Role of the Fcgamma receptor IIA polymorphism in the antiphospholipid syndrome: an international meta-analysis

Human neutrophil Fc gamma receptors: different buttons for different responses

Neutrophils are fundamental cells in host defense. These leukocytes are quickly recruited from the blood to sites of infection or tissue damage. At these sites, neutrophils initiate several innate immune responses, including phagocytosis, production of reactive oxygen species, degranulation to release proteases and other antimicrobial compounds, production of inflammatory mediators, and formation of neutrophil extracellular traps. In addition to their role in innate immunity, neutrophils are now recognized as cells that also regulate adaptive immunity, via interaction with dendritic cells and lymphocytes. Neutrophils also respond to adaptive immunity by interacting with antibody molecules. Indeed, antibody molecules allow neutrophils to have antigen-specific responses. Neutrophils express different receptors for antibodies. The receptors for immunoglobulin G molecules are known as Fcγ receptors. Upon Fcγ receptor aggregation on the cell membrane, these receptors trigger distinct signal transduction cascades that activate particular cellular responses. In this review, we describe the major Fcγ receptors expressed on human neutrophils and discuss how each Fcγ receptor activates a choice of signaling pathways to stimulate particular neutrophil responses.

Novel Strategy to Combat the Procoagulant Phenotype in Heparin-Induced Thrombocytopenia Using 12-LOX Inhibition

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a major concern for all individuals that undergo cardiac bypass surgeries or require prolonged heparin exposure. HIT is a life- and limb-threatening adverse drug reaction with an immune response following the formation of ultra-large immune complexes that drive platelet activation through the receptor FcγRIIA. Thrombotic events remain high following the standard of care treatment with anticoagulants, while increasing risk of bleeding complications. This study sought to investigate a novel approach to treatment of HIT. Recent reports demonstrate increased procoagulant activity in HIT; however, these reports required analysis ex vivo, and relevance in vivo remains unclear.

METHODS

Using human and mouse model systems, we investigated the cooperativity of PARs (protease-activated receptors) and FcγRIIA in HIT. We challenged humanized FcγRIIA transgenic mice with or without endogenous mouse Par4 (denoted as IIA-Par4+/+ or IIA-Par4-/-, respectively) with a well-established model IgG immune complex (anti [α]-CD9). Furthermore, we assessed the procoagulant phenotype and efficacy to treat HIT utilizing inhibitor of 12-LOX (12[S]-lipoxygenase), VLX-1005, previously reported to decrease platelet activation downstream of FcγRIIA and PAR4, using the triple allele HIT mouse model.

RESULTS

IIA-Par4+/+ mice given αCD9 were severely thrombocytopenic, with extensive platelet-fibrin deposition in the lung. In contrast, IIA-Par4-/- mice had negligible thrombocytopenia or pulmonary platelet-fibrin thrombi. We observed that pharmacological inhibition of 12-LOX resulted in a significant reduction in both platelet procoagulant phenotype ex vivo, and thrombocytopenia and thrombosis in our humanized mouse model of HIT in vivo.

CONCLUSIONS

These data demonstrate for the first time the need for dual platelet receptor (PAR and FcγRIIA) stimulation for fibrin formation in HIT in vivo. These results extend our understanding of HIT pathophysiology and provide a scientific rationale for targeting the procoagulant phenotype as a possible therapeutic strategy in HIT.

Platelet FcγRIIA in immunity and thrombosis: Adaptive immunothrombosis

Sepsis and autoimmune diseases remain major causes of morbidity and mortality. The last decade has seen a new appreciation of platelets in host defense, in both immunity and thrombosis. Platelets are first responders in the blood to microbes or non-microbial antigens. The role of platelets in physiologic immunity is counterbalanced by their role in pathology, for example, microvascular thrombosis. Platelets encounter microbes and antigens via both innate and adaptive immune processes; platelets also help to shape the subsequent adaptive response. FcγRIIA is a receptor for immune complexes opsonized by IgG or pentraxins, and expressed in humans by platelets, granulocytes, monocytes and macrophages. With consideration of the roles of IgG and Fc receptors, the host response to microbes and autoantigens can be called adaptive immunothrombosis. Here we review newer developments involving platelet FcγRIIA in humans and humanized mice in immunity and thrombosis, with special attention to heparin-induced thrombocytopenia, systemic lupus erythematosus, and bacterial sepsis. Human genetic diversity in platelet receptors and the utility of humanized mouse models are highlighted.

