CTLA-4 AT-repeat polymorphism reduces the inhibitory function of CTLA-4 in Graves' disease

Molecular Mechanisms in Autoimmune Thyroid Disease

The most common cause of acquired thyroid dysfunction is autoimmune thyroid disease, which is an organ-specific autoimmune disease with two presentation phenotypes: hyperthyroidism (Graves-Basedow disease) and hypothyroidism (Hashimoto’s thyroiditis). Hashimoto’s thyroiditis is distinguished by the presence of autoantibodies against thyroid peroxidase and thyroglobulin. Meanwhile, autoantibodies against the TSH receptor have been found in Graves-Basedow disease. Numerous susceptibility genes, as well as epigenetic and environmental factors, contribute to the pathogenesis of both diseases. This review summarizes the most common genetic, epigenetic, and environmental mechanisms involved in autoimmune thyroid disease.

Genetics of ANCA-associated vasculitis: role in pathogenesis, classification and management

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) comprises granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA), that share features of pauci-immune small-vessel vasculitis and the positivity of ANCA targeting proteinase-3 (PR3-ANCA) or myeloperoxidase (MPO-ANCA). AAV syndromes are rare, complex diseases and their aetio-pathogenesis is mainly driven by the interaction between environmental and genetic factors. In patients with GPA and MPA, the genetic associations are stronger with ANCA specificity (PR3- versus MPO-ANCA) than with the clinical diagnosis, which, in keeping with the known clinical and prognostic differences between PR3-ANCA-positive and MPO-ANCA-positive patients, supports an ANCA-based re-classification of these disorders. EGPA is also made up of genetically distinct subsets, which can be stratified on ANCA-status (MPO ANCA-positive versus ANCA-negative); these subsets differ in clinical phenotype and possibly in their response to treatment. Interestingly, MPO-ANCA-positive patients with either MPA or EGPA have overlapping genetic determinants, thus strengthening the concept that this EGPA subset is closely related to the other AAV syndromes. The genetics of AAV provides us with essential information to understand its varied phenotype. This Review discusses the main findings of genetic association studies in AAV, their pathogenic implications and their potential effect on classification, management and prognosis.

Genetic overlap between type 1 diabetes and other autoimmune diseases

Type 1 diabetes (T1D) is a chronic disease caused by the destruction of pancreatic β cells, which is driven by autoreactive T lymphocytes. It has been described that a high proportion of T1D patients develop other autoimmune diseases (AIDs), such as autoimmune thyroid disease, celiac disease, or vitiligo, which suggests the existence of common etiological factors among these disorders. In this regard, genetic studies have identified a high number of loci consistently associated with T1D that also represent established genetic risk factors for other AIDs. In addition, studies focused on identifying the shared genetic component in autoimmunity have described several common susceptibility loci with a potential role in T1D. Elucidation of this genetic overlap has been useful in identifying key molecular pathways with a pathogenic role in multiple disorders. In this review, we summarize recent advances in understanding the shared genetic component between T1D and other AIDs and discuss how the identification of common pathogenic mechanisms can help in the development of new therapeutic approaches as well as in improving the use of existing drugs.

