Both DQA1 and DQB1 genes are implicated in HLA-associated protection from type 1 (insulin-dependent) diabetes mellitus in a British Caucasian population

Diabetes-science, serendipity and common sense

This paper is dedicated to young researchers in diabetes. One such person was Frederick Banting who, with his colleagues, isolated insulin in 1921, saving the lives of literally millions of people. What factors allowed Banting and other scientists to produce work that has immensely benefited the human race? I propose that it is the combination of good scientific background (the 'prepared mind'), commonly some serendipity taken with a good dose of common sense and supplemented by enthusiasm, tenacity and good mentoring, which drives the 'power of observation' and the ability to take forward the good idea. I give examples from history to support this and then discuss some of the 'truths, perspectives and controversies' within the diabetes arena when I first started in diabetes research in the late 1970s. I describe how my appetite was initially 'whetted' for research by moving to an excellent clinical research environment with encouragement to test ideas and controversies initially in a clinical research programme, followed by more scientific/basic research. The work that I performed as a young doctor and research fellow led to a lifelong professional interest in three major areas-causes and interventions for diabetes vascular disease, studies of the molecular genetics of Type 1 and Type 2 diabetes and work on diabetes in different ethnic groups. I provide a summation of my own and other people's work to demonstrate how research can be progressed and lead to patient benefit as well as providing an incredibly rewarding career. I believe that we need to encourage and put more resources into development of young doctors and scientists wishing to undertake research in our discipline. Areas ripe for much-needed clinical research programmes, for example, include work on best practice/provision of health care, application of the evidence base from clinical trials to achieve public health gains, attention to adherence issues and better-tolerated therapies. Most importantly, a greater emphasis on prevention through public health measures and 'buy in' from the whole population is urgently required.

The HLA Region and Autoimmune Disease: Associations and Mechanisms of Action

The HLA region encodes several molecules that play key roles in the immune system. Strong association between the HLA region and autoimmune disease (AID) has been established for over fifty years. Association of components of the HLA class II encoded HLA-DRB1-DQA1-DQB1 haplotype has been detected with several AIDs, including rheumatoid arthritis, type 1 diabetes and Graves' disease. Molecules encoded by this region play a key role in exogenous antigen presentation to CD4+ Th cells, indicating the importance of this pathway in AID initiation and progression. Although other components of the HLA class I and III regions have also been investigated for association with AID, apart from the association of HLA-B*27 with ankylosing spondylitis, it has been difficult to determine additional susceptibility loci independent of the strong linkage disequilibrium (LD) with the HLA class II genes. Recent advances in the statistical analysis of LD and the recruitment of large AID datasets have allowed investigation of the HLA class I and III regions to be re-visited. Association of the HLA class I region, independent of known HLA class II effects, has now been detected for several AIDs, including strong association of HLA-B with type 1 diabetes and HLA-C with multiple sclerosis and Graves' disease. These results provide further evidence of a possible role for bacterial or viral infection and CD8+ T cells in AID onset. The advances being made in determining the primary associations within the HLA region and AIDs will not only increase our understanding of the mechanisms behind disease pathogenesis but may also aid in the development of novel therapeutic targets in the future.

Human leukocyte antigen-DQ alleles and haplotypes and their associations with resistance and susceptibility to HIV-1 infection

OBJECTIVES

To determine the association of DQ antigens with resistance and susceptibility to HIV-1.

DESIGN

Despite repeated exposure to HIV-1, a subset of women in the Pumwani Sex Worker cohort established in Nairobi, Kenya in 1985 have remained HIV-1 negative for at least 3 years and are classified as resistant. Differential susceptibility to HIV-1 infection is associated with HIV-1 specific CD4 and CD8 T cell responses. As human leukocyte antigen-DQ antigens present viral peptides to CD4 cells, we genotyped human leukocyte antigen -DQ alleles for 978 women enrolled in the cohort and performed cross-sectional and longitudinal analyses to identify associations of human leukocyte antigen -DQ with resistance/susceptibility to HIV-1.

METHODS

DQA1 and DQB1 were genotyped using taxonomy-based sequence analysis. SPSS 13.0 was used to determine associations of DQ alleles/haplotypes with HIV-1 resistance, susceptibility, and seroconversion rates.

