The genetics revolution and the assault on rheumatoid arthritis

The genetics of autoimmune-mediated rheumatic diseases: clinical and biologic implications

This article emphasizes the interpretation of the meaning and significance of the genetic aspects of susceptibility to certain autoimmune-mediated rheumatic diseases. The familial aggregation and identical twin concordance that provides the basis of considering these as genetic diseases are reviewed. Major histocompatibility complex (MHC) genes are taken as the primary examples of candidate genes that regulate the immune response; the potential function of these genes in predisposing to autoimmune diseases is analyzed. Autoimmune diseases are discussed as the consequence of the role of MHC molecules encoded by different alleles that exhibit distinct peptide-binding properties and select a self reactive T-cell repertoire. The low penetrance rates of autoimmune-mediated rheumatic disease is used as an argument that stochastic events in the generation and postthymic maturation of the somatically expressed T-cell repertoire account for the characteristically delayed onset of these diseases. The importance of self-reactivity in the physiologic immune response is used as an argument that the events that are responsible for the development of an autoimmune disease are an untoward exaggeration of normal immune responsiveness, but not a qualitatively distinct biologic event.

Association of the major histocompatibility complex with response to infliximab therapy in rheumatoid arthritis patients

OBJECTIVE

To determine whether major histocompatibility complex (MHC) polymorphisms are associated with a good or poor response to infliximab therapy in patients with rheumatoid arthritis (RA).

METHODS

Seventy-eight infliximab-treated patients with RA were genotyped for HLA-DRB1, HLA-DQA1, HLA-DQB1, MHC class I chain-related gene A (MICA) transmembrane polymorphism alleles, and tumor necrosis factor a (TNFa), TNFb, TNFc, TNFd, TNFe, D6S273, HLA-B-associated transcript 2 (BAT2), and D6S2223 microsatellites. Chi-square tests were performed to compare allele proportions between responder and nonresponder patients. A control sample of 342 healthy individuals was also included to detect linkage disequilibrium between pairs of markers.

RESULTS

Among responders, the frequency of the TNFa11;b4 minihaplotype was increased (41% versus 16% in nonresponders; P = 0.01) and that of the D6S273_3 allele was decreased (32% versus 56% in nonresponders; P = 0.04). The D6S273_4/BAT2_2 pair was much more frequently observed among responders (46% versus 11% in nonresponders; P = 0.001). When compared with controls, this pair of alleles was found to be associated only with the group of responder patients (46% in responders versus 17% in controls; P = 0.00002). Most of the time, these markers are present in a DRB1*0404/D6S273_4/BAT2_2/TNFa11;b4 context. No statistically significant differences were observed for MICA and D6S2223 polymorphisms and for shared epitope status.

CONCLUSION

The data suggest that genetic determinants of response to infliximab therapy exist in the HLA complex.

An intronic SNP in a RUNX1 binding site of SLC22A4, encoding an organic cation transporter, is associated with rheumatoid arthritis

Rheumatoid arthritis is a common inflammatory disease with complex genetic components. We investigated the genetic contribution of the cytokine gene cluster in chromosome 5q31 to susceptibility to rheumatoid arthritis in the Japanese population by case-control linkage disequilibrium (LD) mapping using single nucleotide polymorphisms (SNPs). Here we report that there is significant association between rheumatoid arthritis and the organic cation transporter gene SLC22A4 (P = 0.000034). We show that expression of SLC22A4 is specific to hematological and immunological tissues and that SLC22A4 is also highly expressed in the inflammatory joints of mice with collagen-induced arthritis. A SNP affects the transcriptional efficiency of SLC22A4 in vitro, owing to an allelic difference in affinity to Runt-related transcription factor 1 (RUNX1), a transcriptional regulator in the hematopoietic system. A SNP in RUNX1 is also strongly associated with rheumatoid arthritis (P = 0.00035). Our data indicate that the regulation of SLC22A4 expression by RUNX1 is associated with susceptibility to rheumatoid arthritis, which may represent an example of an epistatic effect of two genes on this disorder.

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.