Type 1 Diabetes and Autoimmune Thyroid Disease-The Genetic Link

Type 1 diabetes (T1D) and autoimmune thyroid disease (AITD) are the most frequent chronic autoimmune diseases worldwide. Several autoimmune endocrine and non-endocrine disorders tend to occur together. T1D and AITD often cluster in individuals and families, seen in the formation of autoimmune polyendocrinopathy (AP). The close relationship between these two diseases is largely explained by sharing a common genetic background. The HLA antigens DQ2 (DQA1*0501-DQB1*0201) and DQ8 (DQA1*0301-DQB1*0302), tightly linked with DR3 and DR4, are the major common genetic predisposition. Moreover, functional single nucleotide polymorphisms (or rare variants) of various genes, such as the cytotoxic T-lymphocyte- associated antigen (CTLA4), the protein tyrosine phosphatase non-receptor type 22 (PTPN22), the interleukin-2 Receptor (IL2Ra), the Vitamin D receptor (VDR), and the tumor-necrosis-factor-α (TNF) that are involved in immune regulation have been identified to confer susceptibility to both T1D and AITD. Other genes including cluster of differentiation 40 (CD40), the forkhead box P3 (FOXP3), the MHC Class I Polypeptide-Related Sequence A (MICA), insulin variable number of tandem repeats (INS-VNTR), the C-Type Lectin Domain Containing 16A (CLEC16A), the Erb-B2 Receptor Tyrosine Kinase 3 (ERBB3) gene, the interferon-induced helicase C domain-containing protein 1 (IFIH1), and various cytokine genes are also under suspicion to increase susceptibility to T1D and AITD. Further, BTB domain and CNC homolog 2 (BACH2), C-C motif chemokine receptor 5 (CCR5), SH2B adaptor protein 3 (SH2B3), and Rac family small GTPase 2 (RAC2) are found to be associated with T1D and AITD by various independent genome wide association studies and overlap in our list, indicating a strong common genetic link for T1D and AITD. As several susceptibility genes and environmental factors contribute to the disease aetiology of both T1D and AITD and/or AP subtype III variant (T1D+AITD) simultaneously, all patients with T1D should be screened for AITD, and vice versa.

Thyroid Dysfunction and Diabetes Mellitus: Two Closely Associated Disorders

Thyroid dysfunction and diabetes mellitus are closely linked. Several studies have documented the increased prevalence of thyroid disorders in patients with diabetes mellitus and vice versa. This review critically discusses the different underlying mechanisms linking type 1 and 2 diabetes and thyroid dysfunction to demonstrate that the association of these two common disorders is unlikely a simple coincidence. We assess the current state of knowledge on the central and peripheral control of thyroid hormone on food intake and glucose and lipid metabolism in target tissues (such as liver, white and brown adipose tissue, pancreatic β cells, and skeletal muscle) to explain the mechanism linking overt and subclinical hypothyroidism to type 2 diabetes and metabolic syndrome. We also elucidate the common susceptibility genes and the pathogenetic mechanisms contributing to the autoimmune mechanism involved in the onset of type 1 diabetes mellitus and autoimmune thyroid disorders. An untreated thyroid dysfunction can impair the metabolic control of diabetic patients, and this association can have important repercussions on the outcome of both of these disorders. Therefore, we offer recommendations for the diagnosis, management, and screening of thyroid disorders in patients with diabetes mellitus, including the treatment of diabetic patients planning a pregnancy. We also discuss the major causes of failure to achieve an optimal management of thyroid dysfunction in diabetic patients and provide recommendations for assessing and treating these disorders during therapy with antidiabetic drugs. An algorithm for a correct approach of these disorders when linked is also provided.

General and Specific Genetic Polymorphism of Cytokines-Related Gene in AITD

Autoimmune thyroid disease (AITD) shows the highest incidence among organ-specific autoimmune diseases and is the most common thyroid disease in humans, including Graves' disease (GD) and Hashimoto's thyroiditis (HT). The susceptibility to autoimmune diseases is affected by increased autoantibody levels, susceptibility gene polymorphisms, environmental factors, and psychological factors, but the pathogenesis remains unclear. Various cytokines and related genes encoding them play important roles in the development and progression of AITD. CD152, an expression product of the CTLA-4 gene, downregulates T cell activation. The A/A genotype polymorphism in the CT60 locus may reduce the production of thyroid autoantibodies. The C1858T polymorphism of the PTNP22 gene reduces the expression of its encoded LYP, which increases the risk of GD and HT. GD is an organ-specific autoimmune disease involving increased secretion of thyroid hormone, whereas HT may be associated with the destruction of thyroid gland tissue and hypothyroidism. These two diseases exhibit similar pathogenesis but opposite trends in the clinical manifestations. In this review, we focus on the structure and function of these cytokines and related genes in AITD, as well as the association of polymorphisms with susceptibility to GD and HT, and attempt to describe their differences in pathogenesis and clinical manifestations.

