis. The aim of this work was to test for evidence of allelic association between autoimmune thyroiditis and thyroglobulin polymorphism markers. We studied six polymorphisms distributed throughout all the thyroglobulin gene: four microsatellites (Tgms1, Tgms2, TGrI29 and TGrI30), one insertion/deletion (Indel) polymorphism (IndelTG-IVS18) and one exonic single nucleotide polymorphism (SNP) (c.7589G>A) in 122 patients with autoimmune thyroiditis compared with 100 non-related normal subjects. No differences in allele and genotype distribution were observed between autoimmune thyroiditis cases and controls for Tgms1, Tgms2, TGrI30, IndelTG-IVS18 and c.7589G>A. However, when we analyzed the patients with the TGrI29 microsatellite we found a significant association between the 199-bp allele and AT (33.7% vs. 24.5% in control group) (P = 0.0372). In addition, a higher prevalence of the 201-bp allele has been observed in control subjects (47.5% vs. 38.1% in patients group), although not statistically significant (P = 0.0536). Our work shows the association between the thyroglobulin gene and autoimmune thyroiditis and reinforce that thyroglobulin is a thyroid-specific susceptibility gene for this disease.

Association of the thyroid stimulating hormone receptor gene (TSHR) with Graves' disease

Graves' disease (GD) is a common autoimmune disease (AID) that shares many of its susceptibility loci with other AIDs. The thyroid stimulating hormone receptor (TSHR) represents the primary autoantigen in GD, in which autoantibodies bind to the receptor and mimic its ligand, thyroid stimulating hormone, causing the characteristic clinical phenotype. Although early studies investigating the TSHR and GD proved inconclusive, more recently we provided convincing evidence for association of the TSHR region with disease. In the current study, we investigated a combined panel of 98 SNPs, including 70 tag SNPs, across an extended 800 kb region of the TSHR to refine association in a cohort of 768 GD subjects and 768 matched controls. In total, 28 SNPs revealed association with GD (P < 0.05), with strongest SNP associations at rs179247 (chi(2) = 32.45, P = 8.90 x 10(-8), OR = 1.53, 95% CI = 1.32-1.78) and rs12101255 (chi(2) = 30.91, P = 1.95 x 10(-7), OR = 1.55, 95% CI = 1.33-1.81), both located in intron 1 of the TSHR. Association of the most associated SNP, rs179247, was replicated in 303 GD families (P = 7.8 x 10(-4)). In addition, we provide preliminary evidence that the disease-associated genotypes of rs179247 (AA) and rs12101255 (TT) show reduced mRNA expression ratios of flTSHR relative to two alternate TSHR mRNA splice variants.

Clinical and molecular analysis of thyroid hypoplasia: a population-based approach in southern Brazil

BACKGROUND

Congenital hypothyroidism (CH) is mainly due to developmental abnormalities leading to thyroid dysgenesis (TD). TD encompasses very distinct morphologic subtypes of disease. This study examined and compared the phenotype in TD variants and searched for genetic alterations in sporadic thyroid hypoplasia (TH), the most misdiagnosed form of CH. This was a longitudinal study over a 14-year period (1990-2004).

METHODS

A continuous series of 353 children with TD was identified using thyroid function tests [thyroxine (T4) and TSH], scintigraphy, and ultrasound as diagnostic tools. Individual phenotypes were analyzed in 253 children with TD. Mutations in the most likely candidate genes were studied in 35 cases of TH.

RESULTS

The overall birth prevalence of permanent CH was 1:4795. Ectopy represented 37% of all cases of permanent primary CH, dyshormonogenesis 28%, agenesis 24%, hypoplasia 10%, and hemiagenesis 1%. The lowest screening T4 level and the highest TSH level were in the agenetic group, followed by TH. The TH group had an improvement in the thyroid function showing less-severe phenotype with aging. In the molecular analysis, one patient was identified with a mutation in the PAX8 gene (155G>C; R52P); four patients had a heterozygous G>C substitution in position -569; two patients showed a (234C>A; P52T) or (2181C>G; D727E) polymorphic variants of the TSH-R gene; and one patient presented a novel heterozygous nonsynonymous substitution, 293G>A; S98N, in the NKX2.5 gene.

