The immunogenetics of autoimmune diabetes and autoimmune thyroid disease

Association of the TGrI29 microsatellite in thyroglobulin gene with autoimmune thyroiditis in a Argentinian population: a case-control study

Autoimmune thyroid disease (AITD) is a multifactorial disorder that involves a putative association with thyroid autoantigen-specific and immune regulatory genes, as well as environmental factors. The thyroglobulin gene is the main identified thyroid autoantigen-specific gene associated to autoimmune thyroiditis. The aim of this work was to test for evidence of allelic association between autoimmune thyroiditis (AT) and thyroglobulin polymorphism markers in Argentinian patients. We studied six polymorphisms distributed throughout all the thyroglobulin gene: four microsatellites (Tgms1, Tgms2, TGrI29, and TGrI30), one insertion/deletion polymorphism (IndelTG-IVS18), and one exonic single nucleotide polymorphism (c.7589G>A) in 100 AT patients and 100 healthy control subjects. No differences in allele and genotype frequencies distribution were observed between autoimmune thyroiditis cases and controls for Tgms1, Tgms2, TGrI30, IndelTG-IVS18, and c.7589G>A. However, when we analyzed autoimmune thyroiditis patients with the TGrI29 microsatellite we found a significant association between the 197-bp allele and autoimmune thyroiditis (33.50% vs. 19.00% in control group) (P = 0.001). In addition, a significant major prevalence of the 197/201-bp genotype has been also seen in autoimmune thyroiditis subjects (59% vs. 24% in control group, P < 0.0001). In conclusion, our work showed the association between the thyroglobulin gene and autoimmune thyroiditis in Argentinian population and supports the described evidence of thyroglobulin as a thyroid-specific gene linked to AITD.

Analysis of the CTLA-4, CD28, and inducible costimulator (ICOS) genes in autoimmune thyroid disease

The cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) gene on 2q33 is associated with autoimmune thyroid diseases (AITDs). Our earlier study in 56 families showed linkage of 2q33 to the presence of thyroid antibodies (TAbs). The goals of this study were to confirm the linkage of the 2q33 region to TAbs, to fine map this region, and study the ICOS gene. We performed a linkage study in an expanded data set of 99 multiplex AITD-TAb families (529 individuals). The highest two-point LOD score of 2.9 was obtained for marker D2S325 on 2q33. To fine map this locus, we genotyped 238 Caucasian AITD patients and 137 controls for five additional markers in the linked locus, which contained the CTLA-4, CD28, and ICOS genes. The A/G single-nucleotide polymorphism at position 49 of CTLA-4 was associated with AITD (P=0.01, OR=1.5), while markers inside CD28 and ICOS were not. Functional studies have shown that the G allele was associated with reduced inhibition of T-cell proliferation by CTLA-4. We concluded that: (1) the AITD gene in the 2q33 locus is the CTLA-4 gene and not the CD28 or ICOS genes; and (2) the G allele is associated with decreased function of CTLA-4.

Intrauterine exposure to maternal enterovirus infection as a risk factor for development of autoimmune thyroiditis during childhood and adolescence

Maternal intrauterine enterovirus infection during pregnancy increases the risk for the offspring to develop type 1 diabetes mellitus. Type 1 diabetes mellitus and autoimmune thyroiditits (AIT) are closely linked. A common pathogenetic factor is possible. The objective of this study was to investigate a possible association between maternal enterovirus infection during pregnancy and the development of AIT in the offspring. Sera taken at delivery from 31 mothers whose children subsequently developed AIT was analyzed for immunoglobulin (Ig)A, IgG, and IgM antibodies against enterovirus, and compared to a control group comprising 233 randomly selected maternal sera. Of the mothers whose children developed AIT, 5 of 31 (16%) were enterovirus IgM-positive, compared to 17 of 233 (7%) in the control group (p = 0.16). The age at diagnosis of AIT was significantly lower in the group of children with IgM-positive mothers compared to children with IgM-negative mothers (p < 0.05). In addition, 3 children (60%) in the IgM-positive group were overtly hypothyroid at diagnosis of AIT, compared to no child (0%) in the IgM-negative group (p < 0.01). No significant differences were found in IgA and IgG antibody titers between the mothers whose children developed AIT and the control group. Although this study did not have enough power to reveal intrauterine exposure to maternal enterovirus infection during pregnancy as a risk factor for development of AIT during childhood and adolescence, it suggested an association with earlier onset of clinical disease in children to enterovirus IgM-seropositive mothers.