RESULTS

Several DQB1 alleles and DQ haplotypes were associated with resistance to HIV-1 infection. These included DQB1*050301 (P = 0.055, Odds Ratio = 12.77, 95% Confidence Interval = 1.44-112), DQB1*0603 and DQB1*0609 (P = 0.037, Odds Ratio = 3.25, 95% Confidence Interval = 1.12-9.47), and DQA1*010201-DQB1*0603 (P = 0.044, Odds Ratio = 17.33, 95% Confidence Interval = 1.79-168). Conversely, DQB1*0602 (P = 0.048, Odds Ratio = 0.68, 95% Confidence Interval = 0.44-1.05) and DQA1*010201-DQB1*0602 (P = 0.039, Odds Ratio = 0.64, 95% Confidence Interval = 0.41-1.03) were overrepresented in the HIV-1 infected population. DQA1*0504-DQB1*0201, DQA1*010201-DQB1*0201, DQA1*0402-DQB1*0402 and DQA1*0402-DQB1*030101 genotypes were only found in HIV-1 positive subjects (Odds Ratio = 0.30-0.31, 95% Confidence Interval = 0.03-3.70), and these women seroconverted rapidly. The associations of these DQ alleles and haplotypes with resistance and susceptibility to HIV-1 were independent of the previously reported human leukocyte antigen-DRB*01, human leukocyte antigen A2/6802, and human leukocyte antigen-A*2301.

CONCLUSION

The associations of DQ alleles and haplotypes with resistance and susceptibility to HIV-1 emphasize the importance of human leukocyte antigen-DQ and CD4 in anti-HIV-1 immunity.

Identification of two independent risk factors for lupus within the MHC in United Kingdom families

The association of the major histocompatibility complex (MHC) with SLE is well established yet the causal variants arising from this region remain to be identified, largely due to inadequate study design and the strong linkage disequilibrium demonstrated by genes across this locus. The majority of studies thus far have identified strong association with classical class II alleles, in particular HLA-DRB1*0301 and HLA-DRB1*1501. Additional associations have been reported with class III alleles; specifically, complement C4 null alleles and a tumor necrosis factor promoter SNP (TNF-308G/A). However, the relative effects of these class II and class III variants have not been determined. We have thus used a family-based approach to map association signals across the MHC class II and class III regions in a cohort of 314 complete United Kingdom Caucasian SLE trios by typing tagging SNPs together with classical typing of the HLA-DRB1 locus. Using TDT and conditional regression analyses, we have demonstrated the presence of two distinct and independent association signals in SLE: HLA-DRB1*0301 (nominal p = 4.9 x 10(-8), permuted p < 0.0001, OR = 2.3) and the T allele of SNP rs419788 (nominal p = 4.3 x 10(-8), permuted p < 0.0001, OR = 2.0) in intron 6 of the class III region gene SKIV2L. Assessment of genotypic risk demonstrates a likely dominant model of inheritance for HLA-DRB1*0301, while rs419788-T confers susceptibility in an additive manner. Furthermore, by comparing transmitted and untransmitted parental chromosomes, we have delimited our class II signal to a 180 kb region encompassing the alleles HLA-DRB1*0301-HLA-DQA1*0501-HLA-DQB1*0201 alone. Our class III signal importantly excludes independent association at the TNF promoter polymorphism, TNF-308G/A, in our SLE cohort and provides a potentially novel locus for future genetic and functional studies.

HLA and eye disease: a synopsis

Human leukocyte antigen (HLA) gene products have been implicated in the pathogenesis of an increasing number of eye diseases, mainly inflammatory in nature. This perspective reviews the current hypotheses for why HLA polymorphisms are associated with specific eye diseases. Statistical problems in studies involving HLA associations are discussed, and possible solutions outlined. The relevance of HLA testing in routine ophthalmic practice, its practical and cost implications is also assessed.

Regression mapping of association between the human leukocyte antigen region and Graves disease

The human leukocyte antigen class II genes DRB1, DQB1, and DQA1 are associated with Graves disease (GD), but, because of strong linkage disequilibrium within this region, the primary etiological variant(s) remains unknown. In the present study, 871 patients with GD and 621 control subjects were genotyped at the DRB1, DQB1, and DQA1 loci. All three loci were associated with GD (P=1.45 x 10(-12), P=3.20 x 10(-5), and P=9.26 x 10(-12), respectively). Stepwise logistic-regression analysis showed that the association could be explained by either DRB1 or DQA1 but not by DQB1. To extend previous results, the amino acid sequence of the exon 2-encoded peptide-binding domain of DRB1 was predicted for each subject, and, by use of logistic regression, each position was analyzed for association with GD. Of 102 amino acids, 70 were uninformative; of the remaining 32 amino acids, 13 were associated with GD (P values ranged from 2.20 x 10(-4) to 1.2 x 10(-12)). The strongest association was at position beta 74. This analysis is consistent with the possibility that position beta 74 of exon 2 of the DRB1 molecule may have a specific and central role in autoantigen presentation by DRB1 to T lymphocytes. However, we cannot yet exclude a primary role for DQA1 or for other polymorphisms that affect DRB1 function or expression.