CD28/CTLA-4/ICOS haplotypes confers susceptibility to Graves' disease and modulates clinical phenotype of disease

Graves' disease, an autoimmune disease with heterogeneous symptoms including Graves' orbitopathy, has a combined genetic/environmental background, where variations within CD28/CTLA-4/ICOS genes are considered as disease markers.Association of CD28c.17+3T>C(rs3116496), CTLA-4g.319C>T(rs5742909), CTLA-4c.49A>G(rs231775), CTLA-4g.*642AT(8_33), CT60(rs3087243), Jo31(rs11571302), ICOSc.1554+4GT(8_15) polymorphisms with susceptibility to Graves' disease and clinical outcome was investigated. The study group comprised of 561 Polish Caucasians, including 172 unrelated Graves' disease patients. CTLA-4c.49A>G, CTLA-4g.319C>T, and CT60 were genotyped by PCR-RFLP; Jo31 and CD28c.17+3C>T by minisequencing; CTLA-4g.*642AT(8_33) and ICOSc.1554+4GT(8_15)-PCR and fluorescence-based technique. CD28c.17+3T>C(rs3116496)T/CTLA-4g.319C>T(rs5742909)C/CTLA-4c.49A>G(rs231775)G/CTLA-4g.*642AT(8_33)(AT_16-21)/CT60(rs3087243)G/Jo31(rs11571302)G/ICOSc.1554+4GT(8_15)(m) and TCA(AT_<16)GT(m) haplotypes increased risk of Graves' disease, especially in males, as well as overall Graves' orbitopathy development with severe outcome. TCG(AT_16-21)GG(l) haplotype increased risk of Graves' disease and reduced the chance of successful medical treatment. Although this haplotype was mainly observed in patients without signs of Graves' orbitopathy, if Graves' orbitopathy developed it favored a Graves' orbitopathy outcome. Haplotype TCA(AT_>21)GT(m) increased Graves' disease risk in women and, in all patients, was linked to Graves' disease without Graves' orbitopathy. TCG(AT_<16)GG(m) haplotype was predominantly observed in patients without Graves' orbitopathy, whereas TCA(AT_16-21)GG(m) was absent in those patients. TCA(AT_16-21)GG(m) occurred in patients with a mild Graves' orbitopathy outcome. The marker CTLA-4g.*642AT(8_33) was the only independent Graves' disease risk factor, whereas CT60 was an independent factor for disease progression. Sporadic Graves' disease was related to presence of CTLA-4c.49A>G[A] and the rare CTLA-4g.319C>T[T] allele variant. Familial background of the disease was exclusively associated with CTLA-4g.*642AT(8_33)[AT_>21]/[AT_>21] genotype. CD28/CTLA-4/ICOS loci may confer inherited susceptibility to Graves' disease or may be involved in susceptibility to Graves' disease and play a pathogenetic role.

Associations of CTLA4 Gene Polymorphisms with Graves' Ophthalmopathy: A Meta-Analysis

Many studies have established that T-lymphocyte antigen-4 (CTLA4) is a susceptible gene for Graves' disease (GD). Also many studies showed the association between the CTLA4 exon-1 49A/G polymorphism and the risk of developing Graves' ophthalmopathy (GO) in GD patients. But those results were inconsistent. In recent years many new studies were published which helped to shed light on the relationship of CTLA4 SNP49 with GO. So we performed the meta-analysis to explore the association between the SNP49 and GO susceptibility in GD patients. Studies up to February 29, 2012, were searched by using PubMed. The odds ratio was used to evaluate the strength of the association. Altogether 12 case-control studies involving 2,505 participants were included in the meta-analysis. Results showed that the G allele was related to the increased risk of GO compared with the A allele under allelic genetic model (OR = 1.14, 95% CI: 1.14–1.72, P = 0.001) in European subgroup. No publication bias was detected. Our results showed that the SNP49 polymorphism of CTLA4 gene was related to increased risk of GO.

