Distribution of HLA-DQA1, -DQB1 and DRB1 alleles in black IDDM patients and controls from Zimbabwe

The phenotype of type 1 diabetes in sub-Saharan Africa

The phenotype of type 1 diabetes in Africa, especially sub-Saharan Africa, is poorly understood. Most previously conducted studies have suggested that type 1 diabetes may have a different phenotype from the classical form of the disease described in western literature. Making an accurate diagnosis of type 1 diabetes in Africa is challenging, given the predominance of atypical diabetes forms and limited resources. The peak age of onset of type 1 diabetes in sub-Saharan Africa seems to occur after 18-20 years. Multiple studies have reported lower rates of islet autoantibodies ranging from 20 to 60% amongst people with type 1 diabetes in African populations, lower than that reported in other populations. Some studies have reported much higher levels of retained endogenous insulin secretion than in type 1 diabetes elsewhere, with lower rates of type 1 diabetes genetic susceptibility and HLA haplotypes. The HLA DR3 appears to be the most predominant HLA haplotype amongst people with type 1 diabetes in sub-Saharan Africa than the HLA DR4 haplotype. Some type 1 diabetes studies in sub-Saharan Africa have been limited by small sample sizes and diverse methods employed. Robust studies close to diabetes onset are sparse. Large prospective studies with well-standardized methodologies in people at or close to diabetes diagnosis in different population groups will be paramount to provide further insight into the phenotype of type 1 diabetes in sub-Saharan Africa.

Association of HLA-DQA1 and -DQB1 alleles with type I diabetes in Arabs: a meta-analyses

This study aimed at assessing the nature and significance of associations between various alleles of HLA-DQA1, HLA-DQB1, and type I diabetes (T1D) in Arab populations. Evidence from literature (published before 20 April 2015) was amassed and analysed through multiple meta-analyses, which yielded effect summary odds ratios and 95% confidence intervals for 24 alleles and 4 haplotypes. A total of 1273 cases and 1747 controls from 16 studies were analysed. High levels of significance were obtained to support higher T1D risk when harbouring DQA1*03:01. The alleles DQB1*02:01 and *03:02 and the haplotypes DR3 and DR4 were significant risk factors, albeit with high publication heterogeneity. The protective effects of DQA1*01:01, DQB1*05:03, *06:02, *06:03, and *06:04 were robustly suggested by all indicators of meta-analyses. The haplotypes DR7 and DR11 were strongly suggested to be protective in Arabs. A relatively small number of studies have emerged from Arab countries, mostly with inadequate power on an individual basis. This study fills the gap by providing significant size effect of human leukocyte antigen (HLA) alleles and completes the continuum of global ethnic differences in this context.

Relative predispositional effects of HLA class II DRB1-DQB1 haplotypes and genotypes on type 1 diabetes: a meta-analysis

The direct involvement of the human leukocyte antigen class II DR-DQ genes in type 1 diabetes (T1D) is well established, and these genes display a complex hierarchy of risk effects at the genotype and haplotype levels. We investigated, using data from 38 studies, whether the DR-DQ haplotypes and genotypes show the same relative predispositional effects across populations and ethnic groups. Significant differences in risk within a population were considered, as well as comparisons across populations using the patient/control (P/C) ratio. Within a population, the ratio of the P/C ratios for two different genotypes or haplotypes is a function only of the absolute penetrance values, allowing ranking of risk effects. Categories of consistent predisposing, intermediate ('neutral'), and protective haplotypes were identified and found to correlate with disease prevalence and the marked ethnic differences in DRB1-DQB1 frequencies. Specific effects were identified, for example for predisposing haplotypes, there was a statistically significant and consistent hierarchy for DR4 DQB1*0302s: DRB1*0405 =*0401 =*0402 > *0404 > *0403, with DRB1*0301 DQB1*0200 (DR3) being significantly less predisposing than DRB1*0402 and more than DRB1*0404. The predisposing DRB1*0401 DQB1*0302 haplotype was relatively increased compared with the protective haplotype DRB1*0401 DQB1*0301 in heterozygotes with DR3 compared with heterozygotes with DRB1*0101 DQB1*0501 (DR1). Our results show that meta-analyses and use of the P/C ratio and rankings thereof can be valuable in determining T1D risk factors at the haplotype and amino acid residue levels.

