Lack of disease associated HLA-DQ restriction fragment length polymorphisms in families with autoimmune thyroid disease

Correlation of HLA-DQ and TNF-α gene polymorphisms with ocular myasthenia gravis combined with thyroid-associated ophthalmopathy

The present study aims to explore the correlation of human leucocyte antigen (HLA)-DQ and tumour necrosis factor (TNF)-α gene polymorphisms with ocular myasthenia gravis (OMG) combined with thyroid-associated ophthalmopathy (TAO). From March 2009 to March 2015, 56 OMG patients complicated with TAO (OMG + TAO group), 134 patients diagnosed with OMG only (OMG group) and 236 healthy individuals (control group) were enrolled in the present study. PCR-sequence specific primer (PCR-SSP) was used for HLA-DQ genotyping and PCR-restriction fragment length polymorphism (PCR-RFLP) for TNF-α genotyping. ELISA kit was applied to detect acetylcholine receptor antibody (AchRAb) level and chemiluminescence immunoassay (CLIA) to measure thyroid-associated antibody (T-Ab) level. Logistic regression analysis was carried out to analyse the risk factors for OMG combined with TAO. DQA1*0103 showed lower frequency in the OMG group than in the control group. DQA1*0301 showed increased and DQB1*0601 showed decreased frequency in the OMG + TAO group. DQB1*0501 showed higher frequency in the OMG and OMG + TAO groups than in the control group. Patients carrying TNF-α -863C > A (CA + AA) might confront with greater risks of OMG combined with TAO. Frequency of DQA1*0103/*0301 and DQB1*0501/*0601, and TNF-α -863C > A, -238G > A and -308G > A were associated with the levels of AchRAb and T-Ab. TNF-α -863C > A (CA + AA) and high level of T-Ab were risk factors for OMG combined with TAO. Our results demonstrate that TNF-α -863 polymorphism is possibly correlated with the risk of OMG combined with TAO.

Common ground: the overlap between Endocrinology and Rheumatology

A number of medical specialities have witnessed a dramatic change in the provision of in patient care over the last decade. Work has moved into outpatient and Day Unit settings and, more recently, into the community. This has led to the amalgamation of speciality based beds with the perceived threat of loss of independence and potential reduction in training opportunities. In reality, our experience of a combined inpatient ward for Rheumatology and Endocrinology patients has been positive, with increased awareness of the coexistence of certain disorders and a resulting enhanced approach to the delivery of patient care, junior doctor education and clinical research. We would like to share our experience by describing some of the overlapping clinical conditions between these specialities that physicians might wish to consider.

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.

Autoimmune thyroid disease susceptibility loci in a large Chinese family

OBJECTIVES

The autoimmune thyroid diseases (AITDs) comprising Graves' disease (GD) and Hashimoto's thyroiditis (HT) are complex genetic diseases, which result from an interaction between predisposing genes and environmental triggers. The aim of our study was to dissect the genetic predisposition to GD and HT in one large Chinese family with multiple members affected with AITD.

PATIENTS

We completed a whole genome screen of a large multiplex Chinese-American family. We enrolled 27 family members from three generations. Eight members were affected with AITD, six had GD and two had HT.

DESIGN

We determined the information limits of the family. Power calculations indicated that the maximum attainable LOD scores were 5.1 assuming dominant inheritance, and 3.4 assuming recessive inheritance. These estimates both assumed 100% penetrance and one gene. Whole genome screening was performed using 400 highly polymorphic and densely spaced microsatellite markers spanning the entire human genome (intermarker distance < 10 cM). Linkage analysis was performed using two-point and multipoint parametric and nonparametric methods.

RESULTS

Initial whole genome screening performed with 400 microsatellite markers identified two markers that showed evidence for linkage to AITD in this family, D11S4191 and D9S175, with two-point LOD scores of 2.31 and 2.05, respectively. Multipoint linkage analysis focusing on the regions containing these markers revealed a maximum multipoint LOD score (MLS) of 2.13 and a nonparametric linkage score (NPL) of 6.1 for D11S4191 and an MLS of 2.01 and NPL of 7.5 for D9S175.

CONCLUSIONS

These results showed that this Chinese family harboured susceptibility loci for AITD which were distinct from those previously found in the Caucasian population. This suggests that different susceptibility loci exist between different ethnic groups. Furthermore, even within a single family from a genetically homogenous population, more than one gene was involved in the genetic susceptibility to AITD, supporting the notion that AITDs are caused by multiple genes of varying influences.

