A revised estimate of twin concordance in systemic lupus erythematosus

Association of the BANK 1 R61H variant with systemic lupus erythematosus in Americans of European and African ancestry

Recently an association was demonstrated between the single nucleotide polymorphism (SNP), rs10516487, within the B-cell gene BANK1 and systemic lupus erythematosus (SLE) as a consequence of a genome wide association study of this disease in European and Argentinean populations. In a bid for replication, we examined the effects of the R61H non-synonymous variant with respect to SLE in our genotyped American cohorts of European and African ancestry. Utilizing data from our ongoing genome-wide association study in our cohort of 178 Caucasian SLE cases and 1808 Caucasian population-based controls plus 148 African American (AA) SLE cases and 1894 AA population-based controls we investigated the association of the previously described non-synonymous SNP at the BANK1 locus with the disease in the two ethnicities separately. Using a Fisher’s exact test, the minor allele frequency (MAF) of rs10516487 in the Caucasian cases was 22.6% while it was 31.2% in Caucasian controls, yielding a protective odds ratio (OR) of 0.64 (95% CI 0.49-0.85; one-sided p = 7.07 × 10⁻⁴). Furthermore, the MAF of rs10516487 in the AA cases was 18.7% while it was 23.3% in AA controls, yielding a protective OR of 0.75 (95% CI 0.55–1.034; one-sided p = 0.039). The OR of the BANK1 variant in our study cohorts is highly comparable with that reported previously in a South American/European SLE case-control cohort (OR = 0.72). As such, R61H in the BANK1 gene confers a similar magnitude of SLE protection, not only in European Americans, but also in African Americans.

Identification of MAMDC1 as a candidate susceptibility gene for systemic lupus erythematosus (SLE)

Background

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder with multiple susceptibility genes. We have previously reported suggestive linkage to the chromosomal region 14q21-q23 in Finnish SLE families.

Principal Findings

Genetic fine mapping of this region in the same family material, together with a large collection of parent affected trios from UK and two independent case-control cohorts from Finland and Sweden, indicated that a novel uncharacterized gene, MAMDC1 (MAM domain containing glycosylphosphatidylinositol anchor 2, also known as MDGA2, MIM 611128), represents a putative susceptibility gene for SLE. In a combined analysis of the whole dataset, significant evidence of association was detected for the MAMDC1 intronic single nucleotide polymorphisms (SNP) rs961616 (P –value = 0.001, Odds Ratio (OR) = 1.292, 95% CI 1.103–1.513) and rs2297926 (P –value = 0.003, OR = 1.349, 95% CI 1.109–1.640). By Northern blot, real-time PCR (qRT-PCR) and immunohistochemical (IHC) analyses, we show that MAMDC1 is expressed in several tissues and cell types, and that the corresponding mRNA is up-regulated by the pro-inflammatory cytokines tumour necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ) in THP-1 monocytes. Based on its homology to known proteins with similar structure, MAMDC1 appears to be a novel member of the adhesion molecules of the immunoglobulin superfamily (IgCAM), which is involved in cell adhesion, migration, and recruitment to inflammatory sites. Remarkably, some IgCAMs have been shown to interact with ITGAM, the product of another SLE susceptibility gene recently discovered in two independent genome wide association (GWA) scans.

Significance

Further studies focused on MAMDC1 and other molecules involved in these pathways might thus provide new insight into the pathogenesis of SLE.

High-density SNP screening of the major histocompatibility complex in systemic lupus erythematosus demonstrates strong evidence for independent susceptibility regions

A substantial genetic contribution to systemic lupus erythematosus (SLE) risk is conferred by major histocompatibility complex (MHC) gene(s) on chromosome 6p21. Previous studies in SLE have lacked statistical power and genetic resolution to fully define MHC influences. We characterized 1,610 Caucasian SLE cases and 1,470 parents for 1,974 MHC SNPs, the highly polymorphic HLA-DRB1 locus, and a panel of ancestry informative markers. Single-marker analyses revealed strong signals for SNPs within several MHC regions, as well as with HLA-DRB1 (global p = 9.99×10⁻¹⁶). The most strongly associated DRB1 alleles were: *0301 (odds ratio, OR = 2.21, p = 2.53×10⁻¹²), *1401 (OR = 0.50, p = 0.0002), and *1501 (OR = 1.39, p = 0.0032). The MHC region SNP demonstrating the strongest evidence of association with SLE was rs3117103, with OR = 2.44 and p = 2.80×10⁻¹³. Conditional haplotype and stepwise logistic regression analyses identified strong evidence for association between SLE and the extended class I, class I, class III, class II, and the extended class II MHC regions. Sequential removal of SLE–associated DRB1 haplotypes revealed independent effects due to variation within OR2H2 (extended class I, rs362521, p = 0.006), CREBL1 (class III, rs8283, p = 0.01), and DQB2 (class II, rs7769979, p = 0.003, and rs10947345, p = 0.0004). Further, conditional haplotype analyses demonstrated that variation within MICB (class I, rs3828903, p = 0.006) also contributes to SLE risk independent of HLA-DRB1*0301. Our results for the first time delineate with high resolution several MHC regions with independent contributions to SLE risk. We provide a list of candidate variants based on biologic and functional considerations that may be causally related to SLE risk and warrant further investigation.

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by autoantibody production and involvement of multiple organ systems. Although the cause of SLE remains unknown, several lines of evidence underscore the importance of genetic factors. As is true for most autoimmune diseases, a substantial genetic contribution to disease risk is conferred by major histocompatibility complex (MHC) gene(s) on chromosome 6. This region of the genome contains a large number of genes that participate in the immune response. However, the full contribution of this genomic region to SLE risk has not yet been defined. In the current study we characterize a large number of SLE patients and family members for approximately 2,000 MHC region variants to identify the specific genes that influence disease risk. Our results, for the first time, implicate four different MHC regions in SLE risk. We provide a list of candidate variants based on biologic and functional considerations that may be causally related to SLE risk and warrant further investigation.