CONCLUSIONS

The prevalence of CH was within the previously reported range of 1:3000-4000. Ectopy was the most common etiology. Clinical analysis revealed distinct hormonal patterns in TH subgroup when compared with other variants of TD, with genetic abnormalities identified only in few cases in the TSH-R, PAX8, and NKX2.5 genes.

Influence of the TSH receptor gene on susceptibility to Graves' disease and Graves' ophthalmopathy

BACKGROUND

A large gene region, called GD-1, was first described by this laboratory as linked to Graves' disease (GD) and included the gene for the thyroid-stimulating hormone receptor (TSHR). Recent studies have now suggested an association of TSHR intronic polymorphisms with GD. We have taken the opportunity to examine a population of well-characterized patients with autoimmune thyroid disease (AITD) typed for an additional thyroid susceptibility gene, the immunoregulatory gene for cytotoxic T-lymphocyte antigen 4 (CTLA-4), to examine its relationship with the susceptibility to GD endowed by TSHR gene polymorphisms.

METHODS

We used TSHR-SNP-rs2268458, located in intron 1 of the TSHR gene, measured using standard PCR-RFLP procedures, as our marker for the TSHR gene association. We genotyped 200 patients with GD, 83 patients with Hashimoto's thyroiditis (HT), and 118 healthy controls (all female Caucasians).

RESULTS

The allele and genotype frequencies from GD patients, but not HT patients, were significantly different from controls. The frequency of the combined genotype (allele) CC + TC was significantly higher in GD patients versus controls, suggesting that the C-containing genotype increased the risk for GD in a dominant manner (p = 0.018, odds ratio [OR] = 1.8). When compared with CTLA-4 (A/G)(49) single-nucleotide polymorphism (SNP), we were unable to demonstrate additive risk in patients with established AITD. Further, subsetting the patients (n = 120) into those with clinically significant Graves' ophthalmopathy (GO) showed no association with the TSHR SNP.

CONCLUSIONS

These results demonstrated that the intronic TSHR-SNP-rs2268458 was associated with GD, but not with HT, thus indicating that the TSHR gene has the potential to increase susceptibility to GD. However, we were not able to demonstrate any additive risk with the CTLA-4 (A/G)(49) SNP, which is, therefore, an independent risk factor for AITD. This suggested that, within the limits of the study population, each of these two genes provided a small contribution to GD susceptibility and that neither was essential. In addition, there was no evidence for the TSHR gene association adding to the risk of developing GO. Direct functional analyses are now needed to help explain the mechanisms of this TSHR gene susceptibility to GD.

Joint genetic susceptibility to type 1 diabetes and autoimmune thyroiditis: from epidemiology to mechanisms

Type 1 diabetes (T1D) and autoimmune thyroid diseases (AITD) frequently occur together within families and in the same individual. The co-occurrence of T1D and AITD in the same patient is one of the variants of the autoimmune polyglandular syndrome type 3 [APS3 variant (APS3v)]. Epidemiological data point to a strong genetic influence on the shared susceptibility to T1D and AITD. Recently, significant progress has been made in our understanding of the genetic association between T1D and AITD. At least three genes have been confirmed as major joint susceptibility genes for T1D and AITD: human leukocyte antigen class II, cytotoxic T-lymphocyte antigen 4 (CTLA-4), and protein tyrosine phosphatase non-receptor type 22. Moreover, the first whole genome linkage study has been recently completed, and additional genes will soon be identified. Not unexpectedly, all the joint genes for T1D and AITD identified so far are involved in immune regulation, specifically in the presentation of antigenic peptides to T cells. One of the lessons learned from the analysis of the joint susceptibility genes for T1D and AITD is that subset analysis is a key to dissecting the etiology of complex diseases. One of the best demonstrations of the power of subset analysis is the CTLA-4 gene in T1D. Although CTLA-4 showed very weak association with T1D, when analyzed in the subset of patients with both T1D and AITD, the genetic effect of CTLA-4 was significantly stronger. Gene-gene and genetic-epigenetic interactions most likely play a role in the shared genetic susceptibility to T1D and AITD. Dissecting these mechanisms will lead to a better understanding of the etiology of T1D and AITD, as well as autoimmunity in general.