Expression, Role, and Regulation of Neutrophil Fcγ Receptors

Neutrophils are best known for their critical role in host defense, for which they utilize multiple innate immune mechanisms, including microbe-associated pattern recognition, phagocytosis, production of reactive oxygen species, and the release of potent proteases, mediators, antimicrobials, and neutrophil extracellular traps. Beyond their well-established contribution to innate immunity, neutrophils were more recently reported to interact with various other cell types, including cells from the adaptive immune system, thereby enabling neutrophils to tune the overall immune response of the host. Neutrophils express different receptors for IgG antibodies (Fcγ receptors), which facilitate the engulfment of IgG-opsonized microbes and trigger cell activation upon cross-linking of several receptors. Indeed, FcγRs (via IgG antibodies) confer neutrophils with a key feature of the adaptive immunity: an antigen-specific cell response. This review summarizes the expression and function of FcγRs on human neutrophils in health and disease and how they are affected by polymorphisms in the FCGR loci. Additionally, we will discuss the role of neutrophils in providing help to marginal zone B cells for the production of antibodies, which in turn may trigger neutrophil effector functions when engaging FcγRs.

The Human FcγRII (CD32) Family of Leukocyte FcR in Health and Disease

FcγRs have been the focus of extensive research due to their key role linking innate and humoral immunity and their implication in both inflammatory and infectious disease. Within the human FcγR family FcγRII (activatory FcγRIIa and FcγRIIc, and inhibitory FcγRIIb) are unique in their ability to signal independent of the common γ chain. Through improved understanding of the structure of these receptors and how this affects their function we may be able to better understand how to target FcγR specific immune activation or inhibition, which will facilitate in the development of therapeutic monoclonal antibodies in patients where FcγRII activity may be desirable for efficacy. This review is focused on roles of the human FcγRII family members and their link to immunoregulation in healthy individuals and infection, autoimmunity and cancer.

Association of Fibrinogen Receptor (Integrin αIIbβ3) Polymorphism in Sudanese Ischemic Stroke Patients

BACKGROUND AND OBJECTIVE

The fibrinogen receptor the human platelet antigen (HPA1 and HPA3) have an essential role in Atherothrombosis. This study aimed to detect the association of αIIbβ3 polymorphism with ischemic stroke in Sudanese patients and its association with the common risk factors.

METHODOLOGY

This is a case-control study. Fifty atherosclerotic with ischemic stroke Sudanese patients were included in present study and were compared to apparently 50 healthy Sudanese subjects at the same ages. The ages of both groups were >18 years. About 5 mL of venous blood sample was taken from each patient and control. The laboratory analyses were done for HbA1c, lipid profile and DNA genotyping by polymerase chain reaction (PCR) followed by FokI and ScrFI digestion.

RESULTS

The result showed that, the risk factors (TRI.G, HDL, HbA1C, and body mass index were associated with the increased risk of ischemic stroke). None of the cholesterol levels and LDL increased the risk of stroke. The risk of ischemic stroke was higher with B/B genotype in HPA3 (p-value 0.009) and A/B genotype in HPA1 (p-value 0.041) and HPA1 (p-value 0.041).

CONCLUSION

The αIIbβ3 polymorphism were with ischemic stroke in Sudanese patients.

Gene therapy in systemic lupus erythematosus

Preclinical studies have provided proof of concept for the feasibility and efficacy of gene therapy in human systemic lupus erythematosus (SLE). Successful efforts include gene constructs that alter the expression of cytokines or limit the cognate interaction of immune cells. Other efforts may include gene modified cell transfersuch as autologousB cells transfectedwith tolerogenicconstructsor T cells in which specific molecular aberrations have been corrected.