HLA class II disease associations in southern Africa

Southern Africa harbors several population groups representing a diversity of gene pool origins. This provides a unique opportunity to study genetic disease predisposition in these populations against a common environmental background. Human leukocyte antigen (HLA) association studies of these populations could improve knowledge on inter-population variation and HLA-related disease susceptibility. The aim of this paper is to review HLA class II disease associations reported for southern African population groups, compare them with findings in other populations and identify those unique to southern Africa. A number of HLA class II disease associations appear to be unique to southern African populations. These include DRB1*14011 association with insulin-dependent diabetes mellitus susceptibility in the Xhosa and DRB1*10 and DQB1*0302 with rheumatoid arthritis susceptibility in the South African (SA) Indian and SA Coloreds, respectively. A noteworthy similarity in class II disease association was observed among southern African Caucasoid and their European parental populations. Unique HLA class II disease associations observed in southern Africa are consistent with the notion that unique environmental and natural selective factors have resulted in certain ethnic-specific HLA class II disease associations, while common HLA class II disease associations found across different populations support the notion that common diseases are caused by common, ancient alleles present in indigenous African populations.

Molecular basis of predisposition to develop type 1 diabetes mellitus in North Indians

Type 1 diabetes (T1D) mellitus is a multifactorial autoimmune disease where more than 90% of insulin-producing pancreatic beta cells are destroyed before the clinical manifestations, warranting a need to identify the children predisposed to get the disease. Of the 20 genomic intervals implicated for the risk to develop T1D, the major histocompatibility complex (MHC) region on chromosome 6p21.31 (IDDM1) has been the major contributor, followed by 5' regulatory region of the insulin (INS) gene on chromosome 11p15.5 (IDDM2). MHC has a role in antigen presentation and IDDM2 has been shown to have a role in transcription of insulin in the thymus. Hence, alleles of human leukocyte antigen (HLA)-DRB1, DQB1, and insulin-linked variable number of tandem repeats (INS-VNTR) were studied in 110 T1D patients and 112 healthy controls using polymerase chain reaction and hybridization with sequence-specific oligonucleotide probes (PCR-SSOP) and PCR restriction fragment length polymorphism (PCR-RFLP), respectively. HLA-DRB1*0301 was significantly increased in the T1D patients along with associated DQB1*0201 followed by DRB1*0401 and DRB1*0405. DRB1*0701 was observed to be the most protective allele followed by DRB1*0403 and DRB1*0404. Although DQB1*0302 which is associated with both the protective and susceptible DR4 alleles was not significantly increased, heterozygous DQB1*0201, *0302 was significantly increased in the TID patients. Because INS-VNTR class I homozygosity was also significantly increased in the patients, simultaneous presence of DRB1*0301 along with homozygous INS-VNTR class I, gave a relative risk (RR) of 70.81. However, a similar analysis of DQB1*0201 and *0302 along with INS-VNTR alleles did not give such high RRs. Thus, the two independently assorting alleles at two loci i.e., DRB1*0301 and INS-VNTR class I, on two different chromosomes may have the potential to predict a prediabetic in North India.

HLA haplotypes associated with type 1 diabetes mellitus in North Indian children

Human leukocyte antigen (HLA) encoded susceptibility to develop type 1 diabetes mellitus (T1DM) has been investigated in children from North India. The results revealed significantly increased prevalence of HLA-A26, -B8, and -B50 among patients and strong positive association of the disease with DRB1*0301 (82.1% vs 13.9%, chi2=71.3, odds ratio [OR]=28.3) and a negative association with DRB1*02 (chi2=12.2, PF=38.5). HLA-DQB1*0201 occurred in 96.4% of the patients, whereas the heterodimer DQA1*0501-DQB1*0201 was present in 82.1% of patients (60.7% in single dose and 21.4% in double dose) and revealed significant deviation from the healthy controls (chi2=74.1, pc=6.0E-10). In addition to DRB1*03, positive association was also observed with DRB1*09 (14.3% vs 1.3%, chi2=13.4) and DRB1*04 (39.3% vs 15.6%, chi2=8.39). No HLA association was observed in relation to residual pancreatic beta-cell function or associated thyroid autoimmunity. Family analysis revealed involvement of multiple DR3+ve haplotypes with T1DM in North Indian children with A26-B8-DRB1*03 (25% vs 3.5%, chi2=16.9, p=3.96E-05) and Ax-B50-DRB1*03 (25% vs 0.7%, chi2=44.7, p=9.88E-11) being the most frequent haplotypes encountered among patients. The classical Caucasian haplotype A1-B8-DRB1*03 was infrequent (7.2%) among the diabetic children. The study highlights the race specificity of HLA association and disease associated HLA haplotypes in T1DM among North Indian children.

