Microsatellite mapping of a susceptible locus within the HLA region for Behçet's disease using Jordanian patients

Behçet's Disease: A Comprehensive Review on the Role of HLA-B*51, Antigen Presentation, and Inflammatory Cascade

Behçet's disease (BD) is a complex, recurring inflammatory disorder with autoinflammatory and autoimmune components. This comprehensive review aims to explore BD's pathogenesis, focusing on established genetic factors. Studies reveal that HLA-B*51 is the primary genetic risk factor, but non-HLA genes (ERAP1, IL-10, IL23R/IL-12RB2), as well as innate immunity genes (FUT2, MICA, TLRs), also contribute. Genome-wide studies emphasize the significance of ERAP1 and HLA-I epistasis. These variants influence antigen presentation, enzymatic activity, and HLA-I peptidomes, potentially leading to distinct autoimmune responses. We conducted a systematic review of the literature to identify studies exploring the association between HLA-B*51 and BD and further highlighted the roles of innate and adaptive immunity in BD. Dysregulations in Th1/Th2 and Th17/Th1 ratios, heightened clonal cytotoxic (CD8+) T cells, and reduced T regulatory cells characterize BD's complex immune responses. Various immune cell types (neutrophils, γδ T cells, natural killer cells) further contribute by releasing cytokines (IL-17, IL-8, GM-CSF) that enhance neutrophil activation and mediate interactions between innate and adaptive immunity. In summary, this review advances our understanding of BD pathogenesis while acknowledging the research limitations. Further exploration of genetic interactions, immune dysregulation, and immune cell roles is crucial. Future studies may unveil novel diagnostic and therapeutic strategies, offering improved management for this complex disease.

A comprehensive overview on the genetics of Behçet's disease

Behçet's disease (BD) is a systemic and inflammatory disease, characterized mainly by recurrent oral and genital ulcers, eye involvement, and skin lesions. Although the exact etiopathogenesis of BD remains unrevealed, a bulk of studies have implicated the genetic contributing factors as critical players in disease predisposition. In countries along the Silk Road, human leukocyte antigen (HLA)-B51 has been reported as the strongest genetically associated factor for BD. Genome-wide association studies, local genetic polymorphism studies, and meta-analysis of combined data from Turkish, Iranian, and Japanese populations have also identified new genetic associations with BD. Among these, other HLA alleles such as HLA-B*15, HLA-B*27, HLA-B*57, and HLA-A*26 have been found as independent risk factors for BD, whereas HLA-B*49 and HLA-A*03 are independent protective alleles for BD. Moreover, other genes have also reached the genome-wide significance level of association with BD susceptibility, including IL10, IL23R-IL12RB2, IL12A, CCR1-CCR3, STAT4, TNFAIP3, ERAP1, KLRC4, and FUT2. Also, several rare nonsynonymous variants in TLR4, IL23R, NOD2, and MEFV genes have been reported to be involved in BD pathogenesis. According to genetic determinants in the loci outside the MHC region that are contributed to the host defense, immunity, and inflammation pathways, it is suggested that immune responses to the pathogen as an important environmental factor and mucosal immunity contribute to BD susceptibility.

Behçet’s Disease: A Review

Behçet’s disease (BD) is a multi-system inflammatory disorder dominated clinically by recurrent oral and genital ulceration, uveitis, and erythema nodosum. Behçet’s disease runs a chronic course, with unpredictable exacerbations and remissions whose frequency and severity may diminish with time. Behçet’s disease typically arises in young adults, although childhood-onset BD has also been reported. The disease can affect both genders and has a worldwide distribution, although it is more prevalent in countries of the ancient Silk Route. The cause of BD remains unknown, although an autoimmune reaction triggered by an infectious agent in a genetically predisposed individual has been suggested. The treatment of BD is symptomatic and empirical, but generally specific to the clinical features of each patient. The majority of affected individuals do not have life-threatening disease, although mortality can be associated with vascular-thrombotic and neurological disease.

