Genetic susceptibility factors in type 1 diabetes: linkage, disequilibrium and functional analyses

Genetics of diabetes

Diabetes mellitus is a complicated disease characterized by a complex interplay of genetic, epigenetic, and environmental variables. It is one of the world's fastest-growing diseases, with 783 million adults expected to be affected by 2045. Devastating macrovascular consequences (cerebrovascular disease, cardiovascular disease, and peripheral vascular disease) and microvascular complications (like retinopathy, nephropathy, and neuropathy) increase mortality, blindness, kidney failure, and overall quality of life in individuals with diabetes. Clinical risk factors and glycemic management alone cannot predict the development of vascular problems; multiple genetic investigations have revealed a clear hereditary component to both diabetes and its related complications. In the twenty-first century, technological advancements (genome-wide association studies, next-generation sequencing, and exome-sequencing) have led to the identification of genetic variants associated with diabetes, however, these variants can only explain a small proportion of the total heritability of the condition. In this review, we address some of the likely explanations for this "missing heritability", for diabetes such as the significance of uncommon variants, gene-environment interactions, and epigenetics. Current discoveries clinical value, management of diabetes, and future research directions are also discussed.

MICA Polymorphism and Genetic Predisposition to T1D in Jordanian Patients: A Case-Control Study

Type 1 diabetes (T1D) is an autoimmune disorder whose etiology includes genetic and environmental factors. The non-classical Major Histocompatibility Complex (MHC) class I chain-related gene A (MICA) gene has been associated with increased susceptibility to T1D as the interaction of MICA to the Natural Killer Group 2D (NK2GD) receptors found on the cell surface of natural killer (NK) cells and T cells is responsible for inducing immune responses. MICA polymorphisms were reported in association with T1D among different ethnic groups. However, data from different populations revealed conflicting results, so the association of MICA polymorphisms with predisposition to T1D remains uncertain. The aim of this sequencing-based study was to identify, for the first time, the possible MICA alleles and/or genotypes that could be associated with T1D susceptibility in the Jordanian population. Polymorphisms in exons 2–4 and the short tandem repeats (STR) in exon 5 of the highly polymorphic MICA gene were analyzed. No evidence for association between T1D and MICA alleles/genotypes was found in this study, except for the MICA*011 allele which was found to be negatively associated with T1D (p = 0.023, OR = 0.125). In conclusion, MICA polymorphisms seem not to be associated with increasing T1D susceptibility in Jordanian patients.

Association of HLA-DRB1 and -DQ Alleles and Haplotypes with Type 1 Diabetes in Jordanians

BACKGROUND

The Human Leukocyte Antigen (HLA) class II genes, particularly the HLADR and -DQ loci, have been shown to play a crucial role in Type 1 Diabetes (T1D) development.

OBJECTIVE

This study is the first to examine the contribution of the HLA-DR/DQ alleles and haplotypes to T1D susceptibility in Jordanians.

METHODS

Polymerase chain reaction sequence-specific primers (PCR-SSP) were used to genotype 41 Jordanian healthy controls and 50 insulin-dependent diabetes mellitus (IDDM) patients.

RESULTS

The following alleles were found to be significant high risk alleles in T1D Jordanian patients: DRB1*04 (OR=3.95, p<0.001), DRB1*0301(OR=5.27, p<0.001), DQA1*0301 (OR=5.67, p<0.001), DQA1*0501(OR=3.18, p=0.002), DQB1*0201(OR=2.18, p=0.03), DQB1*0302 (OR=5.67, p<0.001). However, Jordanians harboring the DRB1*0701 (OR=0.37, p=0.01), DRB1*1101 (OR=0.2, p=0.01), DQA1*0505 (OR=0.31, p=0.02), DQA1*0103 (OR=0.33, p=0.04), DQA1*0201 (OR=0.45, p=0.04), DQB1*0301 (OR=0.23, p=0.001), DQB1*0501 (OR=0.18, p=0.009) alleles had a significantly lower risk of developing T1D.

CONCLUSION

A strong positive association of DRB1*04-DQA1*0301-DQBl*0302 (OR=5.67, p<0.001) and DRB1*0301-DQA1*0501-DQB1*0201 (OR=6.24, p<0.001) putative haplotypes with IDDM was evident in Jordanian IDDM patients whereas DRB1*1101-DQA1*0505- DQB1*0301 (OR=0.23, p=0.03) was shown to have a protective role against T1D in Jordanians. Our findings show that specific HLA class II alleles and haplotypes are significantly associated with susceptibility to T1D in Jordanians.

The Role of Epigenetics in Type 1 Diabetes

Type 1 diabetes (T1D) is an autoimmune disease caused by the interaction between genetic alterations and environmental factors. More than 60 susceptible genes or loci of T1D have been identified. Among them, HLA regions are reported to contribute about 50% of genetic susceptibility in Caucasians. There are many environmental factors involved in the pathogenesis of T1D. Environmental factors may change the expression of genes through epigenetic mechanisms, thus inducing individuals with susceptible genes to develop T1D; however, the underlying mechanisms remain poorly understood. The major epigenetic modifications include DNA methylation, histone modification, and non-coding RNA. There has been extensive research on the role of epigenetic mechanisms including aberrant DNA methylation, histone modification, and microRNA in the pathogenesis of T1D. DNA methylation and microRNA have been proposed as biomarkers to predict islet β cell death, which needs further confirmation before any clinical application can be developed. Small molecule inhibitors of histone deacetylases, histone methylation, and DNA methylation are potentially important for preventing T1D or in the reprogramming of insulin-producing cells. This chapter mainly focuses on T1D-related DNA methylation, histone modification, and non-coding RNA, as well as their possible translational potential in the early diagnosis and treatment of T1D.

Trends in the frequency of HLA DR-DQ haplotypes among children and adolescents with type 1 diabetes mellitus in the Southeast Region of Turkey

OBJECTIVE

The aim of this study was to determine the frequency of HLA DR-DQ haplotypes in children with type 1 diabetes mellitus (T1DM) in the Southeast Region of Turkey.

METHODS

Eighty children and adolescents with T1DM and eighty control subjects participated in the study. HLA-DR, DQ was typed using polymerase chain reaction and sequence-specific priming technique.

RESULTS

HLA DRB1*03 allele was significantly more common in patients than in control subjects. HLA DRB1*11, HLA DRB1*13 and HLA DRB1*14 allele frequencies were significantly lower in patients than in controls. DQB1*02 allele was more common in patients, whereas DQB1*03 allele was more frequent in control subjects. HLA DRB1*03-DQB1*02 haplotype was more frequently observed among patients.

CONCLUSION

These results confirm the similar potential trends in the frequency distribution of HLA susceptibility genes with T1DM previously observed in Turkey and in other Caucasian populations.