Tyrosine kinase 2 and interferon regulatory factor 5 polymorphisms are associated with discoid and subacute cutaneous lupus erythematosus

Lupus erythematosus (LE) is a heterogeneous disease ranging from skin-restricted manifestations to a progressive multisystem disease. The specific skin lesions include chronic cutaneous, subacute cutaneous and acute cutaneous LE. Both genetic and environmental factors are involved in the development of LE. However, reports on the genetic background of cutaneous lupus erythematosus (CLE) forms, namely discoid (DLE) and subacute cutaneous lupus erythematosus (SCLE), are sparse. We investigated whether the known systemic LE (SLE) susceptibility genes also predispose to CLE. Altogether, 219 Finnish patients with DLE or SCLE and 356 healthy controls were recruited. Single nucleotide polymorphisms tagging reported risk genes were genotyped. Tyrosine kinase 2 (TYK2) rs2304256 was associated with increased risk of DLE (P = 0.012, OR = 1.47, 95% CI = 1.01-1.98). Expression of TYK2 was demonstrated by immunohistochemistry in macrophage-like cells and neutrophils and interferon regulatory factor 5 (IRF5) in macrophage- and fibroblast-like cells of DLE, SCLE and SLE skin. IRF5 rs10954213 showed association with DLE (P = 0.017, OR = 1.40, 95% CI = 1.06-1.86) and SCLE (P = 0.022, OR = 1.87, 95% CI = 1.09-3.21). A haplotype of cytotoxic T-lymphocyte-associated protein 4 (CTLA4) showed association with DLE (P = 0.0065, OR = 2.51, 95% CI = 1.25-5.04). Our results show that the TYK2, IRF5 and CTLA4 genes previously associated with SLE also confer risk for DLE and SCLE, suggesting that different LE subphenotypes may share pathogenetic pathways.

Cigarette Smoking,STAT4andTNFRSF1BPolymorphisms, and Systemic Lupus Erythematosus in a Japanese Population

Objective.

Recent studies have identified signal transducer and activator of transcription 4 (STAT4) as a susceptibility gene for systemic lupus erythematosus (SLE) in different populations. Similarly, tumor necrosis factor receptor superfamily, member 1B (TNFRSF1B) has been reported to be associated with SLE risk in Japanese populations. Along with environmental factors such as smoking, both polymorphisms may modulate an individual’s susceptibility to SLE. We investigated these relationships in a case-control study to evaluate risk factors for SLE among Japanese women.

Methods.

We investigated the relationship of theSTAT4rs7574865 andTNFRSF1Brs1061622 polymorphisms to SLE risk with special reference to their combination and interaction with cigarette smoking among 152 SLE cases and 427 controls.

Results.

The TT genotype ofSTAT4rs7574865 was significantly associated with increased risk of SLE (OR 2.21, 95% CI 1.10–4.68). Subjects with at least one G allele ofTNFRSF1Brs1061622 had an increased risk of SLE (OR 1.56, 95% CI 0.99–2.47). The attributable proportion due to the interaction between theTNFRSF1Brs1061622 genotypes and smoking was estimated to be 0.49 (95% CI 0.07–0.92), indicating that 49% of the excess risk for SLE in smokers with at least one G allele was due to an additive interaction. A lack of significant associations ofSTAT4with smoking was observed. No significant gene-gene interactions were found among polymorphisms ofSTAT4andTNFRSF1B.

Conclusion.

Our findings suggest that the association between cigarette smoking and SLE could be differentiated by theTNFRSF1Brs1061622 T allele among female Japanese subjects. This preliminary exploratory result should be confirmed in a larger study.

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.

Occupational exposures and risk of systemic lupus erythematosus

This review summarizes the growing body of epidemiologic and experimental research pertaining to the relationship between SLE and occupational exposures, such as crystalline silica, solvents, and pesticides. Epidemiologic studies, using different designs in different settings, have demonstrated moderate to strong associations between occupational silica exposure and SLE. Recent experimental studies of silica in lupus-prone mice provide support for the idea that, in addition to its known adjuvant effect, silica exposure increases the generation of apoptotic material, an important source of self-antigen. Despite compelling experimental studies of the organic solvent trichloroethylene (TCE) in lupus-prone mice, there is little evidence of an overall association of SLE and occupational exposure to a broad classification of solvents in humans. However, there is a lack of data on SLE in occupational cohorts with exposures to TCE or other specific solvents. One epidemiologic study reported an association of pesticide mixing and SLE, while a recent experimental study reported accelerated disease in pesticide-treated lupus-prone mice. Other occupational exposures worth investigating include asbestos, metals, and UV radiation. Attention should also be given to the role of gene-environment interactions, which may require large, multi-site studies that collect both genetic material and occupational exposure data. The quality of exposure assessment is an important consideration in designing and evaluating these studies. The use of pre-clinical endpoints (e.g. high-titer autoantibodies) in occupational cohorts with well-characterized exposure histories may reveal occupational risk factors for autoimmunity, and may also provide baseline data for studies of determinants of progression to SLE.

