Polymorphisms of TAP 1 and TAP2 genes in Graves' disease

Graves' disease is an autoimmune disorder in which HLA DQA1*0501 and DQB1*0201 confer predisposition. The genes for transporters associated with antigen processing (TAP1 and TAP2) locate near to HLA DQ coding regions and display only a limited degree of polymorphism. Since polymorphisms of TAP might influence susceptibility to Graves' disease by a possibly different selection of antigenic peptides, we investigated sequence variants of TAP1 and TAP2 genes in 235 patients with Graves' disease and 218 random healthy controls by polymerase chain reaction (PCR) followed by sequence specific oligonucleotide analysis (SSO), single strand conformational polymorphism (SSCP) analysis and amplification refractory mutation system (ARMS). TAP1*0301 (Val-333/Asp-637: 71% vs. 55% in controls. p< .0008, RR=2.05) and TAP2*0101 (Val-379/Ala-565/Thr-665/stop-687: 83% vs. 69% in controls, p< .003, RR=2.20) showed a positive association with Graves' disease whereas TAP1*0401 a negative (Ile-333/Gly-637: 4% vs. 13% in controls, p< .001, RR=0.25). After selection of patients and controls for HLA DQA1*0501 a similar association was found for TAP1*0301 (72% vs. 50% in controls, p< .002, RR=2.63) and TAP1*0401 (4% vs. 16% in controls, p< .004, RR=0.22), when matching for HLA DQB1*0201 as well as for TAP1*0401 (3% vs. 16% in controls, p< .005, RR=0.18). Our findings indicate that the positive association of TAP1*0301 and the negative of TAP1*0401 with Graves' disease cannot only be explained by linkage disequilibrium between TAP alleles and HLA DQ. Therefore, these TAP alleles contribute to genetic susceptibility in Graves' disease as additional permissive and protective factors.     

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

Abstract: 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.     

POLYMORPHISM OF THE 5’ FLANKING REGION OF THE HLA-DQA1 GENE IN COELIAC DISEASE

Coeliac disease (CD) is associated with particular HLA genotypes. The susceptibility gene (or genes) has been mapped to the class II region, most probably to the DQ loci. Polymorphism of the upstream promoter region of the DQA1 gene (QAP) has been recently reported. At least ten variants or QAP alleles have been found, some of which are present in the as-acting regulatory sequences. Allelic differences in DQ molecule expression may play a role in susceptibility to CD. We investigated the QAP polymorphism in 102 CD patients and 142 unrelated healthy controls of Czech origin using polymerase chain reaction amplification (PCR) of genomic DNA and oligonucleotide probes. We found a significant frequency increase of the alleles QAP 4.1 (RR = 10.3, p.c. = 10-⁶) and QAP 2.1 (RR = 2.4, p.c. = 0.017) in patients over controls. An increased susceptibility is provided by the presence of both alleles, as is shown by the higher proportion of QAP 4.1, 2.1 heterozygotes among patients than expected from the Hardy-Weinberg equilibrium and by the comparison of the odds ratios for these alleles. There is a strong linkage disequilibrium between the QAP alleles and the DQA1, DQB1, and DRB1 loci. Two haplotypes carrying the QAP alleles whose frequency is increased are predominant in this group of CD patients: DQB1* 0201, DQA1* 0501, QAP 4.1, DRB1* 0301 and DQB1* 0201, DQA1* 0201, QAP 2.1, DRB1* 0701. Thus, the QAP variants are increased as part of these haplotypes and we cannot discriminate if they are responsible for the primary association.     

Endogenous retroviral long terminal repeats of the HLA-DQ region are associated with susceptibility to insulin-dependent diabetes mellitus