Evidence for the role of STAT4 as a general autoimmunity locus in the Korean population

BACKGROUND

Recently, the association of a common STAT4 haplotype with type 1 diabetes (T1D) as well as rheumatoid arthritis has been documented in Caucasians and Koreans. STAT4 is involved in the signalling of interleukin-12 and γIFN, as well as interleukin-23. To discover genes affecting the susceptibility of common autoimmune diseases, we studied the association of polymorphisms in STAT4 with autoimmune thyroid disease (AITD) as well as T1D in the Korean population.

SUBJECTS AND METHODS

Four single-nucleotide polymorphisms on the chromosome 2q (rs11889341, rs7574865, rs8179673, and rs10181656), which were found to associate with rheumatoid arthritis were examined for association in a Korean sample of 428 AITD, 418 T1D patients, and 1060 controls.

RESULTS

The minor alleles of all four single-nucleotide polymorphisms and the reconstructed STAT4 haplotypes conferred significant degree of risk for AITD (p=10(-2) to 10(-4)). Although we found a weak association of rs11889341 with T1D (p<0.05), the same haplotypes were not associated with T1D susceptibility. When we stratified T1D patients according to the age of onset, the minor alleles of all four single-nucleotide polymorphisms and the same haplotypes showed significant association with the susceptibility of T1D in the early-onset subgroup (p<0.01), not in the late-onset subgroup.

CONCLUSION

STAT4 alleles and the same haplotypes might influence cytokine signalling, and therefore the development of AITD as well as T1D. These results reinforce the influence of STAT4 gene as a general autoimmune gene.

The HLA-B 3906 allele imparts a high risk of diabetes only on specific HLA-DR/DQ haplotypes

AIMS/HYPOTHESIS

We investigated the risk associated with HLA-B*39 alleles in the context of specific HLA-DR/DQ haplotypes.

METHODS

We studied a readily available dataset from the Type 1 Diabetes Genetics Consortium that consists of 2,300 affected sibling pair families genotyped for both HLA alleles and 2,837 single nucleotide polymorphisms across the major histocompatibility complex region.

RESULTS

The B*3906 allele significantly enhanced the risk of type 1 diabetes when present on specific HLA-DR/DQ haplotypes (DRB1 0801-DQB1 0402: p = 1.6 × 10(-6), OR 25.4; DRB1 0101-DQB1 0501: p = 4.9 × 10(-5), OR 10.3) but did not enhance the risk of DRB1 0401-DQB1 0302 haplotypes. In addition, the B 3901 allele enhanced risk on the DRB1 1601-DQB1 0502 haplotype (p = 3.7 × 10(-3), OR 7.2).

CONCLUSIONS/INTERPRETATION

These associations indicate that the B 39 alleles significantly increase risk when present on specific HLA-DR/DQ haplotypes, and HLA-B typing in concert with specific HLA-DR/DQ genotypes should facilitate genetic prediction of type 1 diabetes, particularly in a research setting.

WAMI: a web server for the analysis of minisatellite maps

Background

Minisatellites are genomic loci composed of tandem arrays of short repetitive DNA segments. A minisatellite map is a sequence of symbols that represents the tandem repeat array such that the set of symbols is in one-to-one correspondence with the set of distinct repeats. Due to variations in repeat type and organization as well as copy number, the minisatellite maps have been widely used in forensic and population studies. In either domain, researchers need to compare the set of maps to each other, to build phylogenetic trees, to spot structural variations, and to study duplication dynamics. Efficient algorithms for these tasks are required to carry them out reliably and in reasonable time.

Results

In this paper we present WAMI, a web-server for the analysis of minisatellite maps. It performs the above mentioned computational tasks using efficient algorithms that take the model of map evolution into account. The WAMI interface is easy to use and the results of each analysis task are visualized.

Conclusions

To the best of our knowledge, WAMI is the first server providing all these computational facilities to the minisatellite community. The WAMI web-interface and the source code of the underlying programs are available at http://www.nubios.nileu.edu.eg/tools/wami.

Specific association of type 1 diabetes mellitus with anti-cyclic citrullinated peptide-positive rheumatoid arthritis

OBJECTIVE

The co-occurrence of autoimmune diseases such as rheumatoid arthritis (RA) and type 1 diabetes mellitus (DM) has been reported in individuals and families. In this study, the strength and nature of this association were investigated at the population level in a Swedish case-control cohort.

METHODS

For this case-control study, 1,419 patients with incident RA diagnosed between 1996 and 2003 were recruited from university, public, and private rheumatology units throughout Sweden; 1,674 matched control subjects were recruited from the Swedish national population registry. Sera from the subjects were tested for the presence of antibodies to cyclic citrullinated peptide (anti-CCP), rheumatoid factor (RF), and the 620W PTPN22 allele. Information on a history of diabetes was obtained by questionnaire, telephone interview, and/or medical record review. The prevalence of type 1 DM and type 2 DM was compared between patients with incident RA and control subjects and further stratified for the presence of anti-CCP, RF, and the PTPN22 risk allele.

RESULTS

Type 1 DM was associated with an increased risk of RA (odds ratio [OR] 4.9, 95% confidence interval [95% CI] 1.8-13.1), and this association was specific for anti-CCP-positive RA (OR 7.3, 95% CI 2.7-20.0), but not anti-CCP-negative RA. Further adjustment for the presence of PTPN22 attenuated the risk of anti-CCP-positive RA in patients with type 1 DM to an OR of 5.3 (95% CI 1.5-18.7). No association between RA and type 2 DM was observed.

CONCLUSION

The association between type 1 DM and RA is specific for a particular RA subset, anti-CCP-positive RA. The risk of developing RA later in life in patients with type 1 DM may be attributed, in part, to the presence of the 620W PTPN22 allele, suggesting that this risk factor may represent a common pathway for the pathogenesis of these 2 diseases.

Polymorphisms in the cathepsin L2 (CTSL2) gene show association with type 1 diabetes and early-onset myasthenia gravis

Type 1 diabetes (T1D) is an autoimmune disease characterized by loss of beta cells in the pancreas. The CTSL2 gene encodes the cysteine protease cathepsin V involved in antigen presentation in human cortical thymic epithelial cells, and involvement of the protease in autoimmunity has been suggested. This study aimed to evaluate CTSL2 as a candidate gene for T1D, and test whether the gene predisposes more generally to autoimmune diseases. Four polymorphisms aiming at tagging the CTSL2 locus were genotyped in 421 T1D families, and subsequently in 861 rheumatoid arthritis patients, 530 juvenile idiopathic arthritis patients, and 559 controls of Norwegian origin. Additionally, DNA from 83 German myasthenia gravis (MG) patients and 244 controls were investigated. A polymorphism, rs16919034, situated downstream of CTSL2 was associated with T1D (60.8%T, p = 0.008; p(c) = 0.03). An association with early-onset MG (45% in cases vs 36.6% in controls; p = 0.03) was observed for another polymorphism (rs4361859) situated upstream of the gene, but within the same linkage disequilibrium block. No association was observed in rheumatoid arthritis or juvenile idiopathic arthritis. Our findings suggest that the CTSL2 gene is associated with T1D and with early-onset MG.