Fcgamma receptors: structure, function and role as genetic risk factors in SLE

Over 30 years ago, receptors for the Fc region of IgG (FcgammaR) were implicated in the pathogenesis of systemic lupus erythematosus (SLE). Since those pioneering studies, our knowledge of the structure and function of these FcgammaRs has increased dramatically. We now know that FcgammaR contributes to the regulation of acquired immunity and to the regulation of innate immune responses where FcgammaRs act as specific receptors for innate opsonins (CRP and SAP). Our understanding of the genomic architecture of the genes encoding the FcgammaR has also witnessed remarkable advances. Numerous functionally relevant single-nucleotide polymorphism (SNP) variants and copy number (CN) variants have been characterized in the FcgammaR genes. Many of these variants have also been shown to associate with risk to development of SLE and some have been associated with disease progression. This review will provide an overview of the FcgammaR in relation to SLE, including consideration of the role of genetic variants in FcgammaR in SLE pathogenesis. The difficulties in assessing genetic variation in these genes will be discussed. To enhance our understanding of the functional roles of these receptors in SLE, future research will need to integrate our knowledge of SNP variants, CN variants and the functional diversity of these receptors.

Recent insights into the genetic basis of systemic lupus erythematosus

Genetic variation was first shown to be important in systemic lupus erythematosus (SLE or lupus) in the 1970s with associations in the human leukocyte antigen region. Almost four decades later, and with the help of increasingly powerful genetic approaches, more than 25 genes are now known to contribute to the mechanisms that predispose individuals to lupus. Over half of these loci have been discovered in the past 2 years, underscoring the extraordinary success of genome-wide association approaches in SLE. Well-established risk factors include alleles in the major histocompatibility complex region (multiple genes), IRF5, ITGAM, STAT4, BLK, BANK1, PDCD1, PTPN22, TNFSF4, TNFAIP3, SPP1, some of the Fcgamma receptors, and deficiencies in several complement components, including C1q, C4 and C2. As reviewed here, many susceptibility genes fall into key pathways that are consistent with previous studies implicating immune complexes, host immune signal transduction and interferon pathways in the pathogenesis of SLE. Other loci have no known function or apparent immunological role and have the potential to reveal novel disease mechanisms. Certainly, as our understanding of the genetic etiology of SLE continues to mature, important new opportunities will emerge for developing more effective diagnostic and clinical management tools for this complex autoimmune disease.

Evidence for genetic association and interaction between the TYK2 and IRF5 genes in systemic lupus erythematosus

OBJECTIVE

Several candidate genes have been implicated in susceptibility for systemic lupus erythematosus (SLE), a complex autoimmune disease. The proposed genes include members of the type I interferon (IFN) pathway and genes involved in immunological defense functions. Our aim was to systematically replicate 6 such genes, TYK2, IRF5, CTLA4, PDCD1, FCGR2A, and NOD2.

METHODS

Single-nucleotide polymorphisms in TYK2, IRF5, CTLA4, PDCD1, FCGR2A, and NOD2 were genotyped in 277 SLE patients and 356 healthy controls from Finland, giving a power of 42%-70% for different genes at published allele frequencies.

RESULTS

Significant association was seen for rs2304256 (p = 0.0001) and rs12720270 (p = 0.0031) in TYK2 and rs10954213 (p = 0.0043) in IRF5 in our samples, but not for the other genes. We found evidence for genetic interaction (p = 0.014) between rs2304256 in TYK2 and rs10954213 in IRF5, both members of the type I IFN pathway, strengthening the role of the type I IFN pathway in the pathogenesis of SLE.

CONCLUSION

The IFN pathway genes IRF5 and TYK2 may act epistatically in increasing risk for SLE, but our lack of replication does not exclude effects of the other genes studied.

New directions in the treatment of systemic lupus erythematosus

OBJECTIVE

The aim of this review is to provide an up-to-date overview of treatment approaches for systemic lupus erythematosus (SLE), highlighting the multiplicity and heterogeneity of clinical symptoms that underlie therapeutic decisions. Discussion will focus on the spectrum of currently available therapies, their mechanisms and associated side-effects. Finally, recent developments with biologic treatments including rituximab, epratuzumab, tumor necrosis factor (TNF) inhibitors, and belimumab, will be discussed.

RESEARCH DESIGN AND METHODS

A MEDLINE literature search for 'systemic lupus erythematosus' and 'damage' and 'treatment' was undertaken for 1996-2008. Secondary citations were obtained from selected manuscripts. Individual case studies were excluded.

FINDINGS

SLE is an autoimmune disease involving multiple organ systems, a clinical pattern of flares and remissions, and the presence of anti-nuclear autoantibodies. Whereas early symptoms most frequently involve the skin and joints, disease morbidity and mortality are usually associated with cardiovascular events and damage to major organs, particularly the kidneys. Many of the current therapeutic options are considered to be inadequate because of toxicities, accrual of organ damage, and insufficient control of the underlying disease pathology. Improved understanding of SLE pathogenesis and immunology has led to the identification of new treatment targets. Current interest is mainly focused on the targeted immunosuppressive actions provided by biologic therapy. Although the potential long-term beneficial or harmful effects of the new molecular treatments are unclear, their precise molecular targeting may reveal key relationships within the immune system and advance the cause of individualized molecular medicine.

CONCLUSIONS

Biologic compounds that target specific immunologic mechanisms offer a new paradigm in the treatment of SLE, one that may, at best, reverse the course of the disease and, at the very least, might provide some new alternatives to reduce symptoms and limit tissue damage without undue contribution to overall morbidity and mortality.

