Major histocompatibility complex (MHC) factors predisposing to and protecting against Graves' eye disease

Significance of HLA in Graves' disease and Graves' orbitopathy in Asian and Caucasian populations - a systematic review

Introduction

Graves' disease (GD) and Graves' orbitopathy (GO) development were suspected to be HLA-related in both Asian and Caucasian populations. However, most studies were performed with application of serological methods or low resolution genetic typing, which led to inconsistent results even among the same population. The present review is intended to summarize the state-of-art knowledge on the HLA significance in GD and GO in Asians and Caucasians, as well as to find the most significant alleles for each of the populations.

Methods

PubMed was searched for relevant articles using the following search terms: HLA plus thyroid-associated ophthalmopathy or Graves' disease or Graves' orbitopathy or thyroid eye disease or thyroid-associated orbitopathy.

Results

In Asian population GD was found to be associated mostly with B*46:01, DPB1*05:01, DRB1*08:02/03, DRB1*16:02, DRB1*14:03, DRB1*04:05, DQB1*05:02 and DQB1*03:03, while DRB1*07:01, DRB1*01:01, DRB1*13:02, DRB1*12:02 are potentially protective. HLA-B*38:02, DRB1*16:02, DQA1*01:02, DQB1*05:02 can be considered associated with increased risk of GO in Asians, while HLA-B*54:01 may play protective role. In Caucasians, C*07:01, DQA1*05:01, DRB1*03, DQB1*02:01 are associated with GD risk while DRB1*07:01, DQA1*02:01 may be protective. Significance of HLA in the course of GD and novel aspects of HLA amino acid variants and potential HLA-based treatment modalities were also discussed.

Graves' ophthalmopathy: a review of immunogenetics

Graves’ disease (GD) is the most common cause of thyrotoxicosis and often involves the orbits. Graves’ ophthalmopathy (GO), also known as Thyroid Eye Disease (TED), can be clinically significant and advance to sight-threatening stages. Our knowledge of the immunogenetic pathophysiology of GO is rapidly expanding. The present review is an attempt to summarize the current state of knowledge on the immunogenetics of GO. First we briefly review the epidemiology and clinical importance of GO, and then we describe in detail the macromolecular pathogenesis and finally immunogenetics of GO. Discrepancies between the results from various reports and the limitations of the available data are discussed. In particular, there is a scarcity of data from non-Asian populations. While several studies have demonstrated significant associations between polymorphisms in certain genes (especially CTLA-4, HLA-DRB-1, and TNF-α), there is a need for studies that investigate the relationship between polymorphisms and both serum and local concentrations of the resulting proteins. A complete understanding of GO susceptibility and pathogenesis has not been yet possible due to a number of important knowledge gaps that need to be filled by future research.

Genetic profiling in Graves' disease: further evidence for lack of a distinct genetic contribution to Graves' ophthalmopathy

BACKGROUND

Graves' disease (GD), including Graves' ophthalmopathy or orbitopathy (GO), is an autoimmune disease with an environmental and genetic component to its etiology. The genetic contribution to the GO clinical phenotype remains unclear. Previous data from our laboratory and others have suggested that GO has no specific genetic component distinct from GD itself, while other reports have occasionally appeared suggesting that polymorphisms in genes such as CTLA4 and IL23R specifically increase the risk for GO. One of the criticisms of all these reports has been the clinical definition of the GO phenotype as distinct from hyperthyroid GD devoid of clinically significant eye involvement. The objective of this study was to take advantage of a phenotypically pure group of GD patients with GO and examine a series of genes associated with GD to determine if any were more definitively associated with GO rather than Graves' thyroid disease itself.

METHODS

To further examine whether specific susceptibility genes are associated with GO, we have performed further genetic association studies using highly characterized GO patients, many of whom had undergone orbital decompression surgery for their exophthalmos. We genotyped HLA, CTLA4, IL23R, and TSHR genes in a group of 256 Caucasian patients with severe GO (n=199) and less severe GO (n=57), and 90 patients with GD but no clinically apparent GO.

RESULTS

We found that the allele and genotype frequencies were not statistically different between GO and non-GO patients for any of the genes and gene combinations assessed.

CONCLUSIONS

These results provide further evidence that patients with GO do not have a distinct genetic susceptibility to their eye disease and again suggest that environmental and/or epigenetic influences are at play.