Assessing the utility of SELDI-TOF and model averaging for serum proteomic biomarker discovery

The SELDI-TOF technique was used to profile serum proteins from Type 1 diabetes (T1D) patients and healthy autoantibody-negative (AbN) controls. Univariate and multivariate analyses were performed to identify putative biomarkers for T1D and to assess the reproducibility of the SELDI technique. We found 146 protein/peptide peaks (581 total peaks discovered) in human serum showing statistical differences in expression levels between T1D patients and controls, with 84% of these peaks showing technical replication. Because individual proteins did not offer great power for disease prediction, we used our model averaging approach that combines the information from multiple multivariate models to accurately classify T1D and control subjects (88.9% specificity and 90.0% sensitivity). Analyses of a test subset of the data showed less accuracy (82.8% specificity and 76.2% sensitivity), although the results are still positive. Unfortunately, no multivariate model could be replicated using the same samples. This first attempt of high throughput analyses of the human serum proteome in T1D patients suggests that model averaging is a viable method for developing biomarkers; however, the reproducibility of SELDI-TOF is currently not sufficient to be used for classification of complex diseases like T1D.

Environmental factors in the development of Type 1 diabetes

Environmental factors appear to play an important role in the pathogenesis of childhood-onset type 1 diabetes (T1D). The most important factors are thought to be infectious, dietary, perinatal, and psychosocial. Enteroviruses (especially Coxsackie B virus), breastfeeding, the early presence or lack of certain foods, birth weight, childhood over-nutrition, maternal islet autoimmunity, and negative stress events have been shown to be related to the prevalence of T1D. However, clear conclusions to date are limited because most studies lacked power to detect exposure/disease associations, were not prospective or long-term, did not start in infancy, had imprecise or infrequent exposure estimates, had confounding exposures, and failed to account for genetic susceptibility. In addition to the identification of specific antigenic triggers, several more general hypotheses, including the accelerator and hygiene hypotheses, are testable approaches worth pursuing.

Autoimmune destruction of pancreatic beta cells

Type 1 diabetes results from the destruction of insulin-producing pancreatic beta cells by a beta cell-specific autoimmune process. Beta cell autoantigens, macrophages, dendritic cells, B lymphocytes, and T lymphocytes have been shown to be involved in the pathogenesis of autoimmune diabetes. Beta cell autoantigens are thought to be released from beta cells by cellular turnover or damage and are processed and presented to T helper cells by antigen-presenting cells. Macrophages and dendritic cells are the first cell types to infiltrate the pancreatic islets. Naive CD4+ T cells that circulate in the blood and lymphoid organs, including the pancreatic lymph nodes, may recognize major histocompatibility complex and beta cell peptides presented by dendritic cells and macrophages in the islets. These CD4+ T cells can be activated by interleukin (IL)-12 released from macrophages and dendritic cells. While this process takes place, beta cell antigen-specific CD8+ T cells are activated by IL-2 produced by the activated TH1 CD4+ T cells, differentiate into cytotoxic T cells and are recruited into the pancreatic islets. These activated TH1 CD4+ T cells and CD8+ cytotoxic T cells are involved in the destruction of beta cells. In addition, beta cells can also be damaged by granzymes and perforin released from CD8+ cytotoxic T cells and by soluble mediators such as cytokines and reactive oxygen molecules released from activated macrophages in the islets. Thus, activated macrophages, TH1 CD4+ T cells, and beta cell-cytotoxic CD8+ T cells act synergistically to destroy beta cells, resulting in autoimmune type 1 diabetes.

Genetic analysis of the LEW.1AR1-iddm rat: an animal model for spontaneous diabetes mellitus

The LEW.1AR1-iddm/Ztm rat is a new animal model of type 1 diabetes mellitus, which shows an autosomal recessive mode of inheritance for the diabetes-inducing gene. The aim of this study was to define predisposing loci of the diabetic syndrome by linkage analysis using microsatellite markers. A backcross population of 218 rats (BN x LEW.1AR1-iddm) x LEW.1AR1-iddm was analyzed using 157 polymorphic microsatellite markers covering the entire genome. Three genomic regions showed a significant linkage to the diabetic syndrome. The first susceptibility locus on rat Chromosome (RNO) 1 (LOD score 4.13) mapped to the region 1q51-55, which codes for potential candidate genes like Ins1 and Nkx2-3. The second susceptibility locus was also localized on RNO1 in the centromeric region 1p11 (LOD score 2.7) encompassing the Sod2 gene. The third quantitative trait loci (LOD score 2.97) was located on RNO20 within the major histocompatibility complex region. Comparative mapping revealed that the homologous regions in the human genome contain the IDDM loci 1, 5, 8, and 17. The identification of diabetes susceptibility regions of the genetically uniform LEW.1AR1-iddm rat strain will pave the way toward a detailed characterization of the loci conferring diabetes development as well as their functional relevance for the pathogenesis of type 1 diabetes mellitus.

[Molecular diagnosis of diabetes mellitus]

Diabetes mellitus comprises a heterogeneous group of disorders characterized by chronic hyperglycemia. Type 1 and type 2 diabetes result from alterations of various genes, each having partial and additive effects. Thus, the inheritance pattern is rather complex, and environmental factors play an important role in the manifestation and clinical course of the disease. There is no genetic test to diagnose diabetes mellitus type 1 or type 2. However, certain susceptibility genes and genetic variations can be examined for specific scientific questions. Furthermore, defined genetic defects exist of pancreatic beta-cell function (maturity-onset diabetes of the young, mitochondrial diabetes) and insulin action (e.g. insulin resistance syndromes and lipodystrophy syndromes) resembling monogenic disorders. In these cases, genetic tests are crucial for the correct classification of the type of diabetes, genetic counseling, and initiation of the appropriate therapy regimen.