Cigarette smoking, N-acetyltransferase 2 polymorphisms and systemic lupus erythematosus in a Japanese population

Cigarette smoking may be associated with an increased risk of systemic lupus erythematosus (SLE), but the underlying mechanism of this association remains unclear. N-acetyltransferase 2 (NAT2) is highly variable and detoxifies aromatic amines, an important class of carcinogens in tobacco smoke. Individuals who possess homozygous polymorphic alleles have a slower rate of metabolic detoxification of aromatic amines. We investigated the relationship of the NAT2 polymorphism to the risk of SLE with special reference to the interaction with cigarette smoking among 152 SLE cases and 427 controls in a female Japanese population. NAT2*4, NAT2*5B, NAT2*6A and NAT2*7B alleles were detected with polymerase chain reaction–restriction fragment length polymorphism. Individuals carrying the *4/*4 genotype are rapid acetylators, whereas those with homozygous non-*4 genotypes have a slow acetylator phenotype. Cigarette smoking was associated with an increased risk of SLE (odds ratio [OR] = 2.26; 95% confidence interval [CI] = 1.46–3.50). The slow acetylator genotype of NAT2 was significantly associated with an increased risk of SLE (OR = 2.34, 95% CI = 1.21–4.52) compared with the rapid acetylator genotype. A gene-environment interaction was suggested, with a combination of the NAT2 slow acetylator genotype and smoking conferring significantly higher risk (OR = 6.44, 95% CI = 3.07–13.52; attributable proportion due to interaction = 0.50, 95% CI = 0.12–0.88), compared with the NAT2 rapid acetylator genotype and no history of smoking. This study suggests that, in this Japanese population, the NAT2 slow acetylator status may be a determinant in susceptibility to SLE.

Genetic susceptibility to SLE: new insights from fine mapping and genome-wide association studies

Genome-wide association studies and fine mapping of candidate regions have rapidly advanced our understanding of the genetic basis of systemic lupus erythematosus (SLE). More than 20 robust associations have now been identified and confirmed, providing insights at the molecular level that refine our understanding of the involvement of host immune response processes. In addition, genes with unknown roles in SLE pathophysiology have been identified. These findings may provide new routes towards improved clinical management of this complex disease.

Epigenetics and dermatological disease

Epigenetics is the study of differences in phenotype, in the absence of variation in the genetic code. Epigenetics is relevant in the pathogenesis of many skin diseases. In the case of the common skin cancers, aberrant methylation of tumor suppressor gene promoters is associated with their transcriptional inactivation. Environmental carcinogens such as ultraviolet radiation and arsenic may act through epigenetic mechanisms. Hypomethylation is associated with activation of systemic autoimmune diseases, such as systemic lupus erythematosus, subacute cutaneous lupus erythematosus and scleroderma. This may be through a mechanism of immunological cross-reactivity with hypomethylated DNA from pathogenic bacteria. Epigenetic factors may also be relevant in the pathogenesis of psoriasis and other inflammatory skin diseases, as well as in the pathogenesis of the disorders of genomic imprinting with cutaneous features.

Alcohol consumption is not protective for systemic lupus erythematosus

OBJECTIVE

Several studies have suggested that alcohol drinking is protective for the development and progression of systemic lupus erythematosus (SLE). However, a protopathic bias might also explain this apparent association. Our objective was to investigate the association between alcohol consumption and incidence of SLE in a data set that has information on both current and pre-diagnostic alcohol consumption.

METHODS

We performed an Internet-based case-control study of SLE. Cases were diagnosed within 5 years of the study and met > or =4 American College of Rheumatology criteria for SLE. The control participants were tightly matched to cases on demographic and socio-economic characteristics using a propensity score. Participants completed an online exposure assessment. We used conditional logistic regression analyses to test the association of current and pre-diagnostic alcohol consumption with SLE.

RESULTS

The sample comprised 114 cases with SLE and 228 matched controls. Current drinking (>2 days per week) was inversely associated with SLE (OR 0.35, 95% CI 0.13 to 0.98). Having more than two drinks per day was also inversely associated with SLE (OR 0.41, 95% CI 0.18 to 0.93). However, alcohol consumption before SLE diagnosis was not associated with the risk of SLE (p> or =0.4). Analysis of the change in drinking habits showed that people with lupus were more likely to quit drinking before (OR 2.25, 95% CI 0.96 to 5.28) or after (OR 2.38, 95% CI 0.88 to 6.49) being given the SLE diagnosis.

CONCLUSIONS

Our results show that alcohol consumption before SLE diagnosis is not associated with the risk for SLE, and that individuals who develop SLE are more likely to quit.

The clinical characterisation of systemic lupus erythematosus in a Far North Queensland Indigenous kindred

The aetiology of systemic lupus erythematosus (SLE) is thought to involve both genetic and environmental factors. In other complex diseases, analysis of large multi-case families has resulted in insights into biological mechanisms. We have sought to characterise the members of an extended Indigenous family, five of whom have been diagnosed with SLE. Pedigree members were evaluated using the Lupus Screening Questionnaire, clinical interviews and medical records. Participants contributed blood and urine samples for laboratory analysis. A Mendelian pattern of inheritance was not observed. The five affected members (all female) shared two American College of Rheumatology criteria (positive ANA and arthritis) but showed a wide variety of other SLE manifestations. Disease onset, severity and progression were discordant. Including the five individuals with SLE, 15 blood relatives and two non-consanguineous spouses had autoimmune manifestations. Autoimmune haemolytic anaemia (one case), idiopathic thrombocytopenic purpura (ITP) (one case) and hypothyroidism (two cases) were observed in non-SLE affected individuals. Anti-nuclear antibodies were present in 12 blood relatives and one non-consanguineous spouse. Infections (especially of the skin) were observed to be common in the kindred. The lack of clear Mendelian inheritance or phenotypic concordance makes a rare monogenic explanation for SLE unlikely in this family. The finding of familial autoimmunity associated with SLE further supports the hypothesis that a common genetic pathway can precipitate autoimmunity, with further genes and possible environmental factors interacting to produce the eventual phenotype. Future genetic linkage studies may reveal a rare 'autoimmune gene' variant in this kindred.