Ketosis-prone diabetes: dissection of a heterogeneous syndrome using an immunogenetic and beta-cell functional classification, prospective analysis, and clinical outcomes

Ketosis-prone diabetes is heterogeneous. Its causes could include novel beta-cell functional defects. To characterize such defects, 103 patients with diabetic ketoacidosis were evaluated for beta-cell autoimmunity and human leukocyte antigen (HLA) class II alleles, with longitudinal measurements of beta-cell function and biochemical and clinical parameters. They were classified into four A beta groups, based on the presence of glutamic acid decarboxylase (GAD)65, GAD67, or IA-2 autoantibodies (A+ or A-) and beta-cell functional reserve (beta+ or beta-). The group distribution was: 18 A+beta-, 23 A-beta-, 11 A+beta+, and 51 A-beta+. Collectively, the two beta- groups differed from the two beta+ groups in earlier onset and longer duration of diabetes, lower body mass index, less glycemic improvement, and persistent insulin requirement. HLA class II genotyping showed that the A-beta- group differed from the A+beta- group in having lower frequencies of two alleles strongly associated with autoimmune type 1 diabetes susceptibility: DQA*03 and DQB1*02. Similarly, the A-beta+ group differed from the A+beta+ group in having a lower frequency of DQB1*02. Ketosis-prone diabetes comprises at least four etiologically distinct syndromes separable by autoantibody status, HLA genotype, and beta-cell functional reserve. Novel, nonautoimmune causes of beta-cell dysfunction are likely to underlie the A-beta+ and A-beta- syndromes.

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.

HLA typing and immunological characterization of young-onset diabetes mellitus in a Hong Kong Chinese population

AIMS

A study of the Hong Kong Chinese showed that the majority of subjects with young-onset diabetes (age of diagnosis < 35 years) present with a phenotype suggestive of Type 2 diabetes mellitus, although up to 50% subsequently need insulin treatment. The aim of this study was to use a combination of clinical, genetic and immunological markers to characterize the disease phenotype further in such individuals and to determine whether the requirement for insulin is the result of autoimmune disease.

METHODS

One hundred and thirty-seven Hong Kong Chinese with young-onset diabetes were studied, irrespective of their mode of presentation. The subjects were typed for alleles of the HLA-DR and -DQ genes and investigated for the presence of autoantibodies to glutamic acid decarboxylase (GAD). Plasma C-peptide concentration and requirement for insulin were also determined.

RESULTS

One hundred and three subjects presented with a syndrome resembling Type 2 diabetes, while 34 presented with Type 1 diabetes. Of the former group, 35 patients (34.0%) were insulin-deficient, 16 (15.5%) were insulin-treated and seven (6.9%) were positive for GAD autoantibodies. Among the GAD-positive subjects presenting with Type 2 diabetes, the HLA-DRB1*03 allele may be a marker of early progression to insulin therapy.

CONCLUSIONS

Seven subjects with Type 2 diabetes at presentation had autoantibodies to GAD. Causes other than GAD autoimmunity, however, must be sought to explain the high prevalence of insulin deficiency observed in the Chinese patients. This study highlights the heterogeneity of the pathogenic processes leading to the diabetic phenotype.

Complex interaction between HLA DR and DQ in conferring risk for childhood type 1 diabetes

Type 1 (insulin-dependent) diabetes mellitus is associated with HLA DR and DQ factors, but the primary risk alleles are difficult to identify because recombination events are rare in the DQ-DR region. The risk of HLA genotypes for type 1 diabetes was therefore studied in more than 420 incident new onset, population-based type 1 diabetes children and 340 age, sex and geographically matched controls from Sweden. A stepwise approach was used to analyse risk by relative and absolute risks, stratification analysis and the predispositional allele test. The strongest relative and absolute risks were observed for DQB1*02-DQA1*0501/DQB1*0302-DQA1*0301 heterozygotes (AR 1/46, P < 0.001) or the simultaneous presence of both DRB1*03 and DQB1*0302 (AR 1/52, P < 0.001). Stratification analysis showed that DQB1*0302 was more frequent among DRB1*04 patients than DRB1*04 controls (P < 0.001), while DRB1*03 was more frequent among both DQA1*0501 (P < 0.001) and DQB1*02 (P < 0.001) patients than respective controls. The predispositional allele test indicated that DRB1*03 (P < 0.001) would be the predominant risk factor on the DRB1*03-DQA1*0501-DQB1*02 haplotype. In contrast, although DQB1*0302 (P < 0.001) would be the predominant risk factor on the DRB1*04-DQA1*0301-DQB1*0302 haplotype, the predispositional allele test also showed that DRB1*0401, but no other DRB1*04 subtype, had an additive risk to that of DQB1*0302 (P < 0.002). It is concluded that the association between type 1 diabetes and HLA is due to a complex interaction between DR and DQ since (1) DRB1*03 was more strongly associated with the disease than DQA1*0501-DQB1*02 and (2) DRB1*0401 had an additive effect to DQB1*0302. The data from this population-based investigation suggest an independent role of DR in the risk of developing type 1 diabetes, perhaps by providing diseases-promoting transcomplementation molecules.