Delineating the deranged immune system in the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is a systemic autoimmune disease that is characterized serologically by the presence of antiphospholipid antibodies (aPL) and clinically by vascular thrombosis and obstetric complications. The protein β2 glycoprotein I (β2GPI) is identified as the most important autoantigen in this syndrome. Activation of endothelial cells, thrombocytes and placental tissue by anti-β2GPI antibodies relates to the clinical manifestations of APS. This review describes genetic and environmental factors in relation to APS and summarizes the current knowledge on abnormalities in components of both the innate and adaptive immune system in APS. The role of dendritic cells, T-cells, B-cells, monocytes, neutrophils and NK-cells as well as the complement system in APS are discussed. Several gaps in our knowledge on the pathophysiology of APS are identified and a plea is made for future extensive immune cell profiling by a systems medicine approach in order to better unravel the pathogenesis of APS, to gain more insight in the role of the immune system in APS as well as having the potential to reveal biomarkers or novel therapeutic targets.

Contribution of Human FcγRs to Disease with Evidence from Human Polymorphisms and Transgenic Animal Studies

The biological activities of human IgG antibodies predominantly rely on a family of receptors for the Fc portion of IgG, FcγRs: FcγRI, FcγRIIA, FcγRIIB, FcγRIIC, FcγRIIIA, FcγRIIIB, FcRL5, FcRn, and TRIM21. All FcγRs bind IgG at the cell surface, except FcRn and TRIM21 that bind IgG once internalized. The affinity of FcγRs for IgG is determined by polymorphisms of human FcγRs and ranges from 2 × 10⁴ to 8 × 10⁷ M⁻¹. The biological functions of FcγRs extend from cellular activation or inhibition, IgG-internalization/endocytosis/phagocytosis to IgG transport and recycling. This review focuses on human FcγRs and intends to present an overview of the current understanding of how these receptors may contribute to various pathologies. It will define FcγRs and their polymorphic variants, their affinity for human IgG subclasses, and review the associations found between FcγR polymorphisms and human pathologies. It will also describe the human FcγR-transgenic mice that have been used to study the role of these receptors in autoimmune, inflammatory, and allergic disease models.

Definitions of and contributions to cardiovascular disease in systemic lupus erythematosus

Patients with systemic lupus erythematosus (SLE) have a significantly increased risk of cardiovascular disease (CVD). Increased prevalence of atherosclerosis may explain part of this enhanced risk, but SLE related CVD can also result from other mechanisms. Vascular events may be the result of several pathophysiologic mechanisms; some can be caused by atherosclerosis, others may be primarily thrombotic, and some may be due to ongoing inflammation. The traditional risk factors are of importance for the development of CVD in lupus. However, lupus-related factors, such as endothelial dysfunction and inflammation, renal impairment and disease activity, lupus phenotype, autoantibodies and genetic predisposition are equally or even more important. Risk factors may also contribute separately or in combination to increase the risk of atherosclerosis and clinical CVD in SLE. Studies investigating risk factors for CVD in SLE vary with respect to definition of outcome, it is, e.g. common that the terms atherosclerosis and clinical CVD are used interchangeably. Varying definitions and outcomes may thus explain divergent results of different studies and make comparisons difficult. This review summarizes some of the current knowledge regarding risk factors and mechanisms for atherosclerosis and clinical CVD in SLE. Aspects on the importance of CVD definitions and outcomes are briefly discussed.