Identification and characterization of new variants of three associated SNPs and a microsatellite in the TSH receptor gene which are useful for genetic studies

The purpose of the present work was to characterize g.IVS5-69C>T, g.IVS6+13C>T and c.561C>T SNPs and the [CT](n) microsatellite in the TSHR gene for genetic analysis. Exons 6 and 7 of the TSHR gene, including the flanking intronic sequences, were screened for the presence of g.IVS5-69C>T, g.IVS6+13C>T and c.561C>T SNPs by SSCP. We found genetic association between the three SNPs and a total of three different haplotypes were observed. Two were homozygous blocks, g.IVS5-69T/g.IVS6+13G/c.561C (Haplotype TGC, 3.3%) and g.IVS5-69C/g.IVS6+13A/c.561T (Haplotype CAT, 75%). Every individual who was heterozygous for g.IVS5-69C>T was equally heterozygous for g.IVS6+13A>G and c.561T>C (Haplotype CAT/TGC, 21.7%). The [CT](n) microsatellite, localized in intron 7 of the TSHR gene was amplified by PCR and the labeled products were separated in a polyacrylamide denaturing sequencing gel. Three variable numbers of CT motif were identified, two previously reported ([CT](6) and [CT](8)) and one previously unreported ([CT](9)). The construction and expression of the hybrid minigenes using pSPL3 and alpha-globin-fibronectin EDB (pTB) vectors showed that the [CT](n) microsatellite itself does not interfere with exon 8 definition and processing in vitro. In conclusion, g.IVS5-69C>T/g.IVS6+13C>T/c.561C>T haplotypes and [CT](n) microsatellite are informative polymorphic markers and can be used in linkage studies in families with germ line TSHR mutations or autoimmunity thyroid diseases.

A C/T polymorphism in CD40 gene is not associated with susceptibility and phenotype of Graves' disease in Taiwanese

A single nucleotide polymorphism (SNP) located at position-1 in the Kozak sequence of the CD40 gene has been associated with the development of GD in Caucasian and Koreans. This study investigated possible associated between CD40 SNP and the development of GD in a Taiwanese population. To do this, we enrolled 215 Taiwanese patients with GD and 141 controls from the Endocrine Clinic of Kaohsiung Medical University Hospital. This study investigated the association between gene polymorphism and relapse of hyperthyroidism after the discontinuation of medication in three GD patient groups based on time to relapse and a control group, and compared clinical and laboratory data of patients regrouped in three CD40 SNP genotypes. No significant difference in allele or CD40 SNP genotype frequency was observed between patients with GD and control subjects (P = 0.859 and P = 0.959, respectively). Furthermore, we analyzed the distribution of CD40 genotypes and three groups based on time to relapse after drug withdrawal. The cutoff points were 9 months, 9 months to 3 years, and more than 3 yr in subgroups of patients with GD divided by clinical and laboratory variables. Although no significant genotype-phenotype associations were found, the T allele and TT genotype frequency was significantly smaller in GD patients who had developed the disease before 35 years old than those who developed it after 35 years old (x (2) = 6.272, P = 0.043) (TT + CT v.s. CC, x (2) = 4.951, P = 0.030). These findings suggest that this CD40 gene polymorphism is not associated with GD in Taiwan and is, therefore, not contributing to susceptibility to the disease there.

Genetic developments in autoimmune thyroid disease: an evolutionary process

The identification of genes placing individuals at an increased risk for the development of autoimmune thyroid disease (AITD) has been a slow process. However, over the last 20 years or so real progress has been made with the mapping of novel loci, via a number of different approaches. First, through the use of traditional immunological methods, Human Leucocyte Antigen (HLA)/Major Histocompatibility Complex (MHC) was the first gene region to be associated with AITD and consistent replications have been reported. Second, the CTLA-4 gene region on 2q33 was the first non-MHC replicated locus to be primarily identified using the candidate gene method. Third, family-based linkage studies led to the mapping of a new type 1 diabetes locus, the PTPN22 gene, which has subsequently been independently replicated as a susceptibility gene for Graves' disease (GD). Fourth, despite many unsuccessful attempts at implicating the TSHR gene as a susceptibility locus for GD, a recent approach of 'tagging' all the common variation within the gene has led to its identification as the first GD specific locus. Moreover, the use of tag single nucleotide polymorphisms (SNPs) has also been used to implicate the recently identified type 1 diabetes locus, CD25 as a susceptibility gene for GD. Finally, large scale, ongoing genome-wide association studies in multiple autoimmune diseases (AID) states, including AITD seem likely to lead to the identification of additional MHC and non-MHC susceptibility loci.