HLA-DQ6/8 Double Transgenic Mice Develop Auricular Chondritis Following Type II Collagen Immunization: A Model for Human Relapsing Polychondritis

We have generated transgenic (tg) mice expressing HLA-DQ8αβ (DQA1*0301/DQB*0302) or HLA-DQ6αβ (DQA1*0103/DQB1*0601) molecules lacking endogenous murine class II expression (Aβ0) to investigate the ability of these HLA class II to present type II collagen (CII) and induce collagen-induced arthritis. The DQ8αβ tg mice responded strongly to CII, developing severe arthritis, while DQ6αβ tg mice were nonresponsive to CII. The addition of the mixed haplotype DQ8α6β molecule did not significantly influence CII reactivity. To examine the interaction of DQ6αβ and DQ8αβ molecules in vivo, we generated double tg DQ6αβ/8αβ (Aβ0) mice expressing both the α- and β-chains of DQ6 and DQ8 molecules by mating DQ6αβ (Aβ0) and DQ8αβ (Aβ0) tg mice. CII-immunized DQ6αβ/8αβ tg mice developed severe experimental polychondritis, exhibiting both polyarthritis and auricular chondritis. The clinical, serologic, and histologic manifestations of experimental polychondritis are similar to those symptoms in human relapsing polychondritis. The susceptibility of DQ6αβ/8αβ tg mice compared with resistance in the parental strains suggests that expression of both the DQ6αβ and DQ8αβ tgs, unique to the DQ6αβ8αβ tg strain, is important in susceptibility to experimental polychondritis. The DQ6αβ/8αβ tg mice provide a model to investigate putative autoantigens and the mechanisms of pathogenesis involved in relapsing polychondritis as well as the influence of the expression of multiple HLA class II molecules on the disease process.

High affinity presentation of an autoantigenic peptide in type I diabetes by an HLA class II protein encoded in a haplotype protecting from disease

Polymorphism of the genes coding for the human histocompatibility leukocyte antigen class II DR and DQ molecules makes the single largest genetic contribution to the risk of developing insulin-dependent diabetes mellitus (IDDM) and can be associated with highly elevated as well as decreased disease frequency. The mechanism of IDDM risk modification by HLA polymorphism is likely to involve differential presentation of autoantigenic peptides by HLA class II proteins. We have generated T cell lines (TCL) with specificity for the IDDM autoantigen 65 kDa glutamic acid decarboxylase (GAD65) from lymphocytes of two patients carrying HLA class II alleles associated with distinct risk of IDDM (DRB1*0101/0401 and 1302/1501). For both patients, TCL generated at various time points all recognized single epitopes mapped as GAD 88-99 and 248-257, respectively. These epitopes are presented by the DRB1*0101 and DRB5*0101, HLA class II molecules associated with a moderately elevated risk of IDDM, or carried in a strongly protective haplotype, respectively. In an HLA/peptide binding assay, epitope GAD 248-257 was shown to possess high affinity for DRB5*0101. This epitope overlaps with a central GAD peptide binding to the high risk allele DQB1*0302 and containing a Coxsackie P2C-identical mimicry sequence, raising the possibility of competition of DRB5*0101 and DQB1*0302 for binding of a central GAD65 fragment.

Analysis of critical residues of HLA-DQ6 molecules in insulin-dependent diabetes mellitus

Among DQ6 molecules, DQA1*0102-DQB1*0602 is negatively associated with insulin-dependent diabetes mellitus (IDDM), but DQA1*0102-DQB1*0604 shows a neutral to positive association in Swedish children with IDDM. The aim of this study was to identify critical DQB1 residues that may account for the differences in IDDM association observed for these two DQ6 molecules. HLA-DQ genotyping in 425 IDDM patients and 367 matched controls showed DQ6 (B1*0602) in 1% of patients and 25% of controls (odds ratio (OR) 0.02). DQ6 (B1*0604) alone was neutral (9% of patients and 10% of controls) but in combination with DQ8, was positively associated (5% of patients, 1% of controls, OR 9.49). In both these DQ6 molecules the alpha-chain is the same but the beta-chain differs at positions 9, 30, 57, 70, 86 and 87. DQB1*0602 has F9, Y30, D57, G70, A86 and F87, whereas DQB1*0604 has Y9, H30, V57, R70, G86 and Y87. Three-dimensional models of the two DQ6 molecules, based on crystal coordinates of the homologous DR1 molecule, suggest that residue 57 beta will likely play a critical role in peptide-binding selectivity, whereas residue 70 beta is probably is major contact site for the T-cell receptor. The effects of these specific polymorphic substitutions in DQ molecules on peptide binding and T-cell receptor recognition may be significant in IDDM susceptibility.