Molecular targets in immune-mediated diseases: the case of tumour necrosis factor and rheumatoid arthritis

Rheumatoid arthritis is a common autoimmune condition in which, for unknown reasons, synovial joints become the target of a sustained immune response. For many years, rheumatoid arthritis was in the 'too hard basket' in terms of understanding disease mechanisms and providing rational therapy. This has changed dramatically over the last 10 years and rheumatoid arthritis is now at the forefront of biotechnology. In this review, we outline one of the most exciting recent developments, namely antagonists of the cytokine TNF. The preclinical evaluation of TNF in animal models of rheumatoid arthritis, and subsequent clinical trials of TNF inhibitors in patients, provides insight into the 'bench to bedside' paradigm. We therefore briefly review rheumatoid arthritis, animal models of rheumatoid arthritis, the biology of TNF, the pivotal clinical trials of TNF antagonists and the emerging data on side-effects. Tumour necrosis factor inhibitors in rheumatoid arthritis represent the first attempt to achieve sustained blockade of a single cytokine in a human disease. Whilst this approach has been even more successful than might have been predicted, we suggest it is only the beginning of what has become a new therapeutic era.

Epidemiology of autoimmune liver disease

Primary biliary cirrhosis (PBC), autoimmune hepatitis (AIH) and primary sclerosing cholangitis (PSC) are chronic liver diseases that likely have an autoimmune basis to their pathogenesis. Although significant strides have been made in the clinical management of these conditions, their pathogenesis remains obscure. Understanding of various epidemiological factors may shed light on predisposing or causative factors for these diseases. Most is known about the epidemiology of PBC, with only minimal information on that of PSC and AIH. In this review, the current data on the epidemiology of PBC, AIH and PSC are summarized and suggestions are made for future work in this important area.

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.

Dissection of the genetic complexity of arthritis using animal models

The exploding progress in genomic technology and knowledge now opens the possibility to actually identify the molecular mechanisms in disease. However, inflammatory diseases such as rheumatoid arthritis (RA) and multiple sclerosis (MS), are complex and polygenic and remain a challenge. One possible shortcut could be the use of inbred animals as models for RA and MS for the genetic analysis. These models have been extensively characterized and show a similar degree of complexity as the corresponding human diseases. Using these models linkage analysis followed by isolation of the loci in congenic strains have been shown to be highly efficient and have provided fundamental new knowledge on the genetic control of these diseases. The genetically controlled congenic strains are also useful as scientific tools. They can be used for the identification of the disease-associated genes and, thereby, the essential disease pathways that have been selected by nature. We know that this is possible since we have succeeded in identifying the genes within two of the congenic regions; the MHC class II gene Aq controlling immune response and the Ncf1 gene controlling oxidative burst. Both of these genes are associated with T cell activation and arthritis severity.

Functional haplotypes of PADI4, encoding citrullinating enzyme peptidylarginine deiminase 4, are associated with rheumatoid arthritis

Individuals with rheumatoid arthritis frequently have autoantibodies to citrullinated peptides, suggesting the involvement of the peptidylarginine deiminases citrullinating enzymes (encoded by PADI genes) in rheumatoid arthritis. Previous linkage studies have shown that a susceptibility locus for rheumatoid arthritis includes four PADI genes but did not establish which PADI gene confers susceptibility to rheumatoid arthritis. We used a case-control linkage disequilibrium study to show that PADI type 4 is a susceptibility locus for rheumatoid arthritis (P = 0.000008). PADI4 was expressed in hematological and rheumatoid arthritis synovial tissues. We also identified a haplotype of PADI4 associated with susceptibility to rheumatoid arthritis that affected stability of transcripts and was associated with levels of antibody to citrullinated peptide in sera from individuals with rheumatoid arthritis. Our results imply that the PADI4 haplotype associated with susceptibility to rheumatoid arthritis increases production of citrullinated peptides acting as autoantigens, resulting in heightened risk of developing the disease.

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.