Genetic association between a lymphoid tyrosine phosphatase (PTPN22) and type 1 diabetes

The lymphoid-specific phosphatase (LYP) encoded by PTPN22 is involved in preventing spontaneous T-cell activation by dephosphorylating and inactivating T-cell receptor-associated Csk kinase. We have genotyped 396 type 1 diabetic patients and 1,178 control subjects of Caucasian descent from north central Florida and report a strong association between type 1 diabetes and a polymorphism (R620W) in the PTPN22 gene. The homozygous genotype for the T allele encoding the 620W residue is associated with an increased risk for developing type 1 diabetes (odds ratio [OR] = 3.4, P < 0.008), and the heterozygous genotype C/T had an OR of 1.7 (P = 6 x 10(-6)). The C/C homozygous genotype is protective against type 1 diabetes (OR = 0.5, P = 6 x 10(-6)). Furthermore, transmission disequilibrium analysis of 410 affected sibpair and simplex families of Caucasian descent indicated that the type 1 diabetes-associated T allele is transmitted more often (57.2%) than randomly expected (P < 0.003). Together with previous reports of the association between PTPN22 and type 1 diabetes, as well as rheumatoid arthritis and systemic lupus erythematosus, these results provide compelling evidence that LYP is a critical player in multiple autoimmune disorders.

Lack of association between IL-12B gene polymorphism and autoimmune thyroid disease in Japanese patients

Interleukin (IL)-12 is a key factor in cell-mediated immunity that drives the development of Th1 cells and stimulates T lymphocytes and natural killer cells to produce interferon (INF)-gamma. The IL-12B gene, which encodes the p40 subunit of IL-12, is located at chromosome 5q31-33 and a linkage finding for autoimmune thyroid disease (AITD) on 5q31-33 in a Japanese population has been reported. It is also reported that the A/C polymorphism in the 3' untranslated region (UTR) of the IL-12B gene (1188A/C) is associated with IL12B mRNA expression levels. We attempted to determine whether genetic polymorphisms of the IL-12B gene are associated with AITD. One hundred three patients with Hashimoto's thyroiditis, 90 patients with Graves' disease, and 123 healthy control subjects were recruited. We detected the 1188A/C polymorphism using a PCR-RFLP method and the A/T polymorphism in intron 4 of the IL-12B gene using a cycle sequencing method. These IL-12B gene polymorphisms showed strong linkage disequilibrium, and their genotype and allele frequencies in the patients did not differ from those in the control subjects. Our results suggest that IL-12B gene polymorphisms were unlikely to have an effect on the development of Hashimoto's thyroiditis or Graves' disease in Japanese patients.

Mapping non-class II H2-linked loci for type 1 diabetes in nonobese diabetic mice

Major histocompatibility complex (MHC) plays a largely predominant role in the genetic predisposition to type 1 diabetes, in both humans and rodents. While class II loci have long been recognized as essential, they do not fully explain the MHC-linked genetic component of type 1 diabetes. In the present study, using new NOD congenic strains harboring defined chromosomal segments from C57BL/6 mice, we circumscribed three distinct loci influencing murine type 1 diabetes and tightly linked to but separated from the class II region. Our findings might guide the search for additional HLA-linked loci in human type 1 diabetes.

Specific HLA-DRB and -DQB alleles and haplotypes confer disease susceptibility or resistance in Bahraini type 1 diabetes patients

Insofar as genetic susceptibility to type 1 diabetes is associated with HLA class II genes, with certain allelic combinations conferring disease susceptibility or resistance, this study assessed the distributions of HLA-DR and -DQ among 107 unrelated patients with type 1 diabetes and 88 healthy controls from Bahrain, all of Arab origin. The HLA-DRB and -DQB genotypes were determined by PCR-sequence-specific priming. The following alleles showed the strongest association with type 1 diabetes among patients versus controls according to their frequencies: DRB1*030101 (0.430 versus 0.097; P < 0.001), DRB1*040101 (0.243 versus 0.034; P < 0.001), DQB1*0201 (0.467 versus 0.193; P < 0.001), and DQB1*0302 (0.229 versus 0.091; P < 0.001). When the frequencies of alleles in controls were compared to those in patients, negative associations were seen for DRB1*100101 (0.085 versus 0.014; P < 0.001), DRB1*110101 (0.210 versus 0.060; P < 0.001), DQB1*030101 (0.170 versus 0.075; P = 0.006), and DQB1*050101 (0.335 versus 0.121; P < 0.001). In addition, the DRB1*030101-DQB1*0201 (70.1 versus 22.7%; P < 0.001) and DRB1*030101-DQB1*0302 (21.5 versus 0.0%; P < 0.001) genotypes were more prevalent among patients, thereby conferring disease susceptibility, whereas the DRB1*100101-DQB1*050101 (20.5 versus 2.8%; P < 0.001), DRB1*110101-DQB1*030101 (28.4 versus 8.4%; P < 0.001), and DRB1*110101-DQB1*050101 (30.7 versus 0.9%; P < 0.001) genotypes were more prevalent among controls, thus assigning a protective role. These results confirm the association of specific HLA-DR and -DQ alleles and haplotypes with type 1 diabetes and may underline several characteristics that distinguish Bahraini patients from other Caucasians patients.

Como entender a associação entre o sistema HLA e as doenças auto-imunes endócrinas

A introdução de nova nomenclatura para os componentes do complexo principal de histocompatibilidade (Major Histocompatibility Complex - MHC) e a descrição de novos métodos moleculares para a tipificação dos alelos do MHC contribuíram, grandemente, para o entendimento e identificação do extenso polimorfismo do sistema. No entanto, para o não especialista, essas novas aquisições têm dificultado o entendimento do papel do MHC em associação com as doenças. Assim, neste artigo, foram revisados os conceitos atuais acerca dos genes e moléculas do MHC, os métodos de tipificação desses marcadores de histocompatibilidade e a nomenclatura vigente para os componentes do sistema. Esses aspectos são extremamente importantes para o entendimento do polimorfismo do MHC, dando embasamento para a compreensão dos mecanismos propostos de associação desses marcadores com as doenças auto-imunes endócrinas como diabetes mellitus do tipo 1, doença de Graves e tireoidite de Hashimoto, doença de Addison, síndrome poliglandular auto-imune e insuficiência ovariana prematura.

High GAD65 autoantibody levels in nondiabetic adults are associated with HLA but not with CTLA-4 or INS VNTR

OBJECTIVES

To explore the relationship between genetic background and antibody levels in a nondiabetic population. We evaluated if high levels of autoantibodies against the 65 kDa isoform of glutamic acid decarboxylase (GAD65Ab), were associated with high-risk genes, i.e. HLA, CTLA-4 and INS VNTR genes.

DESIGN AND SUBJECTS

Seventy-five (M/F 39/36) subjects exceeding the 95th percentile of GAD65 autoantibody index and 75 age and sex matched subjects below the 95th percentile, randomly selected amongst participants in the Västerbotten Intervention Programme.

METHODS

The GAD65 Ab were measured in a radioligand-binding assay. HLA class II typing was performed by an oligoblot hybridization method. CTLA-4 repeat length was analysed and divided into short forms and long forms. Class I and class III alleles of INS VNTR were detected. Differences in distribution were tested by Pearson chi-square with Yates correction. Odds ratios (OR) were used to compare groups calculated with Cochran's and Mantel-Haenszel statistics.