HLA-DQ gene polymorphism in primary IgA nephropathy in three European populations

MHC Class II genes may contribute to susceptibility to IgA nephropathy (IgAN). We have previously identified a restriction fragment length polymorphism (RFLP) of the DQB1 region that associated with IgAN in British Caucasoids. However, another group, while demonstrating a DQB1 association, was unable to confirm our finding. MHC molecules are heterodimers consisting of an alpha and beta chain, and thus polymorphism of the DQA1 alpha chain may also be important to disease pathogenesis in IgAN. Therefore, we have determined DQA1 alleles and re-examined DQB1 alleles in British Caucasoids with IgAN using an approach that can differentiate between the common DQ alleles; we have also extended our studies to Caucasoid populations from Northern and Southern Europe, thereby addressing the possibility of variation in genetic susceptibility between populations. DNA was prepared from IgAN patients (British, N = 105; Italian, N = 71; Finnish, N = 48) and healthy controls (British, N = 111; Italian, N = 63; Finnish, N = 41). DQA1 alleles were identified by TaqI RFLP and Southern blotting; alleles that could not be fully resolved by Taq Southern blotting were identified by PCR-RFLP. DQB1 alleles were identified by polymerase chain reaction (PCR) based technique (PCR-RFLP). No consistent association of DQ alleles were found between the populations studied. In British patients a decreased frequency of DQB1*0201 was observed (P = 0.008), in Finnish patients a decreased frequency of DQB1*0602 was observed (P = 0.01), and in Italian patients no association between DQ markers and IgAn was found. These data demonstrate population variation in disease association, but no strong or consistent association in the DQ region.

Different contribution of HLA-DR and -DQ genes in susceptibility and resistance to insulin-dependent diabetes mellitus (IDDM)

Previous studies have indicated that certain alleles of HLA-DR and -DQ genes were strongly associated with susceptibility and resistance to insulin-dependent diabetes mellitus (IDDM), and the role of DQ molecule in IDDM has been suggested. To further clarify the association of DQ alleles with IDDM, we determined the nucleotide sequences of full-length cDNA from 13 DQA1 alleles and 14 DQB1 alleles. The sequencing analysis revealed sequence polymorphisms outside the hypervariable region of DQ genes. We then analyzed the DQA1 and DQB1 polymorphisms along with that of DRB genes in 86 B-lymphoblastoid cell lines (B-LCLs) from various ethnic groups and in healthy unrelated Japanese and Norwegian individuals. The allelic and haplotypic distributions in each population revealed the characteristic haplotypic formation in the HLA class II region. HLA genes in 139 Japanese and 100 Norwegian IDDM patients were analyzed. DQB1*0301 was negatively associated with IDDM in both ethnic groups, irrespective of associated DRB1 and DQA1 alleles. In DQB1*0302 positive populations, which represented a positive association with IDDM in both ethnic groups, DRB1*0401, *0404, *0802 haplotypes increased in the patients, whereas DRB1*0406 haplotype decreased. Considering about the hierarchy in DRB1 alleles with IDDM susceptibility (DRB1*0401>*0404>*0403 in Norwegian and DRB1*0802>*0403>*0406 in Japanese), the genetic predisposition to IDDM is suggested to be defined by the combination of DR-associated susceptibility and DQ-associated susceptibility and by the DQ-associated resistance which is a dominant genetic trait.

Population analysis of protection by HLA-DR and DQ genes from insulin-dependent diabetes mellitus in Swedish children with insulin-dependent diabetes and controls

A negative association between insulin-dependent diabetes mellitus (IDDM) and HLA-DR, DQA1 or DQB1 was found in a large population-based investigation of childhood-onset patients (more than 420 patients) and controls (more than 340 controls) from Sweden. The relative risk was decreased for several haplotypes that were negatively associated with IDDM: DR15-DQA1*0102-DQB1*0602, DR7-DQA1*0201-DQB1*0303, DR14-DQA1*0101-DQB1*0503, DR11-DQA1*0501-DQB1*0301, DR13-DQA1*0103-DQB1*0603 and DR4-DQA1*0301-DQB1*0301. In a relative predispositional effect (RPE) analysis, however, only the DR15-DQA1*0102-DQB1*0602 haplotype was significantly decreased, which suggests that the major protective effect for IDDM is carried by this haplotype. This was supported by the observation that all genotypes which were negatively associated with IDDM, except DR7/13, included at least one allele from the DR15-DQA1*0102-DQB1*0602 haplotype. Relative predispositional effect (RPE) analysis of genotypes showed further that the DR15-DQA1*0102-DQB1*0602 haplotype was also negatively associated with IDDM when combined with any other haplotype, whether negatively or positively associated with IDDM. This supports previous suggestions that DR15-DQA1*0102-DQB1*0602 acts dominantly. However, both the stratification and the predispositional allele test failed to distinguish the negative association between IDDM and DR15 from that of DQB1*0602. On the other hand, these tests indicated that DQA1*0102 was not likely to explain the negative association between IDDM and the DR15-DQA1*0102-DQB1*0602 haplotype. We conclude that the major protective effect for IDDM in the population of Swedish children is conferred by the DR15-DQA1*0102-DQB1*0602 haplotype in a dominant fashion, the DQB1*0602 allele being the allele most likely to be responsible for the protective effect of this haplotype, although an effect of the DR15 allele could not be excluded.