Identification of I kappa BL as the second major histocompatibility complex-linked susceptibility locus for rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease with a complex etiology in which environmental factors within a genetically susceptible host maneuver the innate and adaptive arms of the immune system toward recognition of autoantigens. This ultimately leads to joint destruction and clinical symptomatology. Despite the identification of a number of disease-susceptibility regions across the genome, RA's major genetic linkage remains with the major histocompatibility complex (MHC), which contains not only the key immune-response class I and class II genes but also a host of other loci, some with potential immunological relevance. Inside the MHC itself, the sole consistent RA association is that with HLA-DRB1, although this does not encode all MHC-related susceptibility. Indeed, in a set of Japanese patients with RA and a control group, we previously reported the presence of a second RA-susceptibility gene within the telomeric human leukocyte antigen (HLA) class III region. Using microsatellites, we narrowed the susceptibility region to 70 kb telomeric of the TNF cluster, known to harbor four expressed genes (I kappa BL, ATP6G, BAT1, and MICB). Here, using numerous single-nucleotide polymorphisms (SNPs) and insertion/deletion polymorphisms, we identify the second RA-susceptibility locus within the HLA region, as the T allele of SNP 96452 (T/A), in the promoter region (position -62) of the I kappa BL gene (P=.0062). This -62T/A SNP disrupts the putative binding motif for the transcriptional repressor, delta EF1, and hence may influence the transcription of I kappa BL, homologous to I kappa B alpha, the latter being a known inhibitor of NF kappa B, which is central to innate immunity. Therefore, the MHC may harbor RA genetic determinants affecting the innate and adaptive arms of the immune system.

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.

Dissecting the genetic complexity of the association between human leukocyte antigens and rheumatoid arthritis

Rheumatoid arthritis (RA) is an inflammatory disease with a complex genetic component. An association between RA and the human leukocyte antigen (HLA) complex has long been observed in many different populations, and most studies have focused on a direct role for the HLA-DRB1 "shared epitope" in disease susceptibility. We have performed an extensive haplotype analysis, using 54 markers distributed across the entire HLA complex, in a set of 469 multicase families with RA. The results show that, in addition to associations with the DRB1 alleles, at least two additional genetic effects are present within the major histocompatibility complex. One of these lies within a 497-kb region in the central portion of the HLA complex, an interval that excludes DRB1. This genetic risk factor is present on a segment of a highly conserved ancestral A1-B8-DRB1*03 (8.1) haplotype. Additional risk genes may also be present in the HLA class I region in a subset of DRB1*0404 haplotypes. These data emphasize the importance of defining haplotypes when trying to understand the HLA associations with disease, and they clearly demonstrate that such associations with RA are complex and cannot be completely explained by the DRB1 locus.

Differences in idiopathic inflammatory myopathy phenotypes and genotypes between Mesoamerican Mestizos and North American Caucasians: ethnogeographic influences in the genetics and clinical expression of myositis

OBJECTIVE

As part of a larger, worldwide study of the ethnogeography of myositis, we evaluated the clinical, serologic, and immunogenetic features of Mestizo (Mexican and Guatemalan) and North American Caucasian patients with idiopathic inflammatory myopathy (IIM).

METHODS

Clinical manifestations, autoantibodies, HLA-DRB1 and DQA1 alleles, and immunoglobulin Gm/Km allotypes were compared between 138 Mestizos with IIM and 287 Caucasians with IIM, using the same classification criteria and standardized questionnaires.

RESULTS

IIM in Mestizo patients was characterized by a higher proportion of dermatomyositis (69% of adult Mestizos versus 35% of adult Caucasians; P < 0.001) and anti-Mi-2 autoantibodies (30% versus 7% of adults, respectively, and 32% versus 4% of children, respectively; P < 0.01). Genetic risk factors also differed in these populations. Whereas Mestizos had no HLA risk factors for IIM, HLA-DRB1*0301, the linked allele DQA1*0501, and DRB1 alleles sharing the first hypervariable region motif (9)EYSTS(13) were major risk factors in Caucasian patients with IIM. Furthermore, different HLA-DRB1 and DQA1 alleles were associated with anti-Mi-2 autoantibodies (DRB1*04 and DQA1*03 in Mestizos and DRB1*07 and DQA1*02 in Caucasians). Immunoglobulin gamma-chain allotypes Gm(1), Gm(17) (odds ratio for both 11.3, P = 0.008), and Gm(21) (odds ratio 7.3, P = 0.005) and kappa-chain allotype Km(3) (odds ratio 7.3, P = 0.005) were risk factors for IIM in Mestizos; however, no Gm or Km allotypes were risk or protective factors in Caucasians. In addition, Gm and Km phenotypes were unique risk factors (Gm 1,3,17 5,13,21 and Gm 1,17 23 21 and Km 3,3) or protective factors (Km 1,1) for the development of myositis and anti-Mi-2 autoantibodies (Gm 1,2,3,17 23 5,13,21) in adult Mestizos.

CONCLUSION

IIM in Mesoamerican Mestizos differs from IIM in North American Caucasians in the frequency of phenotypic features and in the immune-response genes predisposing to and protecting from myositis and anti-Mi-2 autoantibodies at 4 chromosomal loci. These and other data suggest the likelihood that the expression of IIM is modulated by different genes and environmental exposures around the world.