Association of MICA Alleles with Autoimmune Thyroid Disease in Korean Children

Background. Major histocompatibility complex class I chain-related gene A (MICA) is a ligand for the activating NKG2D receptor expressed on natural killer (NK) cells. We aimed to assess the association of MICA polymorphism with autoimmune thyroid disease (AITD) in Korean children. Methods. Eighty-one patients with AITD were recruited. We analyzed MICA polymorphisms by PCR-SSP and compared the results with those of 70 healthy controls. Results. In AITD, the allele frequencies of MICA∗010 (OR = 2.21; 95% CI, 1.30-3.76, P < 0.003, P(c) < 0.042) were higher than those of controls. Patients who did not have thyroid-associated ophthalmopathy showed higher frequencies of MICA∗010 (OR = 2.99; 95% CI, 1.47-6.08, P < 0.003, P(c) < 0.042) and lower frequencies of MICA∗008 (OR = 0.08; 95% CI, 0.01-0.62, P < 0.001, P(c) < 0.014) compared to those of controls. HLA-B∗46, which shows the strongest association with AITD compared with other HLA alleles, showed the strongest linkage disequilibrium with MICA∗010. Analyses of the associations between MICA∗010 and HLA-B∗46 with AITD suggest an association of the MICA allele with AITD. Conclusions. Our results suggest that innate immunity might contribute to the pathogenesis of AITD.

Compound KIR-HLA genotype analyses in the Iranian population by a novel PCR-SSP assay

Natural killer (NK) cells eliminate infected and transformed cells while still are self-tolerant. Interactions of the independently segregating Killer cell immunoglobulin-like receptors (KIR) and human leucocyte antigens (HLA) loci play a critical role in NK cell regulation. Different compound KIR-HLA genotypes can impart different thresholds of activation to the NK-cell repertoire and such genotypic variation has been found to confer altered risk in a number of human diseases including viral infections, autoimmune disorders, reproduction abnormalities and cancers. In this study, we presented a novel combined KIR-HLA polymerase chain reaction-sequence-specific primers genotyping assay for simultaneous determination of KIR genes and their three major HLA class I ligand groups (C1, C2, and Bw4). Moreover, known inhibitory and activating KIR + HLA (iKIR + HLA: 2DL2/3 + C1, 2DL1 + C2, 3DL1 + Bw4; and aKIR + HLA: 2DS2 + C1, 2DS1 + C2, 3DS1 + Bw4) combinations as well as co-inheritance of aKIR genes and iKIR + HLA pairs were analysed in a total of 200 unrelated healthy Iranian individuals. All tested subjects had at least one of the three iKIR + HLA pairs and the frequencies of various inhibitory combinations in the study group were: 31.5%, three iKIR + HLA pairs, 53.5%, two iKIR + HLA pairs, and 15%, 0ne iKIR + HLA pair. Furthermore, we revealed that majority of Iranians (69%) carry compound genotypes with greater number of inhibitory pairings than activating combinations (iKIR + HLA > aKIR + HLA). Conversely, iKIR + HLA < aKIR (45%) was dominant genotype in the study group. We conclude that selective evolutionary pressure has propensity to maintain KIR-HLA genotypes with more inhibitory combinations to guarantee self-tolerance. In contrast, existence of activating KIR genes without normal endogenous ligands, potentially arms the NK population for competent immunosurveillance and stronger defense against infections.

Update Thyroid-Associated Ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is one of the most vexing problems in endocrinology but its relationship to thyroid autoimmunity is becoming more clear with the realisation that almost all patients with Graves' disease have this condition and almost all patients with ophthalmopathy have some form of thyroid involvement. This suggests cross reactivity between thyroid and retrobulbar antigens, of which one potential candidate has recently been cloned. Together with new information on predisposing factors and the important role of the retrobulbar fibroblasts, these developments shed new light on the aetiology and pathogenesis of this enigmatic disorder.

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.

Receptor-ligand analyses define minimal killer cell Ig-like receptor (KIR) in humans