A meta-analysis of the association between Behçet's disease and MICA-A6

Behçet's disease (BD) is a multi-system inflammatory condition with unknown cause, characterized by a triple-symptom complex of recurrent oral aphthous ulcers, genital ulcers, and uveitis and skin lesions. It predominantly affects people living around the Mediterranean basin and in Japan. The effects of the major histocompatibility complex class I chain related gene A (MICA) A6 allele on susceptibility to Behçet's disease (BD) have been reported previously, however, their results have been unreliable. The present study aimed to determine whether an association between the MICA-A6 allele and BD susceptibility exists. A total of 12 case-control studies, examining the association between MICA-A6 and BD and involving 752 cases and 1,175 controls were included in the present meta-analysis. Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. The results of meta-analysis revealed that the frequency of the MICA-A6 allele in the case group was significantly higher than those in the control groups (P<0.001, OR=2.43, 95% CI: 1.99-2.97). Sub-group analysis by ethnicity indicated that the association between of MICA-A6 gene to BD remained in Asian populations (5 cases and 731 controls) and Caucasian populations (242 cases and 444 controls) with OR=2.65, 95% CI: 2.07-3.38 and OR=2.23, 95% CI: 1.37-3.62, respectively. These findings demonstrate that MICA-A6 gene is associated with susceptibility to BD. The MICA-A6 gene may serve as an early diagnostic marker for BD in the future.

Association between Functional MICA-TM and Behcet's Disease: A Systematic Review and Meta-analysis

The relationships between polymorphisms of the trans-membrane(TM) region located in the major histocompatibility complex (MHC) class I chain-related gene A (MICA) and Behcet's disease (BD) have been discussed previously, however, the results were contradictory. In this study, we thoroughly assess whether MICA-TM gene variants are associated with BD by means of a systematic review and meta-analysis. Our study focused on the effects of polymorphisms of MICA-A4, A5, A5.1, A6, and A9 from the included articles. Sixteen previous original publications representing 1,555 BD patients and 2,086 unrelated healthy controls analyzed the association of BD with MICA-TM gene polymorphisms. For the five alleles, MICA-A6 showed a strongly positive correlation with BD patients and could be viewed as an increased risk factor of BD (OR = 2.34, 95%CI: 2.02-2.70). Furthermore, MICA-A4, A5, A5.1, and A9 exhibited negative associations with BD (OR = 0.71, 95%CI: 0.58-0.86; OR = 0.75, 95%CI: 0.63-0.90; OR = 0.63, 95%CI: 0.44-0.91; OR = 0.70, 95%CI: 0.58-0.84, respectively). Our meta-analysis confirmed MICA-A6 could be responsible for BD in three ethnic regions and should probably be treated as a risk factor for BD. MICA-A4, A5, A5.1, and A9 could be regarded as protective factors, especially in the Middle East and East Asia.

Associations of MICA Polymorphisms with Inflammatory Rheumatic Diseases

Inflammatory rheumatic diseases are characterized by inflammation resulting from the immune dysregulation that usually attacks joints, skin and internal organs. Many of them are considered as complex disease that may be predisposed by multiple genes and/or genetic loci, and triggered by environmental factors such as microbiome and cellular stress. The major histocompatibility complex class I chain-related gene A (MICA) is a highly polymorphic gene that encodes protein variants expressed under cellular stress conditions, and these MICA variants play important roles in immune activation and surveillance. Recently, accumulating evidences from both genetic and functional studies have suggested that MICA polymorphisms may be associated with various rheumatic diseases, and the expression of MICA variants may attribute to the altered immune responses in the diseases. The objective of this review is to discuss potential genetic associations and pathological relevance of MICA in inflammatory rheumatic diseases that may help us to understand pathogenesis contributing to the development of these diseases.

The immunogenetics of Behçet's disease: A comprehensive review

Behçet's disease is a chronic multisystem inflammatory disorder characterized mainly by recurrent oral ulcers, ocular involvement, genital ulcers, and skin lesions, presenting with remissions and exacerbations. It is thought that both environmental and genetic factors contribute to its onset and development. Although the etiology of Behçet's disease remains unclear, recent immunogenetic findings are providing clues to its pathogenesis. In addition to the positive association of HLA-B*51, which was identified more than four decades ago, and which has since been confirmed in multiple populations, recent studies report additional independent associations in the major histocompatibility complex class I region. HLA-B*15, -B*27, -B*57, and -A*26 are independent risk factors for Behçet's disease, while HLA-B*49 and -A*03 are independent class I alleles that are protective for Behçet's disease. Genome-wide association studies have identified associations with genome-wide significance (P < 5 × 10(-8)) in the IL23R-IL12RB2, IL10, STAT4, CCR1-CCR3, KLRC4, ERAP1, TNFAIP3, and FUT2 loci. In addition, targeted next-generation sequencing has revealed the involvement of rare nonsynonymous variants of IL23R, TLR4, NOD2, and MEFV in Behçet's disease pathogenesis. Significant differences in gene function or mRNA expression associated with the risk alleles of the disease susceptibility loci suggest which genes in a disease-associated locus influence disease pathogenesis. These genes encompass both innate and adaptive immunity and confirm the importance of the predominant polarization towards helper T cell (Th) 1 versus Th2 cells, and the involvement of Th17 cells. In addition, epistasis observed between HLA-B*51 and the risk coding haplotype of the endoplasmic reticulum-associated protease, ERAP1, provides a clue that an HLA class I-peptide presentation-based mechanism contributes to this complex disease.