Lifetime exposure to trichloroethylene (TCE) does not accelerate autoimmune disease in MRL +/+ mice

A genetically-prone murine lupus model was used to assess the developmental effects of trichloroethylene (TCE) exposure on disease symptom onset (e.g., autoantibody production and proteinuria), lymphocyte proliferation, splenic B-cell populations, and thymic and splenic T-cell populations. MRL +/+ mice were exposed to TCE (0, 1,400 or 14,000 ppb) via drinking water beginning on gestation day (GD) 0 and continuing until 12 months of age. With the exception of splenic CD4-/CD8-cells in female mice only, no alterations were observed in splenic T-cell populations, numbers of splenic B220+ cells, or in lymphocyte proliferation at 12 months of age. Furthermore, populations of all thymic T-cell subpopulations were decreased in male but not female mice following exposure to 14,000 ppb TCE. Autoantibody levels (anti-dsDNA and anti-GA) were assessed periodically from 4 to 12 months of age. Over this period, no increase in autoantibody levels as compared to control was detected, suggesting that TCE did not contribute to or accelerate the development of autoimmune disease markers following lifetime exposure. Not only does this study offer encouraging results, but it is the first study to approach the development of autoimmunity in a novel lifetime exposure paradigm, using an autoimmune prone model, at environmentally relevant exposure levels.

The genetics of SLE: an update in the light of genome-wide association studies

Understanding the pathogenesis of SLE remains a considerable challenge. Multiple abnormalities of both the innate and adaptive immune system have been described and, furthermore, immunological dysfunction precedes clinical presentation by many years. There is a strong genetic basis to SLE, which means that genetic studies can play a key role in furthering our understanding of this disease. Since susceptibility variants are present from birth and are unaffected by the course of the disease, or by its treatment, genetic analysis is, perhaps uniquely, capable of identifying fundamental, causative, disease mechanisms. Over the last 12 months, there has been a staggering increase in our understanding of SLE genetics. We have seen the identification of new and important SLE susceptibility genes through candidate gene studies, and we have seen the publication of two whole-genome association analyses. The 'hypothesis free' whole-genome studies have provided additional evidence in support of a number of existing susceptibility genes and have identified novel gene candidates. In this article, we review the current SLE genetics literature in the light of these recent advances and we discuss our current understanding of the functional role of the key susceptibility genes. By considering how these genes fall into clusters with shared function we can begin to understand how dysregulation at a number of key immunological steps may predispose to the development of SLE.

Genetic imprinting of autoantibody repertoires in systemic lupus erythematosus patients

Systemic lupus erythematosus (SLE) is an autoimmune disease distinguished by great heterogeneity in clinical manifestations and autoantibody expression. While only a handful of autoantibody specificities have proved useful for clinical diagnosis, to characterize complex lupus-associated autoantibody profiles more fully we have applied proteome microarray technology. Our multiplex microarrays included control ligands and 65-autoantigens, which represent diverse nuclear and cytoplasmic antigens recognized by disease-associated and natural autoantibodies. From longitudinal surveys of unrelated SLE patients, we found that autoantibody profile patterns can be patient-specific and highly stable overtime. From profiles of 38 SLE patients that included 14 sets of SLE twins, autoantibodies to the phospholipid neo-determinants, malondialdehyde (MDA) and phosphorylcholine (PC), which are exposed on apoptotic but not healthy cells, were among the most prevalent and highly expressed. We also found that immunoglobulin M (IgM) reactivity to MDA and PC ligands had significant direct correlations with DNA-containing antigens, while such a general relationship was not found with a panel of RNA-related antigens, or for IgG-autoantibodies. Significantly, hierarchical analysis revealed co-distribution/clustering of the IgM autoantibody repertoire patterns for six of 14 twin sets, and such patterns were even more common (10 of 14) for IgG autoantibody profiles. Our findings highlight the potentially distinct roles of IgM and IgG autoantibodies, as we postulate that the direct correlations for IgM autoantibodies to DNA antigens with apoptosis-related determinants may be due to co-expression arising from common pro-homeostatic protective roles. In contrast, the sharing of IgG autoantibody fingerprints by monozygotic twins suggests that lupus IgG autoantibodies can arise in predisposed individuals in genetically determined patterns.

[Two female siblings with childhood-onset systemic lupus erythematosus]

We herein report two female siblings with childhood-onset Systemic Lupus Erythematosus (SLE) who developed membranous lupus nephritis. The children were diagnosed as having SLE in reverse birth order at ages 11 and 14 years. Younger sister's initial symptom was edema and laboratory findings indicated proteinuria, hypocomplementemia and positive ANA/anti-dsDNA antibody. She was diagnosed as being SLE with membranous lupus nephritis based on International Society of Nephrology/Renal Pathology Society (ISN/RPS) 2003 classification. Elder sister manifested general fatigue and edema twelve months after her sister. Laboratory findings showed proteinuria, hypocomplementemia, and positive ANA/anti-dsDNA antibody. A renal biopsy revealed mixed form of mesangial proliferative glomerulonephritis and membranous nephritis. Moreover, both of them were complicated with secondary Sjögren's syndrome. HLA typing was performed and the siblings were noted to have the same haplotype; A(*)0207, A(*)2402, B(*)4601, B(*)5201, B(*)5201, Cw(*)0102, Cw(*)1202, DRB1(*)0101, DRB1(*)0803.

Is lipstick associated with the development of systemic lupus erythematosus (SLE)?

