A candidate region on 11p13 for systemic lupus erythematosus: a linkage identified in African-American families

Black patients with cutaneous lupus are associated with positive family history of cutaneous lupus and systemic lupus

OBJECTIVES

Various genetic polymorphisms have been associated with an increased risk of cutaneous lupus erythematosus (CLE). However, it is not fully known how often positive family histories occur in patients with CLE. The aims of this study are to determine the rate of positive family history among patients with CLE and to identify risk factors associated with positive family history.

METHODS

A retrospective cohort study was conducted among 338 patients with CLE seen in outpatient dermatology clinics in a tertiary referral centre in Dallas, Texas. The primary outcome was positive family history of CLE and/or SLE, as defined by the presence of self-reported CLE and/or SLE in first-degree or more distant relatives of a patient. Univariate analyses were performed to identify risk factors associated with positive family history of CLE and/or SLE in patients with CLE. Multivariable logistic regression analyses were performed to determine significant predictors of positive family history of CLE and/or SLE.

RESULTS

34% (n=114) of patients reported positive family history of CLE and/or SLE. 7% (n=23) of patients with CLE had relatives with CLE, with 5% (n=18) having a first-degree relative with CLE. 30% (n=102) of patients with CLE had relatives with SLE, and 15% (n=52) had a first-degree relative with SLE. Black patients were more likely to have positive family history of CLE and/or SLE (OR 2.13, 95% CI 1.23 to 3.69, p=0.007).

CONCLUSIONS

More patients with CLE had positive family history of SLE than CLE. Black patients with CLE were more likely to have a relative with CLE and/or SLE. Providers can use this information to counsel patients with CLE on the risk of other family members having CLE and/or SLE. These data may help identify potentially new genetic polymorphisms associated with positive family history.

Associations between PTPN22 and TLR9 polymorphisms and systemic lupus erythematosus: a comprehensive meta-analysis

Previous studies have explored the relationship of PTPN22 and TLR9 polymorphisms with systemic lupus erythematosus (SLE). In consideration of the population stratification, conflicting results and updating data, we conducted a comprehensive meta-analysis, which consists of a total of 17 research articles (9120 cases and 11,724 controls) for PTPN22 and 20 articles (including up to 2808 cases and 3386 controls) for TLR9. Significant association was verified between PTPN22 rs2476601 and SLE in the overall population (OR = 1.511 per T allele, 95% CI 1.338-1.706, P = 2.931 × 10^-11) and under dominant model of T allele (TT+CT vs. CC: OR = 1.531, 95% CI 1.346-1.742, P = 9.17 × 10^-11). Analysis after stratification by ethnicity indicated that PTPN22 rs2476601 was related to SLE in Americans (OR = 2.566, 95% CI 1.796-3.665, P = 2.219 × 10^-7), Europeans (OR = 1.399, 95% CI 1.261-1.552, P = 2.153 × 10^-10), and Africans (OR = 4.14, 95% CI 1.753-9.775, P = 1.0 × 10^-3). We did not observe any association between TLR9 polymorphisms (rs187084, rs352140, rs5743836 and rs352139) and SLE under any model, after excluding the data that were inconsistent with Hardy-Weinberg equilibrium (HWE). In summary, PTPN22 rs2476601 was significantly interrelated with SLE and contributed to susceptibility and development of SLE in Americans, Europeans and Africans in this analysis, while their relationship needs to be validated in Africans by future research.