Is TAP2*0102 allele involved in insulin-dependent diabetes mellitus (type 1) protection?

In this study, we have investigated the frequencies of TAP1 and TAP2 alleles in a group of 226 persons, living in La Reunion Island, consisting of 70 patients with insulin-dependent diabetes mellitus (IDDM) and most of their first degree relatives (i.e., 156 parents and full sibling subjects) and previously HLA DQB1, DQA1, and DRB1 genotyped. The population of this island is constituted by a particular structure of highly crossbreeding people. Interestingly, the new TAP2*0104 allele, previously discovered by our team in Reunion Island, was found to be increased in the IDDM population and the calculated HRR was relatively high (HRR = 3.3). This result seems to be due to a positive linkage disequilibrium between TAP2*0104 allele and the highly diabetogenous DQB1* 0201-DQA1* 0501-DRB1 0301 haplotype (HRR = 9), which suggests that TAP2*0104 cannot be considered as an additional predispositional factor, but more as a genetic susceptibility marker of IDDM. In addition, we show that minor alleles (TAP2D, *0102, *0103, *0104) are associated with a restricted number of HLA DQ-DR haplotypes and each of them exhibits a preferential linkage with one particular haplotype. In contrast with other alleles, and despite a HRR value close to 1, we show that TAP2*0102 allele contributes significantly to a drastic reduction of the diabetogenic effect of DQB1*0201-DQA1*0301.1-DRB*0701 haplotype. Indeed, this haplotype, which is usually preferentially transmitted to affected children, is dominantly transmitted to healthy children when it is associated with TAP2*0102. Therefore, this allele seems to contribute to genetic protection to IDDM.

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.

Family-based association of HLA class II alleles and haplotypes with type I diabetes in Brazilians reveals some characteristics of a highly diversified population

The association of HLA class II haplotypes with type I diabetes was analyzed in 56 Southeastern Brazilian families using affected family-based controls (AFBAC) method. DRB1-DQA1-DQB1 alleles were determined by polymerase chain reaction/sequence-specific primer genotyping. This study first revealed the great haplotype diversity of Brazilians (65 different haplotypes even with incomplete DRB1 subtyping), probably due to the admixture of Africans genes with European and Amerindian genes in this population. The results revealed increased frequencies of the DRB1*03-DQA1*0501-DQB1*02 and DRB1*0401-DQA1*03-DQB1*0302 haplotypes in the patient group The highest risk for type I diabetes was associated with the heterozygote DRB1*03/*04 genotype as largely reported, and DRB1*03/X and DRB1*04/Y genotypes conferred a significant, but much lower disease risk. Protection from type I diabetes revealed some peculiarities in Southeastern Brazilians: a lack of significant protecting effect of the DRB1*1501-DQA1*0102-DQB1*0602 haplotype, and an apparent protection conferred by the DRB1*13-DQB1*0301, DRB1*11-DQB1*0301, and DRB1*01-DQB1*0501 two-locus haplotypes. The risk to type I diabetes in the highly diversified Southeastern Brazilians evidenced specific information to the prediction of the disease in this region of the country.

HLA-DRB1, -DQA1, -DQB1 and DPB1 susceptibility alleles in Cameroonian type 1 diabetes patients and controls

It is known that certain combinations of alleles within the human leucocyte antigen (HLA) complex are associated with susceptibility or resistance to type 1 diabetes. Variable associations of DR and DQ with type 1 diabetes are documented in Caucasians but rarely in African populations; however, the role of HLA-DP genes in type 1 diabetes remains uncertain. In order to investigate the HLA class II associations with type 1 diabetes in Cameroonians, we used sequence-specific oligonucleotide probing (SSOP) to identify DRB1, DQA1, DQB1 and DPB1 alleles in 10 unrelated C-peptide negative patients with type 1 diabetes and 90 controls from a homogeneous population of rural Cameroon. We found a significantly higher frequency of the alleles DRB1*03 (chi2 = 17.9; P = 0.001), DRB1*1301 (chi2 = 37.4; P < 0.0001), DQA1*0301 (chi2 = 18.5; P = 0.001) and DQB1*0201 (chi2 = 37.4; P < 0.001) in diabetes patients compared to the control group. The most frequent alleles in the control population were DQA1*01, DQB1*0602 and DRB1*15. The DRB1*04 allele was not significantly associated with type I diabetes in our study population. We observed no significant difference between patients and controls in DPB1 allele frequency. In conclusion, the data in Cameroonian diabetes patients suggest the existence of HLA class II predisposing and specific protective markers, but do not support previous reports of a primary association between HLA-DP polymorphism and development of type I diabetes.