Mechanisms of autoimmune thyroid diseases: from genetics to epigenetics

Recent advances in our understanding of genetic-epigenetic interactions have unraveled new mechanisms underlying the etiology of complex autoimmune diseases. Autoimmune thyroid diseases (AITDs) are highly prevalent, affecting 1% to 5% of the population. The major AITDs include Graves disease (GD) and Hashimoto's thyroiditis (HT); although these diseases contrast clinically, their pathogenesis involves shared immunogenetic mechanisms. Genetic data point to the involvement of both shared and unique genes. Among the shared susceptibility genes, HLA-DRβ1-Arg74 (human leukocyte antigen DR containing an arginine at position β74) confers the strongest risk. Recent genome-wide analyses have revealed new putative candidate genes. Epigenetic modulation is emerging as a major mechanism by which environmental factors interact with AITD susceptibility genes. Dissecting the genetic-epigenetic interactions underlying the pathogenesis of AITD is essential to uncover new therapeutic targets.

Genetics of primary progressive multiple sclerosis

Multiple sclerosis (MS) patients are classified as either having relapsing onset or progressive onset disease, also known as primary progressive MS (PPMS). Relative to relapsing onset patients, PPMS patients are older at disease onset, are equally likely to be men or women, and have more rapid accumulation of disability that does not respond well to treatments used in relapsing onset MS. Although estimates vary, 5-15% of all MS patients have a PPMS disease course. Genetic variance is a proposed determinant of MS disease course. If distinct genes associated with PPMS were identified study of these genes might lead to an understanding of the biology underlying disease progression and neural degeneration that are the hallmarks of PPMS. These genes and their biological pathways might also represent therapeutic targets. This chapter systematically reviews the PPMS genetic literature. Despite the intuitively appealing notion that differences between PPMS and relapsing onset MS are due to genetics, definite differences associated with these phenotypes at the major histocompatibility complex or elsewhere in the genome have not been found. Recent large-scale genome wide screens identified multiple genes associated with MS susceptibility outside the MHC. The genetic variants identified thus far make only weak individual contributions to MS susceptibility. If the genetic effects that contribute to the differences between PPMS and relapsing MS are similar in magnitude to those that distinguish MS from healthy controls then, given the relative scarcity of the PPMS phenotype, very large datasets will be needed to identify PPMS associated genes. International collaborative efforts could provide the means to identify such genes. Alternately, it is possible that factors other than genetics underlie the differences between these clinical phenotypes.

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 of cytotoxic T lymphocyte associated antigen-4 gene (rs60872763) polymorphism with Crohn's disease and high levels of serum sCTLA-4 in Crohn's disease

BACKGROUND AND AIM

Our aim was to evaluate cytotoxic T lymphocyte associated antigen-4 (CTLA-4) gene polymorphisms in Crohn's disease (CD) and explore soluble CTLA-4 (sCTLA-4) levels in serum of CD patients in central China.

METHODS

A total of 126 Chinese CD patients and 300 healthy controls were enrolled in this study. CTLA-4 (AT)n repeat polymorphism was genotyped by a semiautomatic fluorescently labeled polymerase chain reaction (PCR) method, and CTLA-4 -1661A/G and -1722T/C polymorphisms were genotyped by DNA sequencing. Serum sCTLA-4 and C-reactive protein (CRP) levels were determined by enzyme linked immunosorbent assay (ELISA) and immunonephelometry, respectively.

RESULTS

The frequency of 84 bp allele of CTLA-4 (AT)n repeats was lower in CD patients than in the healthy controls (22.2% vs 33.2%, P = 0.001, odds ratio = 0.58, 95% confidence interval: 0.41-0.81). The 84 bp allele carriers of (AT)n repeats were associated with non-stricturing and non-penetrating disease behavior in CD patients (P = 0.007). Serum sCTLA-4 levels were more elevated in CD patients than in the healthy controls (P < 0.001). Among CD patients, serum sCTLA-4 levels were increased in active disease compared with inactive disease (P = 0.015), and were correlated with CRP levels (r = 0.524, P < 0.001). Serum sCTLA-4 levels were higher in CD patients with stricturing disease behavior than in patients with other disease behaviors (P = 0.009).