Autoimmune response to the thyroid in humans: thyroid peroxidase--the common autoantigenic denominator

Autoimmunity to thyroid peroxidase (TPO), manifest as high affinity IgG class autoantibodies, is the common denominator of human thyroid autoimmunity, encompassing patients with overt hyper- or hypothyroidism as well as euthyroid individuals with subclinical disease. The identification and cloning of TPO (the "thyroid microsomal antigen") provided the critical tool for analyzing B and T cell reactivity to this major thyroid autoantigen. In particular, the availability of immunoreactive TPO permitted the isolation of essentially the entire repertoire of human monoclonal antibodies, a feat unparalled in an organ-specific autoimmune disease. These recombinant autoantibodies (expressed as Fab) provide insight into the genes encoding their H and L chains as well as the conformational epitopes on TPO with which serum autoantibodies interact. Analyses of TPO autoantibody epitopic "fingerprints" indicate a lack of epitope spreading as well as a genetic basis for their inheritance. Limited data are available for the responses and cytokine profiles of T cells to endogenously processed TPO. Moreover, the role of thyroid cells in initiating the autoimmune response to TPO, and of B cells in expanding and/or modulating the response of sensitized T cells, has yet to be established. Finally, because autoantibody (and likely T cell) responses to TPO parallel those to TSH receptor and thyroglobulin, manipulation of T and B cell responses to TPO may provide the basis for the development of immunospecific therapy for autoimmune thyroid disease in general.

A new Graves disease-susceptibility locus maps to chromosome 20q11.2. International Consortium for the Genetics of Autoimmune Thyroid Disease

The autoimmune thyroid diseases (AITDs) include two related disorders, Graves disease (GD) and Hashimoto thyroiditis, in which perturbations of immune regulation result in an immune attack on the thyroid gland. The AITDs are multifactorial and develop in genetically susceptible individuals. However, the genes responsible for this susceptibility remain unknown. Recently, we initiated a whole-genome linkage study of patients with AITD, in order to identify their susceptibility genes. We studied a data set of 53 multiplex, multigenerational AITD families (323 individuals), using highly polymorphic and densely spaced microsatellite markers (intermarker distance <10 cM). Linkage analysis was performed by use of two-point and multipoint parametric methods (classic LOD-score analysis). While studying chromosome 20, we found a locus on chromosome 20q11.2 that was strongly linked to GD. A maximum two-point LOD score of 3.2 was obtained at marker D20S195, assuming a recessive mode of inheritance and a penetrance of.3. The maximum nonparametric LOD score was 2.4 (P=.00043); this score also was obtained at marker D20S195. Multipoint linkage analysis yielded a maximum LOD score of 3.5 for a 6-cM interval between markers D20S195 and D20S107. There was no evidence for heterogeneity in our sample. In our view, these results indicate strong evidence for linkage and suggest the presence of a major GD-susceptibility gene on chromosome 20q11.2.

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.

The immunogenetics of autoimmune diabetes and autoimmune thyroid disease

Although medical genetics is a well-developed area of interest, relatively little is known about the diseases caused by the combination of many genes. These multiinfluenced diseases include the autoimmune endocrine diseases. Recent advances in the techniques for whole-genome screening have shown a variety of loci that are linked to the development of insulin-dependent diabetes mellitus, and similar data are likely to be soon generated in autoimmune thyroid disease. Here, the authors survey the current state of genetic knowledge in these two areas and describe the investigative and analytical techniques that are now available. (Trends Endocrinol Metab 1997;8:63-70). (c) 1997, Elsevier Science Inc.

Cytokines and thyroid function

Cytokines play a crucial role in autoimmune thyroid disease (ATD) through various mechanisms. They are produced in the thyroid by intrathyroidal inflammatory cells, in particular lymphocytes, as well as by the thyroid follicular cells (TFC) themselves and may thus act in a cascade to enhance the autoimmune process (Fig. 1). Cytokines upregulate the inflammatory reaction through stimulation of both T and B cells, resulting in antibody production and tissue injury. In addition, intrathyroidal cytokines induce immunological changes in TFC including enhancement of both major histocompatibility complex (MHC) class I and class II molecule expression, and upregulation of adhesion and complement regulatory molecule expression. Cytokines can also modulate both growth and function of TFC and have a role in extrathyroidal complications of ATD, most importantly thyroid-associated ophthalmopathy (TAO), where they induce fibroblast proliferation and enhance the production of glycosaminoglycans (GAG), resulting in proptosis and the other clinical features of the disease. In addition to these effects, exogenous administration of cytokines has been associated with impairment of thyroid function ranging from the appearance of autoantibodies alone to the development of frank thyroid dysfunction. Cytokines have also been implicated in subacute thyroiditis (SAT) and amiodarone-induced thyroid dysfunction, as well as in thyroid function abnormalities occurring in patients with non-thyroidal illnesses (NTI). Genetic variations in cytokine genes represent potential risk factors for ATD, and disease associations have been described for polymorphisms in IL-1ra and TNF beta genes. Recent experimental evidence suggests the possibility of novel cytokine-based therapeutic approaches for ATD and its complications, in particular TAO.

Infections and autoimmune endocrine disease

The literature examined in this review points to the possible involvement of infectious agents in the pathogenesis of autoimmune endocrine diseases, primarily autoimmune thyroid disease and diabetes mellitus. Various mechanisms have been proposed to explain induction of autoimmunity by infection but it seems that three possibilities may be important in individuals susceptible to developing autoimmune disease: molecular mimicry (perhaps to retroviruses); polyclonal T cell activation (by an endogenous superantigen or an infecting organism); and MHC class II antigen induction. It seems reasonable that all three mechanisms operate together or separately in different individuals. Data continue to accumulate in favour of infectious agents being important initiators of autoimmune disease.