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.

Interleukin (IL)-12, IL-2, and IL-6 gene polymorphisms in Takayasu's arteritis from Turkey.

Takayasu's arteritis (TA) is a chronic arterial inflammation of unknown etiology involving mainly the aorta and its major branches. Genetic polymorphisms of cytokines are screened as susceptibility factors for TA in Turkey. A total of 94 patients with TA were investigated for the genetic polymorphisms of the interleukin genes IL12, IL2,and IL6 and were compared with 108 healthy control subjects using polymerase chain reaction-sequence-specific primer method. The frequencies of IL12B 1188 C allele (p = 0.03, OR = 1.7) and CC genotype (p = 0.007, OR = 3.7) were both higher in TA patients than in control subjects. TT genotype at IL2-330 (p = 0.006, OR = 2.4) and GG genotype at IL6-174 (p = 0.04, OR = 1.9) were more frequent in TA patients. Lower prevalence of GT genotype at IL2-330 (p = 0.005, OR = 0.4), CG genotype at IL6-174 (p = 0.001, OR = 0.4), and AG genotypes at IL6-598 (p = 0.01, OR = 0.4) were also detected. The polymorphism of IL-12 as well as IL-6 and IL-2 genes may contribute to susceptibility and pathogenesis of TA by altering cytokine production and inducing inflammation.

Common Crohn's disease-predisposing variants of the CARD15/NOD2 gene are not associated with Behçet's disease in Turkey.

OBJECTIVE: There are many extra-intestinal findings of Crohn's disease (CD), such as oral and genital ulcers, erythema nodosum, uveitis and arthritis, resembling the manifestations of Behçet's disease (BD). It is also very difficult to distinguish the gastrointestinal involvement of BD from that of CD in some patients. Hence, this study aimed to investigate a possible involvement of the common CD-predisposing CARD15 variants in the genetic susceptibility to BD. METHODS: The study group consisted of 85 consecutive patients with BD (51 male, 34 female) of Turkish origin. Two of them had intestinal involvement. A group of 100 ethnically matched, non-related healthy volunteers were used as controls. All individuals were genotyped for 3 common CARD15 variants (R702W, G908R, and Ll007fsinsC) using a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. RESULTS: None of the three CARD15 variants predisposing to CD was observed in patients with BD, including two patients with intestinal involvement. The R702W mutation was observed in I healthy chromosome, and the 3020insC mutation in 2 chromosomes. No individual was found to be homozygous or compound heterozygous for these variants. CONCLUSION: These findings suggest that 3 most common CD-predisposing CARD15 variants do not constitute a genetic susceptibility factor for BD in Turkey. Further studies would be helpful to rule out a possible contribution of other rare or unknown variants and/or the effects of different ethnic backgrounds.

Human leukocyte antigen-A, -B and -C alleles and human leukocyte antigen haplotypes in Turkey: relationship to other populations.

In this study, we present, for the first time, human leukocyte antigen (HLA) class I allele and haplotype frequencies at the DNA level in a sample of 142 donors from Turkey. HLA typing was performed by medium-to-high resolution polymerase chain reaction sequence-specific oligonucleotide probes method. The most frequent HLA alleles at class I locus were A*0201(0.257), -B*35(0.204) and -Cw*04(0.173). A*0201-B*35-Cw*04(0.056) was the most common three-locus haplotype. Allele and haplotype frequency comparisons and neighbour-joining dendrograms, constructed using DA genetic distances and correspondence analysis using HLA-A, -B and -C, and -DRB1 allele frequencies, revealed similarities with other Mediterranean and European populations, but not with Mongol populations. These results agree with previous studies and confirm that the present day Turkish population is genetically more similar to its geographic neighbours than its historical neighbours in central Asia. The comprehensive HLA data on the Turkish population at the DNA level including up to six-locus putative haplotypes generated in this study will be useful for further studies.

Expression of KIR and C-type lectin receptors in Behcet's disease.