HLA-DQ genes are the main inherited factors predisposing to IDDM. This gene region harbors long terminal repeat (DQ LTR) elements of the human endogenous retrovirus HERV-K, which we analyzed for a possible association with disease. We first investigated whether LTR segregate with DQ alleles in families. Members (n = 110) of 29 families with at least one diabetic child, unrelated patients with IDDM (n = 159), and healthy controls (n = 173) were analyzed. Genomic DNA was amplified for DQ LTR3 by a nested primer approach as well as for DQA1 and DQB1 second exons, to assign DQA1 and DQB1 alleles. DQ LTR segregated in 24 families along with DQ alleles. Of the 29 families, 20 index patients were positive for DQ LTR. The DQ LTR was in all patients on the haplotype carrying the DQA1 ^*0301 and DQB1 ^*0302 alleles. A majority of patients had DQ LTR (62%) compared with controls (38%) (p < 1.3 × 10^{− 5}), even after matching for the high-risk alleles DQA1 ^*0501, DQB1 ^*0201-DQA1 ^*0301, and DQB1 ^*0302 (79% of patients and 48% of controls; p < 0.02). Subtyping for DRB1 ^*04 alleles in all DQB1 ^*0302 ⁺ individuals showed 56% DRB1 ^*0401, DQB1 ^*0302 [LTR⁺ patients vs. 29% controls with the same haplotype (p < 0.002). In conclusion, these data demonstrate the segregation of DQ LTR with DQA1, DQB1 alleles on HLA haplotypes. Furthermore their presence on DRB1 ^*0401-, DQA1 ^*0301-, and DQB1 ^*0302-positive haplotypes suggest that they contribute to DQ-related susceptibility for IDDM. Human Immunology 50, 103–110 (1996)     

HLA-DQA1 AND DQB 1 ALLELE AND GENOTYPE CONTRIBUTION TO IDDM SUSCEPTIBILITY IN AN ETHNICALLY MIXED POPULATION

HLA-DRB1, DQA1 and DQB1 alleles have been determined in 42 families with one IDDM proband and 64 healthy controls, by oligotyping (PCR-SSO) using primers and probes from the XI International Histocompatibility Workshop. A positive DRB1 *03 and DRB1 *04 association with the disease was observed, whereas DRB 1*11 and DRB 1 *07 showed negative association but 19% of patients carried DRB1 alleles different to DRB 1 *03 or *04. When single alleles were considered, DQA1 *03 showed the strongest association with susceptibility to the disease (RR = 8.2, Pc = 0.00001) but this association was outgrown by 2 and 3 allele combinations, with genotype DRB 1 *04-DQA 1 *03-DQB1*0302/DRB1*03- DQA 1*0501- DQB 1*0201 showing the strongest association (RR = 28, Pc = 0.002). Application of the relative predispositional effect (RPE) method to our data, revealed a further susceptibility risk provided by the DRB1*13-DQA1*0102-DQB 1*0604 haplotype once DR3 and DR4 haplotypes were removed. When DQA1-DQB1 genotypes were analysed for presence of Arg 52 (DQ α) and absence of Asp 57 (DQ β), genotypes SS/SS were found significantly increased in diabetics. Interestingly, one of the strongest associations with the disease was observed with the DQA 1*03-DQB 1*0201 combination encoded mainly by genes in trans (RR = 11.7 Pc = 0.00004). These observations and their comparison with DR-DQ haplotypes in more homogeneous ethnic groups support the stronger influence of the DQ molecule rather than the individual DR or DQ alleles in the susceptibility to IDDM. They also emphasize the need for detailed HLA haplotype studies in non-Caucasian and ethnically mixed populations to gain further insight into the nature of genetic and environmental factors contribution to autoimmunity.     

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.     

Strong association between DQA1/DQB1 genotype and early-onset IDDM in Chinese: the association is with alleles rather than specific residues

We report on the role of HLA-DQA1 and DQB1 alleles in determining susceptibility to insulin-dependent diabetes mellitus (IDDM) in Hong Kong Chinese and investigate whether these alleles affect the age of onset of the disease. We studied 76 unrelated Chinese patients and 250 controls. There was no apparent predisposing effect of non-aspartic acid residues at position 57 of the DQβ chain (Asp^57–) but there was an excess of homozygous genotypes containing arginine at position 52 of the DQα chain (Arg⁵²⁺). This excess was mainly attributable to the genotype DQA1*0301/ DQA1*05011 in early-onset disease. There was a significant excess of heterodimers of DQα and DQβ carrying Arg⁵²⁺ and Asp^57– in both early-onset and late-onset disease, but the excess in early-onset disease was mainly attributable to a single heterodimer formed by DQA1*05011 and DQB1*0201. Of three DQA1/ DQB1 genotypes containing a double dose of Arg⁵²⁺ and Asp^57–, only one had a strong association with both early-onset and late-onset disease. We show that early-onset IDDM and late-onset IDDM in Chinese may be separated on the basis of their associated DQA1 and DQB1 genotypes and we conclude that previously reported associations of IDDM with Arg⁵²⁺ and Asp^57– residues in Chinese are secondary to specific combinations of DQA1 and DQB1 alleles. We also show that DRB1 molecules play a distinct role in determining susceptibility to early-onset IDDM but the greatest effect is exerted by specific DR/DQ genotypic combinations.     