HLA-DR and -DQ polymorphism in Cameroon

HLA-DRB1, -DQA1 and -DQB1 allele frequencies were determined by high-resolution polymerase chain reaction using sequence-specific oligonucleotide probes (PCR-SSOP) and/or DNA sequencing in 126 healthy individuals in Cameroon. Eighteen DRB1, 11 DQA1, and 18 DQB1 alleles were observed. The most common alleles at each locus were DRB1*1503 (29%), DRB1*1301 (13%); DQA1*0102 (38%), DQA1*0302 (11%), DQA1*0401 (11%); and DQB1*0602 (31%), DQB1*0301 (13%), DQB1*0501 (12%). Forty-four different haplotypes were identified including 12 novel haplotypes demonstrating the HLA class II diversity resulting from allele combinations in this population. A single predominant DRB1*1503-DQA1*0102-DQB1*0602 haplotype was observed with a frequency of 27%. In summary, this study of HLA class II polymorphism in Cameroon demonstrates the extent of diversity in this population.

HLA class II antigens in South African Blacks with type I diabetes

Type 1 diabetes mellitus is poorly characterised in many African communities, including South Africa, where little is known of the disease epidemiology. This study aimed to identify the HLA class II alleles associated with type 1 diabetes in a group of Zulu subjects in Durban, KwaZulu-Natal by PCR-SSP. The HLA alleles associated with type 1 diabetes included HLA-DQB*0302 (P<0.0001), DRB1*O9 (P<0.0001), DRB1*04 (P=0.002), DRB1*0301 (P=0.003), DQB*02 (P=0.004) and DQA*03 (P=0.035). Estimated haplotypes positively associated with type 1 diabetes included HLA-DRB1 *0301-DQA*0501, DRB1*04-DQA*03, DRB1*04-DQB*0302, DRB1*0301-DQB*0201, DQA*0501-DQB*0201 and DQA*03-DQB*0302. These findings are similar to those reported from Zimbabwe and other populations with type 1 diabetes.

A new predictive model for insulin-dependent diabetes mellitus susceptibility based on combinations of molecular HLA-DRB1 and HLA-DQB1 pockets

With a view to establishing an accurate evaluation of the genetic predisposition to insulin-dependent type I diabetes (IDDM), we have built a model based on the characteristics of the relevant pockets of HLA-DR and -DQ molecules. Three independent populations were investigated. Group I and group II were Caucasoids, while group III was Japanese, including a total of 1,166 IDDM patients and 2,391 healthy controls. We formulate the hypothesis that suceptibility to IDDM is not only explained by the absence of Aspartate 57 (negative charge) from pocket 9 of DQB1 (P9DQ), but also by the presence of an electric charge (+/- vs. neutral), generated by residues 70, 71 and 74 in pockets 4 of DRB1 (P4DR) and DQB1 (P4DQ) molecules. The respective weight of each pocket, was evaluated in a multivariate analysis based on the logistic regression method. The 4 components (2 loci and 2 pockets) were systematically analysed in the computer model. It was clearly shown that the structural characteristics of pockets P9DQ-P4DR and, to a lesser degree that of P4DQ, account for IDDM predisposition. On applying the model to the whole international series, it appears that the highest risk concerns individuals with P9DQ non-Asp 57 and both the charged P4 of DRB1 and P4 of DQB1, conferring a 80% prediction of susceptibility. Conversely, P9DQ Asp and neutral P4DR and P4DQ give the lowest risk with a predictive value of 5%. This model of risk susceptibility prediction fits remarkably well with the observed distribution in a worldwide study. It allows a better evaluation of the respective role of HLA-DR and -DQ molecules as a major component of susceptibility to IDDM.