Exon 33 T/T genotype of the thyroglobulin gene is a susceptibility gene for Graves' disease in Taiwanese and exon 12 C/C genotype protects against it

This study investigates whether Tg gene polymorphisms can be associated with Graves' disease (GD) in a Taiwanese population and identifies potential polygenic susceptive genes for GD. The findings of such a study may have important implications for prognostic prediction and treatment of GD. We performed case control association studies for the 3 discovered Tg single nucleotide polymorphisms (SNPs) (E10, E12, E33) in 215 GD patients and 141 controls. The three SNPs were identified within the Tg gene. These SNPs were analysed by a fluorescent-based restriction fragment length polymorphism method (RFLP) and PCR. The genotype and allele frequencies at E10SNP158, E12SNP and E33SNP in GD patients were compared with those of the controls. In addition, we analysed the interactions between these SNPs and the clinical and laboratory variables. We found a significant difference in the T/T genotype of E33SNP and G/G genotype of E12SNP compared with the control group (p<0.001). We also found the E33SNP T/T genotype to be positively associated with development of GD, whereas the E12SNP G/G genotype protected it.

Susceptibility genes in Graves' ophthalmopathy: searching for a needle in a haystack?

The variety of clinical presentations of eye changes in patients with Graves' disease suggests that complex interactions between genetic, environmental, endogenous and local factors influence the development/severity of Graves' ophthalmopathy (GO). At present, the role of genetic factors in the development of GO remains unknown. Based on small case-control association studies with candidate genes, several susceptibility loci in GO have been proposed. These are human leucocyte antigen (HLA, 6p21.3), cytotoxic T-lymphocyte antigen-4 (CTLA-4, 2q33), tumour necrosis factor (TNF, 6p21.3), interferon-gamma (IFN-gamma, 12q14), intercellular adhesion molecule-1 (ICAM-1, 19p13), and thyroid stimulating hormone receptor gene (TSH-R, 14q31). Unfortunately, these results were either not confirmed or require replication in larger studies. There are many reasons for the lack of reproducibility of association studies in GO, including poor characterization of the studied groups and small sample sizes, which may result in both false positive and negative results. Thus, the genetic background of GO remains to be elucidated in future research. However, the possibility that GO may be a genetically heterogeneous disorder, or that the development of GO may be predominantly influenced by environmental factors such as cigarette smoking, can not be disregarded.

The impact of a TSH receptor gene polymorphism on thyroid-related phenotypes in a healthy Danish twin population

OBJECTIVES

The Asp727Glu polymorphism in the TSH receptor (TSHR) gene is associated with serum TSH levels. However, the proportion of genetic variation accounted for by this polymorphism is unknown. In this study, we (1) examined the association of the Asp727Glu polymorphism with thyroid size, serum levels of TSH, thyroid hormones, and thyroid antibodies in 1241 healthy Danish twin individuals and (2) assessed the contribution of the polymorphism to the trait variation and the genetic variance.

MEASUREMENTS

The effect of the genotype on the traits (mean +/- SD) was established; associations between the TSHR-Asp727Glu polymorphism and measures of thyroid homeostasis were assessed and the effect of the polymorphism on the trait's phenotypic variability was quantified by incorporating the genotype information in structural equation modelling.

RESULTS

The genotype distribution was Asp/Asp 84.9%; Asp/Glu 14.5% and Glu/Glu 0.6%. Carriers of the TSHR-Glu727 allele had lower TSH levels (noncarriers vs. carriers: 1.78 +/- 0.93 vs. 1.60 +/- 0.84 mU/l, P = 0.04). Regression analysis showed an association between the TSHR-Asp727Glu polymorphism and serum TSH (P = 0.007). The polymorphism accounted for 0.91% of the total phenotypic variance in serum TSH levels. Including the genotype in quantitative genetic modelling improved the model fit (P = 0.001); however, the genetic influence on serum TSH not attributable to this specific genetic variant was only reduced from 68.2% to 67.8%. The polymorphism was not significantly associated with thyroid size, thyroid hormones or thyroid antibody levels.

CONCLUSIONS

The TSHR-727Glu allele was associated with decreasing TSH levels; however, the contribution to the genetic variance was very small. No association was found with other thyroid-related measures.