Stromelysin 1 (matrix metalloproteinase 3) and HLA-DRB1 gene polymorphisms: Association with severity and progression of rheumatoid arthritis in a prospective study

OBJECTIVE

To test the hypothesis of an association between a polymorphism in the matrix metalloproteinase 3 (MMP-3) gene promoter and the susceptibility, severity, and progression of rheumatoid arthritis (RA), and to further document the association between HLA-DRB1 alleles encoding the shared epitope (SE) and the severity and progression of RA.

METHODS

Patients with early RA (n = 103) were included in this prospective study. A total radiographic damage score (TDS; by the Sharp/van der Heijde method) was used to quantify RA severity at baseline and after 4 years of followup. The 5A/6A biallelic polymorphism in the MMP-3 gene promoter was analyzed using fluorescence-based polymerase chain reaction (PCR). HLA-DRB1 genotyping was performed using PCR methods. Control subjects (n = 127) were unrelated healthy individuals.

RESULTS

MMP-3 allele carriage rates and allele and genotype frequencies did not differ between patients and controls. The MMP-3 6A/6A genotype was associated with the highest TDS both at baseline and after a 4-year followup and with the highest progression of the TDS over the 4 years of followup. The DRB1 SE+/+ genotype was associated with the highest TDS after a 4-year followup and with the highest progression of the TDS over the 4 years of followup. Patients homozygous for MMP-3 6A and DRB1 SE had the highest progression of the TDS.

CONCLUSION

This study provides the first evidence of an association between a polymorphism in the MMP-3 gene promoter and the severity and progression of RA, but not RA susceptibility. Investigation of this polymorphism could be combined with that of DRB1 gene polymorphism to improve the predictive accuracy and management strategy in early RA.

Shared epitopes and rheumatoid arthritis: disease associations in Greece and meta-analysis of Mediterranean European populations

OBJECTIVES

To assess the strength of the associations between HLA shared epitopes (SE) and rheumatoid arthritis (RA) susceptibility, articular disease severity, and extra-articular features in Mediterranean European populations.

METHODS

One hundred and seventy-four Greek RA patients and 103 controls were evaluated. Data were then included in a meta-analysis of 9 studies of Mediterranean European populations (959 RA patients and 1,405 controls).

RESULTS

In our study population, SE alleles were significantly more common in RA patients than in controls (odds ratio [OR], 2.5; 95% confidence interval [CI], 1.4-4.3). Larsen radiologic score was predicted by SE and disease duration. SE did not increase the risk of any extra-articular manifestation. The meta-analysis showed a pooled OR of 3.7 (95% CI, 2.6-5.2) for susceptibility to RA conferred by SE (OR, 3.4 v 3.9 in Greek v non-Greek populations).

CONCLUSIONS

SE determine articular destruction without increasing the risk of extra-articular manifestations. The immunogenetic associations of RA susceptibility are consistent, but their strength may depend on the SE prevalence in different ethnic groups.

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.

Evaluation of quantitative trait loci regulating severity of mycobacterial adjuvant-induced arthritis in monocongenic and polycongenic rats: identification of a new regulatory locus on rat chromosome 10 and evidence of overlap with rheumatoid arthritis susceptibility loci

OBJECTIVE

To evaluate the regulatory potential of genetic loci controlling Mycobacterium butyricum adjuvant-induced arthritis (Mbt-AIA) using mono- and polycongenic rats.

METHODS

Of 4 quantitative trait loci (QTLs) that regulate Mbt-AIA, F344 alleles at 3 of these loci, Aia1, Aia2, and Aia3, are associated with lower arthritis severity, whereas F344 alleles at Aia4 are associated with greater arthritis severity. In this study, we constructed congenic lines by transferring 1 or more of the F344 genomic segments containing Aia1, Aia2, and Aia3 onto the DA genome. We comparatively evaluated their responses to Mbt-AIA with the responses of parental DA and F344 rats.