A comparative study of the genetics of Behcet's disease in Iraq: international collaboration to transfer clinical and laboratory skills to Baghdad medical school and hospitals

A collaborative project funded by the Iraqi Research Fellowship Programme of the Council for Assisting Refugee Academics was set up to transfer laboratory and clinical skills in between three clinical research teams in the UK, Jordan and Iraq. The project was set up to study the genetics of the potentially debilitating condition, Behçet's Disease (BD). Blood samples were collected from: 38 BD patients, 28 patients with oral ulcers not related to BD and 32 healthy controls. All samples were analysed using Micro SSP HLA Class I B locus kit (B locus, generic). Logistic regression analysis revealed that samples positive for HLA-B51 were 7.4 times more likely to have BD than the healthy control subjects. The results of this study make a valuable addition to the scientific literature. Additional valuable outcomes include the intellectual exchange and transfer of skills in between the collaborating teams, which led to the establishment of an international research collaboration.

Genetic susceptibility to Behcet's disease: role of genes belonging to the MHC region

OBJECTIVE

To review the progress in the field of MHC-related genetic susceptibility to Behçet's disease (BD).

METHOD

Systematic review of the English literature between 1 January 1980 and 31 January 2010 using Medline. Case-control, population-based, observational cohort studies investigating the association between BD and HLA-B*51 subtypes, classical and non-classical HLA alleles and other HLA-related genes were selected. The geographical distribution of BD and these susceptibility genes was also taken into consideration. Case and familial case reports were excluded except for case series with more than two patients.

RESULTS

Ninety articles plus 17 obtained from other sources were included in the systematic review. We have found high evidence that a core component of genetic susceptibility to BD is within the MHC region being primarily related to an HLA-B*51 subtype: HLA-B*5101/B*510101. Moreover, HLA-A*26, HLA-B*15, HLA-B*5701 and TNF-α -1031C were independently associated with BD. Data suggest that other HLA (HLA-C, HLA-DR) and HLA-related [MHC Class I chain-related gene A (MIC-A), TNF-α] genes may play a role in BD co-susceptibility or pathogenesis. Finally, the distinctive geographical distribution of BD suggested an evolutionary selection of HLA-B*51 subtypes as the major susceptibility factors for BD.

CONCLUSION

Further studies must be addressed to clarify the functional relevance of the different genes found to be associated with disease susceptibility and the potential interactions between genes located within and outside the MHC region.

Association of Major Histocompatibility Complex Class I Chain-Related Gene A and HLA-B Alleles with Behçet's Disease in Turkey

PURPOSE

Behçet's disease (BD) is known to be associated with HLA-B*51 in many different ethnic groups. Recently, the major histocompatibility complex class I chain-related gene A (MICA), located near the HLA-B gene, has been proposed as a candidate gene for BD susceptibility in several ethnic groups. To compare the relative contribution of MICA polymorphisms and HLA-B*51 to BD in different ethnic groups, we studied MICA polymorphisms in Turkish BD patients.

METHODS

Thirty-three Turkish BD patients and 65 healthy controls were enrolled for analysis of polymorphisms in the extracellular domains of MICA.

RESULTS

The phenotype frequencies of MICA*009 were significantly higher in BD patients (75.8%) than in controls (29.2%) (P = 0.000015). HLA-B*51 was also significantly more frequent in BD patients (81.8%) than in controls (29.2%) (P = 0.0000007). A strong association existed between MICA*009 and HLA-B*51. To assess the confounding effect of MICA*009 on HLA-B*51, we performed a stratification analysis that showed that BD was distinctly associated only with HLA-B*51.

CONCLUSION

Our results indicate that the major susceptibility gene for BD is HLA-B*51 and that the association between MICA*009 and BD arises from a strong linkage disequilibrium with HLA-B*51. However, we suggest that MICA*009 likely elicits an immune effect secondary to BD.

