Twin concordance rates for rheumatoid arthritis: results from a nationwide study

Disease association of two distinct interleukin-18 promoter polymorphisms in Caucasian rheumatoid arthritis patients

Interleukin (IL)-18 is an important mediator of innate and adaptive immunity. We searched for an association of IL-18 promoter single-nucleotide polymorphisms (SNP) with rheumatoid arthritis (RA) in Caucasians. The entire study population was composed of two independent cohorts from Germany (n=200) and Scotland (n=410). Presence of IL-18 SNP at positions -607 and -137 was determined by allele-specific PCR in 327 RA patients and 283 healthy donors (HD). Diplotype distributions of both loci were in Hardy-Weinberg equilibrium (HWE) in the German and Scottish HD cohorts. In contrast, locus -607 was in HW disequilibrium in German, and locus -137 in Scottish RA patients. Diplotypic exact chi(2) tests suggested that -607CC was overrepresented in German, and -137CC in Scottish RA patients, but conservative chi(2) trend analyses could not prove any significant disease association of these single loci. SNP -607 and -137 were in strong linkage disequilibrium. The -607C(*)-137C haplotype was more prevalent in German RA (3.2 vs 1.2%) and in Scottish RA patients (4.1 vs 0.9%) than in the respective HD cohorts. These observations suggest that SNP of both positions contribute to the genetic background of RA pathogenesis.

Association of a functional single-nucleotide polymorphism of PTPN22, encoding lymphoid protein phosphatase, with rheumatoid arthritis and systemic lupus erythematosus

OBJECTIVE

To assess the possible association between the PTPN22 gene 1858C-->T polymorphism and the predisposition and clinical expression of 2 systemic autoimmune diseases, rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE).

METHODS

Our study population consisted of 826 RA patients, 338 SLE patients, and 1,036 healthy subjects. All subjects were of Spanish Caucasian origin. Genotyping of the PTPN22 gene 1858C-->T polymorphism was performed by real-time polymerase chain reaction technology, using the TaqMan 5'-allele discrimination assay.

RESULTS

The overall distribution of genotypes in the RA patients was significantly different from that in the controls (P = 0.005, by chi-square test with 2 x 3 contingency tables). We observed a statistically significant difference in the distribution of the PTPN22 1858T allele between healthy subjects (7.4%), and RA patients (10.4%) (P = 0.001, odds ratio [OR] 1.45 [95% confidence interval (95% CI) 1.15-1.83]). In addition, PTPN22 1858 C/T and T/T genotypes were present at a significantly higher frequency in SLE patients than in controls (P = 0.02, OR 1.55 [95% CI 1.05-2.29]). Differences were also observed when allele frequencies were compared, with the PTPN22 1858T allele being present at a higher frequency among SLE patients (P = 0.03, OR 1.45 [95% CI 1.01-2.09]).

CONCLUSION

These results suggest that the PTPN22 1858T allele may confer differential susceptibility to RA and SLE in the Spanish population.

Epstein-Barr virus etiology in rheumatoid synovitis

The etiology of rheumatoid arthritis (RA) has remained unknown, although it has been investigated and speculated that both genetic and environmental components contribute to the cause of this disease. Epstein-Barr virus (EBV) has been a strong candidate about for over 25 years as environmental infectious agent(s). There are many circumstantial evidence for association between EBV and RA, but definite evidence is wanting. In present article, we review an increase circumstantial proof which has been investigated so far and demonstrate direct evidence for the presence of EBV in inflamed synovial cells in patients with RA and discuss on the recent finding of signaling lymphocytic-activation molecule (SLAM)-associated protein (SAP), which opened a new approach to understand on impaired function of cytotoxic T cell for EBV in patients with RA.

Dietary risk factors for the development of inflammatory polyarthritis: evidence for a role of high level of red meat consumption

OBJECTIVE

To investigate the association of red meat and other specific dietary components in predicting the development of inflammatory polyarthritis.

METHODS

This nested case-control study was conducted within a prospective population-based study of cancer incidence (European Prospective Investigation of Cancer in Norfolk [EPIC-Norfolk]). EPIC-Norfolk recruited 25,630 subjects ages 45-75 years between 1993 and 1997. Dietary intake was assessed at baseline using a 7-day food diary, and the information was analyzed using dietary analysis software. Patients with new cases of inflammatory polyarthritis were identified by linkage with the Norfolk Arthritis Register, a primary care-based inception study of inflammatory polyarthritis, and were matched for age and sex to 2 controls from EPIC-Norfolk. The risk for development of inflammatory polyarthritis was compared between subjects in the highest and lowest tertiles of dietary intake using conditional logistic regression and was expressed as odds ratios (ORs) with 95% confidence intervals (95% CIs).

RESULTS

Between 1993 and 2002, 88 new patients with inflammatory polyarthritis were identified and matched with 176 controls. Among patients, the level of red meat intake was higher (P = 0.04) and that of vitamin C was lower (P = 0.03) compared with intake among controls, but no difference in total energy intake was observed. Patients were more likely to be smokers. After adjusting for total energy intake, smoking, and other possible dietary confounders, subjects with the highest level of consumption of red meat (OR 1.9, 95% CI 0.9-4.0), meat and meat products combined (OR 2.3, 95% CI 1.1-4.9), and total protein (OR 2.9, 95% CI 1.1-7.5) were at an increased risk for inflammatory polyarthritis.

CONCLUSION

A high level of red meat consumption may represent a novel risk factor for inflammatory arthritis or may act as a marker for a group of persons with an increased risk from other lifestyle causes.

Familial recurrence rates and genetic models of multiple sclerosis

Susceptibility to multiple sclerosis (MS) is determined by both inherited and non-inherited factors. The importance of genetic factors is demonstrated by the increased risk of disease in relatives of MS patients. Our objective was to determine the implications of the observed familial recurrence risks for the genetic basis of MS. We developed a computer program which calculates recurrence risks for monozygotic (MZ) twins, siblings, and second degree relatives, and used it to calculate recurrence risks for a wide variety of genetic models. We investigated models with different numbers of genes, different patterns of interaction between the genes, and dominant or recessive inheritance. The models that best reproduced the observed values had multiple loci with strongly synergistic interaction and autosomal dominant (AD) inheritance. At least six loci were required, and we found no upper limit on the number of loci. Models with genetic heterogeneity, where only a fraction of the risk loci are required for disease, are possible. In models with large numbers of loci the "abnormal" alleles conferring risk of disease are the most common allele. We conclude that a variety of genetic models with multiple genes, dominant inheritance, and synergistic interaction between risk genes are consistent with the observed familial recurrence rates in MS.