Association of the TSHR gene with Graves' disease: the first disease specific locus

The development of autoimmune thyroid disease (AITD) is associated with autoantibodies directed against the thyroid stimulating hormone receptor (TSHR). Previous studies have failed to demonstrate a consistent association between the TSHR and AITD, or any of its sub-phenotypes. In the present study, we analysed the linkage disequilibrium (LD) structure encompassing the TSHR, to identify LD 'blocks' and SNPs, which capture the majority of intra-block haplotype diversity. The haplotype tagging SNPs, plus all common SNPs reported in previous studies were genotyped in 1,059 AITD Caucasian cases and 971 Caucasian controls. A haplotype, across two LD blocks, showed association (P<1 x 10(-6), OR 1.7) with Graves' disease (GD) but not autoimmune hypothyroidism (AIH). We replicated these findings by genotyping the most associated GD SNP, rs2268458, in a separate UK Caucasian cohort of 1,366 AITD cases and 1,061 controls (GD, P=2 x 10(-6), OR 1.3; AIH, P=NS). These results in two independent Caucasian data sets suggest that the TSHR is the first replicated GD-specific locus meriting further fine mapping and functional analysis to identify the aetiological variants.

New insights into antibody-mediated hyperthyroidism

The most common cause of hyperthyroidism is Graves' disease, which represents a typical example of an organ-specific autoimmune condition. The exact triggers for the disease remain unknown, but are likely to involve a complex interaction between multiple environmental factors in a genetically predisposed individual. The main feature of the condition is the presence of thyroid-stimulating antibodies, which activate the thyroid- stimulating hormone receptor, resulting in hyperthyroidism. These antibodies may also be involved in the extrathyroidal complications of the disease. The recent generation of thyroid-stimulating antibodies in animal models and the isolation of monoclonal thyroid-stimulating antibodies from a patient with Graves' disease should allow the detailed study of thyroid-stimulating antibodies-thyroid-stimulating hormone receptor interactions. This will help to shed more light on disease pathogenesis and may offer new treatment strategies in difficult cases, particularly in patients with extrathyroidal complications.

Thyrotropin receptor-associated diseases: from adenomata to Graves disease

The thyroid-stimulating hormone receptor (TSHR) is a G protein-linked, 7-transmembrane domain (7-TMD) receptor that undergoes complex posttranslational processing unique to this glycoprotein receptor family. Due to its complex structure, TSHR appears to have unstable molecular integrity and a propensity toward over- or underactivity on the basis of point genetic mutations or antibody-induced structural changes. Hence, both germline and somatic mutations, commonly located in the transmembrane regions, may induce constitutive activation of the receptor, resulting in congenital hyperthyroidism or the development of actively secreting thyroid nodules. Similarly, mutations leading to structural alterations may induce constitutive inactivation and congenital hypothyroidism. The TSHR is also a primary antigen in autoimmune thyroid disease, and some TSHR antibodies may activate the receptor, while others inhibit its activation or have no influence on signal transduction at all, depending on how they influence the integrity of the structure. Clinical assays for such antibodies have improved significantly and are a useful addition to the investigative armamentarium. Furthermore, the relative instability of the receptor can result in shedding of the TSHR ectodomain, providing a source of antigen and activating the autoimmune response. However, it may also provide decoys for TSHR antibodies, thus influencing their biological action and clinical effects. This review discusses the role of the TSHR in the physiological and pathological stimulation of the thyroid.

Polymorphisms in the TSHR (thyrotropin receptor) gene on chromosome 14q31 are not associated with mental retardation in the iodine-deficient areas of China

Mental retardation (MR) is one of the most frequent handicaps among children. Fetal iodine deficiency disorder (FIDD) is the commonest cause of preventable MR. However, not everyone in the iodine-deficient areas is affected and familial aggregation is common. This suggests that genetic factors may play an important role. Thyroid hormone (TH) plays an important role in fetal and early postnatal brain development. The thyroid-stimulating hormone (TSH, or thyrotropin) receptor (TSHR) is located on the surface of thyroid cells and binds TSH. It results in the production of thyroid hormones via the activation of adenylate cyclase and phospatidylinositol-dependent signaling pathways. Some researchers formulated the hypothesis that TSH receptor expression in the brain may be involved in local thyroid homeostasis through TSH stimulating the DIO2 activity. In the previous study, we have proposed that DIO2 may protect against FIDD in the iodine-deficient areas of China. The TSHR gene, which located on chromosome 14q31 is a potential candidate gene for susceptibility to FIDD. To investigate the potential genetic contribution of TSHR gene, we performed a case-control association study in Chinese Han population from the Qin-Ba mountain regions using four common SNPs in the gene (rs2284716, rs917986, rs2075173 and rs2075179). Pairwise linkage disequilibrium (LD) analysis showed that LD was observed between rs2284716 and rs917986 and between rs2075173 and rs2075179. Single-locus analysis found that all four SNPs in TSHR gene showed no association after correction for multiple testing. Haplotype analysis showed no significant differences in frequency for three sets of haplotypes based on the pariwise LD results. In conclusion, our association results suggest that TSHR gene is not a susceptibility gene for FIDD in the iodine-deficient areas of China.