Association of an Extended Haplotype of HLA Class I Alleles and Their Flanking Microsatellites with Spondyloarthropathies in South Indian Patients

Spondyloarthropathy (SpA) is a complex autoimmune disease known to have an association with the HLA system. The aims of the present study were to compare the suballelic association of HLA-B27 and other HLA class I genes with microsatellite markers spanning the HLA class I region in the South Indian population of Kerala. The five microsatellites were C1_2_A (D6S2793), C1_2_5 (D6S2811), C1_4_1 (D6S2927), MIB (D6S2810), and STR-MICA. HLA typing was performed in 67 SpA patients and 77 ethnically matched healthy controls by polymerase chain reaction using sequence-specific primers, whereas fluorescence-labeled microsatellites were analyzed using GeneScan analysis. There was a significant association of HLA-B27 and Cw*02 with SpA, whereas B*44 had a negative association with the disease. Only two HLA-B27 subtypes, B*2704 and B*2705, were observed in the South Indian population. We were able to successfully predict the major B27 subtype B*2705 based on the C1_2_5 microsatellite. A significant association of different alleles of all the microsatellite markers with SpA was observed. An extended six-locus haplotype, B*2705-Cw*02-STR-MICA(A4)-C1_4_1 (213 bp)-C1_2_5 (178 bp)-MIB (340 bp), was significantly associated with SpA.

Frequencies of HLA-A, HLA-B, HLA-DR, and HLA-DQ phenotypes in the United Arab Emirates population

The high degree of polymorphism of the human leukocyte antigen (HLA) system provides means for the study of diversity in different populations. The aim of this work is to study the HLA phenotype frequencies in the United Arab Emiratis in comparison with other geographically related Arabs, Iranians, and Asians, all living in the United Arab Emirates (UAE). Healthy blood donors and potential kidney or bone marrow donors were typed for HLA class I (n = 1880) and class II (n = 2022). Only one representative member of each family was included to avoid bias. UAE Emiratis, Arabs of Arabian Gulf Peninsula (AGP), Arabs of South Mediterranean (SMR), North African Arabs (NA), Iranians, and Asians. HLA typing was done by microlymphocytotoxicity method and/or low-resolution polymerase chain reaction-sequence-specific primer techniques. As an individual antigen, HLA-A2 had the highest frequency in all populations studied, however, the frequency of the broad antigen A19 surpassed A2 in all the groups except the AGP Arabs and Iranians. B5 was the predominant B antigen in all groups except the SMR and Asians. Amongst the class II broad antigens, DR2 was the most frequent antigen in UAE, AGP Arabs, Iranians, and Asians. The overall frequency of DQ1 was high in all groups except the SMR Arabs who had an almost equal distribution of DQ1 and DQ3. In conclusion, this study indicates that the most frequent antigens in the UAE population are HLA-A19, HLA-A2, HLA-B5, and HLA-DR2. It also sheds light on the similarities between the UAE Emiratis, AGP Arabs, Iranians, and Asians, specially the predominance of DR2 of the class II antigens.

Mapping the HLA association in Behçet's disease: a role for tumor necrosis factor polymorphisms?

OBJECTIVE

Experimental evidence suggests that inappropriate regulation of tumor necrosis factor alpha (TNF alpha) may play a role in the pathogenesis of Behçet's disease (BD). This is supported by recent reports highlighting the efficacy of anti-TNF alpha agents in the treatment of this disease. The TNF gene is encoded in the class III region of the HLA complex adjacent to HLA-B. This genetic proximity to a gene that is already widely implicated in disease susceptibility led us to investigate the association between TNF promoter polymorphisms and susceptibility to BD.

METHODS

We studied 133 UK white Caucasoid patients with BD and 354 healthy controls. We attempted to dissect the contribution of individual polymorphisms in this gene-dense region by linkage disequilibrium mapping across 6 adjacent genes.

RESULTS

We report a novel association with the TNF promoter allele TNF-1031C. Subsequent analysis identified 2 extended HLA haplotypes associated with BD. One of them contained the previously recognized susceptibility gene HLA-B*51, while the other was defined by HLA-B*5701. Both of these haplotypes contained the TNF promoter polymorphism -1031C, an allele that was associated with disease even in individuals who did not carry either HLA-B*51 or HLA-B*5701.

CONCLUSION

The TNF-1031C allele is independently associated with susceptibility to BD in Caucasoid patients. Further studies will be required to determine the functional effects of this polymorphism, its influence in disease pathogenesis, and its role in other ethnic groups.