Correlation of Fc-γ RIIA polymorphisms with latent Epstein-Barr virus infection and latent membrane protein 1 expression in patients with low grade B-cell lymphomas

Fc-γ RIIA (CD32), a member of the family of Fc-γ receptors, participates in the phagocytosis of bound to antibody antigens. The effectiveness of this function varies for its several haplotypes, and it participates in the pathogenesis of viral infections, according to recent studies. The genetic locus of Fc-γ RIIA consists of two allelic genes: 131-Arg (R131) and 131-His (H131). Our aim was to correlate Fc-γ RIIA polymorphisms, by studying the prevalence of each allele using PCR-RFLPs (polymerase chain reaction-restriction fragment length polymorphisms), with latent Epstein-Barr virus (EBV) infection and the expression of latent membrane protein 1 (LMP1) in 40 patients with leukemic low grade B-cell lymphomas. R131 was found in 84.2% of EBV-positive patients, but only in 28.5% of EBV-negative patients (p = 0.001). A similar correlation was found for R131 and LMP1 expression (84.6% vs. 28.5%) (p = 0.002). Our results support the hypothesis that Fc-γ RIIA polymorphisms are a genetic risk factor for latent EBV infection and the expression of its oncogenic latency proteins.

Patients with unstable angina pectoris show an increased frequency of the Fc gamma RIIa R131 allele

Patients with Systemic Lupus Erythematosus (SLE) carry an increased risk for the development of coronary artery disease (CAD). The R131 allele of the Fc gamma receptor IIa (FcγRIIa) is associated with SLE incidence and disease severity but also with CAD. Compared to stable angina pectoris (SAP) the unstable angina (UAP), as a manifestation of destabilizing CAD, is associated with increased risk of persistent instability, myocardial infarction, and death. Identification of clinically relevant determinants for unstable angina promises reduction of UAP-associated mortality in patients with SLE. We conducted a clinical study among 553 consecutive patients with stable angina pectoris (n = 330) and unstable angina pectoris (n = 223). All patients were genotyped for a frequent functional variant at position 131 of the mature FcγRIIa. UAP, but not SAP was significantly associated with the R/R131 genotype (P < 0.001). In troponin-negative patients with angina carrying the R/R131 genotype the odds ratio for suffering from UAP was 4.02 (95% confidence interval, 2.52-6.41) compared to those with non-R/R131 genotypes. In a multivariable analysis, the R/R131 genotype independently predicted the risk for development of UAP in a model adjusted for classical atherogenic risk factors. Our data imply that risk stratification of SLE- and other high risk patients with troponin-negative angina could be significantly improved by FcγRIIa genotyping.

Role of cytokines in systemic lupus erythematosus: recent progress from GWAS and sequencing

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder, known to have a strong genetic component. Concordance between monozygotic twins is approximately 30-40%, which is 8-20 times higher than that of dizygotic twins. In the last decade, genome-wide approaches to understanding SLE have yielded many candidate genes, which are important to understanding the pathophysiology of the disease and potential targets for pharmaceutical intervention. In this paper, we focus on the role of cytokines and examine how genome-wide association studies, copy number variation studies, and next-generation sequencing are being employed to understand the etiology of SLE. Prominent genes identified by these approaches include BLK, FCγR3B, and TREX1. Our goal is to present a brief overview of genomic approaches to SLE and to introduce some of the key discussion points pertinent to the field.

Association of FcgR2a, but not FcgR3a, with inflammatory bowel diseases across three Caucasian populations

BACKGROUND

The Fc receptors II and III (FcgR2a, and FcgR3a) play a crucial role in the regulation of the immune response. The FcgR2a*519GG and FcgR3a*559CC genotypes have been associated with several autoimmune diseases including systemic lupus erythematosus, rheumatoid arthritis, nephritis, and possibly to type I diabetes, and celiac disease. In a large multicenter, two-stage study of 6570 people, we tested whether the FcgR2a and FcgR3a genes were also involved in inflammatory bowel disease (IBD), which includes Crohn's disease (CD) and ulcerative colitis (UC).

METHODS

We genotyped the FcgR2a*A519G and FcgR3a*A559C functional variants in 4205 IBD patients in six well-phenotyped Caucasian IBD cohorts and 2365 ethnically matched controls recruited from the Netherlands, Spain, and New Zealand.