CONCLUSIONS

84 bp allele of CTLA-4 (AT)n repeat polymorphism was associated with CD in central China. sCTLA-4 levels were highly expressed in CD, especially in active disease, and were correlated with CRP levels and disease behavior in CD patients.

Genetic susceptibility to autoimmune thyroid disease: past, present, and future

BACKGROUND

Autoimmune thyroid diseases (AITD), including Graves' disease and Hashimoto's thyroiditis, arise due to complex interactions between environmental and genetic factors. There are sound data coming from epidemiological, family, and twin studies demonstrating a strong genetic influence on the development of AITD. In this review we summarize the new findings on the genetic susceptibility to AITD focusing on emerging mechanisms of susceptibility.

SUMMARY

Candidate gene analysis, whole-genome linkage screening, genome-wide association studies, and whole-genome sequencing are the major technologies that have advanced this field, leading to the identification of at least seven genes whose variants have been associated with AITD. One of the major ones is the HLA-DR gene locus. Recently, it was shown that substitution of the neutral amino acids Ala or Gln with arginine at position beta 74 in the HLA-DR peptide-binding pocket is key to the etiology of both Graves' disease and Hashimoto's thyroiditis. Several other genes have also been shown to confer susceptibility to AITD. These can be classified into two groups: (i) immune regulatory genes (cytotoxic T lymphocyte-associated protein 4, CD40, protein tyrosine phosphatase-22, and CD25) and (ii) thyroid-specific genes (thyroglobulin and thyrotropin receptor genes). The influence of individual genes on the development of AITD when assessed in a population appears to be weaker than would be expected from the data showing strong genetic susceptibility to AITD. Two possible mechanisms explaining this discrepancy are gene-gene interactions and subset effects.

CONCLUSIONS

Significant progress has been made in our understanding of the immunogenetic mechanisms leading to thyroid autoimmunity. For the first time we are beginning to unravel these mechanisms at the molecular level. It is hoped that these new data will be translated into novel therapies and prevention strategies in AITD, such as costimulatory blockade.

The influence of CTLA-4 gene polymorphism on long-term kidney allograft function in Caucasian recipients

The aim of the study was to examine whether CTLA-4 (CD152) and CD28 gene polymorphisms affect the outcome of kidney transplantation (KTx). Polymorphisms of the CTLA-4 gene (-318 C>T, +49 A>G, and the microsatellite polymorphism in the 3'UTR of exon 4 (AT)(n)) and a CD28 gene (IVS3 +17T>C) were investigated in 314 allograft recipients with a mean age of 41.9+/-12 years. The median time since KTx was 97.5 months. The genotypes of the SNPs were determined by SSP-PCR and (AT)(n) genotype by PCR and capillary electrophoresis (ABI Prism 310). In general, no relationship was found between the allele variants and acute rejection or graft function. Univariate and multivariate analyses showed no influence of CTLA-4 or CD28 polymorphism on graft/patient survival. In the individuals bearing the combination of the homozygous variant of low AT repeat number (82 bp) and the homozygous variant A (adenine) in CTLA-4 +49 A>G, higher eGFR was observed at one year after KTx, which was also maintained at 10 years. In summary, 24.2% of the studied patients carrying the "favorable" CTLA-4 genotype exhibited significantly higher allograft function than the 16.9% recipients with the "unfavorable" genotype up to 10 years post transplantation.

