A revised estimate of twin concordance in systemic lupus erythematosus

Primary biliary cirrhosis in monozygotic and dizygotic twins: genetics, epigenetics, and environment

BACKGROUND & AIMS

There is growing evidence that the interplay of genetic susceptibility and environmental factors leads to primary biliary cirrhosis (PBC). In particular, family members of an infected individual have up to a 100-fold higher risk of developing PBC. Although concordant rates for identical twins in other autoimmune diseases range between 25% and 50%, there are no such data on PBC. Accordingly, we evaluated the concordance of PBC in a genetically defined population of twin sets and evaluated the clinical characteristics between concordant subjects.

METHODS

We identified 16 pairs of twins within a 1400-family cohort followed up by several centers worldwide, evaluated the diagnosis of PBC in all individuals, and determined the zygosity of sets reported as identical by the analysis of 2 highly variable HLA class II regions and 5 short tandem repeats.

RESULTS

Eight of 16 sets of twins were monozygotic. In 5 of 8 monozygotic twin sets, both individuals had PBC (pairwise concordance rate, 0.63). Among the dizygotic twins (n = 8), no set was found to be concordant for PBC. Interestingly, the age at onset of disease was similar in 4 of 5 concordant sets of monozygotic pairs; however, there were differences in natural history and disease severity.

CONCLUSIONS

The concordance rate of PBC in identical twins is among the highest reported in autoimmunity. However, discordant pairs were identified. The data show not only the role of genetics but also emphasize that either epigenetic factors and/or environment play a critical role.

Chromosome 17p12-q11 harbors susceptibility loci for systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the presence of autoantibodies against intracellular components, the formation of immune complexes, and inflammation in various organs, typically the skin and kidney glomeruli. The etiology of the disease is not well understood but is most likely the result of the interaction between genetic and environmental factors. In order to identify susceptibility loci for SLE, we have performed genome scans with microsatellite markers covering the whole genome in families from Argentina, Italy, and Europe. The results reveal a heterogeneous disease with different susceptibility loci in different family sets. We have found significant linkage to chromosome 17p12-q11 in the Argentine set of families. The maximum LOD score was given by marker D17S1294 in combination with D17S1293, when assuming a dominant inheritance model (Z = 3.88). We also analyzed a repeat in the promoter region of the NOS2A gene, a strong candidate gene in the region, but no association was found. The locus on chromosome 17 has previously been identified in genetic studies of multiple sclerosis families. Several other interesting regions were found at 1p35, 1q31, 3q26, 5p15, 11q23 and 19q13, confirming previously identified loci for SLE or other autoimmune diseases.

Anti-mannose binding lectin antibodies in sera of Japanese patients with systemic lupus erythematosus

Mannose-binding lectin (MBL) is a key element in innate immunity with functions and structure similar to that of complement C1q. It has been reported that MBL deficiency is associated with occurrence of systemic lupus erythematosus (SLE). We hypothesized that anti-MBL antibodies, if present, would affect the occurrence or disease course of SLE, by reduction of serum MBL levels, interference of MBL functions, or binding to MBL deposited on various tissues. To address this hypothesis, we measured the concentration of anti-MBL antibodies in sera of 111 Japanese SLE patients and 113 healthy volunteers by enzyme immunoassay. The titres of anti-MBL antibodies in SLE patients were significantly higher than those in healthy controls. When the mean + 2 standard deviations of controls was set as the cut off point, individuals with titres of anti-MBL antibodies above this level were significantly more frequent in SLE patients (9 patients) than in controls (2 persons). One SLE patient had an extremely high titre of this antibody. No associations of titres of anti-MBL antibodies and (i) genotypes of MBL gene, (ii) concentrations of serum MBL, or (iii) disease characteristics of SLE, were apparent. Thus, we have confirmed that anti-MBL antibodies are indeed present in sera of some patients with SLE, but the significance of these autoantibodies in the pathogenesis of SLE remains unclear.

Haplotype associations define target regions for susceptibility loci in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by diverse and variable clinical manifestations. The etiology of SLE is still unknown, but both environmental and genetic factors are involved. Recent genome-wide scans and candidate genes studies in different ethnic groups have already suggested susceptibility loci for SLE, but most of the genetic component remains unexplained. We have previously conducted a genome-wide scan in 35 Finnish families multiply affected with SLE. With 417 microsatellite markers, we detected suggestive linkage in regions on chromosomes 6q and 14q as well as HLA on 6p. The 14q locus has also been implicated in three previous genome scans on SLE, whereas a partially overlapping region on 6q was implicated in one previous study. In an effort to obtain additional evidence for susceptibility loci on 6q and 14q and in order to refine their positions, we performed fine mapping at 1 cM density across the suggestive regions of linkage. Our results show evidence for excess sharing of a haplotype on 14q and excess transmission of a haplotype on 6q. Our results are compatible with the idea of a founder effect for susceptibility genes in SLE in central eastern Finland and suggest a path to the isolation of the putative susceptibility genes.

The autoimmune T and B cell repertoires in monozygotic twins discordant for myasthenia gravis

Two pairs of monozygotic twins, discordant for myasthenia gravis (MG) for more than 30 years, were studied regarding T cell and antibody reactivity against disease related autoantigens, the acetylcholine receptor, one idiotypic and one anti-idiotypic human monoclonal antibody. The healthy and myasthenic twins had very similar autoantibody repertoires. IgG fractions from both healthy and myasthenic twins had the same capacity to decrease the free acetylcholine receptor content in mice after passive transfer. In comparison with their myasthenic sisters, the healthy twins had lower T cell responses against the acetylcholine receptor.

Uncovering the genetics of systemic lupus erythematosus: implications for therapy

Although it is well known that genetic factors contribute significantly to the expression of systemic lupus erythematosus (SLE) it was only recently realized, through genome-wide searches, that the number of involved genes is rather large. The published information hints at two facts: first, the number of genomic loci identified in various diverse cohorts is large and not necessarily overlapping; and second, certain loci may be preferentially linked with specific clinical manifestations. The latter may ultimately lead to a better understanding of the nature of the clinical entity that we know as SLE, and identification of groups of patients prone to respond better to treatment or to develop significant adverse effects. Advances attained regarding the nature of the biochemical and molecular defects that underwrite the aberrant function of immune cells parallel the progress made on the genetic origin of the disease. The genetic links need to be connected with aberrant function of their products to validate their significance. It is expected that correction of molecular aberrations either medicinally or by gene therapy will provide the needed specific treatment for patients with SLE.

Polymorphism at the C-reactive protein locus influences gene expression and predisposes to systemic lupus erythematosus

Relative deficiency of pentraxin proteins is implicated in the pathogenesis of systemic lupus erythematosus. The C-reactive protein (CRP) response is defective in patients with acute flares of disease, and mice with targeted deletions of the serum amyloid P component gene (Sap) develop a lupus-like illness. In humans, the genes for CRP (CRP) and SAP (APCS) map to 1q23.2 within an interval linked with SLE. We have investigated the candidate genes CRP and APCS in two cohorts totalling 586 UK simplex SLE families. The inheritance of an intronic dinucleotide repeat and seven single nucleotide polymorphisms in the CRP and APCS genes was examined by application of family-based tests of association and linkage. Basal levels of CRP were influenced independently by two polymorphisms at the CRP locus, CRP 2 and CRP 4. Furthermore, the latter polymorphism was linked/associated with SLE and antinuclear autoantibody production. Thus, the polymorphism associated with reduced basal CRP was also associated with the development of SLE. These data support the hypothesis that defective disposal of potentially immunogenic material is a contributory factor in lupus pathogenesis. The identification of polymorphisms that determine basal CRP levels has implications in ischaemic heart disease, where CRP level is an important predictor of risk.