Lipstick use has been hypothesized to be a risk factor of developing systemic lupus erythematosus (SLE). The objective of this study was to investigate the association between lipstick use and risk of SLE. We performed an Internet-based case-control study of SLE with Google users searching on medical key terms as the source population. Cases were diagnosed within 5 years and met > or =4 ACR criteria for SLE by medical record review. Controls were matched to cases on age, gender, race, ethnicity, region of residence, reference year, education, and income using propensity score. Demographic characteristics and lifestyle factors were collected using an online questionnaire. Conditional logistic regression models were used for the analyses with smoking, alcohol consumption, permanent hair dye use, and chemical hair straightener use adjusted. The analysis included 124 cases and 248 matched controls of whom 96% were females and 81% were whites. The median of disease duration was 2 years (range 0-4 years). Using lipstick at least 3 days/week was significantly associated with increased risk of SLE (adjusted OR = 1.71, 95%CI = 1.04-2.82). There was a trend of greater risk with earlier age of initiation of lipstick use (<16 years vs. never use; OR = 1.95, 95%CI = 1.01-3.76, p trend = 0.02) and with increased frequency of use (7 days/week vs. never use; OR = 1.75, 95%CI = 0.89-3.44, p trend = 0.07). Biologic effects of chemicals present in lipsticks absorbed across the buccal mucosa and confounding from unmeasured lifestyle factors could be the explanation of this association. Epidemiologic studies of SLE should include this exposure in exploring its environmental triggers.

Familial clustering of non-nuclear autoantibodies and C3 and C4 complement components in systemic lupus erythematosus

OBJECTIVE

To determine whether key features of systemic lupus erythematosus (SLE), namely, production of non-nuclear antibodies (anti-C1q and anticardiolipin antibodies [aCL]) and depletion of complement components C3 and C4, aggregate in families. In addition, we examined relationships between anti-C1q and C3 and C4 levels.

METHODS

The study cohort comprised 1,037 predominantly white (82%) nuclear families in which at least 1 member had SLE. Associations of antibody measurements between probands and their unaffected siblings were examined using parametric and nonparametric analyses, along with associations between unaffected siblings and their parents. The heritability of anti-C1q, C3, and C4 was estimated, and interdependencies between these factors were examined in a regression model accounting for the family structure of the data set.

RESULTS

We demonstrated associations between siblings for anti-C1q (odds ratio [OR] 3.74, 95% confidence interval [95% CI] 2.65, 5.28) and IgG and IgM aCL (OR 4.08, 95% CI 1.83, 5.13 and OR 2.06, 95% CI 1.46, 2.91, respectively) and, for anti-C1q, association between unaffected parents and their unaffected offspring (OR 4.34, 95% CI 2.16, 8.72). We also demonstrated significant heritability of anti-C1q, C3, and C4 (approximately 45%). Anti-C1q was negatively associated with C3 and C4 in SLE probands but not in their healthy relatives.

CONCLUSION

Non-nuclear antibodies and C3 and C4 cluster within the families of SLE probands, suggesting that specific autoantibody formation is partly genetically determined, even if the total genetic effect in unaffected relatives is insufficient to cause disease. Anti-C1q antibodies accelerate C3 and C4 depletion in patients with SLE but have no effect in the absence of disease.

General aspects of the genetics of SLE

The application of genetic techniques to the study of systemic lupus erythematosus (SLE) has identified candidate genes with diverse immunological function. There is a growing understanding that susceptibility to SLE is due to a complex interaction of multiple genes and environmental factors, and that many of these may be shared with other autoimmune diseases. In this first of a series of review articles we outline our current understanding of SLE genetics, in particular summarising the results of recent association studies.

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.

International Consortium for Systemic Lupus Erythematosus Genetics (SLEGEN), Harley JB, Alarcón-Riquelme ME, Criswell LA, Jacob CO, Kimberly RP, Moser KL, Tsao BP, Vyse TJ, Langefeld CD, Nath SK, Guthridge JM, Cobb BL, Mirel DB, Marion MC, Williams AH, Divers J, Wang W, Frank SG, Namjou B, Gabriel SB, Lee AT, Gregersen PK, Behrens TW, Taylor KE, Fernando M, Zidovetzki R, Gaffney PM, Edberg JC, Rioux JD, Ojwang JO, James JA, Merrill JT, Gilkeson GS, Seldin MF, Yin H, Baechler EC, Li QZ, Wakeland EK, Bruner GR, Kaufman KM, Kelly JA. Genome-wide association scan in women with systemic lupus erythematosus identifies susceptibility variants in ITGAM, PXK, KIAA1542 and other loci

Systemic lupus erythematosus (SLE) is a common systemic autoimmune disease with complex etiology but strong clustering in families (lambda(S) = approximately 30). We performed a genome-wide association scan using 317,501 SNPs in 720 women of European ancestry with SLE and in 2,337 controls, and we genotyped consistently associated SNPs in two additional independent sample sets totaling 1,846 affected women and 1,825 controls. Aside from the expected strong association between SLE and the HLA region on chromosome 6p21 and the previously confirmed non-HLA locus IRF5 on chromosome 7q32, we found evidence of association with replication (1.1 x 10(-7) < P(overall) < 1.6 x 10(-23); odds ratio = 0.82-1.62) in four regions: 16p11.2 (ITGAM), 11p15.5 (KIAA1542), 3p14.3 (PXK) and 1q25.1 (rs10798269). We also found evidence for association (P < 1 x 10(-5)) at FCGR2A, PTPN22 and STAT4, regions previously associated with SLE and other autoimmune diseases, as well as at > or =9 other loci (P < 2 x 10(-7)). Our results show that numerous genes, some with known immune-related functions, predispose to SLE.