I too, am America: a review of research on systemic lupus erythematosus in African-Americans

Systemic lupus erythematosus (SLE) is a multi-organ autoimmune disorder that can cause significant morbidity and mortality. A large body of evidence has shown that African-Americans experience the disease more severely than other racial-ethnic groups. Relevant literature for the years 2000 to August 2015 were obtained from systematic searches of PubMed, Scopus, and the EBSCOHost platform that includes MEDLINE, CINAHL, etc. to evaluate research focused on SLE in African-Americans. Thirty-six of the 1502 articles were classified according to their level of evidence. The systematic review of the literature reported a wide range of adverse outcomes in African-American SLE patients and risk factors observed in other mono and multi-ethnic investigations. Studies limited to African-Americans with SLE identified novel methods for more precise ascertainment of risk and observed novel findings that hadn't been previously reported in African-Americans with SLE. Both environmental and genetic studies included in this review have highlighted unique African-American populations in an attempt to isolate risk attributable to African ancestry and observed increased genetic influence on overall disease in this cohort. The review also revealed emerging research in areas of quality of life, race-tailored interventions, and self-management. This review reemphasizes the importance of additional studies to better elucidate the natural history of SLE in African-Americans and optimize therapeutic strategies for those who are identified as being at high risk.

Catalase and PPARg2 genotype and risk of systemic lupus erythematosus in Koreans

Catalase (CAT) and peroxisome proliferator activated receptor-g2 (PPARg2) are important regulators of oxidative stress and inflammation, which may contribute to the development of systemic lupus erythematosus (SLE). The objective of this study was to investigate the effects of genetic polymorphisms of CAT and PPARg2 on risk and severity of SLE in a Korean population. DNA was isolated from blood samples collected from 345 patients with SLE and 400 controls. Genotyping for the 2262C!T polymorphism of CAT and the Pro12Ala polymorphism of PPARg2 were performed by PCR-RFLP analysis. The severity of SLE was assessed using the Systemic Lupus International Collaborating Clinics/American College of Rheumatology (SLICC/ACR) damage index (SDI). No association was observed between genotypes for any of the clinical manifestations of SLE. CAT and PPARg2 genotypes were not associated with either risk or severity of SLE. For subjects who were carriers of the high activity Tallele for CATand have the Pro/Pro genotype for PPARg2, the odds ratio (95% confidence interval) for risk of SLE was 0.45 (0.23-1.08). Our results suggest that genetic polymorphisms of CAT and PPARg2 do not play a significant role in the development of SLE in a Korean population. A possible protective effect of a combined genotype warrants further investigation.

Familial Aggregation and Segregation Analysis in Families Presenting Autoimmunity, Polyautoimmunity, and Multiple Autoimmune Syndrome

Studies documenting increased risk of developing autoimmune diseases (ADs) have shown that these conditions share several immunogenetic mechanisms (i.e., the autoimmune tautology). This report explored familial aggregation and segregation of AD, polyautoimmunity, and multiple autoimmune syndrome (MAS) in 210 families. Familial aggregation was examined for first-degree relatives. Segregation analysis was implemented as in S.A.G.E. release 6.3. Data showed differences between late- and early-onset families regarding their age, age of onset, and sex. Familial aggregation of AD in late- and early-onset families was observed. For polyautoimmunity as a trait, only aggregation was observed between sibling pairs in late-onset families. No aggregation was observed for MAS. Segregation analyses for AD suggested major gene(s) with no clear discernible classical known Mendelian transmission in late-onset families, while for polyautoimmunity and MAS no model was implied. Data suggest that polyautoimmunity and MAS are not independent traits and that gender, age, and age of onset are interrelated factors influencing autoimmunity.

Evaluation of TRAF6 in a large multiancestral lupus cohort

OBJECTIVE

Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease with significant immune system aberrations resulting from complex heritable genetics as well as environmental factors. We undertook to study the role of TRAF6 as a candidate gene for SLE, since it plays a major role in several signaling pathways that are important for immunity and organ development.

METHODS

Fifteen single-nucleotide polymorphisms (SNPs) across TRAF6 were evaluated in 7,490 SLE patients and 6,780 control subjects from different ancestries. Population-based case-control association analyses and meta-analyses were performed. P values, false discovery rate q values, and odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated.