OBJECTIVE: Behçet's disease (BD) is a multisystemic disorder with a possible underlying pathology of immune-mediated vasculitis. Genetic susceptibility associated with HLA-B*51 and B*2702 has been implicated in its pathogenesis. Considering the recently defined regulatory mechanisms of NK cells through HLA class I binding receptors, we hypothesized that interactions of NK and T cells through the NK receptors may be important in the pathogenesis of BD. METHODS: The impact of different expression patterns of HLA-recognizing receptors on NK or T cells was analysed in 51 patients with BD and 32 healthy controls. We used flow cytometry to investigate the expression of KIR3DL1 from the polymorphic killer immunoglobulin-like receptor (KIR) family, which binds a shared HLA-Bw4 motif on HLA-B51 and *2702 alleles, and CD94 from the conserved C-type lectin receptor family, which binds HLA-E. Thirty-three of the BD patients and 19 of the controls carried the same HLA-Bw4 motif. RESULTS: CD3(+) T cells were increased in patients with BD compared with controls (81 vs 75%, P = 0.001), whereas the NK cells did not show any difference between the two groups. Increased expression of CD94 in BD was observed on CD16(+)CD56(+) cells (66 vs 57, P = 0.04) and on CD3(+) (7.7 vs 4.0, P < 0.001) and CD3(+)CD56(+) (44 vs 35, P = 0.02) T cells. KIR3DL1 expression on the NK and T cells was not statistically different between the two groups. No effect of HLA-Bw4 motif was observed on the expression of CD94 and KIR3DL1 in both the patients and the controls. CONCLUSION: The absence of a correlation between KIR3DL1 expression and HLA-Bw4 motif confirms previous work reporting that the expression of these molecules is regulated separately. Increased expression of CD94 may suggest that NK receptors play a pathogenic or regulatory role in BD.

Genetic affinities among Mongol ethnic groups and their relationship to Turks.

The central Asian country Mongolia is home to more than 20 tribes and ethnic groups, some of which are related to neighboring Turkic populations. The main Mongolian people, Khalkha, live in central and eastern Mongolia while the Tsaatan minority lives in the north of the country. The Oold minority is from the western Altai mountain region and live in close proximity with Turkic people. We have typed the HLA-A, -B, -Cw, -DRB1 and -DQB1 loci by PCR-SSP in these three Mongolian populations as well as a sample of the German population. To examine their genetic relationships, a sample of the Turkish population already typed at the HLA-A, -B and -DRB1 loci were used. Altogether five populations were analyzed: Khalkha (n = 100), Tsaatan (n = 72), Oold (n = 52), German (n = 260) and (Anatolian) Turkish (n = 498). Nei's unbiased genetic identity (GI) and genetic distance (GD) were estimated from genotypes using PopGene v1.31, and dendrograms were constructed using phylip. The results suggested a close relationship of the Khalkha to the Tsaatan. The Turks and Germans were equally distant to all three Mongolian populations. These results confirmed the lack of strong genetic relationship between the Mongols and the Turks despite the close relationship of their languages (Altaic group) and shared historical neighborhood. This study has provided useful population data for genetic and anthropologic studies bridging eastern and western populations.

Tumour necrosis factor-alpha gene promoter region -308 and -376 G-->A polymorphisms in Behçet's disease.

OBJECTIVE: Contribution of HLA-B51 to the genetic susceptibility for Behçet's disease is well documented and recent studies suggest involvement of other genes. Tumour necrosis factor (TNF) genes are located in the vicinity of the HLA-B locus. Polymorphisms in the promoter region of TNF-alpha gene has been found to be associated with altered TNF secretion, and it may have a prominent role in the increased inflammatory responses of Behçet's disease. METHODS: The study group consisted of 99 Behçet's disease patients and 96 healthy matched controls. All patients fulfilled the International Study Group criteria for Behçet's disease. The TNF-alpha -308 and -376 promoter alleles were assigned by the digestion of each amplified PCR product with NcoI and TasI enzymes, respectively. RESULTS: No significant difference was observed in the distribution of TNF-alpha promoter region polymorphisms between patients with Behçet's disease and controls. There was no association between the presence of uncommon -308A and -376A alleles and the manifestations or severity of Behçet's disease either. The TNF-alpha -308A allele and HLA-B*50 was found to be associated in this series of Turkish patients and controls. CONCLUSION: The role of TNF-alpha promoter region -308 and -376 polymorphisms in the pathogenesis of Behçet's disease is not supported by this data. The overexpression of TNF-alpha in Behçet's disease may be caused by other polymorphisms in the TNF gene or by post-transcriptional mechanisms.

A weak association of HLA-B*2702 with Behçet's disease.