Cytotoxic T-lymphocyte antigen-4-CT60 polymorphism in rheumatoid arthritis

Cytotoxic T-lymphocyte antigen-4 (CTLA-4) is a functional candidate gene with susceptibility to rheumatoid arthritis (RA). The aim of this work was to investigate the possible influence of the recently described CT60A/G dimorphism of the CTLA-4 gene in the susceptibility to RA in Spanish patients. A total of 433 RA patients and 398 control subjects were included in the study. Genotyping of CTLA-4 CT60 was performed using two different methods: polymerase chain reaction restriction fragment length polymorphism system using an amplification-created restriction site and a TaqMan 5'-allelic discrimination assay. In order to validate results obtained by different methods, a quality-control exercise was performed. No significant deviation in the distribution of the alleles or genotypes of the CT60 was found when we compared RA patient and control groups. In addition, no differences in CTLA-4 CT60 genotypic distribution was found when RA patients and controls were stratified by the presence or absence of the shared epitope. In conclusion, our results do not support an association between CT60A/G polymorphism and susceptibility to RA in the Spanish population, although the contribution of other positions located within the 3' region of the CTLA-4 gene to RA susceptibility cannot be discarded.

National databases and rheumatology research I: longitudinal databases in Scandinavia

Nationwide population-based longitudinal databases provide excellent resources for medical research in Scandinavia. These include the Population Registry, the Cancer Registry, the Cause of Death Registry, the Hospital Discharge Registry, and other registers, and are linkable to each other by the personal identification code. The registers have long historical backgrounds, and are regulated strictly by law. This article describes features of the national databases and provides some examples of rheumatology research that use these databases.

Dense genome-wide linkage analysis of rheumatoid arthritis, including covariates

OBJECTIVE

Rheumatoid arthritis (RA) is a heterogeneous disease that exhibits a complex genetic component. Previous RA genome scans confirmed the involvement of the HLA region and generated data on suggestive signals at non-HLA regions, albeit with few overlaps in findings between studies. The present study was undertaken to detect potential RA gene regions and to estimate the number of true RA gene regions, taking into account the heterogeneity of RA, through performance of a dense genome scan.

METHODS

In a study of 88 French Caucasian families (105 RA sibpairs), 1,088 microsatellite markers were genotyped (3.3-cM genome scan), and a multipoint model-free linkage analysis was performed. The statistical assessment of the results relied on 10,000 computer simulations. A covariate-based multipoint model-free linkage analysis was performed on the locations of regions with suggestive evidence for linkage.

RESULTS

Involvement of the HLA region was strongly confirmed (P = 6 x 10(-5)), and 19 non-HLA regions showed suggestive evidence for linkage (P < 0.05); 9 of these overlapped with regions suggested in other published RA genome scans. A routine 12-cM genome scan with the same families would have detected only 7 of the 19 regions, including only 4 of the 9 overlapping regions. From the 10,000 computer simulations, we estimated that 8 +/- 4 regions (mean +/- SD) were true-positives. RA covariate-based analysis provided additional linkage evidence for 3 regions, with age at disease onset, erosions, and HLA-DRB1 shared epitope as covariates.

CONCLUSION

The results of this study provide evidence of 19 non-HLA RA gene regions, with an estimate of 8 +/- 4 as true-positives, and provide additional evidence for 3 regions from covariate-based analysis.

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.

SLC22A4 and RUNX1: identification of RA susceptible genes

Recently we reported that SLC22A4 and RUNX1 are associated with rheumatoid arthritis (RA). SLC22A4 is an organic cation transporter with unknown physiological function, and RUNX1 is a hematological transcriptional regulator that has been shown to be responsible for acute myelogenic leukemia. It is suggested that the association of RUNX1 with RA is due to its regulation of expression of SLC22A4. Because the physiological function of SLC22A4 is still unclear, further investigation is needed into how SLC22A4 affects RA susceptibility. Although the association of RUNX1 with RA was identified as a regulatory factor of SLC22A4, it is possible that RUNX1 is a key molecule in autoimmunity, as it has been reported to be associated with systemic lupus erythematosus and psoriasis, two other autoimmune diseases.

Preclinical experiments

The clinical use of autologous stem cell transplants for the treatment of refractory severe autoimmune diseases was preceded by convincing proof of its underlying principle in animal models. The various categories of experimental autoimmune disease in laboratory rodents are briefly described here, and the rationale that was used in the selection of suitable experimental autoimmune diseases for translational research is explained. The two models that provided the bulk of the data needed for designing the initial clinical treatment protocols were adjuvant arthritis (AA) and experimental allergic encephalomyelitis (EAE), which were both induced in Buffalo rats. In this strain, AA is manifested as a chronic, progressive, systemic polyarthritis and EAE as a chronic, remitting/relapsing form of encephalomyelitis resembling multiple sclerosis. Both diseases can be cured with autologous stem cell transplantation provided that adequate conditioning is given and that the disease has not yet progressed to the stage of 'scarring'. It is basically the inflammatory stages that respond well to this therapy. The success of treatment depends on how completely the autoantigen-specific activated T-lymphocytes and memory cells are eradicated. Because of a lack of information on the nature of the autoantigens involved in human disease and on the size of those cell populations in the animal models as well as in humans, this aspect of translation is difficult. The experiments have, however, provided important guidelines. High-dose conditioning regimens yield better results than low-dose conditioning, certain conditioning agents perform better than others, and care should be taken not to reintroduce too many T-cells with the autologous graft. The clinical results obtained so far indicate a high predictive power of these two animal models, which are therefore recommended strongly for additional preclinical studies.