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.

Common and unique susceptibility loci in Graves and Hashimoto diseases: results of whole-genome screening in a data set of 102 multiplex families

The autoimmune thyroid diseases (AITDs), comprising Graves disease (GD) and Hashimoto thyroiditis (HT), develop as a result of a complex interaction between predisposing genes and environmental triggers. Previously, we identified six loci that showed evidence for linkage with AITD in a data set of 56 multiplex families. The goals of the present study were to replicate/reject the previously identified loci before fine mapping and sequencing the candidate genes in these regions. We performed a whole-genome linkage study in an expanded data set of 102 multiplex families with AITD (540 individuals), through use of 400 microsatellite markers. Seven loci showed evidence for linkage to AITD. Three loci, on chromosomes 6p, 8q, and 10q, showed evidence for linkage with both GD and HT (maximum multipoint heterogeneity LOD scores [HLOD] 2.0, 3.5, and 4.1, respectively). Three loci showed evidence for linkage with GD: on 7q (HLOD 2.3), 14q (HLOD 2.1), and 20q (LOD 3.3, in a subset of the families). One locus on 12q showed evidence of linkage with HT, giving an HLOD of 3.4. Comparison with the results obtained in the original data set showed that the 20q (GD-2) and 12q (HT-2) loci continued to show evidence for linkage in the expanded data set; the 6p and 14q loci were located within the same region as the previously identified 6p and 14q loci (AITD-1 and GD-1, respectively), but the Xq (GD-3) and 13q (HT-1) loci were not replicated in the expanded data set. These results demonstrated that multiple genes may predispose to GD and HT and that some may be common to both diseases and some are unique. The loci that continue to show evidence for linkage in the expanded data set represent serious candidate regions for gene identification.

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.

HLA-DQ polymorphisms modify the risk of thyroid autoimmunity in children with type 1 diabetes mellitus

OBJECTIVE

Type 1 diabetes mellitus (DM1) is frequently accompanied by thyroid autoimmunity (TAI). The aims of the present study were to estimate the prevalence of TAI and to determine the contribution of HLA-DQA1 and -DQB1 polymorphisms to TAI susceptibility among children with DM1. PATIENTS AND METLHODS: Screening for TAI was performed in 285 children with DM1 by measuring autoantibodies against thyroid peroxidase (anti-TPO) and thyroglobulin (anti-Tg). HLA-DQA1 and -DQB1 were genotyped using PCR-SSP.

RESULTS

Repeated positivity of anti-TPO and/or anti-Tg was found in 45/285 children with DM1 (15.8%). The prevalence was significantly higher in girls than in boys (26.7% vs 6.7%; p<10(-5)). The HLA-DQB1*0302 allele conferred susceptibility to TAI in children with DM1 (OR 2.7, 95% CI 1.1-6.4), while the DQB1*05 alleles acted protectively (OR 0.2, CI 95% 0.08-0.7).

CONCLUSIONS

HLA-DQ polymorphisms significantly modify the risk of TAI in children with DM1.

High prevalence of autoimmune thyroid disease in pulmonary arterial hypertension

STUDY OBJECTIVES

An association between thyroid disease and pulmonary arterial hypertension (PAH) has been reported, yet the pathogenetic relationship between these conditions remains unclear. Because immune system dysfunction may underlie this association, we sought to determine the prevalence of autoimmune thyroid disease (AITD) in patients with PAH.

DESIGN AND SETTING

Prospective observational study at a single academic institution.