RESULTS

Aia1, encompassing the rat major histocompatibility complex, reduced arthritis severity in monocongenic rats of both sexes. The arthritis-lowering effects of Aia2 and Aia3 were sex-influenced and were therefore observed in only males and only females, respectively. Polycongenic rats containing F344 genomic regions at Aia1, Aia2, and Aia3 developed Mbt-AIA of relatively greater severity than did F344 rats, implying that in DA and F344 rats, there could be other Mbt-AIA loci in addition to Aia1, Aia2, Aia3, and Aia4. To test the possibility that some of these Mbt-AIA-regulatory loci may colocalize with other arthritis QTLs, we evaluated Mbt-AIA in DA.F344 monocongenic rats containing collagen-induced arthritis QTLs. Cia5 (the QTL region on chromosome 10), but not Cia5a, Cia4, or Cia6, also regulated Mbt-AIA, and was named Aia5.

CONCLUSION

F344 genomic regions at Aia1, Aia2, and Aia3 and the newly identified Aia5 contain genes that reduce Mbt-AIA severity in DA rats. These Mbt-AIA-regulatory loci overlap rheumatoid arthritis-susceptibility loci in humans.

The IDDM13 region containing the insulin-like growth factor binding protein-5 (IGFBP5) gene on chromosome 2q33-q36 and the genetic susceptibility to rheumatoid arthritis

We considered that the constitutive over-expression by cultured rheumatoid arthritis (RA) fibroblast-lineage synoviocytes of genes like IGFBP5 could indicate new candidate susceptibility genes. IGFBP5 is located in a region where an insulin-dependent diabetes mellitus (IDDM) susceptibility locus, IDDM13 (2q33-q36), has been mapped. Previous evidence that non-MHC IDDM loci overlap RA susceptibility loci made IGFBP5 and its region an interesting candidate locus which was tested for linkage. Forty-nine sibships (2-4 affected siblings per sibship) with RA were genotyped with microsatellite markers covering an 11.2 cM interval in the IGFBP5/IDDM13 region. Both the two-point LOD scores and a 'nonparametric' allele-sharing analysis revealed no evidence for linkage (max LOD = 0.54, P = 0.5, respectively). Adjustments for the presence of 'shared-epitope' alleles did not significantly change the LOD scores. These results suggest that, despite the involvement of the 2q33-q36 chromosomal region in another organ-specific autoimmune disease, it is unlikely that this region harbors a RA susceptibility locus.

The shared epitope and severity of rheumatoid arthritis

After two decades of research involving thousands of RA patients, it is still not possible to precisely define the relation of HLA-DRB1 SE alleles to RA severity. Improvements in our understanding require more careful consideration of several factors such as ethnicity, gender, and the specific SE allele and genotype inherited. Large studies of heterogeneous groups of patients are required and indicate the need for collaborative efforts among researchers. In the interim, meta-analysis of the existing literature may provide some insight, because it allows utilization of the tremendous amount of research already completed. A preliminary meta-analysis highlighted the significant heterogeneity among the existing literature, and a more ambitious meta-analysis that uses individual patient-level data is currently ongoing. Profound implications exist for determination of the precise relationship between the SE and RA severity. This information could be valuable in identifying patients at greater risk of severe complications or as a stratification variable for clinical trials. Moreover, patients genetically predisposed to severe disease may benefit from early initiation of more aggressive therapy. Ultimately, clarification of the role of the SE may be valuable for the development of specific therapies directed toward DRB1 and related targets.

Rheumatoid arthritis. The genetic components

Rheumatoid arthritis is a multifactorial disease, with genetic, environmental, and stochastic components to its susceptibility. The search for susceptibility genes is still in progress. Preliminary results suggest the involvement of multiple genes, each with relatively modest effect. Genes within the major histocompatibility complex appear to have the strongest influence on disease susceptibility.

Genetic influences on rheumatoid arthritis in African Americans

Rheumatoid arthritis is a common autoimmune disease characterized by inflammation of the synovial membrane of diarthrodial joints, which often leads to joint damage and disability. There are known associations between major histocompatibility complex class II alleles and susceptibility to rheumatoid arthritis and its severity in Caucasians. African Americans, an admixed population in the United States, has been underrepresented in genetic studies of the susceptibility and severity of rheumatoid arthritis. With the advent of biologic agents, which target specific molecules of the immune system (e.g., tumor necrosis factor, interleukin-1), biologic markers of treatment response in Caucasians and in African Americans would be clinically useful.