The additive role of innate and adaptive immunity in the development of arthritis

The development of rheumatoid arthritis (RA) occurs as a result of interactions between genes and environment. The most well established association with both susceptibility and severity of disease is variations in the major histocompatibility complex (MHC) class II genes. This fact constitutes evidence in favor of a contribution from specific MHC class II restricted adaptive immunity to the pathogenesis of RA. However, considerable difficulties have been encountered in identifying reactivities within the adaptive immune system that are responsible for the development of chronic arthritis in humans. In this article, the authors suggest a hypothesis for arthritis development based on their, as well as others', research. In patients with certain genetic contexts, RA can be initiated by activation of the innate immune system alone. In other patients, the adaptive immune system may be needed for the induction of disease. Additionally, the authors believe that a perpetuation to a severe chronic arthritis occurs only when both the adaptive and the innate immune systems have been recruited.

A review of the MHC genetics of rheumatoid arthritis

Rheumatoid arthritis is a common complex genetic disease, and, despite a significant genetic element, no gene other than HLA-DRB1 has been clearly demonstrated to be involved in the disease. However, this association accounts for less than half the overall genetic susceptibility. Investigation of other candidate genes, in particular those that reside within the major histocompatibility complex, are hampered by the presence of strong linkage disequilibrium and problems with study design.

Occupations and exposures in the work environment as determinants for rheumatoid arthritis

BACKGROUND AND AIMS

Several occupational categories have been associated with rheumatoid arthritis (RA); this study was conducted to further evaluate these associations.

METHODS

Lifelong occupational history together with exposure experiences were collected through a postal questionnaire answered by 293 incident cases and 1346 population based referents. Occupational determinants were evaluated through stratified and multivariate analyses; pooled analyses with previously gathered data on 422 prevalent cases and 858 referents were also performed.

RESULTS

In both materials, significantly increased logistic odds ratios (LORs) were seen for male conductors, freight and transport workers (LOR 17.8, 95% CI 1.5 to 207.8 and LOR 4.7, 95% CI 1.4 to 16.3, respectively), and farmers and farm workers (LOR 2.4, 95% CI 1.1 to 5.2, and LOR 2.2, 95% CI 1.3 to 3.5, respectively). Among women, increased LORs were seen in the separate and the pooled material for printmakers and process engravers (LOR 5.5, 95% CI 0.9 to 32.6, and LOR 3.0, 95% CI 0.9 to 10.3, respectively). Increased risks were seen in both materials for men exposed to asbestos (LOR 2.5, 95% CI 1.0 to 6.8, and LOR 1.6, 95% CI 0.8 to 3.3, respectively), and vibrations (LOR 2.0, 95% CI 0.9 to 4.4, and LOR 2.2, 95% CI 1.3 to 3.8, respectively). The risk for RA increased with increasing duration of exposure to vibrations and mineral dust, respectively.

CONCLUSIONS

There was evidence of a causal relation between exposures to vibrations and mineral dust and development of RA among men. Occupational factors seem to be aetiologically more important for men, and most occupations at risk involve multiple exposures. Several exposures associated with an increased risk for RA are frequent among farmers, and some of the occupations at risk include exposure to organic dust.

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.

Complex genetic predisposition in adult and juvenile rheumatoid arthritis

Background

Rheumatoid arthritis (RA) and juvenile rheumatoid arthritis (JRA) are complex multifactorial diseases caused by environmental influences and an unknown number of predisposing genes. The present study was undertaken in order to investigate association of polymorphisms in candidate genes with RA and JRA in German subjects.

Results

Up to 200 unrelated German RA and JRA patients each and 300–400 healthy controls have been genotyped for HLA-DRB1, TNFa, TNFA -238a/g, TNFA -308a/g, TNFA -857c/t, TNFR1 -609g/t, TNFR1 P12P, TNFR2 del 15bp, IKBL -332a/g, IKBL -132t/a, IKBL C224R, CTLA4 -318c/t, CTLA4 T17A, PTPRC P57P, MIF -173g/c, the MIF and IFNG microsatellites as well as for D17S795, D17S807, D17S1821 by polyacrylamide gel electrophoresis, single-strand conformation polymorphism analysis, restriction fragment length polymorphism analysis or allele specific hybridization. None of the investigated genetic markers is associated with both, RA and JRA, but there are some statistically significant differences between patients and controls that have to be discussed sensibly.

Conclusions

The difficulty in investigating the genetics of complex disorders like RA and JRA may arise from genetic heterogeneity in the clinically defined disease cohorts (and generally limited power of such studies). In addition, several to many genes appear to be involved in the genetic predisposition, each of which exerting only small effects. The number of investigated patients has to be increased to establish the possibility of subdivison of the patients according their clinical symptoms, severity of disease, HLA status and other genetic characteristics.

Dissection of class III major histocompatibility complex haplotypes associated with rheumatoid arthritis

OBJECTIVE

We have previously identified a single-nucleotide polymorphism (SNP) haplotype involving the lymphotoxin alpha (LTA) and tumor necrosis factor (TNF) loci (termed haplotype LTA-TNF2) on chromosome 6 that shows differential association with rheumatoid arthritis (RA) on HLA-DRB1*0404 and *0401 haplotypes, suggesting the presence of additional non-HLA-DRB1 RA susceptibility genes on these haplotypes. To refine this association, we performed a case-control association study using both SNPs and microsatellite markers in haplotypes matched either for HLA-DRB1*0404 or for HLA-DRB1*0401.

METHODS

Fourteen SNPs lying between HLA-DRB1 and LTA were genotyped in 87 DRB1*04-positive families. High-density microsatellite typing was performed using 24 markers spanning 2,500 kb centered around the TNF gene in 305 DRB1*0401 or *0404 cases and 400 DRB1*0401 or *0404 controls. Single-marker, 2-marker, and 3-marker minihaplotypes were constructed and their frequencies compared between the DRB1*0401 and DRB1*0404 matched case and control haplotypes.

RESULTS

Marked preservation of major histocompatibility complex haplotypes was seen, with chromosomes carrying LTA-TNF2 and either DRB1*0401 or DRB1*0404 both carrying an identical SNP haplotype across the 1-Mb region between TNF and HLA-DRB1. Using microsatellite markers, we observed two 3-marker minihaplotypes that were significantly overrepresented in the DRB1*0404 case haplotypes (P = 0.00024 and P = 0.00097).

CONCLUSION

The presence of a single extended SNP haplotype between LTA-TNF2 and both DRB1*0401 and DRB1*0404 is evidence against this region harboring the genetic effects in linkage disequilibrium with LTA-TNF2. Two RA-associated haplotypes on the background of DRB1*0404 were identified in a 126-kb region surrounding and centromeric to the TNF locus.