RESULTS

In the initial Dutch study we found a significant association of FcgR2a genotypes with IBD (P-genotype = 0.02); while the FcgR2a*519GG was more common in controls (23%) than in IBD patients (18%; odds ratio [OR] = 0.75; 95% confidence interval [CI] 0.61-0.92; P = 0.004). This association was corroborated by a combined analysis across all the study populations (Mantel-Haenszel [MH] OR = 0.84; 0.74-0.95; P = 0.005) in the next stage. The Fcgr2a*GG genotype was associated with both UC (MH-OR = 0.84; 0.72-0.97; P = 0.01) and CD (MH-OR = 0.84; 0.73-0.97; P = 0.01), suggesting that this genotype confers a protective effect against IBD. There was no association of FcgR3a*A559C genotypes with IBD, CD, or UC in any of the three studied populations.

CONCLUSIONS

The FcgR2a*519G functional variant was associated with IBD and reduced susceptibility to UC and to CD in Caucasians. There was no association between FcgR3a*5A559C and IBD, CD or UC.

Unravelling the genetic basis of renal diseases; from single gene to multifactorial disorders

Chronic kidney disease is common with up to 5% of the adult population reported to have an estimated glomerular filtration rate of < 60 ml/min/1.73 m(2). A large number of pathogenic mutations have been identified that are responsible for 'single gene' renal disorders, such as autosomal dominant polycystic kidney disease and X-linked Alport syndrome. These single gene disorders account for < 15% of the burden of end-stage renal disease that requires dialysis or kidney transplantation. It has proved more difficult to identify the genetic susceptibility underlying common, complex, multifactorial kidney conditions, such as diabetic nephropathy and hypertensive nephrosclerosis. This review describes success to date and explores strategies currently employed in defining the genetic basis for a number of renal disorders. The complementary use of linkage studies, candidate gene and genome-wide association analyses are described and a collation of renal genetic resources highlighted.

Functional and clinical consequences of Fc receptor polymorphic and copy number variants

Receptors for immunoglobulins (Fc receptors) play a central role during an immune response, as they mediate the specific recognition of antigens of almost infinite diversity by leucocytes, thereby linking the humoral and cellular components of immunity. Indeed, engagement of Fc receptors by immunoglobulins initiates a range of immunoregulatory processes that might also play a role in disease pathogenesis. In the circulation, five main types of immunoglobulins (Ig) exist - namely IgG, IgA, IgE, IgM and IgD and receptors with the ability to recognize and bind to IgG (Fc gamma receptor family), IgE (Fc epsilon RI and CD23), IgA (CD89; Fc alpha/microR) and IgM (Fc alpha/microR) have been identified and characterized. However, it is astonishing that nearly all the known human Fc receptors display extensive genetic variation with clear implications for their function, thus representing a substantial genetic risk factor for the pathogenesis of a range of chronic inflammatory disorders.

The genetics and epigenetics of autoimmune diseases

Self tolerance loss is fundamental to autoimmunity. While understanding of immune regulation is expanding rapidly, the mechanisms causing loss of tolerance in most autoimmune diseases remain elusive. Autoimmunity is believed to develop when genetically predisposed individuals encounter environmental agents that trigger the disease. Recent advances in the genetic and environmental contributions to autoimmunity suggest that interactions between genetic elements and epigenetic changes caused by environmental agents may be responsible for inducing autoimmune disease. Genetic loci predisposing to autoimmunity are being identified through multi-center consortiums, and the number of validated genes is growing rapidly. Recent reports also indicate that the environment can contribute to autoimmunity by modifying gene expression through epigenetic mechanisms. This article will review current understanding of the genetics and epigenetics of lupus, rheumatoid arthritis, multiple sclerosis and type 1 diabetes, using systemic lupus erythematosus as the primary example. Other autoimmune diseases may have a similar foundation.

FcgammaRIIa genotype is associated with acute coronary syndromes as first manifestation of coronary artery disease

OBJECTIVE

Identification of clinically relevant determinants for acute coronary syndromes (ACS) promises reduction of ACS-associated mortality. C-reactive protein (CRP) has proved to be useful identifying people at risk for cardiovascular events. However, it is unknown whether genetic variants at Fcgamma receptor IIa (FcgammaRIIa), the main receptor for CRP, are involved in CRP-related cardiovascular risk. We evaluated the potential impact of FcgammaRIIa through a genetic association study in patients with ACS.