Linkage disequilibrium between TAP2 variants and HLA class II alleles; no primary association between TAP2 variants and insulin-dependent diabetes mellitus

The TAP1 and TAP2 genes, located in the HLA class II region, encode subunits of a peptide transporter. Both genes display limited genetic variability; four different nucleotide substitutions have been found in theTAP2 gene. Here studies on linkage disequilibrium between TAP2 variants and HLA class II alleles are reported, in an attempt to evaluate whether TAP2 variants are associated with insulin-dependent diabetes mellitus (IDDM). As reported previously, a significant decrease of homozygosity for TAP2 alleles encoding alanine at residue 665 (665 Ala) and glut amine at 687 (687 Gin) paralleled by an increase in homozygosity for TAP2 alleles encoding threonine at residue 665 (665 Thr) and a stop codon at 687 (687 Stop), was found in both Finnish and Norwegian IDDM patients compared to random controls. However, a strong linkage disequilibrium between these TAP2 polymorphisms and given HLA-DR and -DQ genes was observed among healthy controls. The frequent 665 Thr and 687 Stop variants were in linkage disequilibrium both with the DR4-DQ8 and the DR3-DQ2 haplotypes, haplotypes which are strongly associated with IDDM. In contrast, the DR1-DQ5 and DR13-DQ6 (e.g. DQB1*0603) haplotypes, which are decreased among IDDM patients, were associated with the 665 Ala and 687 Gin variants. Thus, when DR- and DQ-matched patients and controls were compared, associations of the investigated TAP2 variants and IDDM were no longer detectable. These data, therefore, indicate that the associations previously found between certain TAP2 variants and IDDM are secondary to a primary association between this disease and particular DQαβ heterodimers.     

HLA-DRB1*0401 IS ASSOCIATED WITH SUSCEPTIBILITY TO INSULIN-DEPENDENT DIABETES MELLITUS INDEPENDENTLY OF THE DQB1 LOCUS

The distribution of DRB1*04 alleles and DRB1/DQB1 haplotypes was analysed in 57 DR4⁺ caucasoid subjects with insulin-dependent diabetes mellitus (IDDM) and 96 DR4⁺ healthy controls selected on the basis of DR serology, and the findings were analysed in relation to age at diagnosis of IDDM. DNA samples were amplified using specific DR and DQ primers and hybridized with sequence-specific oligonucleotide probes. A significantly increased combined frequency of DRB 1*0401 and 0402 was observed in IDDM subjects aged ≤12 years at diagnosis (allele frequency 88.4% compared with 62.0% in controls, P < 0.025). There was a non-significant increase in DRB 1*0401 and 0402 in IDDM subjects ≤12 years when compared with IDDM subjects >12 years (P < 0.1). DRB 1 *0404 was decreased in the total IDDM subject group compared with controls (4.8% vs. 19.0%, P < 0.025) but did not reach statistical significance in the individual age at diagnosis groups. In contrast, the frequency of DQB1 *0302 was increased uniformly across both ages at diagnosis groups. In controls DRB 1*0401 occurred in haplotype association with DQB 1*0301 in a significantly greater frequency than with DQB 1*0302. However, 95.0% of DRB 1*0401 IDDM subjects were DQB 1*0302. DRB 1*0404, which was decreased in frequency in IDDM subjects, occurred in association significantly more frequently with DQB 1 *0302 in controls. These results imply that DRB 1 and DQB 1 have independent roles as HLA susceptibility genes in IDDM. DQB1 may have a permissive role whereas DRB1 could influence the rate at which underlying disease progresses to clinical IDDM.     

Genetic heterogeneity between type 1 a and type lb insulin-dependent diabetes mellitus: HLA Class II and TAP gene analysis