CTLA4 -1661A/G and 3'UTR long repeat polymorphisms are associated with ulcerative colitis and influence CTLA4 mRNA and protein expression

Reduced cytotoxic T-lymphocyte antigen 4 (CTLA4) expression has been proposed as a risk for autoimmunity. CTLA4 polymorphisms have been associated with several autoimmune diseases, including ulcerative colitis (UC). In this study, we performed genotyping for CTLA4 -1661A/G, -1722T/C and 3' untranslated region (AT)n repeat polymorphisms in 300 Chinese UC patients and in 700 healthy controls, and evaluated the effects of polymorphisms on full-length (flCTLA4) and soluble CTLA4 (sCTLA4) expression in UC patients. The frequency of the -1661G allele was higher in UC patients than in healthy controls (16.5 vs 11.4%, P=0.003, odds ratio (OR)=1.53, 95% confidence interval (95% CI): 1.17-2.01). The prevalence of (AT)n repeats of the CTLA4 gene carrying long alleles (≥116 bp) was more common in UC patients than in healthy controls (22.0 vs 6.3%, P<0.001, OR=4.21, 95% CI: 2.79-6.33), and was associated with extensive colitis (P=0.008). Among UC patients, long-allele carriers expressed lower levels of flCTLA4 and sCTLA4 mRNA and sCTLA4 protein than did short-allele carriers (P<0.001, P<0.001, P<0.001, respectively). CTLA4 gene -1661A/G and long 3' untranslated region (AT)n repeat polymorphisms are associated with UC in Central China. This is likely from decreased expressions of sCTLA4 mRNA and sCTLA4 protein. Our study suggests that CTLA4 has an important role in susceptibility for UC in Central China.

The etiology of autoimmune thyroid disease: a story of genes and environment

Autoimmune thyroid diseases (AITDs), including Graves' disease (GD) and Hashimoto's thyroiditis (HT) are prevalent autoimmune diseases, affecting up to 5% of the general population. Autoimmune thyroid diseases arise due to complex interactions between environmental and genetic factors. Significant progress has been made in our understanding of the genetic and environmental triggers contributing to AITD. However, the interactions between genes and environment are yet to be defined. Among the major AITD susceptibility genes that have been identified and characterized is the HLA-DR gene locus, as well as non-MHC genes including the CTLA-4, CD40, PTPN22, thyroglobulin, and TSH receptor genes. The major environmental triggers of AITD include iodine, medications, infection, smoking, and possibly stress. Recent data on the genetic predisposition to AITD lead to novel putative mechanisms by which the genetic-environmental interactions may lead to the development of thyroid autoimmunity.

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.

The role of genetics in Graves' disease and thyroid orbitopathy

Graves' disease is a complex autoimmune disorder characterized by multiple systemic manifestations of overproduction of thyroid hormone, and in some cases, orbitopathy. The etiology of this disorder is multifactorial, involving heritable abnormalities of immune regulation as well as environmental triggers. The goal of this paper is to provide a review of recent research investigating candidate genes involved in the pathophysiology of both Graves' disease per se and of thyroid orbitopathy.

The genetic basis of thyroid autoimmunity

Autoimmune thyroid diseases (AITDs), including Graves' disease (GD) and Hashimoto's thyroiditis (HT), are prevalent autoimmune diseases, affecting up to 5% of the general population. AITDs arise due to interplay between environmental and genetic factors. In the past decade, significant progress has been made in our understanding of the genetic contribution to the etiology of AITDs. Excitingly, several AITD susceptibility genes have been identified and characterized. Some of these susceptibility genes are specific to either GD or HT, while others confer susceptibility to both conditions. The first AITD susceptibility gene locus identified was the Human-Leukocyte-Antigen DR (HLA-DR) gene locus. Subsequently, a quintet of non-HLA genes, including the cytotoxic T lymphocyte antigen (CTLA-4), CD40, protein tyrosine phosphatase-22 (PTPN22), thyroglobulin, and thyroid-stimulating hormone receptor (TSHR) gene, has been shown to contribute to the susceptibility to AITDs. Recently, the mechanisms by which these new AITD genes predispose to AITDs have been dissected. In this review, we overview and highlight the recent data on the genes predisposing to AITDs and the putative mechanisms by which they confer susceptibility to disease.