RESULTS

Evidence of associations was detected in multiple SNPs. The best overall P values were obtained for SNPs rs5030437 and rs4755453 (P = 7.85 × 10(-5) and P = 4.73 × 10(-5) , respectively) without significant heterogeneity among populations (P = 0.67 and P = 0.50, respectively, in Q statistic). In addition, SNP rs540386, which was previously reported to be associated with rheumatoid arthritis (RA), was found to be in linkage disequilibrium with these 2 SNPs (r(2) = 0.95) and demonstrated evidence of association with SLE in the same direction (meta-analysis P = 9.15 × 10(-4) , OR 0.89 [95% CI 0.83-0.95]). The presence of thrombocytopenia improved the overall results in different populations (meta-analysis P = 1.99 × 10(-6) , OR 0.57 [95% CI 0.45-0.72], for rs5030470). Finally, evidence of family-based association in 34 African American pedigrees with the presence of thrombocytopenia was detected in 1 available SNP (rs5030437) with a Z score magnitude of 2.28 (P = 0.02) under a dominant model.

CONCLUSION

Our data indicate the presence of association of TRAF6 with SLE, consistent with the previous report of association with RA. These data provide further support for the involvement of TRAF6 in the pathogenesis of autoimmunity.

Functional polymorphisms of the coagulation factor II gene (F2) and susceptibility to systemic lupus erythematosus

OBJECTIVE

Two F2 functional polymorphisms, rs1799963 (G20210A) and rs3136516 (A19911G), are known to be associated with elevated levels/activity of prothrombin (encoded by F2) and risk of thrombosis. Since patients with systemic lupus erythematosus (SLE) have high risk of thrombosis and accelerated atherosclerosis and also high prevalence of anti-prothrombin antibodies, we hypothesized that these two F2 polymorphisms could affect risk of SLE.

METHODS

We investigated these polymorphisms in 627 women with SLE (84% Caucasian Americans, 16% African Americans) and 657 female controls (78% Caucasian Americans, 22% African Americans).

RESULTS

While the rs1799963 A allele was almost absent in African Americans, it was present at ~2% frequency in Caucasian Americans and showed no significant association with SLE. The rs3136516 G allele frequency was significantly higher in Caucasian SLE cases than in controls (48.4% vs 43.7%, respectively) with a covariate-adjusted odds ratio (OR) of 1.22 (95% CI 1.03-1.46, p = 0.023). The association was replicated in African Americans (rs3136516 G allele frequency 91.2% in cases vs 82.2% in controls) with an adjusted OR of 1.96 (95% CI 1.08-3.58, p = 0.022). Stratification of Caucasian SLE patients based on the presence or absence of cardiac and vascular events (CVE) revealed stronger association with the CVE-positive SLE subgroup than the CVE-negative SLE subgroup (OR 1.42 vs 1.20). Prothrombin activity measurements in a subset of SLE cases demonstrated higher activity in the carriers of the rs3136516 G allele.

CONCLUSION

Our results suggest a potential role for prothrombin and the crosstalk between hemostatic and immune/inflammatory systems in SLE and SLE-associated cardiovascular events, which warrants further investigation in independent samples.

Race differences in immunogenetic features and photosensitivity of cutaneous lupus erythematosus from the aspect of Japanese studies

Skin lesions of collagen diseases are influenced by environmental triggers, such as UV light, and are variable in cutaneous lupus erythematosus (LE), such as systemic LE (SLE), chronic discoid LE (CDLE), subacute cutaneous LE (SCLE), and LE tumidus (LET). Although there are a few conflicting reports on photosensitivity in collagen diseases, many Japanese dermatologists feel there are photosensitivity differences in LE between Asians and Caucasians with SCLE and LET. To address this issue, we have carried out genetic studies of Japanese SLE and CDLE patients and reviewed the race differences in photosensitivity of cutaneous LE from Japanese studies. Human leukocyte antigen (HLA) studies in Japanese patients revealed that HLA-DRB1*1501 association was with CDLE and SLE. The association between HLA-Cw6 and CDLE was first reported in a Japanese population, and a HLA-A33-B44-DRB1*1302 haplotype showed a positive association in CDLE. However, these results are not compatible with those from Caucasian subjects. There are no significant associations among HLA studies, photosensitivity, and anti-Ro/SS-A antibodies in Japanese CLE patients. Photosensitivity will be a key factor to dissolve multifactorial complexes of LE etiopathogenesis. An axis of photosensitivity, anti-Ro/SS-A antibodies, and apoptosis via tumor necrosis factor-alpha is the best marker to verify the contribution of genetics in CLE patients. The incidence and degree of photosensitivity of SCLE and LET are much lower in Japanese than in Caucasians. This discrepancy may lead to investigations of CLE pathogenesis through global collaborations.