Linkage at 12q24 with systemic lupus erythematosus (SLE) is established and confirmed in Hispanic and European American families

Systemic lupus erythematosus (SLE) is a chronic, complex, and systemic human autoimmune disease, with both an environmental component and a heritable predisposition. Clinical studies, reinforced by epidemiology and genetics, show impressive variation in disease severity, expression, prevalence, and incidence by ethnicity and sex. To identify the novel SLE susceptibility loci, we performed a genomewide scan with 318 markers on 37 multiplex Hispanic families, using a nonparametric penetrance-independent affected-only allele-sharing method. Three chromosomal regions (12q24, 16p13, and 16q12-21) exceeded our predetermined threshold (Zlr>2.32; nominal P<.01) for further evaluation. Suspected linkages at 12q24, 16p13, and 16q12-21 were tested in an independent data set consisting of 92 European American (EA-1) and 55 African American (AA) families. The linkage at 12q24 was replicated in EA-1 (Zlr=3.06; P=.001) but not in AA (Zlr=0.37; P=.35). Although neither the 16p13 nor the 16q12-21 was confirmed in EA-1 or AA, the suggestive linkage (Zlr=3.06; P=.001) at 16q12-21 is sufficient to confirm the significant linkage, reported elsewhere, at this location. The evidence for linkage at 12q24 in the 129 combined (Hispanic and EA-1) families exceeded the threshold for genomewide significance (Zlr=4.39; P=5.7x10-6; nonparametric LOD=4.19). Parametric linkage analyses suggested a low-penetrance, dominant model (LOD=3.72). To confirm the linkage effect at 12q24, we performed linkage analysis in another set of 82 independent European American families (EA-2). The evidence for linkage was confirmed (Zlr=2.11; P=.017). Therefore, our results have detected, established, and confirmed the existence of a novel SLE susceptibility locus at 12q24 (designated "SLEB4") that may cause lupus, especially in Hispanic and European American families.

Triplets with systemic lupus erythematosus

We present herein the first case report of identical triplets who developed systemic lupus erythematosus (SLE). The children were diagnosed as having SLE in reverse birth order at ages 8, 9, and 11 years. Although genetically identical, each sibling manifested different clinical signs and symptoms; however, all 3 children did manifest skin rash, fatigue, and biopsy-proven glomerulonephritis at different ages. Findings of laboratory studies were similar, including positivity for antinuclear antibodies, anti-native DNA, and anti-double-stranded DNA, as well as low levels of complement. These findings confirmed SLE in each sibling.

Analysis of systemic sclerosis in twins reveals low concordance for disease and high concordance for the presence of antinuclear antibodies

OBJECTIVE

To examine concordance for systemic sclerosis (SSc) in monozygotic (MZ) and dizygotic (DZ) twins.

METHODS

MZ and DZ twins were recruited nationwide. Zygosity was confirmed by DNA fingerprint analysis. The presence of antinuclear antibodies (ANAs) was determined using indirect immunofluorescence with HEp-2 cells as substrate. Identification of SSc-associated serum autoantibodies was performed by immunoprecipitation and double immunodiffusion. Major histocompatibility complex class II alleles were identified by polymerase chain reaction-restriction fragment length polymorphism analysis.

RESULTS

Concordance for SSc was found to be similar in MZ and DZ twins. Overall concordance for SSc was low in the twins (4.7%). Concordance for the presence of ANAs was significantly higher in MZ twins compared with DZ twins. SSc-associated serum autoantibodies occurred exclusively in patients with SSc. The distribution of SSc-associated serum autoantibodies was similar to that observed in our large database of SSc patients. Increased HLA allele sharing was detected in DZ twins, irrespective of disease concordance.

CONCLUSION

These results indicate that inherited genetic factors are not sufficient to explain the development of SSc. Rather, these data indicate that inheritance may play a role in the development of serum autoantibodies in the "healthy" twin sibling of an SSc patient.

Environmental exposure to mercury and its toxicopathologic implications for public health

Mercury is a toxic and hazardous metal that occurs naturally in the earth's crust. Natural phenomena such as erosion and volcanic eruptions, and anthropogenic activities like metal smelting and industrial production and use may lead to substantial contamination of the environment with mercury. Through consumption of mercury in food, the populations of many areas, particularly in the developing world, have been confronted with catastrophic outbreaks of mercury-induced diseases and mortality. Countries such as Japan, Iraq, Ghana, the Seychelles, and the Faroe Islands have faced such epidemics, which have unraveled the insidious and debilitating nature of mercury poisoning. Its creeping neurotoxicity is highly devastating, particularly in the central and peripheral nervous systems of children. Central nervous system defects and erethism as well as arrythmias, cardiomyopathies, and kidney damage have been associated with mercury exposure. Necrotizing bronchitis and pneumonitis arising from inhalation of mercury vapor can result in respiratory failure. Mercury is also considered a potent immunostimulant and -suppressant, depending on exposure dose and individual susceptibility, producing a number of pathologic sequelae including lymphoproliferation, hypergammaglobulinemia, and total systemic hyper- and hyporeactivities. In this review we discuss the sources of mercury and the potential for human exposure; its biogeochemical cycling in the environment; its systemic, immunotoxic, genotoxic/carcinogenic, and teratogenic health effects; and the dietary influences on its toxicity; as well as the important considerations in risk assessment and management of mercury poisoning.

Immunopathology and the gene therapy of lupus

Lupus is a chronic autoimmune inflammatory disease with complex clinical manifestations. In humans, lupus, also known as systemic lupus erythematosus (SLE), affects between 40 and 250 individuals, mostly females, in each 100 000 of the population. There are also a number of murine models of lupus widely used in studies of the genetics, immunopathology, and treatment of lupus. Human patients and murine models of lupus manifest a wide range of immunological abnormalities. The most pervasive of these are: (1) the ability to produce pathogenic autoantibodies; (2) lack of T- and B-lymphocyte regulation; and (3) defective clearance of autoantigens and immune complexes. This article briefly reviews immunological abnormalities and disease mechanisms characteristic of lupus autoimmunity and highlight recent studies on the use of gene therapy to target these abnormalities.

Analysis of gene expression profiles in human systemic lupus erythematosus using oligonucleotide microarray

Epidemiologic studies suggest a strong genetic component for susceptibility to systemic lupus erythematosus (SLE). To investigate the genetic mechanism of pathogenesis of SLE, we studied the difference in gene expression of peripheral blood cells between 10 SLE patients and 18 healthy controls using oligonucleotide microarray. When gene expression for patients was compared to the mean of normal controls, among the 3002 target genes, 61 genes were identified with greater than a two-fold change difference in expression level. Of these genes, 24 were upregulated and 37 downregulated in at least half of the patients. By the Welch's ANOVA/Welch's t-test, all these 61 genes were significantly different (P<0.05) between SLE patients and normal controls. Among these genes with differential expression, IFN-omega and Ly6E (TSA-1/Sca-2) may play an important role in the mechanism of SLE pathogenesis. TSA-1 antigens may represent an important alternative pathway for T-cell activation that may be involved in IFN-mediated immunomodulation. Hierarchical clustering showed that patient samples were clearly separated from controls based on their gene expression profile. These results demonstrate that high-density oligonucleotide microarray has the potential to explore the mechanism of pathogenesis of systemic lupus erythematosus.