PATIENTS

Sixty-three consecutive adults with PAH (ie, sustained pulmonary artery systolic pressure, > 25 mm Hg) were evaluated for clinical, biochemical, and serologic features of AITD.

MEASUREMENTS

Thyroid gland dysfunction was determined by clinical examination for goiter, and by biochemical measurements of thyrotropin and free thyroxine. Immune system dysfunction was determined by serologic measurements of antibodies to thyroglobulin and thyroid peroxidase. First-degree family history of AITD also was ascertained in order to investigate for genetic clustering of autoimmunity.

RESULTS

Thirty-one patients (49%; 95% confidence interval [CI], 37 to 62%) received diagnoses of AITD. Eighteen patients were newly diagnosed, and 9 patients required the initiation of pharmacologic treatment. There was no chronologic relationship between the diagnosis or treatment of PAH and that of AITD. Sixteen patients (25%; 95% CI, 15 to 36%) had 24 first-degree family members with AITD.

CONCLUSIONS

Approximately half of the patients with PAH have concomitant AITD. These two conditions may be linked by a common immunogenetic susceptibility, and the elucidation of this association may advance the understanding of the pathophysiology and treatment of PAH. Systematic surveillance for occult thyroid dysfunction in patients with PAH may prevent the hemodynamic exacerbation of right heart failure.

Genetic dissection of familial autoimmune thyroid diseases using whole genome screening

The autoimmune thyroid diseases (AITDs) are multifactorial disease which are caused by genetic susceptibility and environmental triggers. Various epidemiological and genetic techniques can be employed to study the genetic contribution to disease development. Most epidemiologic data support an important genetic contribution to the development of AITD. The genetic susceptibility to AITD involves several genes with varying effects. Some AITD susceptibility genes are most likely immune modifying genes which increase the susceptibility to autoimmunity in general (e.g. HLA, CTLA-4) while others may be thyroid-specific (e.g. thyroglobulin). These genes probably act in concert to increase the autoimmune reactions in susceptible individuals and direct them towards the thyroid.

The influence of human leucocyte antigen (HLA) genes on autoimmune thyroid disease (AITD): results of studies in HLA-DR3 positive AITD families

OBJECTIVE

Population-based, case-control studies have consistently shown association of Graves' disease (GD) with human leucocyte antigen (HLA)-DR3 in Caucasian populations. HLA association studies in Hashimoto's thyroiditis (HT) have also suggested an association with DR3, as well as with other HLA alleles. In contrast, HLA linkage studies in autoimmune thyroid disease (AITD) have been largely negative. The aim of the present study was to investigate the role of HLA in AITD and to explain the observed associations, but lack of linkage, by examining only AITD families with the associated allele, DR3.

PATIENTS

We studied 99 probands (60 with GD and 39 with HT) from 99 multiplex, multigenerational Caucasian AITD families, and 135 age- and sex-matched Caucasian controls in association studies. In addition, a dataset of 34 Caucasian AITD families (out of the 99 families) with HLA-DR3 positive probands were analysed in linkage studies.

DESIGN

HLA typing was performed using the technique of group-specific polymerase chain reaction-amplification with restriction enzyme digestion. Whole genome screening was performed using the ABI microsatellite panels. For fine mapping of the HLA region, we used the following markers: D6S276, D6S464, D6S439, D6S273, tumour necrosis factor alpha and D6S1610. LOD scores were calculated using the LIPED and GeneHunter programs.

RESULTS

Case-control association analyses using the probands from our 99 Caucasian families showed an association of GD with DRB1*03 [P = 0.00032, relative risk (RR) = 3.4]. Linkage analysis for the HLA region in the 34 DR3 positive AITD families showed negative LOD scores throughout the region. The two-point LOD score at marker D6S273 (the closest to HLA-DRB1) was -3.0, and the multipoint LOD score was -7.6, demonstrating strong evidence against linkage to the HLA region in the subset of DR3 positive families. Whole genome screening in the subset of 34 DR3 positive families revealed one locus showing evidence for linkage to AITD: D3S1580 on chromosome 3q27 with a maximum two-point LOD score of 2.1.