The role of mannose-binding lectin in systemic lupus erythematosus

Susceptibility to systemic lupus erythematosus (SLE) is associated with genetic, hormonal, immunological, and environmental factors. Many genes have been related with the appearance of SLE, including several loci that code different complement components and their receptors. Some genetic deficiencies of complement molecules are strongly associated with SLE, probably because these deficiencies could cause decreased clearance of apoptotic cell material. As a consequence of the apoptotic material accumulation, high levels of autoantigens can be presented inappropriately to the immune system in an inflammatory context, resulting in an imbalance on the mechanisms of immunological tolerance, immune system activation, and autoantibody production. Recent studies proposed a role to the mannose-binding lectin (MBL) in the SLE physiopathogenesis. This protein activates the complement system, and the presence of several polymorphisms at the promoter and coding regions of the MBL-2 gene determines alterations at the plasma levels of MBL. Some of these polymorphisms have been associated with SLE susceptibility, as well as with clinical and laboratory typical features of this disease, cardiovascular events, and infections. Besides, it has been described that the presence of anti-MBL autoantibodies in sera of SLE patients can influence MBL plasma levels and its functional activity.

Polymorphism at the TNF superfamily gene TNFSF4 confers susceptibility to systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a multisystem complex autoimmune disease of uncertain etiology (OMIM 152700). Over recent years a genetic component to SLE susceptibility has been established. Recent successes with association studies in SLE have identified genes including IRF5 (refs. 4,5) and FCGR3B. Two tumor necrosis factor (TNF) superfamily members located within intervals showing genetic linkage with SLE are TNFSF4 (also known as OX40L; 1q25), which is expressed on activated antigen-presenting cells (APCs) and vascular endothelial cells, and also its unique receptor, TNFRSF4 (also known as OX40; 1p36), which is primarily expressed on activated CD4+ T cells. TNFSF4 produces a potent co-stimulatory signal for activated CD4+ T cells after engagement of TNFRSF4 (ref. 11). Using both a family-based and a case-control study design, we show that the upstream region of TNFSF4 contains a single risk haplotype for SLE, which is correlated with increased expression of both cell-surface TNFSF4 and the TNFSF4 transcript. We hypothesize that increased expression of TNFSF4 predisposes to SLE either by quantitatively augmenting T cell-APC interaction or by influencing the functional consequences of T cell activation via TNFRSF4.

Identification of two independent risk factors for lupus within the MHC in United Kingdom families

The association of the major histocompatibility complex (MHC) with SLE is well established yet the causal variants arising from this region remain to be identified, largely due to inadequate study design and the strong linkage disequilibrium demonstrated by genes across this locus. The majority of studies thus far have identified strong association with classical class II alleles, in particular HLA-DRB1*0301 and HLA-DRB1*1501. Additional associations have been reported with class III alleles; specifically, complement C4 null alleles and a tumor necrosis factor promoter SNP (TNF-308G/A). However, the relative effects of these class II and class III variants have not been determined. We have thus used a family-based approach to map association signals across the MHC class II and class III regions in a cohort of 314 complete United Kingdom Caucasian SLE trios by typing tagging SNPs together with classical typing of the HLA-DRB1 locus. Using TDT and conditional regression analyses, we have demonstrated the presence of two distinct and independent association signals in SLE: HLA-DRB1*0301 (nominal p = 4.9 x 10(-8), permuted p < 0.0001, OR = 2.3) and the T allele of SNP rs419788 (nominal p = 4.3 x 10(-8), permuted p < 0.0001, OR = 2.0) in intron 6 of the class III region gene SKIV2L. Assessment of genotypic risk demonstrates a likely dominant model of inheritance for HLA-DRB1*0301, while rs419788-T confers susceptibility in an additive manner. Furthermore, by comparing transmitted and untransmitted parental chromosomes, we have delimited our class II signal to a 180 kb region encompassing the alleles HLA-DRB1*0301-HLA-DQA1*0501-HLA-DQB1*0201 alone. Our class III signal importantly excludes independent association at the TNF promoter polymorphism, TNF-308G/A, in our SLE cohort and provides a potentially novel locus for future genetic and functional studies.

A Genome-Wide Study of Lupus: Preliminary Analysis and Data Release

Systemic lupus erythematosus (SLE) is a complex autoimmune disease in which genetics is one of the underlying risk factors. Complicating the analysis of SLE is the fact that the phenotype is heterogeneous, with variations in clinical features, and subgroups are associated with a variety of different autoantibodies. Many association studies of candidate genes as well as linkage studies have generated significant results, highlighting the multigenetic component of the disease. Those findings need to be replicated by independent laboratories and many other genes still remain to be identified. Here, we present our findings on the first genome-wide association study performed in 105 Caucasian patients and controls using the Affymetrix NspI array. The SLE patients studied here were all characterized by the presence of autoantibodies against the U1-6 small nuclear ribonucleoprotein antigen spliceosomal complex. Testing each SNP individually for association with disease, we identified 7 markers with an uncorrected P-value < 0.0001. Of those, three were in reported regions of linkage, namely 20p12, 2q37, and 4p15. To increase the power of our study, we included 60 controls corresponding to the parents from the publicly available CEPH families. The analysis of the 165 cases and controls leads to 28 SNPs being associated with an uncorrected P-value < 0.0001.