HLA-encoded susceptibility to insulin-dependent diabetes mellitus is determined by DR and DQ genes as well as their linkage disequilibria in a Chinese population

HLA-DRB1 and -DQB1 genes were analyzed in 98 Chinese IDDM patients and 205 control subjects from Taiwan. The DRB1*0301-DQB1*0201 haplotype conferred strong susceptibility (RR = 7.7, pc < 10(-5)). DRB1*0405 also conferred susceptibility (RR = 3.1, Pc < 0.0005) whereas DRB1*0403 (RR = 0.7) and DRB1*0406 (RR = 0.2) conferred protection. Indeed, the relative risk for the DRB1*0405-DQB1*0302 haplotype (RR = 33.7, Pc < 0.002) was 48 and 168 times higher than those conferred by the DRB1*0403-DQB1*0302 and DRB1*0406-DQB1*0302 haplotypes, respectively, suggesting that the protection conferred by DRB1*0403 and 0406 is dominant over DQB1*0302. The strong linkage disequilibrium observed between DQB1*0302 and DRB1*0403(0406) can thus explain the surprising finding that the frequency of DQB1*0302 was not significantly increased in the Chinese IDDM patients (RR = 0.9). Because the DRB1*0405-DQB1*0302 haplotype (RR = 33.7) conferred higher susceptibility than the DRB1*0405-DQB1*0401 (RR = 2.5) or DRB1*0405-DQB1*0301 (RR = 2.1) haplotypes, DQB1*0302 is indeed a susceptibility factor, while both DQB1*0301 and DQB1*0401 may confer protection against IDDM. The increased frequency of the protective DQB1*0401 allele in patients compared to controls is due to linkage disequilibrium between DRB1*0405 and DQB1*0401. Interestingly, the previously demonstrated protective effect of DQB1*0602 was not very strong in the Chinese (RR = 0.4). Our results suggested that HLA-encoded susceptibility to IDDM is determined by the combined effects of all DR and DQ molecules present in an individual. Therefore, the genotypic combinations of DR and DQ genes as well as their linkage disequilibria can influence IDDM susceptibility. At least four DR and DQ molecules conferring high susceptibility (DRB1*0301, DRB1*0405, and DQ alpha/beta 0301/0201 and 0301/0302) occur at high frequency in the Chinese population. However, linkage disequilibria between highly susceptible DR and protective DQ or vice versa (e.g., DRB1*0405-DQB1*0301[0401] and DRB1*0403[0406]-DQB1*0302) are probably responsible for the lower incidence of IDDM in the Chinese.

HLA DPB polymorphism in primary sclerosing cholangitis and primary biliary cirrhosis

In recent years there has been an increasing interest in the link between susceptibility to autoimmune liver disease and genes of the HLA system, although the role of the DPB1 locus in British patients has only been investigated in autoimmune hepatitis. The aim of the current study was to determine the distribution of DPB1 alleles in a large series of British patients with the two other autoimmune liver diseases, primary biliary cirrhosis and primary sclerosing cholangitis, and compare the allele frequencies obtained with those of a geographically matched control group. Polymerase chain reaction sequence-specific oligonucleotide probing was used to assign 18 DPB1 alleles in 82 patients with primary biliary cirrhosis (PBC), 71 patients with primary sclerosing cholangitis (PSC), and 103 controls. The frequencies of the DPB1 alleles were not significantly different comparing patients and controls. However, two important observations were made. Firstly, in primary sclerosing cholangitis, the previously reported association with the haplotype A1-B8-DR3-DQ2 does not extend to the DPB1 locus, suggesting that the genetic determinants of susceptibility for this disease lie closer to the DRB loci. Secondly, in primary biliary cirrhosis there is evidence that the reported association with DR8-DQB1*0402 includes the DPB1*0301 allele. The weak HLA association reported here is in contrast with recent data from Japan, where susceptibility is strongly linked to a particular amino acid residue encoded by the DPB1*0501 allele. These data clearly demonstrate that the alleles of the DPB1 locus are not associated with susceptibility to or protection from either primary biliary cirrhosis or primary sclerosing cholangitis in British patients.