CONCLUSIONS

The HLA locus did not cosegregate with disease in DR3 positive families, suggesting that HLA genes are not major genes for AITD expression even within DR3 positive families; Hence, although HLA-DR3 was associated with GD in the probands, it was most likely a modulating gene and not causative; and, as the DR3 positive families showed evidence for linkage with D3S1580, it may imply that the DR3 gene modulated the effect of a susceptibility gene within the D3S1580 locus.

An interval tightly linked to but distinct from the H2 complex controls both overt diabetes (Idd16) and chronic experimental autoimmune thyroiditis (Ceat1) in nonobese diabetic mice

The major histocompatibility complex (MHC) has long been associated with predisposition to several autoimmune diseases, including type 1 diabetes and autoimmune thyroiditis. In type 1 diabetes, a primary role has been assigned to class II genes, both in humans and in the nonobese diabetic (NOD) mouse model. However, an involvement of other tightly linked genes is strongly suspected. Here, through two independent sets of experiments, we provide solid evidence for the existence of at least one such gene. First, using a new recombinant congenic NOD strain, R114, we definitively individualized the Idd16 locus from the MHC in a 6-cM interval proximal to H2-K. It affords almost complete protection against diabetes and is associated with delayed insulitis. Second, by genome scan, we mapped non-H2 genes associated with the highly penetrant form of chronic experimental autoimmune thyroiditis (EAT) that is elicited in NOD and NOD.H2(k) mice by immunization with thyroglobulin. We identified one major dominant locus, Ceat1, on chromosome 17, overlapping with Idd16. Most importantly, R114 recombinant congenic mice challenged with thyroglobulin did not develop chronic EAT. This new major region defined by both Idd16 and Ceat1 might thus concur to the unique strength of the MHC in autoimmune susceptibility of NOD mice.

SEL1L microsatellite polymorphism in Japanese patients with autoimmune thyroid diseases

The autoimmune thyroid diseases (AITDs), comprising Graves' disease (GD) and Hashimoto's thyroiditis (HT), appear to develop as a result of complex interactions between predisposing genes and environmental triggers. A recently performed genome-wide linkage study identified six loci that showed evidence for linkage to AITD. One locus, GD-1, on chromosome 14q31 was mapped to within 2 centimorgans (cM) of the recently reported multinodular goiter (MNG)-1 locus. Furthermore, microsatellite markers for the thyroid stimulating hormone receptor gene on chromosome 14q31 were associated with AITDs in the Japanese population. A newly isolated growth factor, SEL1L, was recently mapped to 14q31, and we considered it an interesting candidate gene to examine with respect to both GD and MNG. We therefore have analyzed a dinucleotide (CA)n repeat polymorphism in the intron 20 of the SEL1L gene in patients with AITDs and in normal subjects. The polymorphic marker was analyzed by polymerase chain reaction (PCR) followed by electrophoresis on denaturing polyacrylamide gels. There was no significant difference in the distributions of SEL1L alleles between patients and controls. The present results do not support an association between a dinucleotide repeat polymorphism in intron 20 of the SEL1L gene and AITD in Japanese women.

Lack of association between estrogen receptor beta dinucleotide repeat polymorphism and autoimmune thyroid diseases in Japanese patients

BACKGROUND

The autoimmune thyroid diseases (AITDs), such as Graves' disease (GD) and Hashimoto's thyroiditis (HT), appear to develop as a result of complex interactions between predisposing genes and environmental triggers. Susceptibility to AITDs is conferred by genes in the human leukocyte antigen (HLA) and genes unlinked to HLA, including the CTLA-4 gene. Recently, estrogen receptor (ER) beta, located at human chromosome 14q23-24.1, was identified. We analyzed a dinucleotide (CA)n repeat polymorphism located in the flanking region of ERbeta gene in patients with AITDs and in normal subjects. High heterozygosity makes this polymorphism a useful marker in the genetic study of disorders affecting female endocrine systems. We also correlated a ERbeta gene microsatellite polymorphism with bone mineral density (BMD) in the distal radius and biochemical markers of bone turnover in patients with GD in remission.