RESULTS

The DQB1*0201-DQA1*0501-DRB1*03 haplotype was increased in subjects with high GAD65Ab levels (P = 0.04). This increase seemed to be explained by a difference in haplotype frequencies amongst men (P = 0.01). Calculating OR showed a significant association between the DQB1*0201-DQA1*0501-DRB1*03 haplotype and elevated levels of GAD65Ab in all subjects (OR 2.2, 95% CI 1.02-4.9) as well as in men (OR 4.6, 95% CI 1.3-15.9). There was no association between high levels of GAD65Ab and either INS VNTR or CTLA-4 polymorphisms.

CONCLUSION

Our study suggests that adult males with the DQB1*0201-DQA1*0501-DRB1*03 haplotype tend to develop high GAD65Ab titres. As none of these subjects have developed diabetes these data suggest that HLA may be important in GAD65Ab formation but that additional factors are required for the progression to overt type 1 diabetes.

Molecular aspects of type 1 diabetes

Type 1 diabetes is a T cell mediated autoimmune disease, characterised by the selective destruction of pancreatic beta cells, and susceptibility is determined by a combination of genetic and environmental factors. The environmental agents implicated include viruses and dietary factors, although none has yet been shown to be directly responsible for triggering beta cell autoimmunity. The genetic factors that influence disease risk have been subjected to more intensive study and two gene regions of major importance have been identified: the human leucocyte antigen locus and the insulin gene. This review will focus on the mechanisms by which these genes might influence the risk of developing type 1 diabetes.

Islet abnormalities in the pathogenesis of autoimmune diabetes

Type 1 diabetes mellitus is a T-cell-mediated autoimmune disease that results in the destruction of the insulin-producing beta cells in the pancreatic islets of Langerhans. In spite of extensive genetic and immunological studies, mainly performed in the non-obese diabetic (NOD) spontaneous mouse model, the etiology of the autoimmune attack remains unknown. Several autoantigens have been identified and numerous studies have suggested a role for defective regulation of immune function. However, this account does not explain why the autoimmune process specifically affects the insulin-producing beta cells. Thus, abnormal immune regulation might explain the predisposition to autoimmunity in general, but additional factors should then determine the target of the autoimmune attack. Here, we review the evidence that abnormalities in islet cell differentiation and function exist that might trigger the immune system towards beta-cell autoimmunity in humans and NOD mice.

Leptin accelerates autoimmune diabetes in female NOD mice

We have recently shown that leptin, the product of the obese gene, can directly influence T-cell function. In the work presented here, we explored the role of leptin in the development of spontaneous autoimmunity in the nonobese diabetic (NOD) mouse, an animal model for the study of human insulin-dependent diabetes mellitus (type 1 diabetes). We found that expression of serum leptin increased soon before the onset of hyperglycemia and diabetes in susceptible females. A pathogenetic role of leptin was assessed by administering recombinant leptin to young female and male NOD mice. Intraperitoneal injections of leptin accelerated autoimmune destruction of insulin-producing beta-cells and significantly increased interferon-gamma production in peripheral T-cells. These findings indicate that leptin can favor proinflammatory cell responses and directly influence development of autoimmune disease mediated by Th1 responses.

Prevalence of CTLA-4 polymorphism A49G in Ashkenazi Jews

Type 1 diabetes has been associated with numerous genetic loci. One locus, IDD12, includes the gene for cytotoxic T lymphocyte antigen (CTLA-4). A polymorphism at position 49 in the CTLA-4 gene, causing a substitution of Thr --> Ala, has been associated with various autoimmune diseases, including diabetes. The frequency of the polymorphism in European and Oriental populations has been recorded, but the frequency among different ethnic groups within the United States has yet to be established. In the present study, we analyzed 100 DNA samples from Ashkenazi Jews to determine the polymorphism's prevalence in that population. The A/A genotype was found in 49% of individuals, 41% were heterozygous A/G, and 10% possessed the G/G genotype. The prevalence of the A/A genotype in Ashkenazi Jewish population is the highest reported to date. The incidence of the homozygous G/G genotype within Spanish controls, 8.8%, is the lowest, followed by the Ashkenazi general population. The frequency of the non-diabetes-associated A/A genotype shows a similarity to the frequency of the diabetes-susceptible HLA haplotype, DR4-DQ8. The low prevalence of the autoimmune-associated G allele among Ashkenazi Jewish and Spanish populations may explain a lower than expected incidence of diabetes in HLA-susceptible populations.

HLA-DQ and DRB1 polymorphism and susceptibility to type 1 diabetes in Jamaica

Genetic susceptibility to type 1 diabetes is determined by a combination of HLA-DQ and DRB1 alleles. In the present study, HLA associations with type 1 diabetes were investigated in the Jamaican population. DRB1 and DQ genotyping was performed on 45 type 1 diabetic patients and 132 control subjects born and resident in Jamaica. The small number of patients available for study reflected the low prevalence of type 1 diabetes in Jamaica. The results were compared with those from other African heritage populations and white Caucasians. The highest relative risk was associated with the DRB1*03-DQ2/DRB1*04-DQ8 genotype. Both DRB1*0401-DQ8 and DRB1*0408-DQ8 were positively associated with disease. DRB1*0408-DQ8 is uncommon amongst white Caucasians, where DRB1*0401-DQ8 is the major predisposing haplotype. The DRB1*1503-DQ6 haplotype was associated with protection from diabetes in the Jamaican population. This haplotype is rare amongst white Caucasians, where DRB1*1501-DQ6 is the protective haplotype. Data from African heritage populations suggest that DRB1*1503-DQ6 might be less protective than DRB1*1501-DQ6. DRB1*03-DQA1*0401-DQB1*0402 was associated with protection from diabetes in the Jamaican population, whereas in white Caucasians DRB1*08-DQA1*0401-DQB1*0402 is predisposing. These data demonstrate that comparison of genetic associations with type 1 diabetes in races with population-specific DRB1-DQ haplotypes provides new information as to the exact determinants of disease susceptibility. Further support is provided for roles of the DQ genes and the DRB1 gene (or a gene in linkage disequilibrium with it) in determining susceptibility to type 1 diabetes.

Type 1 diabetes islet autoantibody markers

The diagnosis of type 1 diabetes versus other forms of diabetes such as type 2 diabetes is paramount to guiding proper therapy. Several islet autoantibodies have been identified that serve to diagnose immune-mediated, type 1a diabetes in clinically ambiguous cases. These autoantibodies also serve to predict type 1 diabetes in nondiabetic individuals. The most useful islet autoantibodies include islet cell cytoplasmic autoantibodies, insulin autoantibodies, glutamic acid decarboxylase autoantibodies, and insulinoma-associated-2 autoantibodies. Once type 1 diabetes can be safely and reliably prevented, large-scale islet autoantibody screening programs of the general pediatric population may be warranted. It is controversial whether islet autoantibodies influence the course of type 1 diabetes following diagnosis.

