Epistatic interaction between BANK1 and BLK in rheumatoid arthritis: results from a large trans-ethnic meta-analysis

Identification of epistatic SNP combinations in rheumatoid arthritis using LAMPLINK and Japanese cohorts

Genome-wide association studies have enabled the identification of important genetic factors in many trait studies. However, only a fraction of the heritability can be explained by known genetic factors, even in the most common diseases. Genetic loci combinations, or epistatic contributions expressed by combinations of single nucleotide polymorphisms (SNPs), have been argued to be one of the critical factors explaining some of the missing heritability, especially in oligogenic/polygenic diseases. Rheumatoid arthritis (RA) is a complex disease with more than 100 reported SNP associations, as well as various HLA haplotypes and amino acids; however, many associations between RA and inter-chromosomal SNP combinations are unknown. To discover novel associations of epistatic interactions with high odds ratios in RA, we applied the LAMPLINK method, a systematic enumerative procedure for identifying high-order SNP combinations, to a Japanese RA cohort (discovery cohort; 4024 patients with RA and 7731 controls). We validated the identified associations in a different Japanese cohort (validation cohort; 810 RA patients and 6303 controls). In this study, we identified 90 significant genetic associations in the discovery cohort. Among these, 74 (82.2%) associations were replicated in the validation cohort, and eight combinations were inter-chromosomal, all of which comprised rs7765379 or rs35265698 located in the HLA region. These two SNPs exhibited strong correlations with valine at amino acid position 11 in HLA-DRB1 (HLA-DRB1-11-Val). Finally, we discovered that rs9624 showed an association with RA through an epistatic interaction with HLA-DRB1-11-Val. Overall, LAMPLINK showed high reliability for identifying epistatic genetic contributions hidden in complex traits.

Omnibus testing approach for gene-based gene-gene interaction

Genetic interaction is considered as one of the main heritable component of complex traits. With the emergence of genome-wide association studies (GWAS), a collection of statistical methods dedicated to the identification of interaction at the SNP level have been proposed. More recently, gene-based gene-gene interaction testing has emerged as an attractive alternative as they confer advantage in both statistical power and biological interpretation. Most of the gene-based interaction methods rely on a multidimensional modeling of the interaction, thus facing a lack of robustness against the huge space of interaction patterns. In this paper, we study a global testing approaches to address the issue of gene-based gene-gene interaction. Based on a logistic regression modeling framework, all SNP-SNP interaction tests are combined to produce a gene-level test for interaction. We propose an omnibus test that takes advantage of (1) the heterogeneity between existing global tests and (2) the complementarity between allele-based and genotype-based coding of SNPs. Through an extensive simulation study, it is demonstrated that the proposed omnibus test has the ability to detect with high power the most common interaction genetic models with one causal pair as well as more complex genetic models where more than one causal pair is involved. On the other hand, the flexibility of the proposed approach is shown to be robust and improves power compared to single global tests in replication studies. Furthermore, the application of our procedure to real datasets confirms the adaptability of our approach to replicate various gene-gene interactions.

Genetics of rheumatoid arthritis

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease involving symmetric joints and is generally characterized by persistent pain, tenderness, and destruction of joints. The vast majority of RA patients produce autoantibodies, and immune cell involvement in disease development is well recognized, as is the contribution of other types of cells in synovial tissue, like fibroblasts. It is known that there are major genetic associations with the HLA locus, while multiple non-HLA genetic variants display relatively low risk of RA. Both HLA and non-HLA associations suggest that the profiles of genetic associations for autoantibody-positive vs. autoantibody-negative RA are different. Several alleles of HLA-DRB1 are associated with high risk for autoantibody-positive RA, with the strongest risk characterized by valine at position 11 of the protein sequence (HLA-DRB1*04 and *10 alleles). There is a strong protective effect for the risk of autoantibody-positive RA associated with HLA-DRB1*13 alleles. Although major genetic associations have been known for several years, understanding of the specific mechanisms in the development of increased risk of RA for these variations is work in progress. Current studies focus on the binding of immune receptors involved in recognition of putative peptides in activation of T cells, as well as investigation of cell signaling mechanisms. At least a part of RA risk could be explained by gene-gene and gene-environment interactions. There are currently more than 150 candidate loci with polymorphisms that associate with RA, mainly related to seropositive disease, and new discoveries are anticipated in the future from investigation of diverse human populations. This new research will help create a strong foundation for the continuing process of integrating genetic, epigenetic, transcriptomic, and proteomic data in studies of RA.