RESULTS

Fourteen different alleles were found in 133 patients with GD, 114 patients with HT, and 179 controls subjects. The various alleles were designated as allele*1 through allele*14 according to the number of the repeats, from 18 to 30. There was no significant difference in the distributions of ERbeta alleles between patient groups and controls. Although recent study demonstrated a significant relation between a allele*9 in the ERbeta gene and BMD in postmenopausal Japanese women, there were no statistically significant interaction between this allele and BMD in the distal radius, nor biochemical markers in patients with GD in remission.

CONCLUSIONS

The present results do not support an association between the ERbeta microsatellite marker and AITD in the Japanese population. We also suggest that the ERbeta microsatellite polymorphism has at most a minor pathogenic importance in predicting the risk of osteoporosis as a complication of GD.

Estrogen receptor alpha dinucleotide repeat polymorphism in Japanese patients with autoimmune thyroid diseases

BACKGROUND

The autoimmune thyroid diseases (AITDs), comprising Graves' disease (GD) and Hashimoto's thyroiditis (HT), appear to develop as a result of complex interactions between predisposing genes and environmental triggers. Susceptibility to AITDs is conferred by genes in the human leukocyte antigen (HLA) and genes unlinked to HLA, including the CTLA-4 gene. Recently, an association to some estrogen receptor (ER)alpha genotypes with breast cancer, hypertension, osteoporosis, generalized osteoarthritis, and some autoimmune diseases such as rheumatoid arthritis has been reported. We have analyzed a dinucleotide (TA)n repeat polymorphism lying upstream of the human ERalpha gene in patients with AITDs and in normal subjects.

RESULTS

Seventeen different alleles were found in 130 patients with GD, 93 patients with HT, and 190 control subjects. There was no significant difference in the distributions of ERalpha alleles between patients and controls.

CONCLUSIONS

The present results do not support an association between the ERalpha gene and AITD in the Japanese population.

Limited genetic susceptibility to severe Graves' ophthalmopathy: no role for CTLA-4 but evidence for an environmental etiology

Graves' disease (GD) is an autoimmune thyroid disease (AITD) characterized by hyperthyroidism and by the occurrence of a distinctive ophthalmopathy (orbitopathy), which presents with varying degrees of severity. Graves' disease clusters in families but the importance of heredity in the pathogenesis of the associated ophthalmopathy is unclear. We have studied the family history of 114 consecutive, ethnically mixed patients with severe Graves' ophthalmopathy (GO). Patients were selected by unambiguous single ascertainment. Seventy-seven percent of patients were female and 59% smoked. The mean age at onset of their GD was 43 years (range 17-78 years). Forty-one patients (36%) had a family history of AITD, defined as a first- and/or a second-degree relative affected with either Graves' disease (GD) or Hashimoto's thyroiditis (HT). The segregation ratio for AITD in nuclear families in our ascertained Graves' ophthalmopathy families was 0.07 (0.12 in Caucasians only). Hence, the higher prevalence of AITD among relatives of Graves' ophthalmopathy patients agreed with the known genetic predisposition to AITD and this predisposition was stronger in women than in men. However, only 3 of the 114 patients had a family history of severe Graves' ophthalmopathy (all second-degree relatives) and the segregation ratio for GO was 0. These data did not support a major role for familial factors in the development of severe Graves' ophthalmopathy distinct from Graves' disease itself. In addition, we tested 4 candidate genes, human leukocyte antigen (HLA), tumor necrosis factor-beta (TNF-beta), CTLA-4 and the thyrotropin receptor (TSHR), for association with Graves' ophthalmopathy. These were negative except for the HLA and CTLA-4 genes, which were found to be weakly associated with GO giving similar relative risk (RR) as in GD patients without ophthalmopathy. These data suggested that environmental factors, rather than major genes, were likely to predispose certain individuals with AITD to severe Graves' ophthalmopathy. Smoking remains one example of such potential external insults.