Invited review: sex ratio and rheumatic disease

Human illnesses affect men and women differently. In some cases (diseases of sex organs, diseases resulting from X or Y chromosome mutations), reasons for sex discrepancy are obvious, but in other cases no reason is apparent. Explanations for sex discrepancy of illness occur at different biological levels: molecular (e.g., imprinting, X-inactivation), cellular (sex-specific receptor activity), organ (endocrine influences), whole organism (size, age), and environmental-behavioral, including intrauterine influences. Autoimmunity represents a prototypical class of illness that has high female-to-male (F/M) ratios. Although the F/M ratios in autoimmune diseases are usually attributed to the influence of estrogenic hormones, evidence demonstrates that the attributed ratios are imprecise and that definitions and classifications of autoimmune diseases vary, rendering at least part of the counting imprecise. In addition, many studies on sex discrepancy of human disease fail to distinguish between disease incidence and disease severity. In April 2001, the Institute of Medicine of the National Academy of Sciences published Exploring the Biological Contributions to Human Health: Does Sex Matter? (Wizemann T and Pardue M-L, editors). This minireview summarizes the section of that report that concerns autoimmune and infectious disease. Some thyroid, rheumatic, and hepatic autoimmune diseases have high F/M ratios, whereas others have low. Those that have high ratios occur primarily in young adulthood. Gonadal hormones, if they play a role, likely do so through a threshold or permissive mechanism. Examples of sex differences that could be caused by environmental exposure, X inactivation, imprinting, X or Y chromosome genetic modulators, and intrauterine influences are presented as alternate, theoretical, and largely unexplored explanations for sex differences of incidence. The epidemiology of autoimmune diseases (young, female) suggests that an explanation for sex discrepancy of these illnesses lies in differential exposure, vulnerable periods, or thresholds. Biologists have an opportunity to inform medical scientists about sex differences that explain different attack rates in specific diseases, and physicians offer biologists experiments of nature to test theories of sex.

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.

Primary association of a MICA allele with protection against rheumatoid arthritis

OBJECTIVE

To determine whether major histocompatibility complex class I chain-related gene A (MICA) polymorphisms are associated with susceptibility to rheumatoid arthritis (RA) independently of the HLA-DRB1 shared epitope (SE).

METHODS

Fifty-four Spanish families with an affected son or daughter and 211 consecutive RA patients were genotyped for HLA-DRB1, tumor necrosis factor a/b microsatellite alleles, and MICA transmembrane polymorphism. We performed a case-control comparison with the consecutive patients and an independent transmission disequilibrium test with the families.

RESULTS

The frequency of the MICA 6.0 allele was significantly reduced, compared with controls, in the group of SE+ patients (odds ratio 0.39, P = 0.0005). Additionally, the haplotypes containing this allele were preferentially not transmitted to the affected offspring (9 transmitted of 33; P = 0.007), independent of the presence or absence of an SE either in the same haplotype or in the other haplotype in the progenitor.

CONCLUSION

These data suggest that the MICA 6.0 allele is an independent marker of protection against RA in the SE+ group of RA patients.

Major histocompatibility complex class I-recognizing receptors are disease risk genes in rheumatoid arthritis

Rheumatoid arthritis (RA) is a heterogeneous syndrome of which a subset of patients develops vascular inflammation. The genetic determinants that confer risk for rheumatoid vasculitis are not known, but patients with vascular complications are known to have an expansion of CD4(+)CD28(null) T cells, a cell population potentially involved in endothelial damage. CD4(+)CD28(null) T cell clones isolated from RA patients with vasculitis were found to express killer cell immunoglobulin-like receptors (KIRs) with the stimulatory KIR2DS2 often present in the absence of opposing inhibitory receptors with related specificities. To test the hypothesis that the KIR2DS2 gene is involved in the development of vasculitis, association studies were performed. The KIR2DS2 gene was significantly enriched among patients with rheumatoid vasculitis compared with normal individuals (odds ratio 5.56, P = 0.001) and patients with RA but no vasculitis (odds ratio 7.96, P = 0.001). Also, the distribution of human histocompatibility leukocyte antigen (HLA)-C, the putative ligand for KIRs, was significantly different in patients with rheumatoid vasculitis in comparison with the control populations. These data suggest that HLA class I-recognizing receptors and HLA class I genes are genetic risk determinants that modulate the pattern of RA expression. Specifically, KIR2DS2 in conjunction with the appropriate HLA-C ligand may have a role in vascular damage by regulating CD4(+)CD28(null) T cells.