METHODS AND RESULTS

We conducted a genetic association study among 701 consecutive patients with first event of ACS compared to 467 patients with stable angina pectoris. All patients were genotyped for a frequent functional variant at position 131 of the mature FcgammaRIIa, where the arginine (R) allele results in an increased signal transduction upon CRP binding. In our study, the R/R131 genotype was significantly associated with ACS as the first manifestation of coronary artery disease (P=1.2x10(-9), odds ratio 2.86, 95% CI: 2.06-3.99) compared to the non-R/R131 genotype.

CONCLUSIONS

Our data show a genetic association of the FcgammaRIIa R/R131 genotype with a more frequent occurrence of ACS as the first manifestation of coronary artery disease, probably mediated via its interaction with CRP. Genotyping of this FcgammaRIIa variant could help to improve risk stratification in the course of coronary disease in the future.

Fc receptor genes and the systemic lupus erythematosus diathesis

Fc receptors represent a distinct group of hematopoeitic cell surface glycoproteins that have a characterized role in affecting the efficiency of the mononuclear phagocyte system to clear IgG immune complexes. Functional genetic variations in this family of receptors have been identified as heritable susceptibility factors for SLE and lupus nephritis across diverse populations. In this review, we describe the roles of the classical Fc receptors for IgG (Fc gamma) and non-classical Fc-like receptors (FCR1-FCRL6L), Fc receptors for IgE (Fc epsilon RI) and IgA and IgM (Fc alpha/mu R) in SLE diathesis. The combined effects of these genes on SLE pathogenesis, either via linkage disequilibrium or epistasis with additional genetic or environmental factors, provide a challenge for future investigations. The pursuit of a polygenic SLE-profile that includes longitudinal evaluations of SLE and markers involved in the protean clinical manifestations associated with SLE will facilitate our understanding of the cascade of inflammatory events associated with the diathesis.

The synergistic effect of FC gamma receptor IIa and interleukin-10 genes on the risk to develop systemic lupus erythematosus in Thai population

Several linkage analyses have consistently shown that systemic lupus erythematosus (SLE) susceptible genes are located on chromosome 1q21-44. In this study, two major candidate genes, interleukin-10 (IL-10) and Fc gamma receptor IIa (FcgammaRIIa), within these regions were investigated in Thai SLE patients. The genotyping of three single-nucleotide polymorphisms (promoter area: -1082, -819 and -592) within IL-10 gene and one polymorphism (change amino acid at position 131) within FcgammaRIIa gene was determined in 195 SLE patients and 159 ethnically matched controls. The RR/RH genotypes of FcgammaRIIa were found to be significantly increased in SLE patients compared with healthy controls [OR = 2.01, 95% confidence interval (CI) = 1.28-3.14, P= 0.001]. Interestingly, the synergistic effect between RR/RH genotypes of FcgammaRIIa and ACC/ACC haplotype of IL-10 in susceptibility to SLE was observed (OR = 7.84, 95% CI = 1.60-52.04, P= 0.002). In addition, the FcgammaRIIa, RR homozygotes was also strongly associated with anticardiolipin antibody production (OR = 6.09, 95% CI = 1.38-30.54, P= 0.006). The result demonstrated that ACC haplotype of IL-10 gene and FcgammaRIIa R131 polymorphism can be used as marker for genetic susceptibility and severity to SLE in Thai population, particularly individuals carrying both specific genotypes.