Detection of catalase as a major protein target of the lipid peroxidation product 4-HNE and the lack of its genetic association as a risk factor in SLE

Background

Systemic lupus erythematosus (SLE) is a multifactorial disorder characterized by the presence of autoantibodies. We and others have implicated free radical mediated peroxidative damage in the pathogenesis of SLE. Since harmful free radical products are formed during this oxidative process, including 4-hydroxy 2-nonenol (4-HNE) and malondialdehyde (MDA), we hypothesized that specific HNE-protein adducts would be present in SLE red blood cell (RBC) membranes. Catalase is located on chromosome 11p13 where linkage analysis has revealed a marker in the same region of the genome among families with thrombocytopenia, a clinical manifestation associated with severe lupus in SLE affected pedigrees. Moreover, SLE afflicts African-Americans three times more frequently than their European-American counterparts. Hence we investigated the effects of a genetic polymorphism of catalase on risk and severity of SLE in 48 pedigrees with African American ancestry.

Methods

Tryptic digestion followed by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis was used to identify the protein modified by HNE, following Coomassie staining to visualize the bands on the acrylamide gels. Genotyping analysis for the C → T, -262 bp polymorphism in the promoter region of catalase was performed by PCR-RFLP and direct PCR-sequencing. We used a "pedigree disequilibrium test" for the family based association analysis, implemented in the PDT program to analyze the genotyping results.

Results

We found two proteins to be HNE-modified, migrating around 80 and 50 kD respectively. Tryptic digestion followed by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis of the Coomassie stained 80 kD band revealed that the target of HNE modification was catalase, a protein shown to associate with RBC membrane proteins. All the test statistics carried out on the genotyping analysis for the C → T, -262 bp polymorphism in the promoter region of catalase were non-significant (p > 0.05) in our data, which suggested that this SNP is not associated with SLE.

Conclusion

Our results indicate that catalase is one of the proteins modified due to oxidative stress. However, catalase may not be a susceptibility gene for SLE. Nonetheless, catalase is oxidatively modified among SLE patients. This suggests a possible role between oxidative modification of catalase and its affects on enzymatic activity in SLE. An oxidatively modified catalase could be one of the reasons for lower enzymatic activity among SLE subjects, which in turn could favor the accumulation of deleterious hydrogen peroxide. Furthermore, HNE-products are potential neoantigens and could be involved in the pathogenesis of SLE. Decrease in catalase activity could affect the oxidant-antioxidant balance. Chronic disturbance of this balance in patients with SLE may work favorably for the premature onset of atherogenesis with severe vascular effect.

Current status of lupus genetics

Over the past 40 years more than 100 genetic risk factors have been defined in systemic lupus erythematosus through a combination of case studies, linkage analyses of multiplex families, and case-control analyses of single genes. Multiple investigators have examined patient cohorts gathered from around the world, and although we doubt that all of the reported associations will be replicated, we have probably already discovered many of the genes that are important in lupus pathogenesis, including those encoding human leukocyte antigen-DR, Fcγ receptor 3A, protein tyrosine phosphatase nonreceptor 22, cytotoxic T lymphocyte associated antigen 4, and mannose-binding lectin. In this review we will present what is known, what is disputed, and what remains to be discovered in the world of lupus genetics.