Environmental epidemiology and risk factors for autoimmune disease

It has long been recognized that environmental influences play an important role in the risk of developing chronic rheumatic disease. Defining specific pathogenic environmental mediators that may trigger the development or progression of autoimmune disease remains a focus of increasing investigative effort. Factors promoting disease may not be identical to factors that influence the severity or progression of the disorder. Human monozygotic twin studies, animal studies, and genetic models demonstrate that genetic influences strongly determine whether one will develop autoimmunity, however, genes affecting the metabolism of exogenous agents that may trigger disease expression have only recently drawn attention. In this article the authors review recent reports that advance our understanding of previously recognized environmental risk factors and challenge accepted beliefs that increased estrogenic exposures predate the incidence of autoimmune disorders, systemic lupus erythematosus in particular.

Thrombocytopenia identifies a severe familial phenotype of systemic lupus erythematosus and reveals genetic linkages at 1q22 and 11p13

Systemic lupus erythematosus (SLE) is a complicated autoimmune disease with a definite genetic predisposition. Thrombocytopenia predicts severe disease and death in SLE, making the identification of the related genetic risk factors especially important. We selected the 38 pedigrees that had an SLE patient with thrombocytopenia (platelets, < 10 x 10(9)/L [< 100,000/microL]) from a collection of 184 pedigrees multiplex for SLE. Linkages were established at 1q22-23 (maximum logarithm of odds [lod(max)] = 3.71) in the 38 pedigrees and at 11p13 (lod(max) = 5.72) in the 13 African American pedigrees. Nephritis, serositis, neuropsychiatric involvement, autoimmune hemolytic anemia, anti-double-stranded DNA, and antiphospholipid antibody were associated with thrombocytopenia. Other results show that SLE is more severe in the families with a thrombocytopenic SLE patient, whether or not thrombocytopenia in an individual patient is considered. These results are consistent with thrombocytopenia being a component of a severe familial form of SLE and with genes at 1q22-23 and 11p13 contributing to this severe phenotype and to the subsequent high mortality associated with thrombocytopenia in SLE.

[Childhood-onset systemic lupus erythematosus]

Systemic Lupus Erythematosus (SLE) remains a challenging autoimmune disease in term of etiology, pathogenesis and treatment. It is estimated that 10-17% of lupus patients present before the age of 16. SLE in children appears to have more severe organ involvement than in adults. The outcome of childhood SLE has improved during the last decade, but the morbidity remains high.

Rheumatic syndromes associated with complement deficiency

Deficiency of an early component of the classical complement pathway, C1q, C1r/C1s, C4, or C2, regularly produces autoimmunity in man, especially systemic lupus erythematosus. It has long been suggested that disruption of this pathway would lead to the inappropriate handling of immune complexes. An intriguing hypothesis that builds on this idea relates to a defect in clearance of one's own cellular debris, namely apoptotic cells. An attractive feature of this emerging concept is that blebs on apoptotic cells are decorated with antigens to which much of the autoantibody specificity is directed in systemic lupus erythematosus. A second hypothesis, generated primarily from complement deficiencies, relates to an impairment in the humoral immune response or in the regulation of autoreactive B cells. This review begins by summarizing the recognized autoimmune manifestations of complement deficiency and then describes new data derived from targeted gene deletions of complement proteins.

Elevated IL-16 levels in patients with systemic lupus erythematosus are associated with disease severity but not with genetic susceptibility to lupus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by several immunological abnormalities. The pathogenic importance of T cells in this disease is well established. Interleukin-16 (IL-16) is a cytokine which is mainly produced by CD8+ T cells and induces chemotaxis of CD4+ T cells and monocytes. IL-16 levels have been shown to be elevated in SLE patients in a cross-sectional study, but the mechanism is unknown. To explore whether the increased IL-16 levels are associated with genetic background or the disease itself, we investigated the IL-16 level in healthy first-degree family members of SLE patients and SLE patients who were followed over time with regard to disease activity. We observed high IL-16 levels in SLE patients with severe disease compared to SLE patients with non-severe disease and healthy controls. Furthermore, IL-16 levels in first-degree relatives were not different from those in healthy controls. These results suggest that high IL-16 levels are associated with severity of SLE, but not with genetic susceptibility to SLE. Finally, we followed the disease activity of SLE patients over time, which showed significant correlation between the SLE disease activity index and IL-16, ESR and the complement components C3, C4 and CH50. In conclusion, these results implicate an association of IL-16 with SLE.

Linkage and interaction of loci on 1q23 and 16q12 may contribute to susceptibility to systemic lupus erythematosus

OBJECTIVE

Six recent genome scans of different systemic lupus erythematosus (SLE) multiplex family cohorts showed multiple putative susceptibility loci. In the present study, we examined 4 previously identified loci to replicate findings of significant linkage to 1q23 and 16q12, and to support findings of suggestive linkage to 14q21-23 and 20p12 in a cohort of 115 multiethnic nuclear families containing 145 SLE-affected sibpairs.

METHODS

Model-free, multipoint linkage analyses (SIBPAL2, SAGE version 4.0) and exclusion mapping (GeneHunter) were performed.

RESULTS

Linkages to 1q23 (peak at D1S2675, mean allele sharing [MAS] 0.56; P = 0.003) and to 16q12 (peaks between D16S753 and D16S757, MAS 0.57; P = 0.003) were confirmed, but linkage evidence at 20p12 was weak and inconsistent (MAS 0.52-0.56; from P = 0.005 to P not significant). Evidence for linkage to 1q23 and 16q12 was stronger in 68 non-Caucasian affected sibpairs than in 77 Caucasian affected sibpairs. Exclusion mapping ruled out linkage at 14q21-23 (lambda(s) [sib recurrence risk or genotypic risk ratio] = 1.8). Because the pericentromeric region of chromosome 16 has been identified by genome scans in several autoimmune diseases, we postulated that it might harbor an autoimmune modifier gene. To explore this possibility, we tested for an interaction between 16q12 and 1q23, and between 16q12 and 20p12. Haplotype sharing at 1q23 increased concomitantly with increased haplotype sharing at 16q12 (P = 0.008 by nonparametric Jonckheere-Terpstra exact statistical test). No evidence supporting an interaction between 16q12 and 20p12 was observed. Analysis of sibpairs sharing 2 alleles at 16q12 also showed increased allele sharing at 1q23 (MAS from 0.56 to 0.65).

CONCLUSION

These data support the presence of SLE susceptibility genes at 1q23 and 16q12, particularly in non-Caucasians. The skewed distribution of haplotypes suggests that genetic interaction of these two loci may affect SLE susceptibility.

Stratification of pedigrees multiplex for systemic lupus erythematosus and for self-reported rheumatoid arthritis detects a systemic lupus erythematosus susceptibility gene (SLER1) at 5p15.3

OBJECTIVE

Arthritis is a common manifestation in systemic lupus erythematosus (SLE), appearing in approximately 85% of patients. Often, the polyarthritis at presentation of SLE cannot be distinguished from rheumatoid arthritis (RA) by physical examination or history. Indeed, physicians initially tell many SLE patients that they have RA (one source of "self-reported RA"), only to have SLE established later. In addition, RA aggregates in families with an SLE proband. We predicted that pedigrees multiplex for both SLE and for self-reported RA would better isolate particular genetic effects. If this proved to be true, we would then use the increased genetic homogeneity to more easily reveal genetic linkage.