The aim of this study was to compare the genetic susceptibility linked to the HLA Class II region genes of the Major Histocompatibility Complex in isolated insulin-dependent diabetes mellitus (la-IDDM) and insulin-dependent diabetes mellitus associated with another autoimmune endocrinopathy (lb-IDDM). HLA genes DRB1, DQA1 and DQB1 were studied at the genomic level, as well as genes TAP1 and TAP2. One hundred and seventy-nine la-IDDM diabetic patients were compared with 83 lb-IDDM patients. While it appeared that common genetic traits characterize diabetes regardless of the subtype (la or lb), certain features differentiate the two forms of IDDM. Extending the analysis of risk haplotypes DRB1*03 and DRB1*04 to TAP genes elicited a difference between la-IDDM and lb-IDDM patients. Haplo-type DRB1*03 was thus characterized in la-IDDM patients by a lower frequency of alleles TAP1-B (13.5%) and TAP2-B (16.2%), not found in lb-IDDM patients (33.3% for each allele). Likewise, haplotype DRB1*04 is characterized in lb-IDDM patients by a lower frequency of alleles TAP1-C (4.0%) and TAP2-B (8.0%) than in la-IDDM patients (22.2% and 25.9%, respectively). In total, this study showed that extending the characterization of HLA Class II haplotypes to TAP genes discriminates between the forms of diabetes restricted to a specific pancreatic affection and those reflecting a wider autoimmune disorder affecting several organs.     

HLA class II (DRB1, DQA1 and DQB1) associated genetic susceptibility in Iranian multiple sclerosis (MS) patients

The association of HLA class II alleles with multiple sclerosis (MS) has been amply documented. In the present study, the role of HLA class II (DRB1, DQA1 and DQB1) alleles and haplotypes was investigated in 43 unrelated Iranian chronic progressive multiple sclerosis (CP-MS) patients compared with 100 healthy individuals. HLA typing for DRB1, DQA1 and DQB1 was performed by restriction fragment length polymorphism (RFLP). Subtypes of DR4, DR15 and DR16 were defined using polymerase chain reaction (PCR) amplification with sequence-specific primers (PCR-SSP). The results show that, among DR2-positive MS patients and the control group, a positive association with the DRB1*1503, DQA1*0102, DQB1*0602 haplotype (21% vs. 2.7%, P=0.057, RR=9.8) and a negative association with the most frequent DR15 haplotype in the control group, DRB1*15021, DQA1*0103, DQB1*0601 (7% vs. 24.3%, P=0.001), were observed. No significant association was found with the analysed HLA-DRB1, DQA1 and DQB1 alleles.     

HLA‐DPB1*0401 is associated with dominant protection against type 1 diabetes in the general Saudi population and in subjects with a high‐risk DR/DQ haplotype

The human leukocyte antigen (HLA) class II DQB1*0201/0202‐DRB1*04 genotype has been identified as predisposing to type 1 diabetes [insulin‐dependent diabetes mellitus (IDDM)] in the Saudi Arabian population (P = 0.0002; odds ratio = 0.67; 95% confidence interval = 0.009–0.381). In this study, we searched for a factor at the DPB1 locus by analysing DPB1 polymorphism using sequence‐based typing in 86 Saudi IDDM patients and control subjects, all carrying the HLA‐DRB1*04/DQB1*02 haplotype or the known susceptibility allele DQB1*0201/0202. Significant protection was conferred by DPB1*0401, which was observed in 17 of 50 control subjects (55%) and 2 of 36 IDDM patients (5%) with the DQB1*0201/0202 allele (P = 0.0012; odds ratio = 8.75; confidence interval = 1.72–59.70). Our data showing a high frequency of the DPB1*0401 allele even in the presence of the predisposing DQB1*02 allele in healthy subjects may indicate a protective effect of this combination of HLA alleles against type 1 diabetes. This finding supports the hypothesis that protective HLA class II genes can override the risk conferred by HLA‐DQ susceptibility alleles. Further studies using larger cohorts of control subjects and patients should be undertaken to confirm this observation.     

HLA CLASS II POLYMORPHISM AND IDDM SUSCEPTIBILITY IN THE GREEK POPULATION

The frequencies of HLA-DQA1, DQB1 and DRB1 alleles were compared between 50 Insulin-Dependent Diabetes Melitus (IDDM) patients and 49 healthy controls in the Greek population. Statistically significant difference in the frequencies of HLA-DQA1*0501-DQB1*0201 (P = 10^-4), DQA1*0301-DQB1*0201 (P= 0.01) and DQA P0301-DQB 1*0302 (P= 0.001) were observed. The DRB1*0405-DQA1*0301-DQB 1*0201 was the only DR, DQ combination significantly associated with the disease. The unexpected increase of DRB1*0405 observed in the Greek IDDM may suggest as reported in Chinese and Japanese IDDM a contribution of DRβ and DQα in susceptibility. Moreover, in contrast to the Asians, in the Greek, the DRβ, DQα are found with the usual DQβ 57-ve.     