Cytotoxic T-lymphocyte associated antigen 4 gene polymorphisms and autoimmune thyroid disease: a meta-analysis

CONTEXT

Cytotoxic T-lymphocyte associated antigen 4 (CTLA-4) polymorphisms have been widely examined for their associations with autoimmune thyroid diseases [Graves' disease (GD) and Hashimoto thyroiditis (HT)], but their relative population effect remains unclear.

OBJECTIVE

The aim was to generate large-scale evidence on whether the CTLA-4 polymorphisms (A49G and CT60) and haplotypes thereof increase the susceptibility to GD and/or HT.

DESIGN, SETTING, AND PARTICIPANTS

Meta-analyses of group-level data were reviewed from 32 (11,019 subjects) and 12 (4,479) published and unpublished studies for the association of the A49G polymorphism with GD and HT, respectively (PubMed and HuGeNet search until July 2006). There were 15 (n = 7246) and six (n = 3086) studies available for the CT60 polymorphism, respectively. Meta-analyses of individual-level data from 10 (4906 subjects) and five (2386) collaborating teams for GD and HT, respectively, were also reviewed.

MAIN OUTCOME MEASURES

Association of gene variants and haplotypes with GD and HT was measured.

RESULTS

Group-level data suggested significant associations with GD and HT for both A49G [odds ratios 1.49 (P = 6 x 10(-14)) and 1.29 (P = 0.001) per G allele, respectively] and CT60 [1.45 (P = 2 x 10(-9)) and 1.64 (P = 0.003) per G allele, respectively]. Results were consistent between Asian and Caucasian descent subjects. Individual-level data showed that compared with the AA haplotype, the risk conferred by the GG haplotype was 1.49 (95% confidence interval 1.31,1.70) and 1.36 (95% confidence interval 1.16,1.59) for GD and HT, respectively. Data were consistent with a dose-response effect for the G allele of CT60.

CONCLUSION

The CT60 polymorphism of CTLA-4 maps an important genetic determinant for the risk of both GD and HT across diverse populations.

CTLA4 gene polymorphisms and multiple sclerosis in Northern Ireland

Four CTLA4 polymorphisms were investigated in a Northern Irish collection of relapsing-remitting (RR) and primary-progressive (PP) multiple sclerosis (MS) patients. The CTLA4 promoter (-318 C/T), exon 1 (+49 A/G) and intergenic CT60 SNPs, as well as a microsatellite found in the 3' UTR (AT(n)) were analysed in 246 RRMS, 84 PPMS and 158 healthy controls. The A allele of the exon 1 +49 A/G SNP (OR=1.36; 95% CI=1.11-1.81; P=0.038), and more so the AA genotype (OR=1.70; 95% CI=1.11-2.60; P=0.015) were associated with RR, but not PPMS. In the PPMS population, overall allele distribution of the AT(n) microsatellite was significantly different from that in the healthy controls. We did not find any association with the promoter (-318 C/T) or intergenic CT60 SNPs in either of the disease cohorts. In concordance with several recent studies, we detected a trend toward higher carriage rates of the +49 G allele in PP vs RR MS patients (66.7% vs 58.9%), though this was not significant. Our data highlight the CTLA4 +49 A/G and 3'UTR polymorphisms as potential modifiers of disease course in MS.

The CD40, CTLA-4, thyroglobulin, TSH receptor, and PTPN22 gene quintet and its contribution to thyroid autoimmunity: back to the future

Autoimmune thyroid diseases (AITD) are common autoimmune diseases, affecting up to 5% of the general population. Thyroid-directed autoimmunity is manifested in two classical autoimmune conditions, Hashimoto's thyroiditis, resulting in hypothyroidism and Graves' disease resulting in hyperthyroidism. Autoimmune thyroid diseases arise due to an interplay between environmental and genetic factors. In the past decade significant progress has been made in our understanding of the genetic contribution to the etiology of AITD. Indeed, several AITD susceptibility genes have been identified. Some of these susceptibility genes are specific to either Graves' disease or Hashimoto's thyroiditis, while others confer susceptibility to both conditions. Both immunoregulatory genes and thyroid specific genes contribute to the pathogenesis of AITD. The time is now ripe to examine the mechanistic basis for the contribution of genetic factors to the etiology of AITD. In this review, we will focus on the contribution of non-MHC II genes.