Clinical application of NKT cell assays to the prediction of type 1 diabetes

Type 1 diabetes is a disease characterised by disturbed glucose homeostasis, which results from autoimmune destruction of the insulin-producing beta cells in the pancreas. The autoimmune attack, while not yet fully characterised, exhibits components of both mis-targeting and failed tolerance induction. The involvement of non-classical lymphocytes in the induction and maintenance of peripheral tolerance has recently been recognised and natural killer T (NKT) cells appear to play such a role. NKT cells are a subset of T cells that are distinct in being able to produce cytokines such as IL-4 and IFN-gamma extremely rapidly following activation. These lymphocytes also express some surface receptors, and the lytic activity, characteristic of NK cells. Deficiencies in NKT cells have been identified in animal models of type 1 diabetes, and a causal association has been demonstrated by adoptive transfer experiments in diabetes-prone NOD mice. Preliminary work suggests that a similar relationship may exist between deficiencies in NKT cells and type 1 diabetes in humans, although the techniques reported to date would be difficult to translate to clinical use. Here, we describe methods appropriate to the clinical assessment of NKT cells and discuss the steps required in the assessment and validation of NKT cell assays as a predictor of type 1 diabetes.

The genetics of complex autoimmune diseases: non-MHC susceptibility genes

Susceptibility to complex autoimmune diseases (AIDs) is a multigenic phenotype affected by a variety of genetic and environmental or stochastic factors. After over a decade of linkage analyses, the identification of non-major histocompatibility complex (non-MHC) susceptibility alleles has proved to be difficult, predominantly because of extensive genetic heterogeneity and possible epistatic interactions among the multiple genes required for disease development. Despite these difficulties, progress has been made in elucidating the genetic mechanisms that influence the inheritance of susceptibility, and the pace of gene discovery is accelerating. An intriguing new finding has been the colocalization of several AID susceptibility genes in both rodent models and human linkage studies. This may indicate that several susceptibility alleles affect multiple AIDs, or alternatively that genomic organization has resulted in the clustering of many immune system genes. The completion of the human genome sequence, coupled with the imminent completion of the mouse genome, should yield key information that will dramatically enhance the rate of gene discovery in complex conditions such as AID susceptibility.

Genetics of type 1 diabetes

Type 1 diabetes mellitus is a T-cell-mediated autoimmune disease characterized by the selective destruction of pancreatic beta cells. Susceptibility to the disease is determined by a combination of genetic and environmental factors. The genetic factors are termed 'susceptibility genes' as they modify the risk of diabetes but are neither necessary nor sufficient for disease to develop. A large number of chromosomal regions have been identified as containing potential diabetes susceptibility genes. The IDDM1 locus, which encompasses the major histocompatibility complex on chromosome 6, is the major genetic risk factor. The HLA-DQ genes are the primary susceptibility genes within this region, although other genes may also contribute. The IDDM2 locus maps to a variable number of tandem repeats in the insulin gene region on chromosome 11. Further research is necessary to determine the precise location and identity of other diabetes susceptibility genes.

Celiac disease-associated autoimmune endocrinopathies

Celiac disease (CD) is an autoimmune disorder induced by gluten intake in genetically susceptible individuals. It is characterized by the presence of serum antibodies to endomysium, reticulin, gliadin, and tissue transglutaminase. The incidence of CD in various autoimmune disorders is increased 10- to 30-fold in comparison to the general population, although in many cases CD is clinically asymptomatic or silent. The identification of such cases with CD is important since it may help in the control of type I diabetes or endocrine functions in general, as well as in the prevention of long-term complications of CD, such as lymphoma. It is believed that CD may predispose an individual to other autoimmune disorders such as type I diabetes, autoimmune thyroid, and other endocrine diseases and that gluten may be a possible trigger. The onset of type I diabetes at an early age in patients with CD, compared to non-CD, and the prevention or delay in onset of diabetes by gluten-free diet in genetically predisposed individuals substantiates this antigen trigger hypothesis. Early identification of CD patients in highly susceptible population may result in the treatment of subclinical CD and improved control of associated disorders.

HLA alleles and IDDM in children in Hungary: a comparison with Finland

It has been postulated that variation in the distribution of human leukocyte antigen (HLA)-encoded susceptibility alleles for insulin-dependent diabetes mellitus (IDDM) is the genetic basis for variation in the incidence of the disease between populations. The aim of this study was to characterize HLA-encoded susceptibility to IDDM in Hungary and to identify whether HLA-DRB1/DQ-encoded susceptibility could account for the five times lower incidence of disease in Hungary compared with Finland. The haplotypes DRB1*03-DQA1*05-DQB1*02 (DRB1*03-DQ2) and DRB1*04-DQA1*0301-DQB1*0302 (DRB1*04-DQ8) were significantly associated with disease in both populations. Three genotypes incorporating either or both of these haplotypes accounted for over 70% of the diabetic population in both races. The combined background frequency and the degree of risk as measured by odds ratios of these HLA-DRB1-DQ genotypes were not significantly different in the two countries. Comparison of the DRB1*0401-DQ8 haplotype between the two races suggested a role for HLA-B alleles in susceptibility. These data indicate that the susceptibility associated with high risk DRB1-DQ genotypes alone is insufficient to account for the fivefold variation in incidence of IDDM between Hungary and Finland. Other genetic and/or environmental influences must be involved.

Linkage disequilibrium of a type 1 diabetes susceptibility locus with a regulatory IL12B allele

Type 1 diabetes (T1D; or insulin-dependent diabetes mellitus, IDDM) is an autoimmune disease with both genetic and environmental components. In addition to the human leukocyte antigen (HLA) complex, the single major genetic contributor of susceptibility, an unknown number of other unidentified genes are required to mediate disease. Although many loci conferring susceptibility to T1D have been mapped, their identification has proven problematic due to the complex nature of this disease. Our strategy for finding T1D susceptibility genes has been to test for human homologues of loci implicated in diabetes-prone NOD (non-obese diabetic) mice, together with application of biologically relevant stratification methods. We report here a new susceptibility locus, IDDM18, located near the interleukin-12 (IL-12)p40 gene, IL12B. Significant bias in transmission of IL12B alleles was observed in affected sibpairs and was confirmed in an independent cohort of simplex families. A single base change in the 3' UTR showed strong linkage disequilibrium with the T1D susceptibility locus. The IL12B 3' UTR alleles showed different levels of expression in cell lines. Variation in IL-12p40 production may influence T-cell responses crucial for either mediating or protecting against this and other autoimmune diseases.