HW, Bridges Jr. SL, Pisetsky DS, Ward R, Kastner DL, Wilder RL, Pincus T, Callahan LF, Flemming D, Wener MH, Gregersen PK. A genomewide screen in multiplex rheumatoid arthritis families suggests genetic overlap with other autoimmune diseases

Rheumatoid arthritis (RA) is an autoimmune/inflammatory disorder with a complex genetic component. We report the first major genomewide screen of multiplex families with RA gathered in the United States. The North American Rheumatoid Arthritis Consortium, using well-defined clinical criteria, has collected 257 families containing 301 affected sibling pairs with RA. A genome screen for allele sharing was performed, using 379 microsatellite markers. A nonparametric analysis using SIBPAL confirmed linkage of the HLA locus to RA (P < .00005), with lambdaHLA = 1.79. However, the analysis also revealed a number of non-HLA loci on chromosomes 1 (D1S235), 4 (D4S1647), 12 (D12S373), 16 (D16S403), and 17 (D17S1301), with evidence for linkage at a significance level of P<.005. Analysis of X-linked markers using the MLOD method from ASPEX also suggests linkage to the telomeric marker DXS6807. Stratifying the families into white or seropositive subgroups revealed some additional markers that showed improvement in significance over the full data set. Several of the regions that showed evidence for nominal significance (P < .05) in our data set had previously been implicated in RA (D16S516 and D17S1301) or in other diseases of an autoimmune nature, including systemic lupus erythematosus (D1S235), inflammatory bowel disease (D4S1647, D5S1462, and D16S516), multiple sclerosis (D12S1052), and ankylosing spondylitis (D16S516). Therefore, genes in the HLA complex play a major role in RA susceptibility, but several other regions also contribute significantly to overall genetic risk.

Association between a single-nucleotide polymorphism in the promoter of the human interleukin-3 gene and rheumatoid arthritis in Japanese patients, and maximum-likelihood estimation of combinatorial effect that two genetic loci have on susceptibility to the disease

Genetic variants of interleukin-3 (IL-3), a well-studied cytokine, may have a role in the pathophysiology of rheumatoid arthritis (RA); but reports on this association sometimes conflict. A case-control study was designed to investigate association between RA and a single-nucleotide polymorphism (SNP) in the IL-3 promoter region. Comparison of cases of RA versus control individuals yielded a chi(2) value of 14.28 (P=.0002), with a genotype odds ratio of 2.24 (95% confidence interval [95%CI] 1.44-3.49). When female cases with earlier onset were compared with female control individuals, the SNP revealed an even more significant correlation, with chi2=21.75 (P=.000004) and a genotype odds ratio of 7.27 (95%CI 2.80-18.89). The stronger association that we observed in this clinically distinct subgroup (females with early onset), within a region where linkage disequilibrium was not significantly extended, suggested that the genuine RA locus should locate either within or close to the IL-3 gene. Combined genotype data on SNPs on eight other candidate genes were combined with our IL-3 results, to estimate relationships between pairs of loci and RA, by maximum-likelihood analysis. The utility of combining the genotype data in this way to identify possible contributions of various genes to this disease is discussed.

Heavy cigarette smoking is strongly associated with rheumatoid arthritis (RA), particularly in patients without a family history of RA

OBJECTIVES

To investigate the potential relation between cumulative exposure to cigarette smoking in patients with or without rheumatoid arthritis (RA) and a positive family history of the disease.

METHODS

239 outpatient based patients with RA were compared with 239 controls matched for age, sex, and social class. A detailed smoking history was recorded and expressed as pack years smoked. Conditional logistic regression was used to calculate the association between RA and pack years smoked. The patients with RA were also interviewed about a family history of disease and recorded as positive if a first or second degree relative had RA. The smoking history at the time of the study of the patients with RA with or without a family history of the disease was compared directly with that of their respective controls. Patients with RA with or without a family history of the disease were also compared retrospectively for current smoking at the time of disease onset.

RESULTS

An increasing association between increased pack years smoked and RA was found. There was a striking association between heavy cigarette smoking and RA. A history for 41-50 pack years smoked was associated with RA (odds ratio (OR) 13.54, 95% confidence interval (95% CI) 2.89 to 63.38; p<0.001). The association between ever having smoked and RA was modest (OR 1.81, CI 1.22 to 2.19; p=0.002). Furthermore, cigarette smoking in the patients with RA without a positive family history of RA was more prevalent than in the patients with a positive family history of RA for ever having smoked (72% v 54%; p=0.006), the number of pack years smoked (median 25.0 v 4.0; p<0.001), and for smoking at the time of disease onset (58% v 39%; p=0.003).