Screening of SNPs at 18 positional candidate genes, located within the GD-1 locus on chromosome 14q23-q32, for susceptibility to Graves' disease: a TDT study

Graves' disease (GD) is a complex autoimmune thyroid disorder with a strong genetic component. Genome-wide screens resolved several susceptibility loci that contribute to the development of GD. One of the susceptibility loci (GD-1 locus) was mapped on chromosome 14q31. However, a susceptibility gene located within the GD-1 locus remains undefined. Here we screen eighteen single nucleotide polymorphisms (SNPs), each is situated at a corresponding positional candidate gene, located within the GD-1 susceptibility locus on chromosome 14q23-q32, for predisposition to GD using the transmission disequilibrium test in 126 simplex Russian families affected with GD. Among SNPs tested, a significant preferential transmission of the Ala allele (41 transmissions vs. 17 nontransmissions, corrected P=0.031) of the Thr92Ala SNP within the DIO2 gene, encoding type II iodothyronine deiodinase, from parents to affected children was found in a Russian family data set. The Thr92Ala SNP of the DIO2 gene and the D727E substitution of the thyrotropin receptor (TSHR) gene have been found to be in pair-wise linkage disequilibrium. The A92/E727 haplotype showed significant preferential transmission from parents to affected sibling (17 transmissions vs. 8 nontransmissions, P=0.039) in simplex families. This suggests that the Thr92Ala variant of the DIO2 gene is associated or may be in linkage disequilibrium with a functional DIO2 polymorphism which involves in the development of GD in a Russian population.

Association of a thyroglobulin gene polymorphism with Hashimoto's thyroiditis in the Japanese population

OBJECTIVE

The aetiology of the autoimmune thyroid diseases (AITDs), Graves' disease (GD) and Hashimoto's thyroiditis is largely unknown. However, genetic susceptibility is believed to play a major role. Two whole genome scans from Japan and from the USA identified a locus on chromosome 8q24 which showed evidence for linkage with AITD and HT. Recent studies have demonstrated an association between a Tg polymorphisms and AITD, suggesting that Tg is the susceptibility gene on 8q24.

PATIENTS

We studied 308 Japanese AITD patients (194 GD and 114 HT patients) and 417 Japanese control subjects in association studies.

DESIGN

Case-control association studies were performed using D8S284 and D8S272, microsatellite markers located in the 8q24 region, Tgms1 and Tgms2, microsatellite markers in introns 10 and 27, respectively, of Tg, and a SNP in exon 33 of Tg.

RESULTS

No differences in allele frequencies were observed between AITD patients and controls for D8S284, D8S272 and Tgms1. Similarly, for Tgms2 and the exon 33 SNP no significant differences in allele frequency distribution were observed for all AITD patients. However, when analysing the HT patients alone we found a significant association between the 330 bp/352 bp genotype of Tgms2 and HT (HT = 16.7%, controls = 7.1%; corrected P-value = 0.01, OR = 2.6).

CONCLUSION

Our results confirm the previous reports of an association between the Tg gene and AITD and suggest that Tg is an AITD susceptibility gene.

The contribution of immune regulatory and thyroid specific genes to the etiology of Graves' and Hashimoto's diseases

The autoimmune thyroid diseases (AITD) are complex diseases which are caused by an interaction between susceptibility genes and environmental triggers. Genetic susceptibility in combination with external factors (e.g. dietary iodine) are believed to initiate the autoimmune response to thyroid antigens. Abundant epidemiological data, including family and twin studies, point to a strong genetic influence on the development of AITD. Various techniques have been employed to identify the genes contributing to the etiology of AITD, including candidate gene analysis and whole genome screening. These studies have enabled the identification of several loci (genetic regions) that are linked with AITD, and in some of these loci putative AITD susceptibility genes have been identified. Some of these genes/loci are unique to Graves' disease (GD) and Hashimoto's thyroiditis (HT) and some are common to both diseases, indicating that there is a shared genetic susceptibility to GD and HT. The putative GD and HT susceptibility genes include both immune modifying genes (e.g. HLA, CTLA-4) and thyroid specific genes (e.g. TSHR, Tg). Most likely these loci interact and their interactions may influence disease phenotype and severity.