HLA class II immunogenetics of IDDM in Yemenite Jews

The association between HLA-DR and DQ and insulin dependent diabetes mellitus (IDDM) was analyzed in 47 patients and 76 controls of Yemenite Jewish origin. The IDDM susceptibility alleles DRB1*03011, DQA1*0501, DQB1*02 and DRB1*0402, DQA1*0301, DQB1*0302 found in Caucasians had a very strong predisposing effect also in the Yemenite IDDM group. The DRB1*07, DQA1*0201 and DQB1*02 alleles were found to have a strong negative association with IDDM. None of the patients carried DRB1*07 and DQA1*0201 compared with healthy controls (43.7%). Our analysis revealed that the DRB1*03011 DQA1*0501 DQB1*02/DRB1*04 DQA1*03 DQB1*0302 heterozygous genotype confers the highest susceptibility (59.6% in patients vs. 0% in controls). The homozygous DRB1*03 and DRB1*04 genotypes were also found to be positively associated with the disease. 81% of the patients compared to 1.3% of controls carried the susceptibility alleles on both haplotypes. In conclusion, the development of IDDM in Yemenite Jews is strongly dependent on the presence of the susceptibility HLA alleles and on the absence of the DRB1*07 haplotype. The Yemenite Jewish group is uniquely homogenous with regard to genetic susceptibility factors involved in the process of IDDM, and may thus be an ideal model for further genetic studies.

Distribution of HLA-DRB1 alleles in a mixed population with insulin-dependent diabetes mellitus from the southeast of Brazil

HLA class II genes are strongly associated with susceptibility and resistance to insulin-dependent diabetes mellitus (IDDM). The present study reports the HLA-DRB1 genotyping of 41 IDDM patients and 99 healthy subjects from the Southeast of Brazil (Campinas region). Both groups consisted of an ethnic mixture of Caucasian, African Negro and Amerindian origin. HLA-DRB1*03 and *04 alleles were found at significantly higher frequencies among IDDM patients compared to the controls (DRB1*03: 48.8% vs 18.2%, P < 0.005, RR = 4.27; DRB1*04: 43.9% vs 15.1%, P < 0.008, RR = 4.37) and were associated with a susceptibility to the disease. DRB1*03/*04 heterozygosity conferred a strong IDDM risk (RR = 5.44). In contrast, the HLA-DRB1*11 allele frequency was lower among IDDM patients (7.3% vs 26.3% in controls), but the difference was not significant. These data agree with those described for other populations and allow genetic characterization of IDDM in Brazil.

Extensive HLA class II studies in 58 non-DRB1*15 (DR2) narcoleptic patients with cataplexy

Narcolepsy is a sleep disorder that has been shown to be tightly associated with HLA DR15 (DR2). In this study, 58 non-DR15 patients with narcolepsy-cataplexy were typed at the HLA DRB1, DQA1 and DQB1 loci. Subjects included both sporadic cases and narcoleptic probands from multiplex families. Additional markers studied in the class II region were the promoters of the DQA1 and DQB1 genes, two CA repeat polymorphisms (DQCAR and DQCARII) located between the DQA1 and DQB1 genes, three CA repeat markers (G51152, T16CAR and G411624R) located between DQB1 and DQB3 and polymorphisms at the DQB2 locus. Twenty-one (36%) of these 58 non-DR15 narcoleptic patients were DQA1*0102 and DQB1*0602, a DQ1 subtype normally associated with DRB1*15 in DR2-positive narcoleptic subjects. Additional microsatellite and DQA1 promoter diversity was found in some of these non-DR15 but DQB1*0602-positive haplotypes but the known allele specific codons of DQA1*0102 and DQB1*0602 were maintained in all 21 cases. The 37 non-DQA1*0102/DQB1*0602 subjects did not share any particular HLA DR or DQ alleles. We conclude that HLA DQA1*0102 and DQB1*0602 are the most likely primary candidate susceptibility genes for narcolepsy in the HLA class II 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.

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.

DQCAR microsatellite polymorphisms in three selected HLA class II-associated diseases