CONCLUSIONS

Heavy cigarette smoking, but not smoking itself, is strongly associated with RA requiring hospital follow up and is markedly more prevalent in patients with RA without a family history of RA.

Genetic and familial considerations of primary biliary cirrhosis

The genetic basis of human autoimmune diseases is receiving increasing attention. Primary biliary cirrhosis (PBC) is a model autoimmune disease reflective of other organ-specific autoimmune pathology. PBC is an enigmatic autoimmune disease that predominantly affects women and leads to destruction of intrahepatic bile ducts. The serological hallmark of this disease is characterized by antimitochondrial antibodies that specifically react with the E2 components of 2-oxodehydrogenase enzymes, including PDC-E2. There are no clear major histocompatibility complex associations with the development of PBC, despite the observation that first-degree relations of index patients with PBC have a 4-6% prevalence of development of PBC. This risk factor is comparable or higher than any other human autoimmune disease and suggests that a genome-wide approach towards dissection of genetic associations would lead to valuable new insights. In this review, we place these concepts in perspective and highlight in particular the genetic associations in PBC and the importance of studying siblings with PBC who are concordant for disease.

The genetics of rheumatoid arthritis and the need for animal models to find and understand the underlying genes

The causes of rheumatoid arthritis (RA) are largely unknown. However, RA is most probably a multifactorial disease with contributions from genetic and environmental factors. Searches for genes that influence RA have been conducted in both human and experimental model materials. Both types of study have confirmed the polygenic inheritance of the disease. It has become clear that the features of RA complicate the human genetic studies. Animal models are therefore valuable tools for identifying genes and determining their pathogenic role in the disease. This is probably the fastest route towards unravelling the pathogenesisis of RA and developing new therapies.

Update on genetic risk factors for systemic lupus erythematosus and rheumatoid arthritis

The results of twin and family studies clearly implicate an important role for genetic factors in the etiology of systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). However, the complex nature of these diseases has hampered progress in defining the genetic determinants. Recent advances in molecular genetic and statistical methodology offer new hope to overcome these challenges. This review highlights recent efforts to identify genetic risk factors for SLE and RA using allele sharing and other linkage methods. In spite of striking differences between these studies, some agreement in terms of the regions providing evidence of linkage also exists. Thus, together these studies highlight regions of the genome that are likely to contain SLE and RA susceptibility genes. In addition, the results of these studies, in conjunction with progress in other complex human diseases, suggest several important considerations for future studies.

Mapping autoimmunity genes

Rat and mouse models for the major human autoimmune/inflammatory diseases are under intense genetic scrutiny. Genome-wide linkage studies reveal that each model is regulated by multiple genetic loci. Many of these loci colocalize to homologous genomic regions associated with several different autoimmune diseases of mice, rats and humans. Candidate genes are being identified. Polymorphic alleles associated with these chromosomal segments may represent predisposing genetic elements common to a number of human diseases with very different clinical presentations.

The genetics of rheumatoid arthritis: influences on susceptibility, severity, and treatment response

There has been an explosion of knowledge of genetic variations among different populations and the influence of genetics on complex diseases such as rheumatoid arthritis (RA). Although class II major histocompatibility complex (MHC) alleles are important contributors, there are likely multiple other genes that modulate the disease phenotype. Genetic markers may allow prediction of response to particular treatments. Given the recent approval of tumor necrosis factors (TNF) inhibitors and the large number of biologic agents currently undergoing clinical trials, pharmacogenetic markers may prove to be clinically useful.

Genetics of rheumatoid arthritis: confronting complexity

The genetic basis for rheumatoid arthritis (RA) is likely to be extremely complex. Even the role of MHC genes remains to be fully defined, and may involve interactive genetic effects. The difficulty of precisely defining the clinical phenotype, as well as underlying genetic heterogeneity, complicates the problem. In addition, stochastic genetic or physiologic events may contribute to the low penetrance of susceptibility genes. This situation parallels developing paradigms for other autoimmune disorders, in which many different genes each appear to contribute a small amount to overall risk for disease, and where severity and specific phenotypic subtypes are subject to genetic effects. The completion of the human genome project, along with advances in informatics, will be required to reach a deeper understanding of RA. It is likely that this will involve an iterative and interactive process between several different scientific disciplines.