Effect of glutathione S-transferase polymorphisms and proximity to hazardous waste sites on time to systemic lupus erythematosus diagnosis: results from the Roxbury lupus project

OBJECTIVE

The high prevalence of systemic lupus erythematosus (SLE) among African American women may be due to environmental exposures, genetic factors, or a combination of factors. Our goal was to assess association of residential proximity to hazardous waste sites and genetic variation in 3 glutathione Stransferase (GST) genes (GSTM1, GSTT1, and GSTP1) with age at diagnosis of SLE.

METHODS

Residential histories were obtained by interviewing 93 SLE patients from 3 predominantly African American neighborhoods in Boston. Residential addresses and locations of 416 hazardous waste sites in the study area were geocoded using ArcView software. Time-varying Cox models were used to study the effect of residential proximity to hazardous sites, GST genotype, and interaction between genotype and exposure in determining age at diagnosis.

RESULTS

The prevalence of SLE among African American women in these neighborhoods was 3.56 SLE cases per 1,000. Homozygosity for GSTM1-null and GSTP1 Ile105Val in combination was associated with earlier SLE diagnosis (P = 0.03), but there was no association with proximity to 416 hazardous sites. Available data on specific site contaminants suggested that, at a subset of 67 sites, there was higher potential risk for exposure to volatile organic compounds (P < 0.05 with Bonferroni correction). GST genotypes had a significant interaction with proximity (P = 0.03) in analyses limited to these sites.

CONCLUSION

There was no independent association between residential proximity to hazardous waste sites and the risk of earlier SLE diagnosis in this urban population. However, analysis of a limited number of sites indicated that the risk of earlier SLE associated with proximity to hazardous sites might be modulated by GST polymorphisms.

Meta-analysis of genome-wide linkage studies of systemic lupus erythematosus

A genetic contribution to the development of systemic lupus erythematosus (SLE) is well established. Several genome-wide linkage scans have identified a number of putative susceptibility loci for SLE, some of which have been replicated in independent samples. This study aimed to identify the regions showing the most consistent evidence for linkage by applying the genome scan meta-analysis (GSMA) method. The study identified two genome-wide suggestive regions on 6p21.1-q15 and 20p11-q13.13 (P-value=0.0056 and P-value=0.0044, respectively) and a region with P-value<0.01 on 16p13-q12.2. The region on chromosome 6 contains the human leukocyte antigen cluster, and the chromosome 16 and 20 regions have been replicated in several cohorts. The potential importance of the identified genomic regions are also highlighted. These results, in conjunction with data emerging from dense single nucleotide polymorphism typing of specific regions or future genome-wide association studies will help guide efforts to identify the actual predisposing genetic variation contributing to this complex genetic disease.

Familial aggregation and linkage analysis of autoantibody traits in pedigrees multiplex for systemic lupus erythematosus

Autoantibodies are clinically relevant biomarkers for numerous autoimmune disorders. The genetic basis of autoantibody production in systemic lupus erythematosus (SLE) and other autoimmune diseases is poorly understood. In this study, we characterized autoantibody profiles in 1,506 individuals from 229 multiplex SLE pedigrees. There was strong familial aggregation of antinuclear antibodies (ANAs), anti-double-stranded DNA (dsDNA), anti-La/SSB, anti-Ro/SSA, anti-Sm, anti-nRNP (nuclear ribonucleoprotein), IgM antiphospholipid (aPL) antibodies (Abs) and rheumatoid factor (RF) across these families enriched for lupus. We performed genome-wide linkage analyses in an effort to map genes that contribute to the production of the following autoantibodies: Ro/SSA, La/SSB, nRNP, Sm, dsDNA, RF, nuclear and phospholipids. Using an approach to minimize false positives and adjust for multiple comparisons, evidence for linkage was found to anti-La/SSB Abs on chromosome 3q21 (adjusted P=1.9 x 10(-6)), to anti-nRNP and/or anti-Sm Abs on chromosome 3q27 (adjusted P=3.5 x 10(-6)), to anti-Ro/SSA and/or anti-La/SSB Abs on chromosome 4q34-q35 (adjusted P=3.4 x 10(-4)) and to anti-IgM aPL Abs on chromosome 13q14 (adjusted P=2.3 x 10(-4)). These results support the hypothesis that autoantibody production is a genetically complex trait. Identification of the causative alleles will advance our understanding of critical molecular mechanisms that underlie SLE and perhaps other autoimmune diseases.