Interactions between inhibitory killer cell immunoglobulin-like receptors (iKIR) and human leukocyte antigen (HLA) class I molecules regulate natural killer (NK) cell responses to eliminate infected and transformed cells while maintaining tolerance to healthy cells. Unlinked polymorphic gene families encode KIR receptors and HLA class I ligands and their independent segregation results in a variable number and type of iKIR + HLA pairs inherited in individuals. The diversity in the co-inheritance of iKIR + HLA pairs and activating KIR (aKIR) genes in 759 unrelated individuals from four ethnic populations was analyzed. Every individual studied inherited a minimum of one iKIR + HLA pair; suggesting that major histocompatibility complex class I-dependent inhibitory KIR signaling is essential for human NK cell function. In contrast, 13.4% of the study group lacked all aKIR genes. Twenty percent of the study group carried only one of the four iKIR + HLA pairs. Interestingly, 3% of the study group carrying only KIR2DL3 + HLA-C1 as an iKIR + HLA pair lacked aKIR genes. These data suggest that a single iKIR can constitute the minimal KIR repertoire for human NK cells. Genotypes carrying an equal number of iKIR + HLA pairs and aKIR genes represented 20% of the study group. The remaining individuals had either a dominant inhibitory KIR genotype (iKIR + HLA > aKIR) or a dominant activating KIR genotype (iKIR + HLA < aKIR). Genotypes encoding these imbalanced inhibitory and activating interactions may contribute to susceptibility or resistance to human diseases.

Human thyroid autoantigens and proteins of Yersinia and Borrelia share amino acid sequence homology that includes binding motifs to HLA-DR molecules and T-cell receptor

We previously reported that the spirochete Borrelia burgdorferi could trigger autoimmune thyroid diseases (AITD). Subsequently, we showed local amino acid sequence homology between all human thyroid autoantigens (human thyrotropin receptor [hTSH-R], human thyroglobulin [hTg], human thyroperoxidase [hTPO], human sodium iodide symporter [hNIS]) and Borrelia proteins (n = 6,606), and between hTSH-R and Yersinia enterocolitica (n = 1,153). We have now updated our search of homology with Borrelia (n = 11,198 proteins) and extended our search on Yersinia to the entire species (n = 40,964 proteins). We also searched the homologous human and microbial sequences for peptide-binding motifs of HLA-DR molecules, because a number of these class II major histocompatibility complex (MHC) molecules (DR3, DR4, DR5, DR8, and DR9) are associated with AITD. Significant homologies were found for only 16 Borrelia proteins (5 with hTSH-R, 2 with hTg, 3 with hTPO, and 6 with hNIS) and only 19 Yersinia proteins (4 with hTSH-R, 2 with hTg, 2 with hTPO, and 11 with hNIS). Noteworthy, segments of thyroid autoantigens homologous to these microbial proteins are known to be autoantigenic. Also, the hTSH-R homologous region of one Borrelia protein (OspA) contains an immunodominant epitope that others have found to be homologous to hLFA-1. This is of interest, as the hLFA-1/ICAM-1 ligand/receptor pair is aberrantly expressed in the follicular cells of thyroids affected by Hashimoto's thyroiditis. A computer-assisted search detected antigenic peptide binding motifs to the DR molecules implicated in AITD. In conclusion, our in silico data do not directly demonstrate that Borrelia and Yersinia proteins trigger AITD but suggest that a restricted number of them might have the potential to, at least in persons with certain HLA-DR alleles.

Current perspective on the pathogenesis of Graves' disease and ophthalmopathy

Graves' disease (GD) is a very common autoimmune disorder of the thyroid in which stimulatory antibodies bind to the thyrotropin receptor and activate glandular function, resulting in hyperthyroidism. In addition, some patients with GD develop localized manifestations including ophthalmopathy (GO) and dermopathy. Since the cloning of the receptor cDNA, significant progress has been made in understanding the structure-function relationship of the receptor, which has been discussed in a number of earlier reviews. In this paper, we have focused our discussion on studies related to the molecular mechanisms of the disease pathogenesis and the development of animal models for GD. It has become apparent that multiple factors contribute to the etiology of GD, including host genetic as well as environmental factors. Studies in experimental animals indicate that GD is a slowly progressing disease that involves activation and recruitment of thyrotropin receptor-specific T and B cells. This activation eventually results in the production of stimulatory antibodies that can cause hyperthyroidism. Similarly, significant new insights have been gained in our understanding of GO that occurs in a subset of patients with GD. As in GD, both environmental and genetic factors play important roles in the development of GO. Although a number of putative ocular autoantigens have been identified, their role in the pathogenesis of GO awaits confirmation. Extensive analyses of orbital tissues obtained from patients with GO have provided a clearer understanding of the roles of T and B cells, cytokines and chemokines, and various ocular tissues including ocular muscles and fibroblasts. Equally impressive is the progress made in understanding why connective tissues of the orbit and the skin in GO are singled out for activation and undergo extensive remodeling. Results to date indicate that fibroblasts can act as sentinel cells and initiate lymphocyte recruitment and tissue remodeling. Moreover, these fibroblasts can be readily activated by Ig in the sera of patients with GD, suggesting a central role for them in the pathogenesis. Collectively, recent studies have led to a better understanding of the pathogenesis of GD and GO and have opened up potential new avenues for developing novel treatments for GD and GO.