DQCAR is a very polymorphic CA repeat microsatellite located between the HLA DQA1 and DQB1 gene. Previous studies have shown that specific DQCAR alleles are in tight linkage disequilibrium with known HLA DR-DQ haplotypes. Of special interest was the fact that haplotypes containing long CA repeat alleles (DQCAR > 111) were generally more polymorphic within and across ethnic groups. In these latter cases, several DQCAR alleles were found even in haplotypes containing the same flanking DQA1 and DQB1 alleles. In this work, three HLA class II associated diseases were studied using the DQCAR microsatellite. The aim of this study was to test if DQCAR typing could distinguish haplotypes with the same DRB1, DQA1 and DQB1 alleles in control and affected individuals. To do so, patients with selected HLA DR-DQ susceptibility haplotypes were compared with HLA DR and DQ matched controls. This included: Norwegian subjects with Celiac disease and the HLA DRB1*0301, DQA1*05011, DQB1*02 haplotype; Japanese subjects with Type 1 (insulin-dependent) Diabetes Mellitus and the HLA DRB1*0405, DQA1*0302, DQB1*0401 haplotype; and French patients with corticosensitive Idiopathic Nephrotic Syndrome and the HLA DRB1*0701, DQA1*0201, DQB1*0202 haplotype. These specific haplotypes were selected from our earlier work to include one haplotype bearing a short DQCAR allele (celiac disease and DR3,DQ2-DQCAR99) and two haplotypes bearing long DQCAR alleles (Diabetes Mellitus and DR4,DQ4-DQCAR 113 or 115 Idiopathic Nephrotic syndrome and DR7,DQ2-DQCAR 111-121). Additional DQCAR diversity was found in both control and patients bearing haplotypes with long CA repeat alleles. The results indicate that DQCAR typing did not improve specificity in combination with high resolution DNA HLA typing as a marker for these three disorders.

HLA disease associations: models for the study of complex human genetic disorders

The genes of the human leukocyte antigen (HLA) region, the major histocompatibility complex (MHC) of humans, control a variety of functions involved in immune response and influence susceptibility to over 40 diseases. Theoretical studies in the development of models to determine the modes of inheritance of the HLA-associated diseases have led to a better understanding of the inheritance patterns in insulin-dependent diabetes mellitus (IDDM), rheumatoid arthritis, multiple sclerosis, ankylosing spondylitis, hemochromatosis, celiac disease, and others. It is now clear that many of the HLA-associated diseases involve heterogeneity in their HLA components, as well as non-HLA genetic factors. This review is presented using HLA-associated diseases, and in particular IDDM, as the example of interest, but the observations and techniques presented have direct relevance to the study of all human diseases with a complex genetic component. Three methods for localizing disease-predisposing genes are presented: (1) association studies, including population, family, and relative predispositional effects, (2) affected sib pair and other affected-relative methods, and (3) lod score analysis. A variety of complementary methods for studying the mode(s) of inheritance of the alleles at the disease-predisposing locus and for identifying the alleles and amino acids directly involved in the disease process also are presented.

Particular HLA-DQ molecules play a dominant role in determining susceptibility or resistance to type 1 (insulin-dependent) diabetes mellitus

Genes in the HLA complex are by far the most important in determining genetic predisposition or resistance to Type 1 (insulin-dependent) diabetes mellitus. In this review evidence is presented that the HLA genes mainly involved are those encoding some particular HLA-DQ molecules. Both among Black, Caucasian and Japanese subjects particular cis or trans encoded DQ molecules are significantly associated with susceptibility, while others are associated with resistance. A varying degree of susceptibility or resistance seems to be conferred by these DQ molecules, where those determining resistance are dominant over those determining susceptibility. The degree of genetic predisposition to develop Type 1 diabetes carried by an individual would therefore be the result of his or her particular combination of DQ molecules. A primary association to particular DQ molecules explains previously found associations to other HLA complex genes by linkage disequilibrium. Some mechanisms by which particular DQ molecules may determine susceptibility or resistance are also discussed. Potential islet beta-cell reactive CD4+ T-cells may escape negative selection (deletion) in the thymus, but normally become anergized or remain ignorant extra-thymically. However, under particular circumstances they may be triggered. The DQ molecules associated with Type 1 diabetes susceptibility may preferentially bind and present triggering and/or beta-cell derived peptides to such T cells, causing beta-cell destruction. The finding that particular DQ molecules determine susceptibility may lead to new methods of preventing development of Type 1 diabetes in susceptible individuals.

Sequence-specific oligonucleotide typing in Shona patients with rheumatoid arthritis and healthy controls from Zimbabwe

Seventy-two patients with rheumatoid arthritis (RA) and 82 controls have been typed with the XI Histocompatibility Workshop DRB1 and DQB1 sequence-specific oligonucleotide probes. The increase of DRB1*04 corresponds to an increase of the serologically defined DR4, previously found in a small group of Zimbabwean RA patients and we now show that this increase is due to the subtype DRB1*0405 in association with DQB1*0302. In addition there is a clearcut increase of DRB1*1001 equivalent to the serologically defined DR10. There was no increase amongst RA patients of DRB1*0102 which was the predominant DR1 sub-type amongst controls. In the course of our investigation, we observed a DRB1*04 variant which corresponds to DRB1*0412, newly defined in the XIth Histocompatibility Workshop.