Risk factors for rheumatoid arthritis

Both genetic and environmental factors contribute to the development of rheumatoid arthritis (RA). A long-term latent process often precedes the onset of arthritis. Hence, the ultimate causes of RA cannot be clarified by studying only the inflamed joints. Longitudinal studies focusing on risk factors are crucial in approaching the true aetiology. At present, most information gained from epidemiological studies is contradictory or vague. For instance, there is no consensus concerning the long-term effects of pregnancy or the putative protective role of oral contraceptives. There is no doubt that diet plays a role, but no specific nutrient has proved to be either protective or deleterious. Smoking is the only environmental risk factor that has been firmly verified epidemiologically for RA. It can be reasonably regarded as a contributory cause of RA. Studying the immunological effects of exposure to cigarette smoke may offer an opportunity to combine information from basic and epidemiological research to clarify the causal chains leading to RA.

The genetic control of rheumatoid factor production in a rat model of rheumatoid arthritis

OBJECTIVE

To investigate the genetic regulation of rheumatoid factor (RF) in a rat model of rheumatoid arthritis, in order to gain understanding of the enigmatic role of RF in the disease.

METHODS

IgM-RF and IgG-RF, as well as total levels of immunoglobulins of different subclasses, were measured in sera from rats with pristane-induced arthritis (PIA). The major gene regions were identified by linkage analysis of genetically segregating crosses.

RESULTS

The production of RF was found to correlate with development of arthritis and to be higher in females than in males. Surprisingly, the relatively arthritis-resistant E3 strain had higher levels of RF than the arthritis-susceptible DA strain. In an (E3 x DA)F(2) cohort a major locus controlling the levels of IgM-RF in serum was identified on chromosome 11 (Rf1) and another on chromosome 16 (Rf3), and these were not related to arthritis susceptibility. However, the Rf2 locus on chromosome 4 controlled IgG-RF levels, IgG2a levels, and chronic arthritis in males (Pia5). Some previously defined arthritis loci (Pia4, Pia6, Pia7, and Pia8) were found to also control immunoglobulin levels in serum.

CONCLUSION

RFs are produced in the rat PIA model and correlate with development of arthritis. Gene regions controlling RF and serum immunoglobulin levels were identified, of which some cosegregated with arthritis. This suggests a new focus of study to elucidate the role of RF in the pathogenesis of arthritis.

Chronicity of pristane-induced arthritis in rats is controlled by genes on chromosome 14

To address the possibility that genes specifically control the chronic phase of arthritis we have isolated a congenic fragment from the resistant E3 rat on the susceptible DA rat background. The isolated fragment covers the Pia6 quantitative trait locus on chromosome 14, which previously has been identified to be linked to chronic pristane induced arthritis (PIA) in gene segregation experiments of an (E3 x DA)F(2)-cross. Heterozygous Pia6 congenic rats (DA.Pia6) were protected from chronic active arthritis specifically, as determined by macroscopic scoring, histopathology and release of cartilage oligomeric matrix protein (-reflecting ongoing cartilage destruction). The difference was seen only during the chronic active phase of arthritis starting approximately 5 weeks after onset of arthritis. Interestingly, the plasma concentration of the lipocalins alpha(1)-acid glycoprotein and alpha(1)-microglobulin was found significantly altered in nai;ve congenic rats compared to the DA rat. The concentration of alpha(1)-microglobulin was found to be significantly higher throughout the disease course, while alpha(1)-acid glycoprotein had a lower concentration in nai;ve rats, which was highly significant in the chronic phase. The altered concentrations of these proteins already before development of chronic arthritis may provide a clue to the pathogenic process controlled by the Pia6 genes. We conclude that the active relapsing chronic arthritis is under a unique genetic control that is different from the control of acute arthritis and postulate that the liver plays an important role in this regulation.

Genetics and clinical practice in rheumatology

The dramatic advances made recently in human genome research are fueling considerable interest in genetic testing. A specific feature of genetic testing is that the results are final and impact not only the patient, but also the entire family. Those elements should be factored into the risk/benefit ratio evaluation. In France, legislation the differentiates diagnostic tests in symptomatic patients from predictive tests in asymptomatic patients with affected family members. Only multidisciplinary groups with both clinical and genetic expertise can order predictive tests. In all cases the physician must sign a statement that informed consent was obtained from the patient prior to testing. The test must be done in an accredited laboratory and the result communicated by the physician to the patient. Patient confidentiality must be respected, particularly regarding family members. In monogenic diseases, the diagnostic weight of genetic testing is often considerable, although the limitations should be borne in mind. In multifactorial diseases, genetic testing seeks to identify risk factors that are usually associated with a low level of risk. The result should be interpreted in the light of the clinical presentation, family history, and genetic background. The predictive value is closely dependent on the clinical presentation but is generally limited, most notably when family members are affected. Great care should be taken to avoid causing undue anxiety among individuals with positive test results. Diseases that illustrate these aspects include Paget's disease of bone, of which inherited variants caused by a mutation in a single gene on chromosome 5 have been identified recently, and rheumatoid arthritis, which is a multifactorial disease.

Peptidylarginine deiminase type 4: identification of a rheumatoid arthritis-susceptible gene

Recent studies using linkage disequilibrium and SNPs uncovered a rheumatoid arthritis (RA)-susceptible haplotype in the gene encoding peptidylarginine deiminase (PADI) type 4. This gene is one of four known PADI genes that encode enzymes to change arginine into citrulline in proteins. Post-translational modifications of proteins, including peptidyl citrullination, are related to autoimmunity, and peptidyl citrulline is a known target of one of the most RA-specific autoantibodies. Further research on PADI4, its citrullination of native peptides, subsequent breakdown of tolerance, and the role of these peptides in the development of RA, is expected to bring a better understanding of autoimmunity and arthritis, and advancements in the medical care of RA.