The Role of BANK1 in B Cell Signaling and Disease

The B cell scaffold protein with ankyrin repeats (BANK1) is expressed primarily in B cells and with multiple but discrete roles in B cell signaling, including B cell receptor signaling, CD40-related signaling, and Toll-like receptor (TLR) signaling. The gene for BANK1, located in chromosome 4, has been found to contain genetic variants that are associated with several autoimmune diseases and also other complex phenotypes, in particular, with systemic lupus erythematosus. Common genetic variants are associated with changes in BANK1 expression in B cells, while rare variants modify their capacity to bind efferent effectors during signaling. A BANK1-deficient model has shown the importance of BANK1 during TLR7 and TLR9 signaling and has confirmed its role in the disease. Still, much needs to be done to fully understand the function of BANK1, but the main conclusion is that it may be the link between different signaling functions within the B cells and they may act to synergize the various pathways within a cell. With this review, we hope to enhance the interest in this molecule.

BLK and BANK1 variants and interactions are associated with susceptibility for primary Sjögren's syndrome and with some clinical features

BLK and BANK1 in primary Sjögren's syndrome (pSS) have scarcely been evaluated and the results are inconclusive. The aim of our study was to determine whether single nucleotide variants (SNVs) located within BLK or BANK1 are associated with susceptibility, clinical and serological features, and smoking in pSS. BLK rs13277113A/G, BANK1 rs10516487G/A and rs3733197G/A were genotyped in 203 cases and 424 controls using a TaqMan® SNP genotyping assay. The BLK rs13277113A allele showed association with pSS under the allelic (OR 1.35, p = 0.02), and recessive (OR 1.83, p = 0.003) model, while, BANK1 rs3733197G/A showed association under the dominant model (OR 2.90, p = 0.043). Interactions between BANK1 and BLK genotypes also showed association (OR 2.36, p < 0.0001). In addition, BLK rs13277113A/G was associated with protection against arthritis and BANK1 rs10516487G/A with both arthritis and keratoconjunctivitis sicca, meanwhile, BANK1 rs3733197G/A was associated with smoking in patients with pSS. This is the first study to describe an association between BLK and susceptibility to pSS in a Latin-American population. Our data also shows a first evidence of association between interactions of BLK and BANK1 in pSS, and association of BLK and BANK1with arthritis, keratoconjunctivitis sicca and smoking in patients with pSS.

Genome-wide association study identifies risk loci for progressive chronic lymphocytic leukemia

Prognostication in patients with chronic lymphocytic leukemia (CLL) is challenging due to heterogeneity in clinical course. We hypothesize that constitutional genetic variation affects disease progression and could aid prognostication. Pooling data from seven studies incorporating 842 cases identifies two genomic locations associated with time from diagnosis to treatment, including 10q26.13 (rs736456, hazard ratio (HR) = 1.78, 95% confidence interval (CI) = 1.47-2.15; P = 2.71 × 10-9) and 6p (rs3778076, HR = 1.99, 95% CI = 1.55-2.55; P = 5.08 × 10-8), which are particularly powerful prognostic markers in patients with early stage CLL otherwise characterized by low-risk features. Expression quantitative trait loci analysis identifies putative functional genes implicated in modulating B-cell receptor or innate immune responses, key pathways in CLL pathogenesis. In this work we identify rs736456 and rs3778076 as prognostic in CLL, demonstrating that disease progression is determined by constitutional genetic variation as well as known somatic drivers.