METHODS

From a collection of 160 pedigrees multiplex for SLE, we selected 36 pedigrees that also contained >or=2 members with self-reported RA (19 pedigrees were African American, 14 were European American, and 3 were of other ethnic origin). Data from a genome scan of 307 microsatellite markers were evaluated for SLE linkage by contemporary genetic epidemiologic techniques.

RESULTS

The most significant evidence of linkage to SLE was obtained at 5p15.3 in the European American pedigrees by both parametric (logarithm of odds [LOD] score 6.2, P = 9.3 x 10(-8)) and nonparametric (LOD score 6.9, P = 1.7 x 10(-8)) methods. The best-fitting model for this putative SLE gene in this region was a recessive gene with a population frequency of 5% and with 50% penetrance in females and 15% penetrance in males at virtually 100% homogeneity.

CONCLUSION

For a genetically complex disease phenotype, an unusually powerful linkage has been found with SLE at 5p15.3 in European American pedigrees multiplex for SLE and for self-reported RA. This result predicts the presence of a gene at the top of chromosome 5 in this subset of patients that is important for the pathogenesis of SLE.

A major susceptibility locus for systemic lupus erythemathosus maps to chromosome 1q31

A set of 87 multicase families with systemic lupus erythemathosus (SLE) from European (Iceland, Sweden, England, Norway, Italy, and Greece) and recently admixed (Mexico, Colombia, and the United States) populations were genotyped and analyzed for 62 microsatellite markers on chromosome 1. By parametric two-point linkage analysis, six regions (1p36, 1p21, 1q23, 1q25, 1q31, and 1q43) were identified that have LOD scores of Z>or=1.50, with different contributions, depending on the population of origin of the families (European or admixed American). All of the regions have been described previously and have therefore been confirmed in this analysis. The locus at 1q31 showed a significant three-point LOD score of Z=3.79 and was contributed by families from all populations, with several markers and under the same parametric model. Analysis of a known mutation in the CD45 gene did not support the role that this mutation plays in disease. We conclude that the locus at 1q31 contains a major susceptibility gene, important to SLE in general populations.

A genetic marker within the CD44 gene confirms linkage at 11p13 in African-American families with lupus stratified by thrombocytopenia, but genetic association with CD44 is not present

Systemic lupus erythematosus (SLE) is complicated from both a clinical and genetic standpoint. We have stratified SLE families by the presence of thrombocytopenia, which is associated with increased mortality among SLE patients, and found genetic linkage at chromosome 11p13 in African-American families. In the present study we have evaluated CD44, a gene very close (0.5 cM) to the peak LOD score marker, as a candidate gene. Using a newly identified short DNA repeat within the CD44 gene, we find a LOD score of 2.7, which confirms linkage within this genetic interval. However, using a panel of four single nucleotide markers spanning the CD44 gene, we find no genetic association with SLE. Therefore, these data further suggest an SLE susceptibility gene at 11p13, but also imply that an ancestral mutation in the CD44 gene does not account for the linkage.

Risk factors for development of systemic lupus erythematosus: allergies, infections, and family history

We examined risk factors for systemic lupus erythematosus (SLE) in 265 recently diagnosed patients in North Carolina and South Carolina and 355 control subjects identified through driver's license records and frequency matched to patients by age, sex, and state. Analyses were limited to exposures before diagnosis (cases) or reference year (control subjects). SLE patients were more likely than control subjects to report a history of allergy to medications (odds ratio [OR] 3.1, 95% confidence interval [CI], 2.1-4.5), particularly to antibiotics. SLE risk increased with history of shingles (OR 2.5, 95% CI 1.1-5.9) and with frequent (more than once per year) cold sores in the 3 years before diagnosis (OR 2.8, 95% CI 1.4-5.4). There was little association with history of mononucleosis, a marker of late infection with Epstein-Barr virus, implanted medical devices, or hepatitis B vaccination. History of lupus in parents or siblings was associated with an increased risk (OR 3.3, 95% CI 1.2-8.6). Further research is needed to clarify whether medication allergies and specific infectious agents are involved in the etiology of SLE. Published by Elsevier Science Inc.

Familiality and co-occurrence of clinical features of systemic lupus erythematosus

OBJECTIVE

To evaluate familiality of 15 clinical and laboratory features in systemic lupus erythematosus (SLE)-affected sibpairs, and to estimate correlations with the age at SLE diagnosis in affected sibpairs and parent-offspring pairs.

METHODS

Concordance rates and sibling risk ratios were used as indicators of familiality for 15 manifestations of SLE. Pearson's correlations and paired t-tests were used to compare the age at SLE diagnosis in affected sibpairs and in parent-offspring pairs.

RESULTS

Increased sibling risk ratios (1.9-3.9) for thrombocytopenia, discoid rash, neurologic disorder (defined as seizure or psychosis), and hemolytic anemia were observed in 159 SLE-affected sibpairs. Among these clinical features, paired expression of hemolytic anemia plus thrombocytopenia and hemolytic anemia plus neurologic disorder appeared to be more frequent in 709 SLE patients than would be expected by chance (P < 0.00001 and P < 0.007, respectively). The ratio of the presence of both hemolytic anemia and neurologic disorder was approximately 13 times higher in the younger affected sib than in the older affected sib (P < 0.02). Familiality of patient age at SLE diagnosis, as observed by relative correlations, was greater in 125 affected sibpairs (r = 0.67, P < 0.0001) than in 37 affected parent-offspring pairs (r = 0.47, P = 0.003). The median +/- SD age at SLE diagnosis was significantly lower in offspring (21.5 +/- 10.1 years) than in their parents (41.6 +/- 15.8 years) (P < 0.0001) but was not different in sibpairs. The combined non-Caucasian sibpairs had a younger mean age at SLE diagnosis compared with Caucasian sibpairs (P = 0.014).

CONCLUSION

Evidence for familiality of thrombocytopenia, discoid rash, neurologic disorder, hemolytic anemia, and co-occurring neurologic disorder plus hemolytic anemia in SLE was observed in 159 affected sibpairs. Familiality of the age at SLE diagnosis in relative pairs suggests that shared genes and/or shared environmental exposures impact disease susceptibility. Shared immediate environmental triggers appear less compelling, because the average time between dates of diagnosis was 11 years in parent-offspring pairs and 7.5 years in affected sibpairs. The significantly earlier age at disease diagnosis in offspring compared with their parents suggests that some forms of anticipation might play a role in susceptibility to SLE. Stratifying families by subphenotypes that are familial may reduce heterogeneity and facilitate identification of genetic risk factors for SLE.

The genetics of systemic lupus erythematosus: putting the pieces together

With lambda(s) estimates of 10 to 20 and other evidence of familial aggregation, as well as a monozygotic twin concordance rate >20, systemic lupus erythematosus (SLE) would appear to be a very promising phenotype using modern genetic approaches. Indeed, genetic associations are already known at numerous candidate loci including various HLA alleles, complement component genes, Fcgamma receptors, and others, and murine genetic studies of lupus models have provided additional candidate genes and potential syntenic linkages to evaluate in man. The completed genetic linkage studies performed on various collections of pedigrees multiplex for SLE have identified 60 susceptibility loci with varying degrees of evidence for linkage in man. Seven of these meet or exceed the threshold for significant linkage (LOD > or = 3.3 or P < or = 0.00005) at 1q22-23, 1q41, 2q37, 4p16, 6p21-11, 16q13 and 17p13. In addition, these linkages usually dominate in one ethnicity or another, suggesting that the responsible polymorphisms, once identified, will also vary by ethnicity. Evidence that these linkages can be reproduced range from outright independent confirmation (1q41, 4p16 and 6p21) to additional suggestive evidence in the genomic region of the purported linkage (1q22-23 and 2q37). The results now available suggest that human lupus genetics are robust and that gene identification should be possible using existing genetic approaches and technologies.