Differential gene expression in pristane-induced arthritis susceptible DA versus resistant E3 rats

Arthritis susceptibility genes were sought by analysis of differential gene expression between pristane-induced arthritis (PIA)-susceptible DA rats and PIA-resistant E3 rats. Inguinal lymph nodes of naïve animals and animals 8 days after pristane injection were analyzed for differential gene expression. mRNA expression was investigated by microarray and real-time PCR, and protein expression was analyzed by flow cytometry or ELISA. Twelve genes were significantly differentially expressed when analyzed by at least two independent methods, and an additional five genes showed a strong a tendency toward differential expression. In naïve DA rats IgE, the bone marrow stromal cell antigen 1 (Bst1) and the MHC class II beta-chain (MhcII) were expressed at a higher level, and the immunoglobulin kappa chain (Igkappa) was expressed at a lower level. In pristane-treated DA rats the MHC class II beta-chain, gelatinase B (Mmp9) and the protein tyrosine phosphatase CL100 (Ptpn16) were expressed at a higher level, whereas immunoglobulins, the CD28 molecule (Cd28), the mast cell specific protease 1 (Mcpt1), the carboxylesterase precursor (Ces2), K-cadherin (Cdh6), cyclin G1 (Ccng1), DNA polymerase IV (Primase) and the tumour associated glycoprotein E4 (Tage) were expressed at a lower level. Finally, the differentially expressed mRNA was confirmed with protein expression for some of the genes. In conclusion, the results show that animal models are well suited for reproducible microarray analysis of candidate genes for arthritis. All genes have functions that are potentially important for arthritis, and nine of the genes are located within genomic regions previously associated with autoimmune disease.

Estrogen and other female reproductive risk factors are not strongly associated with the development of rheumatoid arthritis in elderly women

OBJECTIVE

Endogenous and exogenous reproductive hormones have been associated with rheumatoid arthritis (RA) in women, but data are inconsistent and no studies have assessed RA risk factors exclusively in elderly women.

METHODS

The authors examined the association between reproductive factors, exogenous hormone exposure, and RA in a prospective cohort study of 31,336 Iowa women who were aged 55 to 69 years at cohort baseline in 1986.

RESULTS

During 11 years of follow-up, 158 incident cases of RA were identified and validated. Age at last pregnancy (P trend =.01) and age at menopause (P trend =.03) were inversely associated with RA, whereas a history of polycystic ovary syndrome (relative risk [RR], 2.58; 95% confidence interval [CI], 1.06 to 6.30), endometriosis (RR, 1.72; 95% CI, 0.93 to 3.18), and former use of hormone replacement therapy (RR, 1.47; 95% CI, 1.04 to 2.06) were positively associated with RA. In multivariate analysis models, a history of polycystic ovary syndrome remained the most consistent predictor of RA, whereas the RRs for other factors attenuated.

CONCLUSION

Few reproductive factors showed a strong or statistically significant association with RA in elderly women. The association of polycystic ovary syndrome may be indicative of perturbations of endocrine-immune activity that may influence the development of RA. This prospective cohort study adds to the understanding of the potential contribution of hormonal factors to the cause of RA in older women.

Normal intestinal microbiota in the aetiopathogenesis of rheumatoid arthritis

A series of observations have led to the hypothesis that normal intestinal microbiota in patients with rheumatoid arthritis may harbour, for genetic reasons, bacteria with cell walls capable of inducing arthritis. Differences occur between bacterial species, and even between strains of a single species, because some cell walls induce experimental chronic arthritis, whereas some others induce only a transient acute arthritis or no arthritis at all. In susceptible subjects, with continuous seeding of bacterial products from the gut, the synovial inflammation is followed by erosion, exposition of cartilage antigens, and self perpetuating chronic arthritis.

A comparative genetic analysis between collagen-induced arthritis and pristane-induced arthritis

OBJECTIVE

To compare the genetic regulation of collagen-induced arthritis (CIA) with that of pristane-induced arthritis (PIA) in rats.

METHODS

A genome-wide linkage analysis of an (E3 x DA)DA backcross of rats with CIA (n = 364 male rats; the same strain combinations as previously used to determine the genetic control of PIA) was performed. The strongest loci in both CIA and PIA (i.e., Cia12/Pia4 and Cia13/Pia7) were isolated in congenic strains. Susceptibility in both congenic strains was tested in rats with CIA and in rats with PIA.

RESULTS

We found a striking, although not complete, similarity of the arthritis-controlling loci in CIA and in PIA, as well as the previously defined loci associated with cartilage destruction, antibody production, and the acute-phase response. All major PIA quantitative trait loci (QTLs) identified in early severe arthritis were also strong regulators of CIA. The 2 strongest QTLs, Cia12/Pia4 on chromosome 12 and Cia13/Pia7 on chromosome 4, were also analyzed in congenic strains with DA or E3 as the background genome. Consistent with the results of linkage analysis, the congenic strain experiments showed that the chromosome 4 locus was more penetrant in CIA than in PIA, while the chromosome 12 locus almost completely dominated the control of PIA severity.

CONCLUSION

The underlying genetic control of CIA was found to have many, but not all, pathogenic mechanisms in common with PIA, despite the use of a cartilage-specific antigen (type II collagen) to induce CIA but not PIA.

Positional cloning of Ncf1--a piece in the puzzle of arthritis genetics

Positional cloning of susceptibility genes in complex diseases like rheumatoid arthritis in humans is hampered by aspects like genetic heterogeneity and environmental variations, while genetic studies in animal models contain several advantages. With animal models, the environment can be controlled, the genetic complexity of the disease is minimized and the disease onset can be predicted, which simplify diagnosis and characterization. We use pristane-induced arthritis in rats to investigate the inheritance of arthritis. Until now, we have identified 15 loci that significantly predispose rats to the development of arthritis. One of these arthritis loci has been isolated and confirmed to be caused by a polymorphism in the Ncf1 gene. In this review, we outline the methods used to identify Ncf1 as one single susceptibility gene in a complex puzzle of inherited factors that render susceptibility to a complex autoimmune disorder like arthritis.

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.

Identification and isolation of dominant susceptibility loci for pristane-induced arthritis

Rheumatoid arthritis is a chronic inflammatory autoimmune disorder, controlled by multiple genes as well as environmental factors. With animal models, like the pristane-induced arthritis (PIA) in rats, it is possible to reduce the environmental effects and the genetic heterogeneity to identify chromosomal regions harboring genes responsible for the arthritis development. The PIA model has proved to be useful for identifying gene regions controlling different phases of the disease based on intercrosses between the resistant E3 and the susceptible DA rat. We have now performed a high-powered backcross analysis that confirms previous intercross-based data but also identifies additional loci. Earlier identified PIA loci were reproduced with high significance; Pia1 (MHC region on chromosome 20), Pia4 (chromosome 12), and Pia7 (chromosome 4) are all major regulators of PIA severity and were also found to operate in concert. These three loci were verified in congenic strains using both disease- and arthritis-inflammatory-related subphenotypes as traits. We were also able to detect five new quantitative trait loci with dominant effects on PIA: Pia10, Pia12, Pia13, Pia14, and Pia15 on chromosomes 10, 6, 7, 8, and 18, respectively. These data highlight the usefulness of the statistical power obtained in a backcross of a complex disease like arthritis.