This study aimed to analyse the association of HLA-B alleles other than -B51 with Behçet's disease (BD). We also investigated the frequency of HLA-B alleles sharing the same natural killer cell immunoglobulin-like receptor (KIR) binding sequence with HLA-B51. Broad-genotyping of HLA-B locus by PCR-SSOP in 174 Turkish BD patients and 191 healthy controls confirmed the strong association of B*51 with BD (60.9% in BD patients, 24.6% in healthy controls, OR = 4.78). No other HLA-B allele was identified showing an association with BD after adjusting for multiple testing or by using relative predispositional effects (RPE) analysis after the deletion of B*51. HLA-B alleles reacting with the sequence specific oligonucleotide probe 23, which corresponds to the KIR binding site of B*51, were found to be positive in 127 BD patients (73%) and 90 controls (47%) (OR = 3.03, 95% CI 2-4.7). The repeated RPE analysis after separating HLA-B alleles carrying B51-KIR binding sequence as distinct alleles within a broad-type allele group revealed B*2702 allele as the only allele showing an association with BD after the deletion of B*51. Selective increase of B*2702, the only B*27 allele carrying the same KIR binding sequence with B*51, warrants investigation of the possibility of interaction of HLA molecules with KIRs on NK or other T cells in the pathogenesis of BD.

Lack of association of HLA-B*51 with a severe disease course in Behçet's disease.

OBJECTIVE: To investigate the previously reported association of HLA-B51 with the manifestations and severity of Behçet's disease (BD). METHODS: The study group consisted of 148 consecutive BD patients (89 male, 59 female) with a minimum disease duration of 5 yr followed up at an out-patient BD clinic in a tertiary referral centre. The patients were classified into three severity groups (mild, moderate, severe) using a modified form of the BD total activity index. HLA-B alleles were determined by DNA amplification using the polymerase chain reaction and sequential hybridization with sequence-specific oligonucleotide probes. RESULTS: The frequencies of genital ulceration [odds ratio (OR)=3.1, 95% confidence interval (CI) 1.3-7.5], skin findings (erythema nodosum, folliculitis or acne-like lesions) (OR=4.4, 95% CI 1.1-17.7), a positive skin pathergy test (OR=3.4, 95% CI 1.1-10.9) and eye disease (OR=1.8, 95% CI 0.9-3.7) were all higher in B*51-positive patients. By contrast, no significant association was observed between B*51 positivity and a severe disease course, and B*51 homozygosity did not exhibit a prominent association with the severity of BD. Male sex was found to be the strongest determinant of the severity of BD by logistic regression analysis (OR=4.7, 95% CI 1.9-11.2). CONCLUSION: HLA-B*51 does not exhibit a strong association with a more severe disease course in BD. The involvement of other genetic and/or environmental factors seems to be required and to be more important than B*51 for the progression of BD.

Molecular analysis of HLA-DRB1, -DQA1 and -DQB1 polymorphism in Turkey.

We report the evaluation of MHC class II polymorphism in the population of Turkey. HLA-DRB1, -DQA1 and -DQB1 have been investigated by polymerase chain reaction and sequence-specific oligonucleotide probe hybridisations (PCR/SSO) and sequence-specific priming (SSP) in 250 randomly selected healthy individuals. We also report the allelic distribution of these genes. The most frequent alleles detected were DRB1*1101 (0.104), *0301 (0.092), *0701 (0.090), DQA1*0501 (0.334), *0102 (0.164) and *03 (0.148) and DQB1*0301 (0.256), *02 (0.164), *0302 (0.128). The frequent 'putative' three-locus haplotypes carry the most frequent alleles at these loci. The most frequently detected class II "haplotypes" are DRB1*1101 DQA1*0501 DQB1*0301 (0.100), DRB1*0301 DQA1*0501 DQB1*02 (0.092) and DRB1*0701 DQA1*0201 DQB1*02 (0.072). The distribution of alleles and 'putative' haplotypes has shown common features with other Mediterranean populations. The results extend the HLA map to another Mediterranean country and provide a database for further HLA-disease association studies and transplantation applications.

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.

The distribution of HLA-DRB alleles in ulcerative colitis patients in Turkey.

Recently described distinct associations of HLA class II genes with ulcerative colitis (UC) suggest a genetic heterogeneity for disease susceptibility. In this study, HLA-DRB alleles of UC patients (n = 59) from Turkey were investigated and compared with healthy controls (n = 244). Using molecular genotyping by polymerase chain reaction (PCR) and sequence-specific oligonucleotide hybridization, we have shown a positive association of UC patients with the HLA-DRB1*1502 allele (10/59 vs. 16/244; P = 0.02; OR: 2.9) and a negative association with the DRB1*13 allele (7/59 vs. 64/244; P = 0.03; OR: 0.38) compared to controls. HLA-DRB1*0701 was significantly increased in perinuclear antineutrophil cytoplasmic antibody (pANCA)-positive UC patients compared to pANCA-negative patients (8/32 vs. 0/27; P = 0.005), whereas DRB1*1502 was observed more frequently in pANCA-negative patients (8/27 vs. 2/32; P = 0.03). These results extended the reported positive association of DRB1*1502 with UC to another population and supported the genetic susceptibility associated with HLA genes for disease development.