FcgammaRII and multi-system autoimmune disease

The FcR are a crucial link in the immune response between humoral and cellular immunity and cell-based effector systems, mediating a wide variety of physiological and biochemical responses. The FcR for IgG (FcgammaR) and in particular the most widely expressed of these, FcgammaRII, are important in regulating adaptive immunity. Disruption of their function is a key factor in the development of autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), which are characterized by chronic, multi-organ inflammation. Studies of the FcgammaRII include structure/function relationships, investigation of the associations between FcR polymorphisms and human disease and animal studies using knockout or transgenic mouse models. These investigations showed that the various forms of FcgammaRII interact with immune complexes to either initiate or inhibit inflammation. In conjunction with environmental antigens and genotype, the FcgammaRII activating and inhibitory receptors determine the nature and magnitude of response to antigens. In this review, the structure and function of the FcgammaRIIs and their role in immune complex-mediated auto-immunity are discussed.

V Meeting of the European Forum on Antiphospholipid Antibodies

The "V Meeting of the European Forum on Antiphospholipid Antibodies" was organized in Barcelona, Catalonia, Spain, on December 2-3, 2005. This biannual meeting becomes a real forum for the interchange of information on current research on the field antiphospholipid antibodies and the antiphospholipid syndrome, as well as a starting point for many new research projects. About 170 physicians and researchers from a great variety of medical specialities (internists, rheumatologists, hematologists, obstetricians, pediatricians, neurologists, cardiologists, immunologists, and biologists, among others) coming from 20 European countries attended the sessions. This report summarizes the main studies and new research projects presented during this Forum Meeting.

Autoimmunity in systemic lupus erythematosus: integrating genes and biology

Susceptibility to the autoimmune phenotype of systemic lupus erythematosus (SLE) is heritable. Linkage analysis and recent advances in the field of single nucleotide polymorphisms (SNPs) have resulted in the identification of several genetic loci and functional allelic variants of signaling proteins which have become the mainstay of understanding disease susceptibility and exploring the basis of autoimmunity in SLE. However, genetic heterogeneity and possible epistatic interactions among genetic elements have precluded replication of these findings in multiple population groups and thus complicated their interpretation. In this regard, the discovery that a plethora of normal signaling proteins are expressed in abnormal amounts in immune cells from patients with SLE has gained significance. Thus, the key to precise elucidation of the pathologic basis of autoimmunity in SLE lies in tying genetics and disease biology. This review highlights recent discoveries of important functional genetic variants and altered expression of normal signaling proteins that network together to disrupt peripheral tolerance and initiate the autoimmune process in SLE.

Impact of violations and deviations in Hardy-Weinberg equilibrium on postulated gene-disease associations

The authors evaluated whether statistically significant violations of Hardy-Weinberg equilibrium (HWE) or the magnitude of deviations from HWE may contribute to the problem of replicating postulated gene-disease associations across different studies. Forty-two gene-disease associations assessed in meta-analyses of 591 studies were examined. Studies with disease-free controls in which HWE was violated gave significantly different results from HWE-conforming studies in five instances. Exclusion of the former studies resulted in loss of statistical significance of the overall meta-analysis in three instances and more than a 10% change in the summary odds ratio in six. Exclusion of HWE-violating studies changed the formal significance of the estimated between-study heterogeneity in three instances. After adjustment for the magnitude of the deviation from HWE for the controls, formal significance was lost in another three instances. Studies adjusted for the magnitude of deviation from HWE tended to become more heterogeneous among themselves, and, for seven gene-disease associations, between-study heterogeneity became significant, while it was not so in the unadjusted analyses. Gene-disease association studies and meta-analyses thereof should routinely scrutinize the potential impact of HWE violations as well as nonsignificant deviations from the exact frequencies expected under HWE. Postulated genetic associations with modest-sized odds ratios and borderline statistical significance may not be robust in such sensitivity analyses.