Rheumatoid arthritis: proposal for the use of anti-microbial therapy in early cases

Rheumatoid arthritis (RA) is a chronic disease, affecting women more than men, especially in those possessing the "shared epitope" (EQK/RRAA) amino acid sequences present in HLA-DR1/4 molecules. Proteus mirabilis carries sequences showing molecular mimicry to the "shared epitope" and to type XI collagen of hyaline cartilage. Elevated levels of antibodies to P. mirabilis have been reported from 14 different countries involving 1375 RA patients and the microbe has been isolated from urine cultures of such patients. Our working hypothesis is that the disease develops as a result of repeated episodes of Proteus upper urinary tract infections. Prospective studies involving the trial of anti-Proteus measures in RA patients should be evaluated in the management of this disease. Antibiotics, high fluid intake, and fruit extracts, such as cranberry juice, have all been found to be effective in the treatment of urinary tract infections. Such measures could be used as possible additional adjuncts to the standard therapy with NSAIDs and DMARDs.

A poly(ADP-ribose) polymerase haplotype spanning the promoter region confers susceptibility to rheumatoid arthritis

OBJECTIVE

To investigate the association of the poly(ADP-ribose) polymerase 1 (PARP-1) gene promoter polymorphism with rheumatoid arthritis (RA) predisposition.

METHODS

An association study with 213 Spanish RA patients and 242 healthy subjects was carried out to investigate the association of all known PARP-1 gene promoter polymorphisms, i.e., a CA microsatellite repeat, a poly(A)(n), and 3 single point mutations (C410T, C1362T, and G1672A), with disease susceptibility. Additionally, we analyzed the distribution of PARP-1 polymorphisms in 58 Spanish families with 1 or more affected members.

RESULTS

Upon complete genotyping of the panel of 455 samples, strong linkage disequilibrium was observed among the 5 PARP-1 polymorphisms. Only 2 PARP-1 haplotypes were detected: haplotype A (410T-[A](10)-[CA](10-12)-1362C, which includes short PARP-1 CA alleles) and haplotype B (410C-[A](11)-[CA](13-20)-1362T, always paired with long PARP-1 CA variants). Regarding the G1672A variation, although linkage disequilibrium was detected, it did not seem to be part of the conserved haplotypes described. Haplotype B was statistically overrepresented in the RA patient group compared with the healthy subjects (odds ratio 1.42, 95% confidence interval 1.06-1.91, P = 0.019). In addition, a significant dose effect of PARP-1 haplotype carriage on disease predisposition was observed. Of note, within haplotype B, the PARP-1 CA 97-bp allele was found to be the RA-predisposing marker (odds ratio 2.17, 95% confidence interval 1.27-3.72, P = 0.003, corrected P < 0.05).

CONCLUSION

Our results demonstrate the existence of 2 unique PARP-1 haplotypes in the Spanish population and provide the first evidence that PARP-1 haplotypes play a role in susceptibility to RA.

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.

Genetic epidemiology: disease susceptibility and severity

Genetic factors are increasingly recognized to have an important contribution to the occurrence of both inflammatory and noninflammatory rheumatic disease. Although identifying the specific genetic mechanisms involved in the rheumatic diseases continues to present considerable challenges, the prospect of identifying individual gene action has been brought closer by a number of recent developments. These include newer approaches to phenotype definition, refinements in statistical tools for analysis, and the advent of newer technologies, including the use of microarrays. In this article, we review some of these developments together with the recent literature on the contribution of both broad and specific genetic factors to the spectrum of rheumatic disease. We also consider contemporary opinions on the potential impact of genetic discoveries to human health.

Genetic epidemiology of rheumatoid arthritis

Building on the spectacular success of molecular genetics in defining the biological basis of many rare single gene disorders over the past decade, epidemiologists have turned their attention to unravelling the complex genetic mysteries of common disorders, such as rheumatoid arthritis (RA). As a prelude to any such endeavour it is obviously important to establish that there is a significant genetic component to the disease. The classical approaches of twin and other family recurrence risk studies, coupled with prevalence studies in different ethnic and migrant populations, have been used to estimate the environmental and genetic contributions to RA. However, developing a consensus on these estimates has proved difficult, thereby providing an early warning to the unwary investigator that the road to gene discovery in RA is likely to be a rough ride.

Epidemiology of rheumatoid arthritis: determinants of onset, persistence and outcome

Rheumatoid arthritis (RA) is the most common chronic inflammatory joint disease. There is some evidence that it may have been brought from North America to Europe during the 18th century. Its arrival in rural parts of the developing world is still more recent. The incidence and prevalence of RA appear to have fallen in Europe, North America and Japan in the last 50 years. During this time the peak age of onset has risen. Risk factors for the development of RA include genetic factors, an adverse pregnancy outcome, smoking, obesity and recent infections. The oral contraceptive pill and some dietary constituents may be protective. Older age and female gender are risk factors both for the development of RA and for a worse outcome. This risk factor profile offers some opportunities for primary and secondary prevention. However, treatment is the greatest determinant of RA outcome.

Association between tumor necrosis factor receptor II and familial, but not sporadic, rheumatoid arthritis: evidence for genetic heterogeneity

OBJECTIVE

Tumor necrosis factor alpha (TNFalpha) binds the receptors TNFRI and TNFRII. Results of genome scans have suggested that TNFR2 is a candidate rheumatoid arthritis (RA) locus. A case-control study in a UK Caucasian population has shown an association between a TNFR2 genotype (196R/R in exon 6) and familial, but not sporadic, RA. The present study was undertaken to test this association in the French Caucasian population.

METHODS

To test for an association in sporadic RA, 100 families were genotyped for the 196M/R polymorphism and analyzed using the transmission disequilibrium test and haplotype relative risk. To test for an association in familial RA, RA index cases from 100 affected sibpair (ASP) families were genotyped for 196M/R. Linkage analysis was performed with 3 TNFR2 microsatellite markers.