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.

Two HLA DRB 1 alleles confer independent genetic susceptibility to Graves disease: relevance of cross-population studies

Recent studies of Graves disease (GD) employing genome scanning techniques excluded the major histocompatibility complex as a contributor to disease liability. These findings contradict earlier population association studies. Our own earlier studies have also emphasized that genetic variation in human populations may give novel clues to disease liability and manifestations. To this end, we studied HLA class II alleles in 47 Latvian GD patients and 111 matched healthy controls. As expected, we found that DRB1*03 and DQA1*0501 (OR = 3.6, P = 0.029 and OR 2.35, P = 0.0373, respectively) were associated with GD. Unforeseen, DRB1*04 was found to be significantly increased in the patients compared to controls (OR 3.267, corrected P = 0.0319). The two DRB1 alleles conferred two non-overlapping and independent susceptibilities to GD, in that only three patients were positive for both alleles, and the removal of each allele in turn resulted in only the other DRB1 allele showing significant association with the disease. There was no heterogeneity between the two patient groups (DRB1*03 positive and DRB1*04 positive) in clinical characteristics or disease manifestations. The phenotype DRB1*03 and/or DRB1*04 was found in 34/47 patients compared to 27/111 controls yielding an OR of 7.395 (P corrected = 0.000019). We examined the structural basis of DRB1 susceptibility to GD in light of this and previous studies, showing that DRB1*03, 04, and 08 were positively associated with the disease, whereas DRB1*07 was negatively associated. Differences in protein sequences were noted at residues 54, 57, 59, and 66; positions 54, 57, and 66 are on the same face of the alpha helix. The canonical arginine 54 is replaced by glutamine in DRB1*07. At position 66, asparagine in DRB1*03 and tyrosine in DRB1*04 are replaced by phenylalanine in DRB1*07. Residue 59, likely involved in pocket formation in the antigen binding groove, is modified by replacement of tyrosine in DRB1*03, 08, and 04 and by leucine in DRB1*07. The predicted differences in the shape and charges of the proximal reaches of the antigen binding groove between DRB1*07, and 03, 04, and 08, could determine whether or not a peptide from an auto-antigen would be bound or not. Genetic variation among human populations may yield important clues to specific disease liability.

Primary role of the HLA class II DRB1*0301 allele in Graves disease

The association of the Graves disease (GD) with HLA DR3 and DQA1*0501 in Caucasians has been described previously. From these studies it could not be determined whether one specific locus was primarily involved. Using a case-control study design, we have examined the role of HLA class II gene polymorphisms in the predisposition for GD in a group of Belgian subjects. We demonstrated that both DRB1*0301 and DQA1*0501 alleles conferred significant susceptibility in the DRB1*0301-DQA1*0501 haplotype. The DRB1*0301 allele was the primary susceptibility allele for GD, however, because the susceptibility provided by DQA1*0501 was most likely due to it being in linkage disequilibrium with DRB1*0301. The DRB1*0701/x and DQA1*0201/x genotypes and the DRB1*0701-DQA1*0201 haplotype provided protection with an equal RR of 0.29. Predictive value calculations showed that testing for DRB1*0301 gave the highest positive predictive value for GD in females and males. This was, however, 10 times higher in females and predicted a 3.63% risk for a random female to develop GD.

Thyroid-associated ophthalmopathy: clinical features, pathogenesis, and management

Thyroid-associated ophthalmopathy (TAO) is a progressive eye disorder characterized by immune-mediated inflammation of the extraocular muscles and orbital connective tissue. TAO is linked, in a unique way, with thyroid autoimmunity, in particular Graves' hyperthyroidism. Our working hypothesis for the pathogenesis of TAO is that recognition of a thyrotropin receptor (TSHR)-like protein in the orbital preadipocytes by antibodies may be the initial event leading to homing of lymphocytes into the orbital tissues. In the course of thyroid inflammation, antibodies and T cells reactive against G2s expressed in thyroid membranes cross-react with the protein in the eye muscle fiber, leading to eye muscle damage and dysfunction. Those patients with anti-G2s antibodies develop ocular myopathy. Antibodies against flavoprotein, the 64-kDa protein, which are produced in the context of eye muscle fiber damage and mitochondrial rupture, are sensitive markers of immune-mediated fiber necrosis in patients with ophthalmopathy but do not directly damage the eye muscle. Antibodies against type XIII collagen, which is localized in the plasma membranes of orbital fibroblast, may be a new marker for the congestive ophthalmopathy subtype of TAO. The measurement of antibodies against key eye muscle and orbital connective tissue autoantigens may have a role in the management of active ophthalmopathy and its prediction in patients with Graves' hyperthyroidism.