The association between fcgammaRIIIB polymorphisms and systemic lupus erythematosus in Korea

Polymorphisms of FcgammaR have been proposed as genetic factors that influence susceptibility to SLE. FcgammaRIIIB polymorphism in systemic lupus erythematosus (SLE) have been studied in various populations, but the results were inconsistent. The aim of this study was to determine the association of FcgammaRIIIB polymorphism in Korean lupus patients. One-hundred and eighty-three SLE patients (166 female, 17 male) meeting 1982 ACR criteria and 300 Korean disease-free controls were enrolled. Genotyping for the FcgammaRIIIB NA1/NA2 was performed by PCR of genomic DNA using allele-specific primers. There was no significant skewing in the distribution of the three FcgammaRIIIB genotypes, and alleles between SLE and the controls. The frequency of FcgammaRIIIB genotypes in SLE patients and controls was FcgammaRIIIB NA1/NA1 27.9% versus 26%, NA1/NA2 55.2% versus 51.7%, NA2/NA2 16.9% versus 22.3%, respectively. The gene frequencies of NA1 allele were 0.56 in the SLE and 0.52 in controls, respectively. Among clinical manifestations, thrombocytopenia was more common in FcgammaRIIIB NA2/NA2 genotype (P = 0.04, OR 2.4, 95% CI 1.0-5.4), and NA2 allele (P = 0.03, OR 1.7, 95% CI 1.1-2.8). Although FcgammaRIIIB polymorphism was not associated with the development of SLE in Korean, thrombocytopenia was associated with FcgammaRIIIB NA2/NA2 genotype, and NA2 allele.

Genetics of susceptibility and severity in systemic lupus erythematosus

PURPOSE OF REVIEW

The genetic basis of systemic lupus erythematosus, a complex genetic trait, may provide important insights into autoimmune disease. Innovation in both practical and theoretical approaches will assist in accelerating the pace of discovery and our understanding of pathogenesis.

RECENT FINDINGS

Significant progress has been made in the last year with respect to the refinement of genetic intervals to promising candidate genes involved in systemic lupus erythematosus pathogenesis and specific phenotype susceptibility. This review highlights these discoveries and suggests platforms that may affect the future of analysis of this complex disease.

SUMMARY

Understanding the genetic basis for systemic lupus erythematosus disease and sub-phenotype susceptibility will have a substantial effect on the therapeutic interventions used to care for patients.

Primary versus secondary antiphospholipid syndrome: is this lupus or not?

Antiphospholipid syndrome is a hypercoaguable state characterized by recurrent venous and/or arterial thrombosis and/or pregnancy complications of fetal loss, pre-eclampsia, or eclampsia in the presence of antiphospholipid antibodies. It was first described in the setting of systemic lupus erythematosus and subsequently recognized to also exist as an independent condition and in conjunction with a variety of other autoimmune, infectious, and malignant illnesses. These diseases have been called primary antiphospholipid syndrome and secondary antiphospholipid syndrome. However, the two conditions can have significant overlapping features. This paper reviews the similarities and the differences between the two conditions.

The role of FcgammaRIIA and IIIA polymorphisms in autoimmune diseases

Our knowledge about the role of human Fc receptors for IgG (FcgammaR) has increased considerably within the last several years. These receptors vary in their affinity for IgG, their preferences for IgG subclasses, the cell type-specific expression patterns, and the intracellular signals that they elicit. Additional FcgammaR heterogeneity is introduced by the presence of well characterized genetic polymorphisms. Allelic variants of FcgammaR genes may influence phagocyte biologic activity, providing a basis for inherited predisposition to disease. Recent evidence suggests that certain FcgammaR alleles are genetic risk factors for systemic autoimmune diseases and the development of major manifestations of these diseases. The FcgammaRIIA-R/H131 polymorphism is an important determinant of predisposition to systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS). FcgammaRIIA-R131, the low-binding IgG2 allele, seems to confer risk for APS under a recessive model, whereas its effect on SLE susceptibility probably has a dose-response character. The population-attributable fraction of lupus cases due to the R131 allele is 13% and for APS cases is at least 10%, in subjects of European descent. The FcgammaRIIIA-V/F158 polymorphism has a significant impact on renal involvement in lupus patients. The proportion of nephritis cases that could be attributed to the low-binding IgG1 and IgG3 F158 allele is approximately 10-14%. These genetic associations have been well documented in meta-analyses including a large number of studies. Besides the epidemiologic and pathophysiologic interest, this knowledge may be of use in the future in designing novel therapeutic interventions.