Bilateral simultaneous optic neuropathy in adults: clinical, imaging, serological, and genetic studies

To elucidate the cause(s) of acute or subacute bilateral simultaneous optic neuropathy (BSON) in adult life, a follow up study of 23 patients was performed with clinical assessment, brain MRI, HLA typing, and mitochondrial DNA analysis. The results of CSF electrophoresis were available from previous investigations in 11 patients. At follow up, five (22%) had developed clinically definite multiple sclerosis, four (17%) had mitochondrial DNA point mutations indicating a diagnosis of Leber's hereditary optic neuropathy (LHON). The remaining 14 patients (61%) still had clinically isolated BSON a mean of 50 months after the onset of visual symptoms: three of 14 (21%) had multiple MRI white matter lesions compatible with multiple sclerosis, three of 14 (21%) had the multiple sclerosis associated HLA-DR15/DQw6 haplotype, and one of seven tested had CSF oligoclonal IgG bands; in total only five (36%) had one or more of these risk factors. The low frequency of risk factors for the development of multiple sclerosis in these 14 patients suggests that few will develop multiple sclerosis with more prolonged follow up. It is concluded that: (a) about 20% of cases of BSON without affected relatives are due to LHON; (b) multiple sclerosis develops after BSON in at least 20% of cases, but the long term conversion rate is likely to be considerably less than the rate of over 70% seen after an episode of acute unilateral optic neuritis in adult life.

Analysis of antibody markers, DRB1, DRB5, DQA1 and DQB1 genes and modeling of DR2 molecules in DR2-positive patients with insulin-dependent diabetes mellitus

HLA-DR2 is negatively associated with insulin-dependent diabetes mellitus (IDDM). The aim of the present study was to analyze DR2-positive patients among 425 consecutively diagnosed unrelated Swedish children with IDDM and in 367 matched controls. HLA-DRB, -DQA and -DQB were determined by Taq I restriction fragment length polymorphism analysis. Amplification by polymerase chain reaction (PCR) and hybridization with sequence-specific oligonucleotide probes was done for DQA1, DQB1 and DRB1 and DRB5. DR2 was positive in 11/425 patients (3%) and 101/367 (28%) controls (OR 0.07, p < 0.0001). Of the 11 DR2-positive patients, PCR was done in 10, of whom 8 were positive for DRB1*1601-DRB5*0201 compared to 4/96 (4%) controls (OR 92.0: p < 0.001) while the remaining 2 were positive for DRB1*1501-DRB5*0101 compared to 92/96 (96%, OR 0.01; p < 0.001). In 2 patients, a recombination between the haplotypes DQB1*0502-DQA1*0102 (DQ5)-DRB1*1601-DRB5*0201 (DR16 Dw21) and DQB1*0301-DQA1*0501 (DQ7)-DRB1*1602-DRB5*0202 (DR16 Dw22) was observed resulting in the DQB1*0301-DQA1*0501 (DQ7) DRB1*1601-DRB5*0201 (DR16 Dw22) haplotypes. The second haplotype was DR3 DQ2 in 6/11 and DR4 DQ8 in 2/11 DR2-positive patients. In all 3 DQB1*0602-DQA1*0102-DR15-positive patients the second haplotype was DR4-positive. In order to test whether physicochemical properties of the DR2 molecules were associated with IDDM, we constructed three-dimensional models of the peptide binding and T-cell recognition sites (alpha 1 and beta 1 domains) of five subtypes of DR2-DRB1, based on the published DR1 crystal structure. No correlations were observed for DR molecule physicochemical properties and diabetes susceptibility. Islet cell antibodies, insulin autoantibodies and GAD65 antibodies, were measured in DR2-positive patients (n = 11) and controls (n = 101). Despite the presence of the DR2 haplotype the antibody markers were significantly elevated in the patients compared to the controls (GAD65 3/10 patients and 2/101 controls; ICA 7/11 patients and 1/101 controls and IAA 3/11 patients and 0/101 controls). In conclusion, of the five subtypes of DR2, only one, the DRB1*1501, DRB5*0101, DQB1*0602-DQA1*0102 haplotype, was negatively associated with IDDM. DQ may therefore confer more protection from the disease than DR.

Comparative analysis of the genetic associations of HLA-DR3 and tumour necrosis factor alpha with human IDDM

Insulin-dependent diabetes mellitus (IDDM) is associated with class II molecules of the MHC on chromosome 6, in particular HLA-DR and -DQ alleles, but a pathogenic role for TNF-alpha in the class III region of the MHC has also been implied. We therefore tested whether there was any independent association between a biallelic TNF polymorphism and IDDM. The TNF2 allele was present in 61 of 114 (54%) IDDM patients compared to 101 of 253 (40%) control subjects (odds ratio 1.73; p < 0.02). Stratification analysis in individuals matched for HLA-DR3 revealed, however, that this association was not independent of HLA-DR3 and is most likely to be a result of linkage disequilibrium between these alleles.

