The BTNL2 A allele variant is frequent in Danish patients with sarcoidosis

The role of the host-microbiome and metabolomics in sarcoidosis

Sarcoidosis is a complex inflammatory fibrotic disease that affects multiple organ systems. It is characterized by the infiltration of lymphocytes and mononuclear phagocytes, which form non-caseating granulomas in affected organs. The lungs and intrathoracic lymph nodes are the most commonly affected organs. The underlying cause of sarcoidosis is unknown, but it is believed to occur in genetically predisposed individuals who are exposed to pathogenic organisms, environmental contaminants, or self and non-self-antigens. Recent research has suggested that the microbiome may play a role in the development of respiratory conditions, including sarcoidosis. Additionally, metabolomic studies have identified potential biomarkers for monitoring sarcoidosis progression. This review will focus on recent microbiome and metabolomic findings in sarcoidosis, with the goal of shedding light on the pathogenesis and possible diagnostic and therapeutic approaches.

SNP Variants in Major Histocompatibility Complex Are Associated with Sarcoidosis Susceptibility-A Joint Analysis in Four European Populations

Sarcoidosis is a multiorgan inflammatory disorder with heritability estimates up to 66%. Previous studies have shown the major histocompatibility complex (MHC) region to be associated with sarcoidosis, suggesting a functional role for antigen-presenting molecules and immune mediators in the disease pathogenesis. To detect variants predisposing to sarcoidosis and to identify genetic differences between patient subgroups, we studied four genes in the MHC Class III region (LTA, TNF, AGER, BTNL2) and HLA-DRA with tag-SNPs and their relation to HLA-DRB1 alleles. We present results from a joint analysis of four study populations (Finnish, Swedish, Dutch, and Czech). Patients with sarcoidosis (n = 805) were further subdivided based on the disease activity and the presence of Löfgren’s syndrome. In a joint analysis, seven SNPs were associated with non-Löfgren sarcoidosis (NL; the strongest association with rs3177928, P = 1.79E−07, OR = 1.9) and eight with Löfgren’s syndrome [Löfgren syndrome (LS); the strongest association with rs3129843, P = 3.44E−12, OR = 3.4] when compared with healthy controls (n = 870). Five SNPs were associated with sarcoidosis disease course (the strongest association with rs3177928, P = 0.003, OR = 1.9). The high linkage disequilibrium (LD) between SNPs and an HLA-DRB1 challenged the result interpretation. When the SNPs and HLA-DRB1 alleles were analyzed together, independent association was observed for four SNPs in the HLA-DRA/BTNL2 region: rs3135365 (NL; P = 0.015), rs3177928 (NL; P < 0.001), rs6937545 (LS; P = 0.012), and rs5007259 (disease activity; P = 0.002). These SNPs act as expression quantitative trait loci (eQTL) for HLA-DRB1 and/or HLA-DRB5. In conclusion, we found novel SNPs in BTNL2 and HLA-DRA regions associating with sarcoidosis. Our finding further establishes that polymorphisms in the HLA-DRA and BTNL2 have a role in sarcoidosis susceptibility. This multi-population study demonstrates that at least a part of these associations are HLA-DRB1 independent (e.g., not due to LD) and shared across ancestral origins. The variants that were independent of HLA-DRB1 associations acted as eQTL for HLA-DRB1 and/or -DRB5, suggesting a role in regulating gene expression.

The BTNL2 G16071A gene polymorphism increases granulomatous disease susceptibility: A meta-analysis including FPRP test of 8710 participants

OBJECTIVE

The butyrophilin-like 2 (BTNL2) G16071A gene polymorphism has been implicated in the susceptibility to granulomatous diseases, but the results were inconclusive. The objective of the current study was to precisely explore the relationship between BTNL2 G16071A gene polymorphism and granulomatous disease susceptibility by the meta-analysis including false-positive report probability (FPRP) test.

METHODS

A systematic literature search in the PubMed, Embase, and Wanfang databases, China National Knowledge Internet, and commercial Internet search engines was conducted to identify studies published up to April 1, 2016. The odds ratio (OR) with 95% confidence interval (CI) was used to assess the effect size. Statistical analysis was conducted using the STATA 12.0 software and FPRP test sheet.