Clinical review 103: T helper type 1 and 2 cytokines mediate the onset and progression of type I (insulin-dependent) diabetes

Type I (insulin-dependent) diabetes mellitus (IDDM) is an autoimmune disease that results from the destruction of insulin-secreting pancreatic islet beta-cells by autoreactive cells and their mediators. Although its exact cause is not completely understood, it is well established that IDDM is associated with dysregulated humoral and cellular immunity, exemplified by altered production of and response to macrophage- and T cell-derived cytokines and a shift in T helper (Th) cell differentiation in favor of a pathogenic Th1 pathway. Th1 cytokines, including interleukin-2 and interferon-gamma, induced islet beta-cell destruction directly by accelerating activation-induced cell death (apoptosis) and by up-regulating the expression of select adhesion molecules, Th1 cytokines facilitated the pancreatic homing of autoreactive leukocytes, hence enhancing beta-cell destruction. More recently, a role for Th2 cytokines in IDDM pathogenesis was described. Accordingly, local production of Th2 cytokines, in particular interleukin-10, accelerated beta-cell destruction by enhancing autoreactive cell infiltration of the pancreas (insulitis) through modulation of the release of other cytokines and by modulating the microvasculature. Whereas both Th1 and Th2 cytokines are present in peripheral T cells and in the pancreas in IDDM, the mechanism of action and the kinetics of a cell damage induced by Th1 and Th2 cytokines appeared to be distinct. Collectively, this supports the idea that IDDM is not an exclusive Th1-mediated disorder as was suggested, and that both Th1 and Th2 cells and their respective mediators participate and cooperate in inducing and sustaining pancreatic islet beta-cell destruction in IDDM.

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.

Linkage analysis of candidate genes in autoimmune thyroid disease. II. Selected gender-related genes and the X-chromosome. International Consortium for the Genetics of Autoimmune Thyroid Disease

Hashimoto's thyroiditis (HT) and Graves' disease (GD) are autoimmune thyroid diseases (AITD) in which multiple genetic factors are suspected to play an important role. Until now, only a few minor risk factors for these diseases have been identified. Susceptibility seems to be stronger in women, pointing toward a possible role for genes related to sex steroid action or mechanisms related to genes on the X-chromosome. We have studied a total of 45 multiplex families, each containing at least 2 members affected with either GD (55 patients) or HT (72 patients), and used linkage analysis to target as candidate susceptibility loci genes involved in estrogen activity, such as the estrogen receptor alpha and beta and the aromatase genes. We then screened the entire X-chromosome using a set of polymorphic microsatellite markers spanning the whole chromosome. We found a region of the X-chromosome (Xq21.33-22) giving positive logarithm of odds (LOD) scores and then reanalyzed this area with dense markers in a multipoint analysis. Our results excluded linkage to the estrogen receptor alpha and aromatase genes when either the patients with GD only, those with HT only, or those with any AITD were considered as affected. Linkage to the estrogen receptor beta could not be totally ruled out, partly due to incomplete mapping information for the gene itself at this time. The X-chromosome data revealed consistently positive LOD scores (maximum of 1.88 for marker DXS8020 and GD patients) when either definition of affectedness was considered. Analysis of the family data using a multipoint analysis with eight closely linked markers generated LOD scores suggestive of linkage to GD in a chromosomal area (Xq21.33-22) extending for about 6 cM and encompassing four markers. The maximum LOD score (2.5) occurred at DXS8020. In conclusion, we ruled out a major role for estrogen receptor alpha and the aromatase genes in the genetic predisposition to AITD. Estrogen receptor beta remains a candidate locus. We found a locus on Xq21.33-22 linked to GD that may help to explain the female predisposition to GD. Confirmation of these data in HT may require study of an extended number of families because of possible heterogeneity.