Rare genetic variants in systemic autoimmunity

Autoimmune disease is a substantial cause of morbidity and is strongly influenced by genetic risk. Extensive efforts have characterized the overall genetic basis of many autoimmune diseases, typically by investigation of common variants. While these common variants have modest effects and may cumulatively predispose to disease, it is also increasingly apparent that rare variants have significantly greater effect on phenotype and are likely to contribute to autoimmune disease. Recent advances have illustrated the next fundamental step in elucidating the genetic basis of autoimmunity, moving beyond association to demonstrate the functional consequences of these variants.

An update on genetic susceptibility in lupus nephritis

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by multiple system involvement and positive serum autoantibodies. Lupus nephritis (LN) is the most common and serious complication of SLE, and it is the main cause of death in patients with SLE. Abnormalities in the immune system lead to LN and involve a variety of cells (T cells, B cells, macrophages, NK cells, etc.), cytokines (interleukin, tumor necrosis factor α, etc.) and their related pathways. Previous studies have shown that the interactions of genetic, epigenetic and environmental factors contribute to the pathogenesis and development of LN. In recent years, one genome-wide association study (GWAS) and a number of gene association studies have explored the susceptibility genes of LN, including immunization-, inflammation-, adhesion- and other pathway-related genes. These genes participate in or suggest the pathogenesis and progression of LN. In this review, we summarize the genetic susceptibility of LN and discuss the possible mechanism underlying the susceptibility genes of LN.

Association of BLK and BANK1 Polymorphisms and Interactions With Rheumatoid Arthritis in a Latin-American Population

Introduction

BLK has been identified as a risk factor to rheumatoid arthritis (RA) primarily in Asian or European-derived populations. However, this finding has not been evaluated in other populations such as Latin-Americans, except for Colombians. On the other hand, BANK1 single nucleotide variants (SNVs) have been scarcely studied in RA patients.

Objective

The aim of this study was to determine whether the BLK rs2736340T/C, rs13277113A/G, and BANK1 rs10516487G/A (R61H) and rs3733197G/A (A383T) polymorphisms are risk factors to RA in a sample of patients from Central Mexico.

Materials and Methods

We studied 957 women; 487 controls and 470 patients with RA by means of a TaqMan® SNP genotyping assay with fluorescent probes for the BLK rs13277113A/G, rs2736340T/C and BANK1 10516487G/A (R61H) and rs3733197G/A (A383T) variants.

Result

The BLK rs2736340T/C and rs13277113A/G variants were associated with risk for RA: C vs T; OR 1.39, p = 0.001, and G vs A; OR 1.37, p = 0.004, respectively. In addition, there was also an association between BANK1 R61H and RA: A vs G; OR 1.49, p = 0.003, but no with BANK1 A383T. We also identified an interaction significant between genotypes of BLK rs2736340T/C-BANK1 rs10516487G/A and RA: OR 1.65, p = 0.0001.

Conclusions

Our data suggest that both BLK and BANK1 confer susceptibility to RA in Mexican patients. The individual association of BANK1 rs1054857G/A with RA had not been previously reported in a particular population (except for pooled patients from several countries), therefore, our study presents the first evidence of association between this BANK1 variant and RA.

An update on genetic susceptibility in lupus nephritis

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by multiple system involvement and positive serum autoantibodies. Lupus nephritis (LN) is the most common and serious complication of SLE, and it is the main cause of death in patients with SLE. Abnormalities in the immune system lead to LN and involve a variety of cells (T cells, B cells, macrophages, NK cells, etc.), cytokines (interleukin, tumor necrosis factor α, etc.) and their related pathways. Previous studies have shown that the interactions of genetic, epigenetic and environmental factors contribute to the pathogenesis and development of LN. In recent years, one genome-wide association study (GWAS) and a number of gene association studies have explored the susceptibility genes of LN, including immunization-, inflammation-, adhesion- and other pathway-related genes. These genes participate in or suggest the pathogenesis and progression of LN. In this review, we summarize the genetic susceptibility of LN and discuss the possible mechanism underlying the susceptibility genes of LN.