Immunogenetics of Hashimoto's thyroiditis

Hashimoto's thyroiditis (HT) is an organ-specific T-cell mediated disease. It is a complex disease, with a strong genetic component. To date, significant progress has been made towards the identification and functional characterization of HT susceptibility genes. In this review, we will summarize the recent advances in our understanding of the genetic input to the pathogenesis of HT.

Immunoregulatory and susceptibility genes in thyroid and polyglandular autoimmunity

The etiology of autoimmune thyroid diseases (AITD) is based on genetic and nongenetic factors. Genome-wide screening and linkage analyses have identified several chromosomal regions that are linked to AITD. These are HT-1 (on chromosome 13q33) and HT-2 (chromosome 12q22) for Hashimoto's thyroiditis (HT), and GD-1 (chromosome 14q31), GD-2 (chromosome 20q11.2), and GD-3 (chromosome Xq21) for Graves' disease (GD). Several genes have been proposed as susceptibility or immunoregulatory genes. Most promising genes are those of the major histocompatibility complex (MHC) complex (chromosome 6), the cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) gene (chromosome 2), the CD40 (chromosome 20), the thyroglobulin gene (chromosome 8), and the autoimmune regulator gene (chromosome 21). This review summarizes evidence for pathogenetic involvement of several of these genes in various forms of autoimmune thyropathies. Most genetic data refer to GD, whereas less data are available for HT and thyroid-associated ophthalmopathy. Scarce data refer to AITD within the autoimmune polyglandular syndromes I and II. The realization of family studies in large samples from different populations might provide further insight in the genetic contribution to AITD. Data are also needed on the interaction among susceptibility genes. Finally, additional functional studies are warranted to clarify the possible role of allelic variants in the underlying pathogenic mechanisms of AITD.

CT60 single nucleotide polymorphisms of the cytotoxic T-lymphocyte-associated antigen-4 gene region is associated with Graves' disease in an Italian population

Graves' disease (GD) is an autoimmune and polygenic disorder. Several studies have shown that human leukocyte antigen (HLA) class II and the cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) gene are involved in the genetic susceptibility. We performed a case control study on 150 patients with GD and 301 controls, matched for age and gender, to verify the association of three polymorphisms located in CTLA-4 region (A49G, [AT](n)-3'UTR, and CT60) and of HLA-DRB1 and DQB1 loci with the disease in an Italian population. The prevalence of patients with GD carrying the G allele of CT60 was significantly higher compared to control subjects (p = 0.02, odds ratio [OR] = 1.82). The allelic frequency of the G allele of CT60 was also significantly higher in patients with GD (p = 0.02). The G allele frequency of A49G in patients was significantly higher compared to control subjects (p = 0.04). The 280 allele phenotype frequency of (AT)(n)-3'UTR was also significantly higher in patients (p = 0.04). The G allele of A49G, the G allele of CT60, and the 280 allele of (AT)(n)-3'UTR microsatellite were significantly increased in patients with GD with thyroid-associated ophthalmopathy (TAO) compared to controls (p = 0.04, p = 0.03, and p = 0.02, respectively), however, we did not find any significant difference between TAO and non-TAO patients. We also found the HLA-DRB1*03 allele to be associated with GD; interestingly, the association of the CTLA-4 markers was independent from the HLA DRB1*03 status. These results highlight the role of the CTLA-4 locus, in addition to HLA, in the susceptibility to GD. Inside the CTLA-4 region, CT60 appears to be the most associated polymorphism to GD, however, further studies are needed to identify the etiologic variant.