RESULTS

In total, all 4324 cases and 4386 controls from 14 eligible studies were included in the current meta-analysis. By the overall meta-analysis, we found a significant association between BTNL2 G16071A gene polymorphism and granulomatous disease susceptibility (A vs G: OR = 1.25, 95% CI = 1.07-1.45, P = 0.005). The meta-regression analyses showed that a large proportion of the between-study heterogeneity was significantly attributed to the ethnicity (A vs G, P = 0.013) and the types of granulomatous diseases (A vs G, P = 0.002). By the subgroup meta-analysis, the BTNL2 G16071A gene polymorphism was associated with granulomatous disease susceptibility in Caucasians (A vs G: OR = 1.37, 95% CI = 1.18-1.58, P < 0.001). Moreover, a significant relationship between the BTNL2 G16071A gene polymorphism and sarcoidosis susceptibility (A vs G: OR = 1.52, 95% CI = 1.39-1.66, P < 0.001) was found. However, to avoid the "false-positive report," we further investigated the significant associations observed in the present meta-analysis by the FPRP test. Interestingly, the results of FPRP test indicated that the BTNL2 G16071A gene polymorphism was truly associated with sarcoidosis susceptibility (A vs G, FPRP < 0.001). Additionally, the FPRP test confirmed that the BTNL2 G16071A gene polymorphism was associated only with granulomatous disease susceptibility among Caucasians (A vs G, FPRP < 0.001) at the level of a prior probability, which was 0.001.

CONCLUSION

The meta-analysis indicated that BTNL2 G16071A gene polymorphism may as a likelihood factor contributed to granulomatous disease susceptibility, especially increasing the sarcoidosis susceptibility. In addition, the polymorphism may be greatly associated with likelihood of granulomatous diseases among Caucasians.

Immunogenetics of Disease-Causing Inflammation in Sarcoidosis

Sarcoidosis is a systemic inflammatory disorder characterised by tissue infiltration by mononuclear phagocytes and lymphocytes with associated non-caseating granuloma formation. Originally described as a disorder of the skin, sarcoidosis can involve any organ with wide-ranging clinical manifestations and disease course. Recent studies have provided new insights into the mechanisms involved in disease pathobiology, and we now know that sarcoidosis has a clear genetic basis largely involving human leukocyte antigen (HLA) genes. In contrast to Mendelian-monogenic disorders--which are generally due to specific and relatively rare mutations often leading to a single amino acid change in an encoded protein--sarcoidosis results from genetic variations relatively common in the general population and involving multiple genes, each contributing an effect of varying magnitude. However, an individual may have the necessary genetic profile and yet the disease will not develop unless an environmental or infectious factor is encountered. Genetics appears also to contribute to the huge variability in clinical phenotype and disease behaviour. Moreover, it has been established that sarcoidosis granulomatous inflammation is a highly polarized T helper 1 immune response that starts with an antigenic stimulus followed by T cell activation via a classic HLA class II-mediated pathway. A complex network of lymphocytes, macrophages, and cytokines is pivotal in the orchestration and evolution of the granulomatous process. Despite these advances, the aetiology of sarcoidosis remains elusive and its pathogenesis incompletely understood. As such, there is an urgent need for a better understanding of disease pathogenesis, which hopefully will translate into the development of truly effective therapies.

Granuloma genes in sarcoidosis: what is new?

PURPOSE OF REVIEW

Nonnecrotizing granulomas in the affected organ are the hallmark of sarcoidosis. This review summarizes most recent genetic findings in sarcoidosis with a focus on genes that might influence granuloma formation or resolution. Specific results in multiple ethnic groups and certain clinical subphenotypes, such as extra-pulmonary organ involvement, are discussed.

RECENT FINDINGS

Associations of genetic variants in antigen-presenting molecules (HLA-DRB1) were shown to confer risk to sarcoidosis and certain disease phenotypes in populations of different ethnic origins. Specific DRB1 alleles, such as *0301 and *0302, appear to confer protection against chronic disease, but in an ethnic-specific manner illustrating the extensive genetic heterogeneity and complexity at this locus. Mechanistic studies of putative sarcoid antigens lend further credence to a role of HLA-DRB1 in disease pathogenesis. With relevance to granuloma formation, genes involved in apoptotic processes and immune cell activation were further confirmed (ANXA11 and BTNL2) in multiple ethnicities; others were newly identified (XAF1). Linking mechanism to clinical application, a TNF variant was shown to correlate with anti-TNF response in sarcoidosis patients.

SUMMARY

The investigation of known and novel risk variants for sarcoidosis and specific clinical phenotypes in various ethnicities highlights the genetic complexity of the disease. Detailed subanalysis of disease phenotypes revealed the potential for prediction of extra-pulmonary organ involvement and therapy response based on the patient's genotype.

Identification of Immune-Relevant Factors Conferring Sarcoidosis Genetic Risk

RATIONALE

Genetic variation plays a significant role in the etiology of sarcoidosis. However, only a small fraction of its heritability has been explained so far.

OBJECTIVES

To define further genetic risk loci for sarcoidosis, we used the Immunochip for a candidate gene association study of immune-associated loci.