Evolutionary footprint of epistasis

Variation of an inherited trait across a population cannot be explained by additive contributions of relevant genes, due to epigenetic effects and biochemical interactions (epistasis). Detecting epistasis in genomic data still represents a significant challenge that requires a better understanding of epistasis from the mechanistic point of view. Using a standard Wright-Fisher model of bi-allelic asexual population, we study how compensatory epistasis affects the process of adaptation. The main result is a universal relationship between four haplotype frequencies of a single site pair in a genome, which depends only on the epistasis strength of the pair defined regarding Darwinian fitness. We demonstrate the existence, at any time point, of a quasi-equilibrium between epistasis and disorder (entropy) caused by random genetic drift and mutation. We verify the accuracy of these analytic results by Monte-Carlo simulation over a broad range of parameters, including the topology of the interacting network. Thus, epistasis assists the evolutionary transit through evolutionary hurdles leaving marks at the level of haplotype disequilibrium. The method allows determining selection coefficient for each site and the epistasis strength of each pair from a sequence set. The resulting ability to detect clusters of deleterious mutation close to full compensation is essential for biomedical applications. These findings help to understand the role of epistasis in multiple compensatory mutations in viral resistance to antivirals and immune response.

Interaction analysis between BLK rs13277113 polymorphism and BANK1 rs3733197 polymorphism, MMEL1/TNFRSF14 rs3890745 polymorphism in determining susceptibility to rheumatoid arthritis

Two pairwise genetic interactions (B cell lymphocyte kinase (BLK) rs13277113,B cell scaffold protein with ankyrin repeats 1 (BANK1) rs3733197and BLK rs13277113 membrane metalloendopeptidase like 1 (MMEL1)/ tumor necrosis factor receptor superfamily member 14 (TNFRSF14) rs3890745) have been demonstrated in determining susceptibility to rheumatoid arthritis (RA) without replication, thus this study was performed to examine whether abovementioned genetic polymorphisms were associated with RA and further tests were performed to see whether aforementioned genetic interactions existed in RA among Chinese population. A total of 328 patients with RA and 449 healthy control subjects were included in the current study. The polymorphisms were genotyped using the ligase detection reaction-polymerase chain reaction (LDR-PCR) technology. The association of RA with each polymorphism was analyzed by multivariate logistic regression model. Interaction analysis was done by multiple methods. Significant difference in genotype distribution of BLK rs13277113 polymorphism between RA patients and healthy controls was found (p = 1.01 × 10^-2). The major allele A of BLK rs13277113 polymorphism was significantly increased in RA patients compared with controls (OR = 1.36, 95% CI = 1.08-1.71, p = 9.27 × 10^-3). Significant association of RA with the major allele A of BLK rs13277113 polymorphism under dominant model was also detected (OR = 2.74, 95% CI = 1.42-5.29, p = 2.73 × 10^-3). However, we did not find significant association between neither BANK1 rs3733197 polymorphism nor MMEL1/TNFRSF14 rs3890745 polymorphism and RA. Non-significant evidence was found for neither additive nor multiplicative interaction for these two pairwise genetic polymorphisms (BLK rs13277113-BANK1 rs3733197; BLK rs13277113-MMEL1/TNFRSF14 rs3890745). Significant association of RA with G allele of BANK1 rs3733197 polymorphism was only found among individuals carrying A/A genotype of the BLK rs13277113 polymorphism (OR = 1.49, 95% CI = 1.01-2.18, p = .04). In summary, our results indicated that the BLK rs13277113 polymorphism was involved in the genetic background of RA in Chinese population and the association of BANK1 rs3733197 polymorphism with RA was dependent on the genotype of BLK rs13277113 polymorphism, highlighting B-cell response implicated in the pathogenesis of RA.