What is the evidence of genetic factors in the etiology of Graves' disease? A brief review

Graves' disease (GD) is generally thought of as a multifactorial disorder in which genetic susceptibility interacts with environmental and endogenous factors to cause disease. The importance of genetic factors is suggested by the clustering of GD within families and by a higher concordance rate for disease in monozygotic than dizygotic twins. This has, however, recently been shown to be less pronounced than previously thought. During the last decade, much effort has been put into characterization of the genetic background of GD. Until recently most studies have examined associations between GD and the human leukocyte antigen (HLA) region, but recent advances in molecular techniques have opened the way for whole-genome screening. A number of HLA and non-HLA candidate genes have been proposed, but despite several large investigations within multiplex families no major susceptibility genes have been identified. This brief review discusses relevant articles published from 1940 through 1997 regarding the influence of genetic factors in the etiology of GD. Ongoing studies will focus on whole genome screening in multiplex families as well as population based twin studies. However, the possibility of GD being a heterogeneous disease without a single well-defined genotype and phenotype should be left open.

What is the evidence of genetic factors in the etiology of Graves' disease? A brief review

Graves' disease (GD) is generally thought of as a multifactorial disorder in which genetic susceptibility interacts with environmental and endogenous factors to cause disease. The importance of genetic factors is suggested by the clustering of GD within families and by a higher concordance rate for disease in monozygotic than in dizygotic twins. This has, however, recently been shown to be less pronounced than previously thought. During the last decade much effort has been put into characterization of the genetic background of GD. Until recently, most studies have examined associations between GD and the human leukocyte antigen (HLA) region, but recent advances in molecular techniques have opened the way for whole genome screening. A number of HLA and non-HLA candidate genes have been proposed, but despite several large investigations within multiplex families no major susceptibility genes have been identified. This brief review discusses relevant articles published from 1940 through 1997 regarding the influence of genetic factors in the etiology of GD. Ongoing studies focus on whole genome screening in multiplex families as well as population-based twin studies. However, the possibility of GD being a heterogeneous disease without a single well-defined genotype and phenotype should be left open.

The genetic susceptibility to Graves' disease

Graves' disease (GD) develops as a result of a complex interaction between genetic susceptibility genes and likely environmental factors. Most epidemiological data support an important genetic contribution to the development of GD. The concordance rate of GD in monozygotic twins is 30-60% and in dizygotic twins 3-9%, and thyroid autoantibodies have been reported in up to 50% of the siblings of patients with GD. For many years now, HLA studies have consistently shown an increased frequency of HLA-DR3 in Caucasian patients with GD; but with only a risk ratio of 3-5. However, recent advances in human genome mapping techniques have enabled the study of many other candidate genes. Of these additional, non-HLA genes, only CTLA-4 has been consistently found to be associated with GD. Using a linkage based approach which only detects highly significant susceptibility genes we have recently reported preliminary results which demonstrated that a marker located approximately 25 cM from the TSH receptor gene on chromosome 14q31 is linked to GD and in the same vicinity as the IDDM-11 locus. Such results, if confirmed, may signal the presence of a gene family related to endocrine autoimmunity on chromosome 14q31.

HLA-DR4 associated response to corticosteroids in Graves' ophthalmopathy patients

Fifty-seven patients with severe Graves' ophthalmopathy were treated with corticosteroids. Therapeutic outcome was assessed according to predetermined criteria as response (n = 37) or non-response (n = 20) to therapy. Patients were typed for HLA-A, -B, -C, -DR and -DQ. HLA-DR4 was completely absent in the 20 non-responder patients (corrected p value = 0.042). In the responder group 14 of the 37 patients were HLA-DR4 positive. This study shows that in Graves' ophthalmopathy patients the presence of HLA-DR4 is associated with a good response to corticosteroid therapy. The frequency of HLA-DR4 in the Graves' ophthalmopathy population as a whole, however, was not different from normal (25% versus 26%). But as reported previously, the frequency of HLA-DR3 was significantly increased in the Graves' ophthalmopathy patients when compared to healthy blood donors (47% versus 24%, corrected p value = 0.02). No significant deviations were found in the HLA-A, -B, or -C loci.