MICA polymorphism is associated with type 1 diabetes in the Korean population

OBJECTIVE

Recent studies have demonstrated that MICA (major histocompatibility complex class I chain-related genes) on the short arm of the chromosome 6 are associated with susceptibility to various autoimmune diseases in Caucasians. The aim of our study was to investigate the role of MICA in type 1 diabetes susceptibility independent of the HLA DR-DQ polymorphism in genetically distinct Koreans.

RESEARCH DESIGN AND METHODS

A total of 119 patients selected from Korean Seoul type 1 diabetes registry and 134 nondiabetic unrelated control subjects were typed for exon 5 polymorphism of MICA in addition to HLA DR-DQ typing. A total of 52 simplex families of type 1 diabetes were also studied.

RESULTS

The MICA microsatellite allele consisting of six repetitions of GCT/AGC (A6) was present at a significantly lower frequency in the diabetic patient group (Pc < 0.01; Pc = P value after Bonferroni correction) than in the control population. The MICA microsatellite allele consisting of four repetitions (A4) was present at a higher frequency in diabetic patients (P < 0.05). This deviated distribution was not changed even after controlling for the HLA DRB1-DQB1 haplotype. Transmission/disequilibrium test revealed significant deviation of transmission for alleles at the A6 polymorphism within the MICA gene (P < 0.05).

CONCLUSIONS

We could assess that the MICA gene might be associated with type 1 diabetes transracially independent of the HLA gene.

Linkage of rheumatoid arthritis to insulin-dependent diabetes mellitus loci: evidence supporting a hypothesis for the existence of common autoimmune susceptibility loci

OBJECTIVE

To seek potential autoimmune disease susceptibility loci by testing for linkage and linkage disequilibrium between insulin-dependent diabetes mellitus (IDDM) susceptibility loci and rheumatoid arthritis (RA).

METHODS

Five IDDM susceptibility loci map to 2 chromosomal regions, chromosome 2q31-34 (IDDM7, 12, and 13) and chromosome 6q25-27 (IDDM5 and 8). Microsatellite markers within these regions were genotyped in 255 RA families, by fluorescence-based genotyping technology. Evidence for linkage disequilibrium was assessed using the extended transmission disequilibrium test (ETDT) program.

RESULTS

With the ETDT, we found evidence for linkage disequilibrium of the marker D6S446, at IDDM8, with RA (P < 0.0001). There was additional evidence for linkage disequilibrium with 2 markers at IDDMS (D6S311 and D6S440) (P = 0.016 and P = 0.017, respectively). There was no evidence for significant linkage disequilibrium of RA with any markers at IDDM7, 12, or 13.

CONCLUSION

These results support the hypothesis that there are autoimmune disease genes at IDDM5 and IDDM8.

Modulation of human leukocyte antigen and intracellular adhesion molecule-1 surface expression in malignant and nonmalignant human thyroid cells by cytokines in the context of extracellular matrix

Interactions between malignant cells and their environment are achieved via cell-surface receptors and adhesion molecules. The extracellular matrix (ECM) and ECM-bound cytokines modulate the expression of cell-surface molecules on target malignant cells, which may lead to changes in their susceptibility to cytolysis, in their ability to present antigens, and in the induction of local immune-cell activation and patrol. Eventually, these alterations may culminate in either the destruction, or escape and proliferation, of the tumor. We studied the effects of the ECM and its components in a "naive" form or following binding of the inflammatory cytokines interferon gamma (IFNgamma) and tumor necrosis factor alpha (TNFalpha) on the surface expression of human leukocyte antigen (HLA) class-I, HLA class-II (HLA-DR), and intracellular adhesion molecule-1 (ICAM-1), on nonmalignant and malignant thyroid cells. The basal expression of HLA class-I molecules was not significantly changed either by naive ECM and its components or by ECM-bound cytokines. ECM synergized with IFNgamma and TNFalpha in inducing HLA-DR molecules on nonmalignant and malignant thyrocytes, with higher HLA-DR levels on the malignant cells. The laminin component, in particular, synergized with IFNgamma. Basal ICAM-1 expression on nonneoplastic cells was not significantly affected by the cytokines when grown in the absence of ECM, but was significantly upregulated when cells were cultured on ECM. In contrast, in malignant thyrocyte cultures, ECM significantly attenuated IFNgamma- and TNFalpha-mediated enhancement of ICAM-1 expression. We concluded that signals derived from ECM-embedded cytokines participate in the regulation of key thyroid cell surface molecules and, thus, may affect the final outcome of human thyroid malignancies.

Assessment of the non-HLA-DR-DQ contribution to IDDM1 in British Caucasian families: analysis of LMP7 polymorphisms

AIMS

Whilst HLA-DRB1 and HLA-DQ alleles contribute to IDDM1, the major determinant of genetic susceptibility to Type 1 diabetes mellitus, other major histocompatibility complex (MHC)-encoded genes may also be involved. The LMP7 (large multifunctional proteasome 7) gene is a potential candidate. The aim of this study was to assess whether LMP7 confers susceptibility to Type 1 diabetes independently of linkage disequilibrium with HLA-DRB1 and HLA-DQ.

METHODS

The diallelic LMP7 polymorphism (LMP7*A or *B) was determined in 142 multiplex families from the British Diabetic Association Warren Repository. At least one parent was heterozygous for LMP7 in 112 families and these were informative for calculation of the statistic Tsp. This gives a valid chi2 test of the null hypothesis of no association or no linkage.

RESULTS

An excess of transmissions of LMP7*A was observed from parents to affected offspring and the Tsp statistic was significant for association in the presence of linkage. LMP7*A was in positive, and LMP7*B in negative, linkage disequilibrium with the HLA-DRB1*03-DQ2, DRB1*04-DQ8 (group of all DRB1*04 subtypes), DRB1*0401-DQ8 and DRB1*0404-DQ8 haplotypes, although the linkage disequilibrium coefficient (delta) value was not statistically significant for DRB1*0404-DQ8. Analysis of HLA-DR-DQ-LMP7 haplotypes and Tsp analysis of HLA-matched-homozygous parents showed no association between LMP7 alleles and Type I diabetes independent of linkage disequilibrium with HLA-DR-DQ haplotypes associated with increased risk of disease. A contribution of LMP7 alleles to susceptibility to Type 1 diabetes in subjects with low-risk HLA-DR-DQ haplotypes could not be excluded.

CONCLUSIONS

LMP7 alleles do not contribute to genetic susceptibility to Type 1 diabetes in subjects with high-risk-associated HLA-DR-DQ haplotypes.