B-cell lymphocyte kinase polymorphisms rs13277113, rs2736340, and rs4840568 and risk of autoimmune diseases: A meta-analysis

BACKGROUND

B-cell lymphocyte kinase (BLK) is an inhibitor of B cells that has an important influence on several autoimmune diseases, but there is a lack of comprehensive analysis of its association with autoimmune diseases. Hence, it is meaningful to conduct a comprehensive analysis.

METHODS

A systematic literature search was performed on the PubMed, ScienceDirect, and Web of Science databases up to June 30, 2016. The data were extracted and quality-assessed before conducting the meta-analysis. The odds ratios (ORs) and 95% confidence intervals (95% CIs) were assessed with the STATA version 12.0 software. Subgroup and sensitivity analysis were conducted to explore potential sources of heterogeneity.

RESULTS

Altogether, 33 studies with 68,874 cases and 90,684 controls, 24 studies with 31,095 cases and 39,077 controls for rs13277113, 21 studies with 26,388 cases and 40,635 controls for rs2736340, and 4 studies with 11,391 cases and 10,972 controls for rs4840568 were included in this meta-analysis. The results revealed that the BLK rs13277113 and rs2736340 polymorphisms increased the risk of autoimmune diseases in the total analysis (A vs G: OR = 1.33, 95% CI = 1.27-1.39, P < .01; T vs C: OR = 1.34, 95% CI = 1.27-1.41, P < .01), and rs4840568 was positively associated with systemic lupus erythematosus (SLE) (A vs G: OR = 1.32, 95% CI = 1.22-1.43, P = .01).

CONCLUSION

This meta-analysis shows that the BLK (rs13277113, rs2736340, rs4840568) polymorphisms may be a risk factor for developing autoimmune diseases, especially for Asian populations and SLE.

The BANK1 SLE-risk variants are associated with alterations in peripheral B cell signaling and development in humans

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the development of autoantibodies that drive disease pathogenesis. Genetic studies have associated nonsynonymous variants in the BANK1 B cell scaffolding gene with susceptibility to SLE and autoantibodies in lupus. To determine how the BANK1 SLE-risk variants contribute to the dysregulated B cell program in lupus, we performed genotype/phenotype studies in human B cells. Targeted phospho-proteomics were used to evaluate BCR/CD40 signaling in human B cell lines engineered to express the BANK1 risk or non-risk variant proteins. We found that phosphorylation of proximal BCR signaling molecules was reduced in B cells expressing the BANK1 risk protein compared to the non-risk protein. Similar to these findings, we observed decreased B cell signaling in primary B cells from genotyped healthy control subjects carrying the BANK1 risk haplotype, including blunted BCR- and CD40-dependent AKT activation. Consistent with decreased AKT activation, we found that BANK1 risk B cells expressed increased basal levels of FOXO1 protein and increased expression of FOXO1 target genes upon stimulation compared to non-risk B cells. Healthy subjects carrying the BANK1 risk haplotype were also characterized by an expansion of memory B cells. Taken together, our results suggest that the SLE susceptibility variants in the BANK1 gene may contribute to lupus by altering B cell signaling, increasing FOXO1 levels, and enhancing memory B cell development.

Immunochip Analyses of Epistasis in Rheumatoid Arthritis Confirm Multiple Interactions within MHC and Suggest Novel Non-MHC Epistatic Signals

OBJECTIVE

Studying statistical gene-gene interactions (epistasis) has been limited by the difficulties in performance, both statistically and computationally, in large enough sample numbers to gain sufficient power. Three large Immunochip datasets from cohort samples recruited in the United Kingdom, United States, and Sweden with European ancestry were used to examine epistasis in rheumatoid arthritis (RA).