Genetic linkage of systemic lupus erythematosus with chromosome 11q14 (SLEH1) in African-American families stratified by a nucleolar antinuclear antibody pattern

Systemic lupus erythematosus (SLE) is an autoimmune disease with complex genetics. We evaluated pedigrees multiplex for SLE that had an affected with antinucleolar antibodies to increase the homogeneity for genetic linkage analysis. We found a significant linkage effect on chromosome 11q14 at marker D11S2002 in African-American Pedigrees. This effect produced a maximum LOD score of 5.62 using a dominant inheritance model with 95% penetrance in males and 99% penetrance in females. The results were supported by multipoint linkage analysis. Fine mapping of the region with two additional markers within 6 cM of D11S2002 further provided evidence of linkage in this region. Linkage at D11S2002, named SLEH1, was previously found in some of these same African-American pedigrees multiplex for SLE, but who were stratified by hemolytic anemia (Kelly et al, submitted). In conclusion, an important SLE susceptibility gene, SLEH1 at 11q14, is identified in African-Americans when stratifying pedigrees by antinucleolar autoantibodies.

Genome scan stratified by the presence of anti-double-stranded DNA (dsDNA) autoantibody in pedigrees multiplex for systemic lupus erythematosus (SLE) establishes linkages at 19p13.2 (SLED1) and 18q21.1 (SLED2)

Anti-double-stranded DNA (anti-dsDNA) is arguably one of the most specific autoantibodies in systemic lupus erythematosus (SLE). This antibody is associated with more severe SLE and with glomerulonephritis. From 196 pedigrees multiplex for SLE, we selected those that had any SLE affected positive for anti-dsDNA by the Crithidia luciliae kinetoplast imunofluorescence assay. This stratification strategy tested the hypothesis that anti-dsDNA would identify a more genetically homogeneous group of pedigrees, in which previously undetected linkage effects could be established. A genome screen data for linkage to SLE was available at 307 microsatellite markers for this selected group of 71 pedigrees: 37 European-American, 29 African-American, and five others. The most significant results were obtained at 19p13.2 (LOD(max) = 4.93), named SLED1, in the 37 European-American pedigrees using a dominant model with mixed penetrances (92% for females and 49% for males) at 100% homogeneity (theta = 0). A second linkage effect, SLED2, was established in the 29 African-American pedigrees at 18q21.1 (LOD(max) = 3.40) using a recessive model with 100% penetrance (theta = 0.1). Parametric and non-parametric multipoint analyses were performed, which provided further evidence and support of susceptibility genes residing in these regions. In conclusion, two powerful linkages have been detected with SLE based on the presence of anti-dsDNA. These findings show SLE to be a richly complicated disease phenotype that is now ripe for important new discovery through a genetic approach.

Evidence for a susceptibility gene (SLEH1) on chromosome 11q14 for systemic lupus erythematosus (SLE) families with hemolytic anemia

Hemolytic anemia is a forme fruste of systemic lupus erythematosus (SLE), being observed months or even years before the onset of other clinical manifestations in some patients. We hypothesized that hemolytic anemia in those SLE-affected patients would identify a group of SLE pedigrees that share a high degree of genetic homogeneity. From 160 multiplex SLE pedigrees, we sought evidence for linkage in 35 (16 African-American, 17 European-American, and 2 Hispanic) who had at least one SLE-affected patient with hemolytic anemia. Significant linkage was present at 11q14 in the 16 African-American pedigrees, yielding a maximum two-point logarithm of odds (LOD) score of 4.5 at D11S2002. The segregation pattern of SLE in these African-American pedigrees suggested a dominant mode of inheritance and, when maximized across penetrance and disease allele frequencies, produced a multipoint LOD of 4.7. Multipoint analysis yielded a multipoint heterogeneity LOD score of 3.6 (alpha = 0.63), again with maximum LOD at D11S2002. Finally, markers typed 7 centimorgans to either side of D11S2002 achieved LOD scores of 3 or better by using the maximized model, supporting linkage to 11q14. Clearly, pedigree ascertainment based on select clinical manifestations is an important tool, capable of revealing otherwise cryptic genetic linkages in complex genetic diseases. Thus, we show strong evidence for an SLE susceptibility gene, SLEH1, near D11S2002 in African-American pedigrees multiplex for SLE that have at least one SLE-affected patient with hemolytic anemia.

Long-term followup of children with neonatal lupus and their unaffected siblings

OBJECTIVE

To determine in a longitudinal cohort study whether children with varied manifestations of neonatal lupus or their unaffected siblings later develop autoantibodies and/or rheumatic diseases.

METHODS

To obtain information on the health of children ages >or=8 years who had manifestations of neonatal lupus (affected group) and their unaffected siblings (unaffected group), questionnaires were sent to mothers (with anti-SSA/Ro and/or anti-SSB/La antibodies) who were enrolled in the National Institute of Arthritis and Musculoskeletal and Skin Diseases/Hospital for Joint Diseases Research Registry for Neonatal Lupus. Children of healthy mothers referred by the Registry enrollees comprised the control group. Further data were provided by review of medical records.

RESULTS

Fifty-five mothers enrolled in the Registry returned questionnaires on 49 children with neonatal lupus and their 45 unaffected siblings. Six children with definite rheumatic/autoimmune diseases were identified: 2 with juvenile rheumatoid arthritis, 1 with Hashimoto thyroiditis, 1 with psoriasis and iritis, 1 with diabetes mellitus and psoriasis, and 1 with congenital hypothyroidism and nephrotic syndrome. All had neonatal lupus, and their mothers had manifestations of autoimmune diseases (Sjögren's syndrome in 4, systemic lupus erythematosus/Sjögren's syndrome in 1, and undifferentiated autoimmune disease in 1). Antinuclear antibodies were present in 4 of 55 sera tested (2 of 33 affected children and 2 of 22 unaffected children). No serum contained antibodies reactive with SSA/Ro or SSB/La antigens.

CONCLUSION

These data suggest that children with neonatal lupus require continued followup, especially prior to adolescence and if the mother herself has an autoimmune disease. While there was no apparent increased risk of systemic lupus erythematosus, the development of some form of autoimmune disease (systemic or organ-specific) in early childhood may be of concern. During adolescence and young adulthood, individuals with neonatal lupus and their unaffected siblings do not appear to have an increased risk of developing systemic rheumatic diseases.