RESULTS

The TNFR2 196R/R genotype was not associated with sporadic RA (odds ratio [OR] 0.59, P = 0.72), but was associated with familial RA (OR 4.0, P = 0.026). The association was most marked in the context of TNFR2 "twin-like" RA sibs (affected sibs sharing both TNFR2 haplotypes) (OR 9.2, P = 0.0017). Linkage analysis results were consistent with the association; most of the TNFR2 linkage evidence was found in the subgroup of families with 196R/R ASP index cases.

CONCLUSION

This study is the first to replicate evidence of the involvement of TNFR2 in RA genetic heterogeneity. Our data refine the initial hypothesis, to suggest that a TNFR2 recessive factor, in linkage disequilibrium with the 196R allele, plays a major role in a subset of families with multiple cases of RA.

Cytokines and anti-cytokine biologicals in autoimmunity: present and future

The increasing understanding of the role of cytokines in autoimmunity, and the observation that tumour necrosis factor alpha (TNFalpha) is central to the inflammatory and destructive process common to several human autoimmune diseases, has led to a new generation of therapeutics, the TNFalpha blocking agents. In this article, we review the current knowledge of the role of cytokines in autoimmunity as unravelled by studies both in the laboratory and the clinic. In addition, we discuss future prospects of the anti-TNFalpha therapy that may involve combination therapy with other anti-cytokine or anti-T cell biologicals, or the use of small chemicals targeting molecules involved in TNFalpha production such as NF-kappaB and p38 MAPK. The future developments of anti-TNFalpha and anti-cytokine therapy in general will be interesting.

Influence of human leukocyte antigen-DRB1 on the susceptibility and severity of rheumatoid arthritis

BACKGROUND AND OBJECTIVES

All human leukocyte antigen (HLA)-DRB1 alleles associated with rheumatoid arthritis (RA) encode a conserved amino acid sequence (QKRAA, QRRAA, or RRRAA) at position 70-74 in the third hypervariable region (HVR3) of the DRbeta(1) chain, which is commonly called the shared epitope (SE). Several studies, however, have associated the HLA-DRB1 gene in RA severity and progression rather than with susceptibility. Moreover, the association with disease severity and presence of the SE varies among different ethnic populations. HLA-DRB1 alleles also influence the disease onset. In this manuscript, the role of the HLA genes in RA was examined.

METHODS

A retrospective review of the literature was conducted to analyze the influence of the HLA-class II genes on the susceptibility, severity and protection against RA.

RESULTS

The HLA-DRB1*0401/*0404 genotype was associated with a higher risk for early disease onset in more severe forms in patients from the United Kingdom (UK). In northwest Spain, RA onset under 40 years is strongly associated with HLA-DRB1*0401 and *0404. In contrast, RA onset above 60 years is associated with HLA-DRB1*01. The protection against RA linked to some HLA-DRB1 alleles encoding a DERAA sequence of amino acids at position 70-74 in the HVR3 of the DRbeta1 chain, and specifically aspartic acid (D) at position 70 of this chain, recently was confirmed in both UK and northwest Spanish populations. Besides HLA-class II, other genes may be implicated in RA. Polymorphism in the tumor necrosis factor (TNF) region seems to be associated with RA, even in patients without the HLA-DRB1 SE. However, other genes such as interleukin-1 (IL-1) and corticotropin-releasing hormone may play a role in susceptibility to RA.

CONCLUSIONS

The additive effect of various genes may account for the development of RA and its clinical severity.

Cigarette smoking and the risk of rheumatoid arthritis among postmenopausal women: results from the Iowa Women's Health Study

PURPOSE

To determine whether cigarette smoking increases the risk of rheumatoid arthritis among postmenopausal women.

SUBJECTS AND METHODS

We followed a cohort of 31 336 women in Iowa who were aged 55 to 69 years in 1986 and who had no history of rheumatoid arthritis. Through 1997, 158 cases of rheumatoid arthritis were identified and validated based on review of medical records and supplementary information provided by physicians. Multivariable Cox proportional hazards regression was used to derive rate ratios (RRs) and 95% confidence intervals (CIs) for the association between cigarette smoking and rheumatoid arthritis.

RESULTS

Compared with women who had never smoked, women who were current smokers (RR = 2.0; 95% CI: 1.3 to 2.9) or who had quit 10 years or less before study baseline (RR = 1.8; 95% CI: 1.1 to 3.1) were at increased risk of rheumatoid arthritis, but women who had quit more than 10 years before baseline were not at increased risk (RR = 0.9; 95% CI: 0.5 to 2.6). Both the duration and intensity of smoking were associated with rheumatoid arthritis. Multivariable adjustments for age, marital status, occupation, body mass index, age at menopause, oral contraceptive use, hormone replacement therapy, alcohol use, and coffee consumption did not alter these results.

CONCLUSION

These results suggest that abstinence from smoking may reduce the risk of rheumatoid arthritis among postmenopausal women.

Whole-genome linkage analysis of rheumatoid arthritis susceptibility loci in 252 affected sibling pairs in the United Kingdom

OBJECTIVE

To undertake a systematic whole-genome screen to identify regions exhibiting genetic linkage to rheumatoid arthritis (RA).

METHODS

Two hundred fifty-two RA-affected sibling pairs from 182 UK families were genotyped using 365 highly informative microsatellite markers. Microsatellite genotyping was performed using fluorescent polymerase chain reaction primers and semiautomated DNA sequencing technology. Linkage analysis was undertaken using MAPMAKER/SIBS for single-point and multipoint analysis.

RESULTS

Significant linkage (maximum logarithm of odds score 4.7 [P = 0.000003] at marker D6S276, 1 cM from HLA-DRB1) was identified around the major histocompatibility complex (MHC) region on chromosome 6. Suggestive linkage (P < 7.4 x 10(-4)) was identified on chromosome 6q by single- and multipoint analysis. Ten other sites of nominal linkage (P < 0.05) were identified on chromosomes 3p, 4q, 7p, 2 regions of 10q, 2 regions of 14q, 16p, 21q, and Xq by single-point analysis and on 3 sites (1q, 14q, and 14q) by multipoint analysis.