METHODS

A full pairwise search was conducted in the UK cohort using a high-throughput tool and the resultant significant epistatic signals were tested for replication in the United States and Swedish cohorts. A forward selection approach was applied to remove redundant signals, while conditioning on the preidentified additive effects.

RESULTS

We detected abundant genome-wide significant (p < 1.0e-13) epistatic signals, all within the MHC region. These signals were reduced substantially, but a proportion remained significant (p < 1.0e-03) in conditional tests. We identified 11 independent epistatic interactions across the entire MHC, each explaining on average 0.12% of the phenotypic variance, nearly all replicated in both replication cohorts. We also identified non-MHC epistatic interactions between RA susceptible loci LOC100506023 and IRF5 with Immunochip-wide significance (p < 1.1e-08) and between 2 neighboring single-nucleotide polymorphism near PTPN22 that were in low linkage disequilibrium with independent interaction (p < 1.0e-05). Both non-MHC epistatic interactions were statistically replicated with a similar interaction pattern in the US cohort only.

CONCLUSION

There are multiple but relatively weak interactions independent of the additive effects in RA and a larger sample number is required to confidently assign additional non-MHC epistasis.

The SLE variant Ala71Thr of BLK severely decreases protein abundance and binding to BANK1 through impairment of the SH3 domain function

The B-lymphocyte kinase (BLK) gene is associated genetically with several human autoimmune diseases including systemic lupus erythematosus. We recently described that the genetic risk is given by two haplotypes: one covering several strongly linked single-nucleotide polymorphisms within the promoter of the gene that correlated with low transcript levels, and a second haplotype that includes a rare nonsynonymous variant (Ala71Thr). Here we show that this variant, located within the BLK SH3 domain, is a major determinant of protein levels. In vitro analyses show that the 71Thr isoform is hyperphosphorylated and promotes kinase activation. As a consequence, BLK is ubiquitinated, its proteasomal degradation enhanced and the average life of the protein is reduced by half. Altogether, these findings suggest that an intrinsic autoregulatory mechanism previously unappreciated in BLK is disrupted by the 71Thr substitution. Because the SH3 domain is also involved in protein interactions, we sought for differences between the two isoforms in trafficking and binding to protein partners. We found that binding of the 71Thr variant to the adaptor protein BANK1 is severely reduced. Our study provides new insights on the intrinsic regulation of BLK activation and highlights the dominant role of its SH3 domain in BANK1 binding.

Genetic, genomic and epigenetic studies as tools for elucidating disease pathogenesis in primary Sjögren's syndrome

Primary Sjögren's syndrome (pSS) is characterized by lymphoid infiltration of lacrimal and salivary glands leading to xerophthalmia and xerostomia. pSS is a complex disease involving both genetic and environmental risk factors. Technological advances over the past 10 years have revolutionized genetics and genomics research enabling high-throughput characterization and analysis of DNA and RNA in patient samples on a genome-wide scale. Further, application of high-throughput methods for characterization of epigenetic variation, such as DNA methylation status, is increasingly being applied to AID populations and will likely further define additional risk factors for disease risk and outcome. Main results obtain in pSS through these various approaches are reviewed here.

Detecting epistasis in human complex traits

Genome-wide association studies (GWASs) have become the focus of the statistical analysis of complex traits in humans, successfully shedding light on several aspects of genetic architecture and biological aetiology. Single-nucleotide polymorphisms (SNPs) are usually modelled as having additive, cumulative and independent effects on the phenotype. Although evidently a useful approach, it is often argued that this is not a realistic biological model and that epistasis (that is, the statistical interaction between SNPs) should be included. The purpose of this Review is to summarize recent directions in methodology for detecting epistasis and to discuss evidence of the role of epistasis in human complex trait variation. We also discuss the relevance of epistasis in the context of GWASs and potential hazards in the interpretation of statistical interaction terms.