Apoptosis of the teratocarcinoma cell line Tera-1 leads to the cleavage of HERV-K10gag proteins by caspases and/or granzyme B

Redistribution, post-translational modifications and coclustering with viral antigens contribute to the immunogenicity of apoptotic cell-derived autoantigens. Almost all known targets of the humoral autoimmune response in systemic lupus erythematosus (SLE) are cleaved by caspases or granzyme B during apoptosis. Antibodies against retroviral proteins can frequently be detected in the sera of SLE patients without overt retroviral infections. These antibodies may represent cross-reactive antibodies or may have been induced by proteins encoded by endogenous retroviral sequences. We used Tera-1 cells that abundantly express a group-specific antigen of human endogenous retroviruses, HERV-K10gag polyprotein, to investigate its processing during apoptosis. Tera-1 cells induced to undergo apoptosis showed an altered HERV-K10gag processing compared with viable cells. In addition, granzyme B was able to cleave HERV-K10gag isolated from viable Tera-1 cells. Similar to nuclear autoantigens, endogenous retroviral proteins are cleaved during the execution phase of apoptosis. These post-translational modifications may result in the generation of T-cell neoepitopes or a changed epitope hierarchy of retroviral proteins. Therefore, immunogenicity of retroviral antigens in SLE patients may result from a similar mechanism as described for nuclear autoantigens.

Further evidence for a strong genetic influence on the development of autoimmune thyroid disease: the California twin study

To determine the heritable component of Graves' disease (GD) more precisely, a disease survey questionnaire completed by 13,726 California-born twin pairs over the age of 37 years was used as the foundation of this study. On the basis of this survey, each member of pairs reporting a past diagnosis of GD was then sought for an extensive telephone interview to seek diagnostic confirmation. Successful diagnostic evaluation occurred in 108 cases, of which 99 affected twin pairs form the basis of this report. The results indicate that the estimated pairwise concordance for is 17% in monozygotic (MZ) twins, and 1.9% in dizygotic (DZ) twins, which are in close agreement with a recent report from a Danish twin population. Moreover, the reported 3.9% occurrence of GD found in the first-degree relatives of affected twin pairs supports these findings. In contrast, only 0.45% of all twins, 0.27% of the spouses of twins, and approximately 0.16% of the first-degree relatives of unaffected twins were reported to have GD. Additionally, among the unaffected MZ twins of patients with GD, 17% reported having chronic thyroiditis and 10% other nonthyroid autoimmune conditions such as lupus erythematosus, pernicious anemia, or idiopathic thrombocytopenic purpura. Thus, a genetic predisposition appears to be shared for both thyroid and some nonthyroid autoimmune diseases. While it seems that GD is a strongly and nonspecifically heritable condition, the relatively low level of twin concordance indicates that this disease likely requires a nonheritable etiologic determinant(s) as well.

Genetic linkage and association of Fcgamma receptor IIIA (CD16A) on chromosome 1q23 with human systemic lupus erythematosus

OBJECTIVE

Although low-affinity alleles of human Fcgamma receptor types IIA and IIIA (FcgammaRIIA and FcgammaRIIIA, respectively) polymorphisms have been associated with systemic lupus erythematosus (SLE) in case-control studies, the relative contribution of these genes to SLE susceptibility has not been resolved.

METHODS

We analyzed the distribution of alleles of FcgammaRIIA, FcgammaRIIIA, and FcgammaRIIIB in 126 multiplex-SLE pedigrees and FcgammaRIIA and FcgammaRIIIA in a case-control replication study, using allele-specific polymerase chain reaction and direct sequencing of genomic DNA. Statistical tests of association were performed to detect evidence of linkage between the single nucleotide polymorphisms and SLE.

RESULTS

We found evidence for linkage at both the FcgammaRIIIA (single-point nonparametric linkage [NPL] 1.8, P = 0.038; multipoint NPL 2.7, P = 0.004) and the FcgammaRIIA (single-point NPL 2.0, P = 0.021; multipoint NPL 2.6, P = 0.006) loci, but not the FcgammaRIIIB locus. Family-based tests of association demonstrated increased transmission of the low-affinity F176 allele at the FcgammaRIIIA locus (odds ratio [OR] 2.18, P = 0.0005 by transmission disequilibrium test and P = 0.002, by pedigree disequilibrium test [PDT]), but little evidence of preferential transmission of alleles at FcgammaRIIA (P = 0.089 by PDT). Stratification by ethnicity showed preferential transmission of the associated FcgammaRIIIA allele both in families of African American ancestry and in those of European American ancestry. Despite significant linkage disequilibrium between these genes, 2- and 3-locus haplotype analysis of the extended Fcgamma receptor cluster did not reveal any significant association beyond that observed with FcgammaRIIIA alone. In a large case-control replication study of 438 patients with SLE and 219 controls, FcgammaRIIIA provided the strongest evidence of an FcgammaR-SLE association (additive model: V/V 176 versus V/F 176 OR 1.51, V/V 176 versus F/F 176 OR 1.98, P = 0.007).

CONCLUSION

To our knowledge, these data are the first to demonstrate linkage and both family-based and case-control-based association of FcgammaRIIIA with SLE. These data provide genetic evidence supporting a role for the physiologically relevant single nucleotide polymorphism of the FcgammaRIIIA gene in the pathophysiology of this complex genetic disease.

Heritable breast cancer in twins

Known major mutations such as BRCA1/2 and TP53 only cause a small proportion of heritable breast cancers. Co-dominant genes of lower penetrance that regulate hormones have been thought responsible for most others. Incident breast cancer cases in the identical (monozygotic) twins of representative cases reflect the entire range of pertinent alleles, whether acting singly or in combination. Having reported the rate in twins and other relatives of cases to be high and nearly constant over age, we now examine the descriptive and histological characteristics of the concordant and discordant breast cancers occurring in 2310 affected pairs of monozygotic and fraternal (dizygotic) twins in relation to conventional expectations and hypotheses. Like other first-degree relatives, dizygotic co-twins of breast cancer cases are at higher than usual risk (standardised incidence ratio (SIR)=1.7, CI=1.1-2.6), but the additional cases among monozygotic co-twins of cases are much more numerous, both before and after menopause (SIR=4.4, CI=3.6-5.6), than the 100% genetic identity would predict. Monozygotic co-twin diagnoses following early proband cancers also occur more rapidly than expected (within 5 years, SIR=20.0, CI=7.5-53.3). Cases in concordant pairs represent heritable disease and are significantly more likely to be oestrogen receptor-positive than those of comparable age from discordant pairs. The increase in risk to the monozygotic co-twins of cases cannot be attributed to the common environment, to factors that cumulate with age, or to any aggregate of single autosomal dominant mutations. The genotype more plausibly consists of multiple co-existing susceptibility alleles acting through heightened susceptibility to hormones and/or defective tumour suppression. The resultant class of disease accounts for a larger proportion of all breast cancers than previously thought, with a rather high overall penetrance. Some of the biological characteristics differ from those of breast cancer generally.

Increased prevalence of renal disease in systemic lupus erythematosus families with affected male relatives

OBJECTIVE

To distinguish familial differences from sex-related differences in the clinical manifestations of systemic lupus erythematosus (SLE).

METHODS

A total of 372 affected individuals from 160 multiplex SLE pedigrees were analyzed. Twenty-five of these pedigrees contained at least 1 affected male relative. Comparisons of the presence of each of the 11 1982 American College of Rheumatology criteria for SLE were made between female family members with affected male relatives and those without affected male relatives, using Fisher's exact tests.

RESULTS

The presence of renal disease was significantly increased in female family members with an affected male relative when compared with those with no affected male relative (68% and 43%, respectively; P = 0.002). This trend remained after stratifying by race and was most pronounced in European Americans. A familial basis for differences in hematologic and immunologic manifestations was also suggested, while arthritis and dermatologic features appeared to be most influenced by sex.