Update on human systemic lupus erythematosus genetics

PURPOSE OF REVIEW

Susceptibility to systemic lupus erythematosus (SLE) has a genetic component. In recent years, nine complete genome scans using family collections that differ greatly in ethnic compositions and geographic locations have identified several strong, confirmed SLE susceptibility loci. Evidence implicating individual gene polymorphisms (or haplotypes) within some of the linked intervals has been reported. This review highlights recent findings that may lead to the identification of putative genes and new insights in the pathogenesis of SLE.

RECENT FINDINGS

Eight of the best-supported SLE susceptibility loci are 1q23, 1q25-31, 1q41-42, 2q35-37, 4p16-15.2, 6p11-21, 12p24, and 16q12. These are chromosomal regions exhibiting genome-wide significance for linkage in single studies and suggestive evidence for linkage in other samples. Linkage analyses conditioning on pedigrees in which one affected member manifesting a particular clinical condition have also yielded many chromosomal regions linked to SLE. The linked interval on chromosome 6p has been narrowed to 0.5 approximately 1.0 Mb (million basepairs) of 3 MHC class II containing risk haplotypes in white subjects. Cumulative results have shown that hereditary deficiencies of complement component C4A (a MHC class III gene) confer risk for SLE in almost all ethnic groups studied. The FcgammaR genes (located at 1q23) have been convincingly demonstrated to play an important role in susceptibility to SLE (and/or lupus nephritis). The evidence for the intronic single nucleotide polymorphism of program cell death gene 1 (PDCD1 at 2q37) to confer susceptibility is promising but not yet compelling. Within several established susceptibility loci, evidence for association of positional candidate genes is emerging.

SUMMARY

Further replications of linkage and association are the immediate task. The respective contribution of each susceptibility gene, relationships between genotypes and phenotypes, and potential interactions between susceptibility gene products need to be elucidated. This line of investigation is now well poised to provide novel insights into how genetic variants can affect functional pathways leading to the development of SLE.

Current advances in the human lupus genetics

Genetic predisposition has been firmly established as a key element in susceptibility to systemic lupus erythematosus (SLE). During the past three decades, association studies have assessed many genes for potential roles in predisposing to SLE. These studies have identified a few risk factors including hereditary deficiency of complement components, major histocompatibility complex class II alleles, and allelic variants for the Fc portion of IgG (FCGR) genes. In recent years, a few groups have completed linkage analyses in data sets from families containing multiple members affected with SLE. Results from these initial genome scans are encouraging; approximately eight chromosomal regions have been identified exhibiting evidence for significant linkage to SLE and have been confirmed using independent cohorts (1q23, 1q25-31, 1q41-42, 2q35-37, 4p16-15.2, 6p11-21, 12q24, and 16q12), suggesting the high likelihood of the presence of one or multiple SLE susceptibility genes at each locus. Another approach of linkage analyses conditioned on pedigrees where one affected member manifesting a particular clinical condition has also identified many chromosomal regions linked to SLE. Within several established susceptibility loci, evidence for association of positional candidate genes is emerging. Within 2q35-37, an intronic single nucleotide polymorphism (SNP) of the positional candidate gene program cell death 1 gene has been associated with SLE susceptibility. The SLE-associated SNP affects a transcription factor, RUNX1, binding site. Recently, SNPs of novel positional candidate genes that influence RUNX1 binding motifs have also been associated with other autoimmune diseases, suggesting the possibility of a common theme shared among susceptibility genes for autoimmune diseases. In the coming years, susceptibility genes responsible for the observed linkage will be identified, and will lead to further delineating genetic pathways involved in susceptibility to SLE.