The Bgl II RFLP associated with type 1 diabetes in DR3-positive subjects is not due to a DQA1 promoter region polymorphism

Type 1 (insulin-dependent) diabetes is strongly associated with the HLA genes encoding DR3 and DR4 and their associated DQ alleles. While 70% of all Caucasian diabetic patients carry the DR3-associated allele DQA1*0501, this allele also occurs in up to 40% of the healthy population. A DQA1 Bgl II 7.2 kb RFLP has been shown to identify a disease-associated subset of DR3-positive subjects. We examined the frequency of this RFLP pattern in 43 diabetic and 25 control DR3-positive subjects and found it to be present in 27 (65%) and 5 (20%) respectively (p = 0.0012). The promoter of the DR3-associated DQA1*0501 allele was amplified in four diabetic subjects who were positive, and four control subjects who were negative, for the 7.2 kb band. The promoter was digested with Bgl II to determine whether polymorphism within the promoter created a disease-associated Bgl II restriction site, which might influence disease susceptibility by an effect on gene transcription. No amplified promoter fragment contained a Bgl II restriction site, suggesting that the disease-associated 7.2 kb band does not result from DQA1 promoter region polymorphism but may be due to polymorphism elsewhere on the DR3 haplotype.

The HLA association with Graves' disease is sex-specific in Hong Kong Chinese subjects

OBJECTIVE

Graves' disease is associated with different HLA genes in Caucasians and the Chinese, in whom the HLA associations may be stronger in males than females. Common HLA-associated susceptibility in both races may occur at the HLA-DQ loci. The aims of this study were to examine the HLA-A, B, DR and DQ associations with Graves' disease in a Hong Kong Chinese population and to determine whether the HLA associations differ between the sexes and between subjects with and without thyrotoxic periodic paralysis.

DESIGN

HLA-A, B and DR types were determined by serological typing and DQA1 and DQB1 alleles by oligonucleotide probing of the respective enzymatically amplified gene.

PATIENTS

Ninety-seven Chinese patients with Graves' disease (31 males with, 35 males without and 31 females without thyrotoxic periodic paralysis) and 105 racially matched healthy controls.

MEASUREMENTS

Frequencies of HLA types/alleles at each locus were compared between patients and controls and between the Graves' subgroups using the chi 2-test.

RESULTS

HLA-B46, DR9 and DQB1*0303 were associated with Graves' disease in males only; these associations were weaker in males with thyrotoxic periodic paralysis. DR12, DQA1*0401 and DQB1*0301 were protective, regardless of sex or the presence of thyrotoxic periodic paralysis. The positive HLA associations in the Hong Kong Chinese were distinct from those in Caucasians whereas the protective haplotype was similar to that described in Caucasians.

CONCLUSIONS

These findings call in question the role of HLA genes in disease susceptibility but suggest a role for HLA in protection from Graves' disease.

MHC genes in autoimmunity

In the last year progress has been made towards elucidating the roles of the MHC gene products in autoimmunity. A major advance has been the recent determination of the crystallographic structure of the human MHC class II molecule, which will be invaluable in delineating the minimum structural requirements for peptides that induce autoimmune disease. In addition, the use of animal models and transgenic mouse technology is continuing to increase our understanding of the involvement of the MHC gene products in immunopathogenesis.

An investigation of the association between HLA-DQ heterodimers and type 1 (insulin-dependent) diabetes mellitus in five racial groups

The association between HLA-DQ alpha Arg52-HLA-DQ beta non-Asp57 heterodimers and type 1 (insulin-dependent) diabetes was compared in Japanese, Chinese, Caucasian, North Indian Asian, and Afro-Caribbean patients to determine their importance in disease susceptibility. The potential to encode four Arg52-non-Asp57 DQ heterodimers, two in cis and two in trans, was significantly associated with increased risk of type 1 diabetes in all races except the Japanese. The possibility of encoding two Arg52-non-Asp57 heterodimers was also significantly associated with increased risk of the disease in all races except the Japanese. The possibility of encoding one heterodimer was not significantly associated with type 1 diabetes in any of the races studied. Heterogeneity testing revealed significant differences in RR values for four, two, and one heterodimers in all races except the Japanese and significant differences in RR for four and two heterodimers when compared across the races. This, together with the lack of an association between Arg52-non-Asp57 heterodimers and type 1 diabetes in the Japanese, suggests that, assuming the same genetic basis for disease in all races, the heterodimer is unlikely to be of primary importance in susceptibility to the disease.