CONCLUSION

Our results demonstrate that the increased prevalence of renal disease previously reported in men with SLE is, in large part, a familial rather than sex-based difference, at least in multiplex SLE families. Distinguishing familial from sex-related differences may facilitate efforts to understand the genetic and hormonal factors that underlie this complex autoimmune disease.

Recent advances in the genetics of systemic lupus erythematosus

In recent years, we have witnessed an explosion in our understanding of the biology of SLE through the study of lupus-prone mice and the identification and subsequent narrowing of the genomic intervals likely responsible for SLE in human beings. The data from these efforts support the hypothesis that multiple genes contribute to disease susceptibility. Clearly, there is no single locus operating in all families multiplex for SLE, and the degree of ethnic and genetic heterogeneity seems to be quite significant. In this respect, the genetics of SLE resemble those of many other complex genetic diseases. The list of candidate genes and pathways (see Table 1) implicated in the pathogenesis of SLE is expanding at a rapid rate. Understanding how alterations in these genes and pathways lead to the lupus phenotype is the primary objective of future genetic studies in SLE.

Commentary on "Genetic linkage and transmission disequilibrium of marker haplotypes at chromosome 1q41 in human systemic lupus erythematosus", by RR Graham et al

Genome-wide linkage analysis studies in families with systemic lupus erythematosus (SLE) have revealed consistent evidence of linkage to several regions of the genome. In a previous issue of this journal, Graham and colleagues described their approach to following up the linkage data for one of these regions, 1q41-42. Using methods based on the transmission disequilibrium test, the region likely to harbour a SLE disease gene was refined to 2.3 Mb. This commentary discusses their approach and identifies lessons that may be applicable to the investigation of other complex diseases.

Complement and systemic lupus erythematosus

Complement is implicated in the pathogenesis of systemic lupus erythematosus (SLE) in several ways and may act as both friend and foe. Homozygous deficiency of any of the proteins of the classical pathway is causally associated with susceptibility to the development of SLE, especially deficiency of the earliest proteins of the activation pathway. However, complement is also implicated in the effector inflammatory phase of the autoimmune response that characterizes the disease. Complement proteins are deposited in inflamed tissues and, in experimental models, inhibition of C5 ameliorates disease in a murine model. As a further twist to the associations between the complement system and SLE, autoantibodies to some complement proteins, especially to C1q, develop as part of the autoantibody response. The presence of anti-C1q autoantibodies is associated with severe illness, including glomerulonephritis. In this chapter the role of the complement system in SLE is reviewed and hypotheses are advanced to explain the complex relationships between complement and lupus.

Linkage analysis of human systemic lupus erythematosus-related traits: a principal component approach

OBJECTIVE

To identify chromosomal regions containing genes involved in the susceptibility to human systemic lupus erythematosus (SLE)-related traits.

METHODS

In the context of a genome scan, we analyzed 101 SLE-affected sibpairs with respect to dermatologic, renal, immunologic, hematologic, neurologic, cardiopulmonary, and arthritic characteristics. Phenotypes were redefined in terms of principal components, which are synthetic variables composed of linear combinations of the original traits. Using 9 principal components obtained from these 7 traits plus age at SLE onset and race, we analyzed genome scan data with the multivariate version of the new Haseman-Elston regression model.

RESULTS

The largest linkage for an individual trait was on chromosome 2 at 228 cM (immunologic; P = 0.00048). The most significant linkage to an individual principal component was on chromosome 4 at 208 cM (P = 0.00007). The largest multivariate linkage was on chromosome 7 at 69 cM (P = 0.0001). Of the individual organ systems, dermatologic involvement had the largest effect (P = 0.0083) at this peak at 7p13 on chromosome 7. Further analyses revealed that malar rash, a subtype of dermatologic involvement, was linked significantly (P = 0.00458) to this location.

CONCLUSION

These results provide evidence of the presence and locations of genes that are involved in the genetic susceptibility to SLE-related traits in humans.

Evidence for a susceptibility gene, SLEV1, on chromosome 17p13 in families with vitiligo-related systemic lupus erythematosus

Both systemic lupus erythematosus (SLE) and vitiligo are autoimmune disorders that have strong evidence of complex genetic contributions to their etiology, but, to date, efforts using genetic linkage to find the susceptibility genes for either phenotype have met with limited success. Since autoimmune diseases are thought to share at least some of their genetic origins, and since only a small minority (16 of 92) of the European-American pedigrees multiplex for SLE in our collection have one or more affected members with vitiligo, we hypothesized that these pedigrees might be more genetically homogeneous at loci important to both SLE and vitiligo and, hence, have increased power for detection of linkage. We therefore evaluated genomewide microsatellite-marker-scan data for markers at an average marker density of approximately 11 cM in these 16 European-American pedigrees and identified a significant linkage at 17p13, where the maximum multipoint parametric LOD score was 3.64 (P<4.3x10(-5)) and the nonparametric linkage score was 4.02 (P<2.8x10(-5)), respectively. The segregation behavior of this linkage suggests a recessive mode of inheritance with a virtually homogeneous genetic effect in these 16 pedigrees. These results support the hypotheses that SLE and vitiligo may share important genetic effects and that sampling on the basis of clinical covariates dramatically improves power to identify genetic effects.

Delineating the genetic basis of systemic lupus erythematosus

Genetic predisposition plays a crucial role in susceptibility to systemic lupus erythematosus (SLE) in both human patients and animal models. Recent progress in experimental systems and human linkage analysis is providing key insights into the genetic basis for susceptibility and elucidating the manner in which genetic interactions mediate severe disease pathogenesis. Genes in multiple pathways appear to participate in specific elements of the disease, and epistatic interactions among these genes play an important role in both aggravating and suppressing disease development.

Lupus autoantibodies recognize the product of an alternative open reading frame of SmB/B'

An unusual feature of the gene for the spliceosomal protein SmB/B' is the presence of an unusually long alternative open reading frame (aORF) which could encode 220 amino acids. We cloned and expressed this aORF protein and used immunological assays to determine its antigenicity in patients with systemic lupus. Sera from 10 of 22 (46%) anti-Sm positive lupus patients showed significant binding to the SmB' aORF protein by ELISA while neither the normal controls nor anti-Sm negative lupus patient controls showed significant reactivity. Antigenicity of the SmB' aORF protein was further localized to the C-terminus using a deletion construct. This is the first known example in which the product of an alternative open reading frame acts as an autoantigen in human disease. These results are consistent with the possibility that generation of anti-Sm autoantibodies in a subset of lupus patients is due to abnormal processing and expression of an aORF SmB/B' message, by an as yet unidentified mechanism.

Lupus in the family--analysis of a cohort followed from 1978 to 1999

Familial lupus is recognised but rarely described in mother-daughter case pairs. We describe the prevalence of lupus occurring in the first degree relatives of a cohort of 300 lupus patients under long-term follow-up at a specialised lupus clinic. Three instances of mothers and their daughters who both developed the disease are described in detail to try and ascertain whether there are any particular clinical/serological/genetic factors in common which might explain the phenomenon.