Associations of MHC class II alleles with insulin-dependent diabetes mellitus (IDDM) in patients from North India.

Thirty-four insulin-dependent diabetes mellitus (IDDM) patients from North India were studied with respect to their HLA class II alleles including those of the DRB1, DQA1, DQB1 and DPB1 loci, using the polymerase chain reaction (PCR) and hybridization with sequence-specific oligonucleotide probes (SSOP). They were compared with the class II alleles of 94 normal adult controls from the same ethnic background. The results show a statistically significant increase of DRB1*03011 (p < 0.00001), DQB1*0201 (p < 0.007), DQA1*0501 (0.0027) and DPB1*2601 (p < 0.0042) in patients compared to controls. DR*04 was not significantly increased. However, homozygosity for DRB1*03011 was increased more than expected. DRB1*1501 and *1502 did not show a significant decrease in the patients. However, DRB1*0701 was decreased significantly, but this difference did not remain significant when the p value was corrected for the number of alleles tested. Similarly, DPB1*2601 was increased significantly in the patients but did not remain significant after p was corrected for the number of alleles tested. However, DPB1*2601 was increased, and remained significant after correction, in patients not having HLA-DR3. We also studied the possible role of aspartic acid at codon 57 of the DQ beta chain in protection against development of diabetes, and arginine at codon 52 of the DQ alpha chain in susceptibility. We observed an increase in non-Asp57 alleles in DQ beta and Arg52 in DQ alpha in the patients, however, this effect seems to be due to the fact that the most prevalent haplotype in diabetic patients: DRB1*03011-DQA1*0501-DQB1*0201, has DQB1 and DQA1 alleles which carry non-Asp57 and Arg52, respectively.     

HLA CLASS II AND SUSCEPTIBILITY AND RESISTANCE TO INSULIN-DEPENDENT DIABETES MELLITUS IN A POPULATION FROM THE NORTHWEST OF SPAIN

The role of HLA class II alleles in genetic predisposition to insulin-dependent diabetes mellitus(IDDM) was examined using Polymerase Chain Reaction/oligonucleotide probe typing (PCR/SSOs) of eight HLA class II loci in 58 IDDM patients and 50 healthy controls from the Northwest of Spain (Asturias). We compared the distribution of HLA class II alleles, haplotypes and genotypes between IDDM patients and controls, and tested three recently proposed HLA-IDDM susceptibility theories. By using the aetiologic fraction (δ) as an almost absolute measure of the strongest linkage of disequilibrium of a HLA marker to the putative Type I susceptibility locus, it has been found that the strength of association of the HLA markers may be quantified as follows: DQA1 *03-DQB1 *0302 or DQA1 *0501-DQB1 *0201 > DR3 or DR4; presence of more than one dimer DQαβ of the six proposed by Rønningen > non-Asp57 DQβ and Arg52 DQα > Arg52 DQα > non-Asp57 DQβ/non-Asp57 DQβ > DRB1*0301; DQA1*0501-DQB1*0201 > DQA1*03-DQB1*0302; DQB1*0302. The presence of at least one Asp57 DQβ allele was the best protection HLA marker to IDDM in our population. Therefore, the above data confirm that IDDM susceptibility to HLA locus is linked more to DQ than DR.     

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 (χ² = 17.9; P = 0.001), DRB1*1301 (χ² = 37.4; P < 0.0001), DQA1*0301 (χ² = 18.5; P = 0.001) and DQB1*0201 (χ² = 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 class II alleles associated with celiac disease susceptibility in a Southern European population

Susceptibility to celiac disease in Northern Europe is associated with the human leukocyte antigens (HLA) B8, DR3 and DQ2, which exist together on an extended haplotype. The strong predominance of this haplotype within the Northern European celiac populations, together with the linkage disequilibrium which occurs between these loci, does not allow identification of the gene(s) primarily associated with disease susceptibility. Studies from Southern Europe using both serology and examination of restriction fragment length polymorphisms (RFLP) have demonstrated associations with DR3, DR7 and DQ2, suggesting that the DQ locus is primarily involved. We investigated 43 celiac patients and 41 healthy controls from Rome, Italy, using sequence-specific oligonucleotide (SSO) probes, in conjunction with gene amplification by the polymerase chain reaction (PCR), to determine alleles at the DRB, DQA1, DQB1 and DPB1 loci: 19% of celiac patients possessed the alleles DRB1*0301 DRB3*0101, 33% DRB1*0301 DRB3*0201 and 33% of celiac patients were heterozygous for DRB1*1101-1201/DRB1*0701. The strongest association with celiac disease susceptibility was the combination of alleles DQA1*0501 DQB1*0201 (91% celiac patients vs. 12% controls; p = 0.000002). There was no additional susceptibility associated with alleles at the DPB locus. This study confirms the hypothesis that susceptibility is associated with a particular combination of DQ alleles and the ethnic variation in DR frequencies is secondary to linkage disequilibrium with these DQ alleles.     