METHODS

Altogether the study population comprised over 19,000 individuals. In a two-stage design, 1,726 German sarcoidosis cases and 5,482 control subjects were genotyped for 128,705 single-nucleotide polymorphisms using the Illumina Immunochip for the screening step. The remaining 3,955 cases, 7,514 control subjects, and 684 parents of affected offspring were used for validation and replication of 44 candidate and two established risk single-nucleotide polymorphisms.

MEASUREMENTS AND MAIN RESULTS

Four novel susceptibility loci were identified with genome-wide significance in the European case-control populations, located on chromosomes 12q24.12 (rs653178; ATXN2/SH2B3), 5q33.3 (rs4921492; IL12B), 4q24 (rs223498; MANBA/NFKB1), and 2q33.2 (rs6748088; FAM117B). We further defined three independent association signals in the HLA region with genome-wide significance, peaking in the BTNL2 promoter region (rs5007259), at HLA-B (rs4143332/HLA-B*0801) and at HLA-DPB1 (rs9277542), and found another novel independent signal near IL23R (rs12069782) on chromosome 1p31.3.

CONCLUSIONS

Functional predictions and protein network analyses suggest a prominent role of the drug-targetable IL23/Th17 signaling pathway in the genetic etiology of sarcoidosis. Our findings reveal a substantial genetic overlap of sarcoidosis with diverse immune-mediated inflammatory disorders, which could be of relevance for the clinical application of modern therapeutics.

BTNL2 gene polymorphism and sarcoidosis susceptibility: a meta-analysis

BACKGROUND

Butyrophilin-like 2 (BTNL2) rs2076530 gene polymorphism has been implicated in susceptibility to sarcoidosis. However, results from previous studies are not consistent. To assess the association of BTNL2 polymorphism and sarcoidosis susceptibility, a meta-analysis was performed.

METHODS

PubMed, Embase were searched for eligible case-control studies. Data were extracted and pooled odds ratios (OR) with 95% confidence intervals (CI) were calculated.

RESULTS

Ten studies involving a total of 3303 cases and 2514 controls were included in this meta-analysis. Combined data indicated that BTNL2 rs2076530 polymorphism was associated with sarcoidosis susceptibility in allelic model (A vs. G, OR = 1.59, 95%CI: 1.47-1.72), dominant model (AA + AG vs. GG, OR = 2.10, 95%CI: 1.67-2.65), and recessive model (AA vs. AG + GG, OR = 1.93, 95%CI: 1.49-2.50).

CONCLUSIONS

This meta-analysis indicates that BTNL2 rs2076530 polymorphism contributes to the risk of sarcoidosis.

Interleukin-12 family cytokines and sarcoidosis

Sarcoidosis is a systemic granulomatous disease predominantly affecting the lungs. It is believed to be caused by exposure to pathogenic antigens in genetically susceptible individuals but the causative antigen has not been identified. The formation of non-caseating granulomas at sites of ongoing inflammation is the key feature of the disease. Other aspects of the pathogenesis are peripheral T-cell anergy and disease progression to fibrosis. Many T-cell-associated cytokines have been implicated in the immunopathogenesis of sarcoidosis, but it is becoming apparent that IL-12 cytokine family members including IL-12, IL-23, IL-27, and IL-35 are also involved. Although the members of this unique cytokine family are heterodimers of similar subunits, their biological functions are very diverse. Whilst IL-23 and IL-12 are pro-inflammatory regulators of Th1 and Th17 responses, IL-27 is bidirectional for inflammation and the most recent family member IL-35 is inhibitory. This review will discuss the current understanding of etiology and immunopathogenesis of sarcoidosis with a specific focus on the bidirectional impact of IL-12 family cytokines on the pathogenesis of sarcoidosis.

Association of six well-characterized polymorphisms in TNF-α and TNF-β genes with sarcoidosis: a meta-analysis

Backgrounds

In this study, we aimed to investigate the association of six well-characterized polymorphisms in tumor necrosis factor alpha and beta (TNF-α and TNF-β) genes with the risk for sarcoidosis via a comprehensive meta-analysis.