Familial lupus erythematosus. Clinical and immunologic features of 125 multiplex families

Evidence for a genetic susceptibility to systemic lupus erythematosus (SLE) in humans is based on the high concordance rate observed in identical twins and on the relatively high incidence of familial cases. Although recent genetic studies have lead to significant advances in the identification of new susceptibility genes in SLE, no large clinico-pathologic study of familial SLE has been reported to date. In the present study, we describe the main clinical and immunologic features of 125 lupus multiplex families including at least 2 cases of SLE and/or discoid lupus erythematosus (DLE), recruited through a French national survey starting in July 1997. Medical records of all affected members were reviewed by the same investigator, all available family members were interviewed using the same standardized procedure, and blood was drawn for autoantibodies typing. Clinical and immunologic features of 90 probands from multiplex SLE families were compared with those of 100 sporadic SLE patients sharing the same French Caucasian origin. The 125 lupus multiplex families included 282 affected members (2.3 patients per family); of the 125 families, 96 were of French Caucasian origin. One hundred multiplex families included 2 affected relatives, while 25 included 3 or more affected individuals. The relationship between affected members was sibs (45%), parent-offspring (31%), and second-degree (24%). An autosomal dominant mode of inheritance was strongly suggested in 1 extended pedigree with 6 clinically affected members, and a recessive pattern was suspected in 5 other families. No obvious mode of inheritance could be suspected in most of the remainder. Among French Caucasians, sex ratio, mean age at onset, and clinical and biologic SLE-related manifestations were not significantly different in multiplex compared with sporadic SLE cases. The analysis of these 125 multiplex families suggests a genetic heterogeneity that should be considered for ongoing genomic screening.

The Fcgamma receptor IIIA-158F allele is a major risk factor for the development of lupus nephritis among Caucasians but not non-Caucasians

OBJECTIVE

To determine whether inheritance of Fcgamma receptor (FcgammaR) alleles conferring lower affinity for IgG binding increases the risk of developing lupus nephritis.

METHODS

We compared the frequency of low-affinity alleles of two FcgammaR polymorphisms (FcgammaRIIA and FcgammaRIIIA) among 235 patients with systemic lupus erythematosus (SLE) and proven nephritis (nephritis patients) and among 352 SLE patients with no evidence of renal disease (non-nephritis control subjects). The ethnic distribution of patients in the study was 49% Caucasian, 20% Hispanic, 17% Asian/Pacific Islander, 12% African American, and 2% from other ethnic groups. All patients were genotyped for the FcgammaRIIA-131R/H and FcgammaRIIIA-158V/F polymorphisms. We used contingency table analysis to compare allele and genotype distributions for nephritis patients and nonnephritis control subjects, including ethnic-specific strata. Multivariate logistic regression analyses included sex and disease duration as covariates.

RESULTS

Univariate and multivariate analyses demonstrated a striking association between the low-affinity FcgammaRIIIA-158F allele and FF genotype and the risk of nephritis among Caucasians, but not among non-Caucasians (multivariate odds ratio [OR] 2.6 for Caucasians with FF genotype), (P = 0.0017). This association was even stronger among Caucasians with severe nephritis (OR 4.4, P < 0.0001). In contrast, inheritance of the low-affinity FcgammaRIIA-131R allele (and RR genotype) was not associated with an increased risk of lupus nephritis among any of the ethnic groups examined.

CONCLUSION

The FcgammaRIIIA-158F allele is a major risk factor for the development of lupus nephritis among Caucasians, but not among non-Caucasians. These results suggest that ethnic variation is critical in defining the specific genetic factors underlying the pathogenesis of SLE, and they have important prognostic and therapeutic implications as well.

Genetic studies of human lupus in families

Systemic lupus erythematosus (SLE) is a complex multigenic disease in which the contributing genetic systems are being rapidly identified. Most of the currently recognized genes have been discovered from case-control association studies, but, increasingly, family linkage studies are being employed to confirm previous genetic associations, to examine their relative contributions, and to identify new susceptibility loci. Most of the loci identified thus far appear to contribute only modest effects on susceptibility overall but rather influence more strongly disease expression and/or severity. MHC class II alleles, for example, seem to show only weak linkage to SLE itself but instead mediate specific T cell driven pathogenic autoantibodies which produce many of the clinical disease features, similar to their effects in many other autoimmune diseases. On the other hand, complete and partial hereditary deficiencies of early complement components are more lupus-specific. Homozygous complement deficiencies, while powerful risk factors, are rare causes of lupus and heterozygous deficiencies exert only modest effects on susceptibility. Other genes, such as low-binding IgG Fc receptor alleles (FcgammaIIa and FcgammaIIIa), appear to promote nephritis by modifying the efficiency of immune complex clearance. A variety of cytokine genes appear also to promote severity, including those for TNFalpha, IL-10, IL1 receptor antagonist, and perhaps others (IL-6, IL-4 and TNFalpha receptor). Family studies and recent genome-wide scans in lupus and other autoimmune diseases support the likelihood that some susceptibility loci, as yet unidentified, predispose to several or many autoimmune diseases. Only thorough the identification and elucidation of function of these many genes is the pathogenic picture of lupus likely to be complete.

Xenobiotic acceleration of idiopathic systemic autoimmunity in lupus-prone bxsb mice

The diverse genetic backgrounds of lupus-prone murine models, which produce both quantitative and qualitative differences in disease expression, may be a valuable resource for studying the influence of environmental exposure on autoimmune disease in sensitive populations. We tested this premise by exposing autoimmune-prone BXSB and the nonautoimmune C57BL/6 mice to the heavy metal mercury. Although both strains express a nonsusceptible H-2 haplotype, exposure to mercury accelerated systemic autoimmunity in both male and female BXSB mice, whereas the C57BL/6 mice were resistant. The subclasses of antichromatin antibodies elicited in BXSB mice by mercury exposure were more consistent with the predominant Th1-type response of idiopathic disease than with the Th2-type response found in mercury-induced autoimmunity (HgIA). The appearance and magnitude of both humoral and cellular features of systemic autoimmunity correlated with the mercury dose. Furthermore, environmentally relevant tissue levels of mercury were associated with exacerbated systemic autoimmunity. These studies demonstrate that xenobiotic exposure can accelerate spontaneous systemic autoimmunity, and they support the possibility that low-level xenobiotic exposure enhances susceptibility to systemic autoimmunity in genetically susceptible individuals.

Fine mapping of the SLEB2 locus involved in susceptibility to systemic lupus erythematosus

We have previously reported linkage of systemic lupus erythematosus to chromosome 2q37 in multicase families from Iceland and Sweden. This locus (SLEB2) was identified by linkage to the markers D2S125 and D2S140. In the present study we have analyzed additional microsatellite markers and SNPs covering a region of 30 cM around D2S125 in an extended set of Nordic families (Icelandic, Swedish, and Norwegian). Two-point linkage analysis in these families gave a maximum lod score at the position of markers D2S2585 and D2S2985 (Z = 4.51, PIC = 0.65), by applying a "model-free" pseudo-marker linkage analysis. Based on multipoint linkage analysis in the Nordic families, the most likely location of the SLEB2 locus is estimated to be in the interval between D2S125 and the position of markers D2S2585 and D2S2985, with a peak multipoint lod score of Z = 6.03, assuming a dominant pseudo-marker model. Linkage disequilibrium (LD) analysis was performed using the data from the multicase families and 89 single-case families of Swedish origin, using the same set of markers. The LD analysis showed evidence for association in the single-case and multicase families with locus GAAT3C11 (P < 0.0003), and weak evidence for association was obtained for several markers located telomeric to D2S125 in the multicase families. Thirteen Mexican families were analyzed separately and found not to have linkage to this region. Our results support the presence of the SLEB2 locus at 2q37.