Thyroid-stimulating hormone receptor and its role in Graves' disease

The thyroid-stimulating hormone (TSH, or thyrotropin) receptor (TSHR) mediates the activating action of TSH to the thyroid gland, resulting in the growth and proliferation of thyrocytes and thyroid hormone production. In Graves' disease, thyroid-stimulating autoantibodies can mimic TSH action and stimulate thyroid cells. This leads to hyperthyroidism and abnormal overproduction of thyroid hormone. TSHR-antibodies-binding epitopes on the receptor molecule are well studied. Mechanism of TSHR-autoantibodies production is more or less clear but a susceptibility gene, which is linked to their production, is still unknown. Genetic studies show no linkage between the TSHR gene and Graves' disease. Among three common polymorphisms in the TSHR gene, only the D727E germline polymorphism in the cytoplasmic tail of the receptor showed an association with the disease, and this association is weak. The absence of a strong genetic effect of the TSHR polymorphisms in such a common and complex disorder as Graves' disease may be explained by a high degree of evolutionary conservation in TSHR. This can be shown by naturally existing germline and somatic mutations in the TSHR gene that cause various types of nonautoimmune and hereditary thyroid disease.

Amino acid substitutions in the thyroglobulin gene are associated with susceptibility to human and murine autoimmune thyroid disease

The 8q24 locus, which contains the thyroglobulin (Tg) gene, was previously shown to be strongly linked with autoimmune thyroid disease (AITD). We sequenced all 48 exons of the Tg gene and identified 14 single-nucleotide polymorphisms (SNPs). Case control association studies demonstrated that an exon 10-12 SNP cluster and an exon 33 SNP were significantly associated with AITD (P < 0.01). Haplotype analysis demonstrated that the combination of these two SNP groups was more significantly associated with AITD (P < 0.001). Gene-gene interaction studies provided evidence for an interaction between HLA-DR3 and the exon 33 SNP, giving an odds ratio of 6.1 for Graves' disease. We then sequenced exons 10,12, and 33 of the mouse Tg gene in 19 strains of mice. Fifty percent of the strains susceptible to thyroiditis had a unique SNP haplotype at exons 10 and 12, whereas none of the mouse strains that were resistant to thyroiditis had this SNP haplotype (P = 0.01). We concluded that Tg is a susceptibility gene for AITD, both in humans in and in mice. A combination of at least two Tg SNPs conferred susceptibility to human AITD. Moreover, the exon 33 SNP showed evidence for interaction with HLA-DR3 in conferring susceptibility to Graves' disease.

Searching for the autoimmune thyroid disease susceptibility genes: from gene mapping to gene function

The autoimmune thyroid diseases (AITD) are complex diseases that are caused by an interaction between susceptibility genes and environmental triggers. Genetic susceptibility, in combination with external factors (e.g., dietary iodine), is believed to initiate the autoimmune response to thyroid antigens. Abundant epidemiological data, including family and twin studies, point to a strong genetic influence on the development of AITD. Various techniques have been used to identify the genes contributing to the etiology of AITD, including candidate gene analysis and whole genome screening. These studies have enabled the identification of several loci (genetic regions) that are linked with AITD, and in some of these loci putative AITD susceptibility genes have been identified. Some of these genes/loci are unique to Graves' disease (GD) and Hashimoto's thyroiditis (HT), and some are common to both diseases, indicating that there is a shared genetic susceptibility to GD and HT. The putative GD and HT susceptibility genes include both immune modifying genes (e.g., human leukocyte antigen, cytotoxic T lymphocyte antigen-4) and thyroid-specific genes (e.g., TSH receptor, thyroglobulin). Most likely these loci interact, and their interactions may influence disease phenotype and severity. It is hoped that in the near future additional AITD susceptibility genes will be identified and the mechanisms by which they induce AITD will be unraveled.