Cis-trans complementation of DQA1-DQB1 genes are modulated by DQ alleles: an immunogenetics analysis of DQ association with the down-regulatory function of CD8 cells in trichosanthin-induced immunosuppression

The initiation of a CD8 cell-mediated pathway (M⁺) was adopted as a phenotypic trait to analyse genetic predisposition in trichosanthin (Tk)-induced immunosuppression. Tk is a natural protein antigen with 247 amino acid residues. Based on DNA typing for DR, DQ, DP and TAP genes, data in this paper indicate that only DQ genes were primarily involved and that the alleles DQA1*0501 and DQB1*0201 were strongly associated with the M⁺ phenotype in cis (on DR3 haplotype) or trans (on DR5/DR7 heterozygotes) complementation. This is consistent with our observation that only the DQ-positive cells were capable of expanding after being co-cultured with Tk for 96h. Two points of interest were noted. (1) The susceptible haplotype DRB1*0301-DQA1*0501-DQB1*0201 showed an association with the M⁺ phenotype only if combined with DRB1*04-, DRB1*08-, or DRB1*09-related haplotypes. When co-presented with DRB1*11-, DRB1*15-, DRB1*07-related haplotypes, however, no cis complementation could be detected. A detailed analysis of the association patterns indicated that the DQB1 locus of the non-susceptible haplotypes was the main factor for up- or down-modulation. (2) For M⁺ phenotype-related trans complementation in Tk-induced suppression, it was found that not only DQA1*0501-DQB1*0201 (DR5/7) alleles, but also associated DQA1*0301-DQB1*0201 (DR4/7, 9/7) alleles, were involved. The allele DQB1*0201 was not associated with the DQA1 alleles in DRB1*01-, DRB1*15-, DRB1*13-, DRB1*07-related haplotypes. The results obtained indicate that there are some additional genetic factors involved in the functional expression of cis and trans complementation of DQA1 and DQB1 genes, among which the DQ alleles play a critical role as self-regulators.     

Prevalence of human leukocyte antigen DQA1 and DQB1 alleles in Kuwaiti Arab children with type 1 diabetes mellitus

The prevalence of human leukocyte antigen (HLA) DQB1 and DQA1 alleles has been determined in 78 Kuwaiti Arab children with insulin-dependent diabetes mellitus (IDDM) and in 57 normal healthy controls with similar ethnic background. The typing of HLA-DQ alleles was carried out using an allele-specific DNA-based polymerase chain reaction (PCR) SSP method. DR typing was also performed in 212 control subjects using PCR-SSP (sequence specific primer) method. A significantly higher frequency of DQB1*0201 allele was found in IDDM cases compared to the controls (p<0.001). There was no significant difference in the prevalence of DQB1 alleles *0302, *0501, and *0602 between IDDM cases and the controls. In contrast, DQB1 alleles *0301, *0402, *0502, *0602, and *0603 were represented at a somewhat higher frequency in controls compared to the IDDM cohort. The frequency of DQA1 allele *0301, which encode for an Arg at codon 52, was significantly higher in the IDDM patients compared to the controls (p<0.001). The frequency of DQA1 allele *0302 was also higher in IDDM cases than controls (p = 0.034) but the difference was less pronounced than DQA1*0301. Amongst the Arg52 alleles, no significant difference was detected in the frequency of *0401 between IDDM cases and the controls and the allele *0501 was detected only in controls. For non-Arg52 alleles *0103, *0104, and *0201, the differences in the two groups were not significant, with the exception of allele *0104 (p = 0.024). DR3 was the most common type in the Kuwaiti general population (28%) and DRB1*0301 was detected in 41% of the individuals with DR3 specificity. Analysis of HLA-DQBI/DQA1 haplotypes from IDDM cases and controls revealed a significantly high frequency of haplotype DQA1*0301/DQB1*0201 between Kuwaiti IDDM cases (49/78, 63%) and the controls (8/57, 14%).     

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.