Linkage analysis of systemic lupus erythematosus induced in diabetes-prone nonobese diabetic mice by Mycobacterium bovis

Systemic lupus erythematosus induced by Mycobacterium bovis in diabetes-prone nonobese diabetic mice was mapped in a backcross to the BALB/c strain. The subphenotypes-hemolytic anemia, antinuclear autoantibodies, and glomerular immune complex deposition-did not cosegregate, and linkage analysis for each trait was performed independently. Hemolytic anemia mapped to two loci: Bah1 at the MHC on chromosome 17 and Bah2 on distal chromosome 16. Antinuclear autoantibodies mapped to three loci: Bana1 at the MHC on chromosome 17, Bana2 on chromosome 10, and Bana3 on distal chromosome 1. Glomerular immune complex deposition did not show significant linkage to any genomic region. Mapping of autoantibodies (Coombs' or antinuclear autoantibodies) identified two loci: Babs1 at the MHC and Babs2 on distal chromosome 1. It has previously been reported that genes conferring susceptibility to different autoimmune diseases map nonrandomly to defined regions of the genome. One possible explanation for this clustering is that some alleles at loci within these regions confer susceptibility to multiple autoimmune diseases-the "common gene" hypothesis. With the exception of the H2, this study failed to provide direct support for the common gene hypothesis, because the loci identified as conferring susceptibility to systemic lupus erythematosus did not colocalize with those previously implicated in diabetes. However, three of the four regions identified had been previously implicated in other autoimmune diseases.

Age and sex based genetic locus heterogeneity in type 1 diabetes

BACKGROUND

Two genome scans for susceptibility loci for type 1 diabetes using large collections of families have recently been reported. Apart from strong linkage in both studies of the HLA region on chromosome 6p, clear consistent evidence for linkage was not observed at any other loci. One possible explanation for this is a high degree of locus heterogeneity in type 1 diabetes, and we hypothesised that the sex of affected offspring, age of diagnosis, and parental origin of shared alleles may be the bases of heterogeneity at some loci.

METHODS

Using data from a genome wide linkage study of 356 affected sib pairs with type 1 diabetes, we performed linkage analyses using parental origin of shared alleles in subgroups based on (1) sex of affected sibs and (2) age of diagnosis.

RESULTS

Among the results obtained, we observed that evidence for linkage to IDDM4 on chromosome 11q13 occurred predominantly from opposite sex, rather than same sex sib pairs. At a locus on chromosome 4q, evidence for linkage was observed in sibs where one was diagnosed above the age of 10 years and the other diagnosed below 10 years of age.

CONCLUSIONS

We show that heterogeneity tests based on age of diagnosis, sex of affected subject, and parental origin of shared alleles may be helpful in reducing locus heterogeneity in type 1 diabetes. If repeated in other samples, these findings may assist in the mapping of susceptibility loci for type 1 diabetes. Similar analyses can be recommended in other complex diseases.

HLA-DR and -DQ associations with insulin-dependent diabetes mellitus in a population of Turkey

Genetic susceptibility to insulin-dependent diabetes mellitus (IDDM) has been shown to be associated with MHC in many studies. To extend this data with a population with relatively low IDDM incidence, MHC DRB, DQA, and DQB have been investigated by polymerase chain reaction and sequence specific oligonucleotide probe hybridization (PCR/SSO) in 178 IDDM patients from Turkey and compared to 248 healthy controls. Significant differences are detected between IDDM and control groups in the frequencies of DRB1*0402 DQA1*03 DQB1*0302 (28.1% vs. 5.2%, p < 0.0001, OR: 7.1) and DRB1*0301 DQA1*0501 DQB1*02 (57% vs. 18.1%, p < 0.0001, OR: 6.1). Among the negative associations, the most strong ones are with DRB1*1401 DQA1*0101 DQB1*0503 (0.6% vs. 8.9%, p < 0.0001, OR: 0.1), DRB1*1502 DQA1*0103 DQB1*0601 (1.1% vs. 7.7%, p = 0.0023, OR: 0.1), DRB1*1301 DQA1*0103 DQB1*0603 (0.6% vs. 6.9%, p = 0.0039, OR: 0.2) and DRB1*1101 DQA1*0501 DQB1*0301 (3.9% vs. 12.1%, p < 0.0001, OR: 0.2). When the DRB, DQA or DQB genotypes of the susceptible alleles are compared, the most strong susceptibility marker of the disease is found to be DRB1*0301/*04 (31.4% vs. 2.8%, p < 0.0001, OR: 15.8) and among these, heterozygote genotype DRB1*0301/*0401 (4.5% vs. 0, p = 0.0008, OR: 24.8). These results confirm the positive associations with IDDM previously observed in other Caucasian populations and reveal many negative and strong associations which maybe underlining several characteristics that distinguish Turkish diabetics form other Caucasians.

IL4 and IL4Ralpha genes are not linked or associated with type 1 diabetes

Previous studies have shown the immunoregulatory functions IL-4 in type 1 diabetes mellitus. Therefore, the genes involved in the IL-4 regulatory pathway are candidates for diabetes susceptibility genes. Here we have evaluated IL4 and the alpha subunit of the IL-4 receptor (IL4Ralpha) genes using the affected sibpair (ASP) and transmission/disequilibrium test (TDT). We analyzed 309 diabetic families from the United States and 87 families from various European countries. There was no evidence that either of these two genes are linked or associated with type 1 diabetes. Means by which IL-4 directed signals could indirectly alter diabetes susceptibility are proposed.

Mapping autoimmunity genes

Rat and mouse models for the major human autoimmune/inflammatory diseases are under intense genetic scrutiny. Genome-wide linkage studies reveal that each model is regulated by multiple genetic loci. Many of these loci colocalize to homologous genomic regions associated with several different autoimmune diseases of mice, rats and humans. Candidate genes are being identified. Polymorphic alleles associated with these chromosomal segments may represent predisposing genetic elements common to a number of human diseases with very different clinical presentations.

The aetiology of Type I diabetes

The aetiology of Type I diabetes involves both genetic and environmental factors. The genes implicated are 'susceptibility genes', which modify risk. Individual susceptibility genes may not be required and are not sufficient for disease development. The strongest genetic risk component is encoded within the major histocompatibility complex (MHC) and is designated IDDM I. The HLA-DQ genes contribute to the risk, but so may other MHC-encoded genes. The susceptibility encoded by IDDM2 refers to a variable number of tandem repeats in the insulin gene region. Many other genomic regions have been designated as susceptibility intervals potentially containing candidate genes. Environmental factors appear to be important in disease expression in either a causative or a protective role. Epidemiological data indicate that such factors operate from early in life. Viral infection(s) may have a disease-initiating and/ or accelerating effect. A potential diabetogenic role for cows' milk protein remains unconfirmed. Further research is necessary to elucidate fully the aetiological factors involved and how they interact.