Methods And Findings

The electronic MEDLINE (Ovid) and PubMed databases covering the period from the earliest possible year to June 2013 were searched. Total 13 qualified articles including 1584 patients with sarcoidosis and 2636 controls were recruited. The data were analyzed by RevMan software, and risk estimates were expressed as odds ratios (ORs) and 95% confidence intervals (95% CIs). Analyses of the full data set failed to identify any significant association of TNF-α gene -307A (OR=1.25; 95% CI: 0.98-1.59), -1031C (OR=0.88; 95% CI: 0.71-1.1), -863A (OR=0.89; 95% CI: 0.72-1.11), -238A (OR=0.97; 95% CI: 0.71-1.32), and -857T (OR=1.14; 95% CI: 0.74-1.77) alleles, but a significant association for TNF-β 252A allele (OR=1.65; 95%CI = 1.33-2.04; P<0.00001). Under a random-effects allelic model, there was marginally significant increased risk of sarcoidosis for -307A allele among Caucasians (OR=1.25; 95% CI: 0.96-1.62; P=0.09) but not among Asians (OR=2.12; 95% CI: 0.31-14.27; P=0.44). There was a low probability of publication bias as reflected by the fail-safe number.

Conclusions

This meta-analysis extended previous findings on the association between the TNF-α and TNF-β genetic polymorphisms and sarcoidosis, by showing that the TNF-β gene A252G polymorphism might be a potential risk factor for the development of sarcoidosis.

Replication of genetic loci for sarcoidosis in US black women: data from the Black Women's Health Study

In the United States, incidence and mortality from sarcoidosis, a chronic, granulomatous disease, are increased in black women. In data from the Black Women's Health Study, a follow-up of US black women, we assessed two SNPs (rs2076530 and rs9268480) previously identified in the BTNL2 gene (chromosome 6p21), of which rs4424066 and rs3817963 are perfect proxies, to determine if they represent independent signals of disease risk. We also assessed whether local ancestry in four genomic regions previously identified through admixture mapping was associated with sarcoidosis. Finally, we assessed the relation of global percent African ancestry to risk. We conducted a nested case-control study of 486 sarcoidosis cases and 943 age- and geography-matched controls. Both BTNL2 SNPs were associated with risk of sarcoidosis in separate models, but in a combined analysis the increased risk was due to the A-allele of the rs3817963 SNP; each copy of the A-allele was associated with a 40 % increase in risk of sarcoidosis (p = 0.02) and was confirmed by our haplotypic analysis. Local African ancestry around the rs30533 ancestry informative marker at chromosome 5q31 was associated with a 29 % risk reduction (p = 0.01). Therefore, we adjusted our analysis of global African ancestry for number of copies of African alleles in rs30533. Subjects in the highest quintile of percent African ancestry had a 54 % increased risk of sarcoidosis. The present results from a population of African-American women support the role of the BTNL2 gene and the 5q31 locus in the etiology of sarcoidosis, and also demonstrate that percent African ancestry is associated with disease risk.

BTNL2 gene polymorphism associations with susceptibility and phenotype expression in sarcoidosis

A functional polymorphism within butyrophilin-like 2 (BTNL2) gene has been described as a potential risk factor for sarcoidosis. The association between chronicity and the rs2076530 SNP A allele has also been reported. This study evaluates the BTNL2 rs2076530 G/A allele associations with sarcoidosis susceptibility and disease evolution in a Portuguese cohort of patients. A case-control study of 151 patients and 150 controls was performed. Allele frequencies were compared with Chi-square test in a univariate analysis and with logistic regression in a multivariate analysis. BTNL2 rs206530 A allele frequencies were significantly higher in sarcoidosis with no linkage disequilibrium with HLA-DRB1 alleles, except in the subgroup of patients with Löfgren syndrome where the determinant allele was HLA-DRB1*03. The A allele was also increased in those with isolated thoracic disease, with no differences regarding radiological stages or disease evolution. HLA-DRB1*03, besides the association with Löfgren syndrome was significantly related with disease resolution. Our data confirms the association of BTNL2 rs2076530 A allele with sarcoidosis susceptibility in a Portuguese population. We found independent genetic risk factors in clinically distinct disease phenotypes: BTNL2 rs2076530 A allele in patients without Löfgren syndrome or with isolated thoracic disease, and HLA-DRB1*03 in Löfgren syndrome or disease resolution.

HLA Immune Function Genes in Autism

The human leukocyte antigen (HLA) genes on chromosome 6 are instrumental in many innate and adaptive immune responses. The HLA genes/haplotypes can also be involved in immune dysfunction and autoimmune diseases. It is now becoming apparent that many of the non-antigen-presenting HLA genes make significant contributions to autoimmune diseases. Interestingly, it has been reported that autism subjects often have associations with HLA genes/haplotypes, suggesting an underlying dysregulation of the immune system mediated by HLA genes. Genetic studies have only succeeded in identifying autism-causing genes in a small number of subjects suggesting that the genome has not been adequately interrogated. Close examination of the HLA region in autism has been relatively ignored, largely due to extraordinary genetic complexity. It is our proposition that genetic polymorphisms in the HLA region, especially in the non-antigen-presenting regions, may be important in the etiology of autism in certain subjects.