Differential expression in lupus-associated IL-10 promoter single-nucleotide polymorphisms is mediated by poly(ADP-ribose) polymerase-1

Systemic lupus erythematosus (SLE) is a complex, multifactorial autoimmune disease characterized by the dysregulation of T and B cells that leads to hyperactivity of B cells and production of autoantibodies, and involves both environmental and genetic factors. Interleukin-10 (IL-10) is a candidate susceptibility gene in SLE. In particular, three IL-10 promoter single-nucleotide polymorphisms (SNPs; -1082A/G, -819T/C and -592A/C) are strongly associated with the pathogenesis of SLE. We found that the homozygous GCC haplotype linked to greater SLE severity confers higher IL-10 gene transcriptional activity than the ATA haplotype in macrophages that encounter apoptotic cells, because of the differential DNA binding to the -592 SNP by a nuclear protein uniquely induced by apoptotic cells. We identified this protein as poly(ADP-ribose) polymerase-1, confirmed its physiological role and characterized its molecular properties in modulating IL-10 production during phagocytosis of apoptotic cells. This study unveils a novel direct link between DNA damage repair/apoptosis pathways and IL-10-mediated immune regulation.

What can epidemiology tell us about systemic lupus erythematosus?

Systemic lupus erythematosus (SLE) is an often-severe autoimmune rheumatic disease most commonly diagnosed in women in their childbearing years. It is thought to develop when genetically predisposed individuals are exposed to one or more environmental triggers. This review outlines the epidemiologic evidence for several putative risk factors including cigarette smoke, hormonal and reproductive factors, environmental silica and infectious exposures, as well as many yet to be identified. We also review the evidence for factors associated with increased disease activity and adverse outcomes in SLE. We review the literature on the epidemiology of SLE, its distribution, potential risk factors for its onset and for adverse outcomes. The information considered in this review was gathered through extensive review of the literature. Online Pubmed literature searches, previous reviews of the epidemiology of SLE and original studies were employed. Epidemiologic studies have helped to identify some of these potential risk factors, including exogenous hormone use, cigarette smoking, infections such as Epstein-Barr virus (EBV) and crystalline silica exposure, but many more have yet to be studied. These exposures may interact with multiple genetic factors in determining susceptibility to SLE. While epidemiologic research has contributed an enormous amount to our understanding of the disease and its pathogenesis, there are many more avenues of epidemiologic research that deserve to be pursued.

Early environmental exposure and the development of lupus

Systemic lupus erythematosus (SLE) is a complex trait with evidence of polygenic inheritance influenced by environmental factors. However, the precise underlying causes of SLE remain unclear. A number of environmental exposures have been associated with lupus or related autoimmune phenomena. Evidence suggests that some environmental exposures need to be present many years before the onset of SLE. Both SLE and rheumatoid arthritis (RA) can occur in very young children and this supports the possibility that important environmental factors must be present during or before this time. In addition, the immune pathology, including autoantibody production, in adult lupus may begin years before clinical disease. There is also evidence that the developing immune system demonstrates developmental plasticity and can be permanently altered or 'programmed' by the early environment. We describe how early life environmental influences including infectious exposure may lead to autoantibody production in later life thus beginning the journey that leads to autoimmune diseases such as lupus in susceptible individuals.

Abrogation of lupus nephritis in activation-induced deaminase-deficient MRL/lpr mice

We generated MRL/lpr mice deficient in activation-induced deaminase (AID). Because AID is required for Ig hypermutation and class switch recombination, these mice lack hypermutated IgG Abs. Unlike their AID wild-type littermates, AID-deficient MRL/lpr mice not only lacked autoreactive IgG Abs but also experienced a dramatic increase in the levels of autoreactive IgM. This phenotype in AID-deficient mice translated into a significant reduction in glomerulonephritis, minimal mononuclear cell infiltration in the kidney, and a dramatic increase in survival to levels comparable to those previously reported for MRL/lpr mice completely lacking B cells and well below those of mice lacking secreted Abs. Therefore, this study wherein littermates with either high levels of autoreactive IgM or autoreactive IgG were directly examined proves that autoreactive IgM Abs alone are not sufficient to promote kidney disease in MRL/lpr mice. In addition, the substantial decrease in mortality combined with a dramatic increase in autoreactive IgM Abs in AID-deficient MRL/lpr mice suggest that autoreactive IgM Abs might not only fail to promote nephritis but may also provide a protective role in MRL/lpr mice. This novel mouse model containing high levels of autoreactive, unmutated IgM Abs will help delineate the contribution of autoreactive IgM to autoimmunity.

Identification of molecular biomarkers for multiple sclerosis

Multiple sclerosis is a demyelinating disease of the central nervous system with a presumed autoimmune etiology. Previous microarray analyses identified conserved gene expression signatures in peripheral blood mononuclear cells of patients with autoimmune diseases. We used quantitative real-time polymerase chain reaction analysis to identify a minimum number of genes of which transcript levels discriminated multiple sclerosis patients from patients with other chronic diseases and from controls. We used a computer program to search quantitative transcript levels to identify optimum ratios that distinguished among the different categories. A combination of a 4-ratio equation using expression levels of five genes segregated the multiple sclerosis cohort (n=55) from the control cohort (n=49) with a sensitivity of 91% and specificity of 98%. When autoimmune and other chronic disease groups were included (n=78), this discriminator still performed with a sensitivity of 79% and a specificity of 87%. This approach may have diagnostic utility not only for multiple sclerosis but also for other clinically complex autoimmune diseases.

Monozygotic twins concordant for idiopathic thrombocytopenic purpura and discordant for systemic lupus erythematosus and lupus nephritis

We report on identical twin sisters with systemic lupus erythematosus and lupus nephritis after initial presentation as idiopathic thrombocytopenic purpura. The patients had diverse clinical signs, symptoms and pathological findings of lupus nephritis. The changes in antinuclear antibodies and anti-double-stranded DNA antibodies were quite different. We conclude that even with an identical genetic background and the same environment, the expression of systemic lupus erythematosus and subsequent progression to lupus nephritis in twins was distinct, and antinuclear antibodies and anti-double-stranded DNA antibodies are helpful for clinical monitoring.