CONCLUSION

Linkage to the MHC region was confirmed. Eleven non-HLA regions demonstrated evidence of suggestive or nominal linkage, but none reached the genome-wide threshold for significant linkage (P = 2.2 x 10(-5)). Results of previous genome screens have suggested that 6 of these regions may be involved in RA susceptibility.

Association of familial and sporadic rheumatoid arthritis with a single corticotropin-releasing hormone genomic region (8q12.3) haplotype

OBJECTIVE

Rheumatoid arthritis (RA) is a common disabling autoimmune disease with a complex genetic component. We have previously described linkage of a region of chromosome 8q12.3 with RA and association of the microsatellite marker CRHRA1 with RA in 295 affected sibling-pair families. In the current study we aimed to physically link the RA-associated marker with the corticotropin-releasing hormone (CRH) candidate gene, and to examine the genomic region for additional short tandem repeat (STR) genetic markers in order to clarify the association with RA.

METHODS

We examined the association of 2 STR markers with disease in the original 295 multicase families and in a cohort of 131 simplex families to refine our understanding of this genetic region in disease susceptibility in sporadic and familial RA. Genomic library screening and sequencing were used to generate physical sequences in the CRH genomic region. Bioinformatic analysis of the sequence flanking the CRH structural gene was used to screen for additional STRs and other genetic features. Genotyping was carried out using a standard fluorescence approach. Estimations of haplotype frequencies were performed to assess linkage disequilibrium. The transmission disequilibrium test was performed using TRANSMIT.

RESULTS

Physical cloning and sequencing analyses identified the genomic region linking the CRHRA1 marker and the CRH structural locus. Moreover, we identified a further STR, CRHRA2, which was in strong linkage disequilibrium with CRHRA1 (P = 4.0 x 10(-14)). A haplotype, CRHRA1*10;CRHRA2*14, was preferentially carried by unaffected parents at a frequency of 8.6% compared with the expected frequency of 3.1%. This haplotype was overtransmitted in the multiply affected families (P = 0.0077) and, similarly, in the simplex families (P = 0.024). Combined analysis of both family cohorts confirmed significant evidence for linkage (P = 4.9 x 10(-4)) and association (P = 5.5 x 10(-3)) for this haplotype with RA.

CONCLUSION

In demonstrating significant linkage disequilibrium between these 2 markers, we have refined the disease-associated region to a single haplotype and confirmed the significance of this region in our understanding of the genetics of RA.

The inheritance of rheumatoid arthritis in Iceland

OBJECTIVE

Rheumatoid arthritis (RA) is the most common form of inflammatory arthritis. Although there is a large body of evidence suggesting that RA is immune mediated, the etiology remains unresolved. Twin studies have shown disease concordance rates of approximately 15% in monozygotic twins and 4% in dizygotic twins, while the estimated risk ratio for siblings of RA patients ranges from 5 to 8. Our goal was to use genealogic data from Iceland to further investigate the genetic component of RA.

METHODS

Data were obtained from a population-based, computerized genealogy database that was developed to examine multigenerational relationships among individuals in the relatively homogeneous population of Iceland. Using an algorithm, the minimum founder test, we calculated the least number of founders required to account for a list of RA patients, and compared it with 1,000 sets of same-sized matched control groups. In addition, we estimated the kinship coefficient and risk ratios for relatives of the RA patients.

RESULTS

Several familial clustering tests demonstrated that the RA patients were more related to each other than were the average control set of Icelanders. A significantly fewer number of founders was necessary to account for our patient list than for the random sets of matched controls (P < 0.001), and the average pairwise identity-by-descent sharing was greater among the patients than among the control sets (P < 0.001). In addition, there was an increased risk of RA in first- and second-degree relatives of the patients; e.g., for siblings, the risk ratio was 4.38 (95% confidence interval 3.26-5.67), and for uncles/aunts, the risk ratio was 1.95 (95% confidence interval 1.52-2.43).

CONCLUSION

The familial component of RA is shown to extend beyond the nuclear family, thus providing stronger evidence for a significant genetic component to RA.

Rheumatoid arthritis

Rheumatoid arthritis is a systemic inflammatory disorder that mainly affects the diarthrodial joint. It is the most common form of inflammatory arthritis, and has a substantial societal effect in terms of cost, disability, and lost productivity. Although the pathogenesis of rheumatoid arthritis remains incompletely understood, much insight into the cellular and molecular mechanisms involved has been gained in the past decade. On the basis of these insights, new therapies have been developed, and clinical trials have shown the efficacy of aggressive treatment of patients with active disease. In this review, we discuss improvements in our understanding of the pathophysiology of inflammatory synovitis in rheumatoid arthritis, and improvements in therapy for patients with the disorder. The past decade has seen substantial advances in these areas. Future studies will be directed at improving methods for early diagnosis and identification of patients with progressive disease, and at improving methods to identify candidates for subclasses of disease-modifying antirheumatic drugs (DMARDs). Long-term safety and efficacy data for the new DMARD agents and combination regimens will also further delineate efficacy and toxicity and thus the appropriate clinical context for use of these therapeutic approaches. The continuing elucidation of pathophysiological pathways relevant in rheumatoid arthritis, coupled with continuing advances in biotechnology and rational drug design, offer substantial hope for the continued development of increasingly potent and specific pharmacotherapy for treatment of rheumatoid arthritis.

The genetics of complex autoimmune diseases: non-MHC susceptibility genes

Susceptibility to complex autoimmune diseases (AIDs) is a multigenic phenotype affected by a variety of genetic and environmental or stochastic factors. After over a decade of linkage analyses, the identification of non-major histocompatibility complex (non-MHC) susceptibility alleles has proved to be difficult, predominantly because of extensive genetic heterogeneity and possible epistatic interactions among the multiple genes required for disease development. Despite these difficulties, progress has been made in elucidating the genetic mechanisms that influence the inheritance of susceptibility, and the pace of gene discovery is accelerating. An intriguing new finding has been the colocalization of several AID susceptibility genes in both rodent models and human linkage studies. This may indicate that several susceptibility alleles affect multiple AIDs, or alternatively that genomic organization has resulted in the clustering of many immune system genes. The completion of the human genome sequence, coupled with the imminent completion of the mouse genome, should yield key information that will dramatically enhance the rate of gene discovery in complex conditions such as AID susceptibility.