AICAR-T = aminoimidazole carboxamide ribonucleotide transformylase; CRH = corticotropin-releasing hormone; DMARD = disease-modifying antirheumatic drug; IL = interleukin; MHC = major histocompatibility complex; MTHFR = methylenetetrahydrofolate reductase; RA = rheuma-toid arthritis; RANK = receptor activator of nuclear factor κκκκκB; RANKL = RANK ligand; SE = shared epitope; SNP = single nucleotide poly-morphism; TNF = tumor necrosis factor; TPMT = thiopurine methyl-transferase
From the Division of Rheumatology, Mayo Clinic College of Medicine, Roches-ter, Minn. Dr Turesson is now with Malmö University Hospital, Malmö, Sweden.
Address correspondence to Eric L. Matteson, MD, MPH, Division of Rheumatology, Mayo Clinic College of Medicine, 200 First St SW, Rochester, MN 55905 (e-mail: [email protected]). Individual reprints of this article and the entire series on Genetics in Clinical Practice will be available for purchase from our Web site www.mayoclinicproceedings.com.
© 2006 Mayo Foundation for Medical Education and Research
Genetics of Rheumatoid Arthritis
CARL TURESSON, MD, PHD, AND ERIC L. MATTESON, MD, MPH
Rheumatoid arthritis (RA) is a heterogeneous autoimmune disor-der of unknown cause with variable clinical expression. About 70% of patients are women. Genetic factors play an important role and likely account for about 60% of disease susceptibility and expres-sion. The association with the HLA-DRB1 gene is the best under-stood, although several non-HLA loci have been linked to RA, including the 18q21 region of the TNFRSR11A gene, which en-codes the receptor activator of nuclear factor κκκκκB, important in bone resorption in RA. Genetic factors are also important in the treatment of RA because the activity of enzymes relevant in the metabolism of drugs such as methotrexate and azathioprine, including methylenetetrahydrofolate reductase and thiopurine methyltransferase, are in part genetically determined.
Mayo Clin Proc. 2006;81(1):94-101
R
heumatoid arthritis (RA) is a chronic inflammatory disorder that is characterized by polyarthritis with often progressive joint damage and disability, immuno-logic abnormalities, systemic inflammation, increased comorbidity, and premature mortality. Populations of pa-tients with diagnosed RA are clinically heterogeneous, and no single test defines RA. The etiology is incompletely understood and likely to be multifactorial and variable in different subsets of patients.There is extensive evidence for a role for genetic factors in RA. Studies of monozygotic twins have revealed in-creased concordance rates of RA compared to dizygotic twins.1,2 A study using the Icelandic population-based
ge-nealogy database showed that patients with RA were more related to each other than were control groups of Icelanders and that the familial component extended beyond the nuclear family.3 In models based on nationwide studies of
twins with RA from Finland1 and the United Kingdom,2 the
heritability of RA, ie, the extent to which liability to disease is explained by genetic variation in the population, has been estimated at 60%.4
In addition to traditional genetic factors, several envi-ronmental factors have been implicated as predictors of RA.5 The 2- to 3-fold higher prevalence of the disease in
women, primarily due to an increased female incidence before menopause,6 has been interpreted as indicating a
role for hormonal or reproductive factors; about 70% of patients with RA are women. Smoking is a well-estab-lished risk factor for the development of RA7,8 and also
seems to be a predictor of disease severity.9-11 Interestingly,
a recent study found smoking to be a predictor primarily in the subset of patients with RA-associated HLA-DRB1 genotypes, indicating that genetic and environmental fac-tors could interact in predisposing to RA.12
SUSCEPTIBILITY GENES
Rheumatoid arthritis has been associated with polymorphic variants in the HLA-DRB1 genes.13,14 It has been shown that
DRB1-subtypes associated with RA in different popula-tions share a region encoding a similar amino acid se-quence (the shared epitope [SE]).15 These subtypes include
some of those corresponding to the HLA-DR4 serotype (HLA-DRB1*0401/0404/0405/0408), HLA-DR1 subtypes (HLA-DRB1*0101/0102), and HLA-DRB1*1001, *1402, and *1406. The shared amino sequence is the QKRAA/ QRRAA/RRAAA pattern in position 70-74 on the HLA-DR β chain. HLA-DRB1 alleles with a negative association with RA have a clear homology for different sequences in the named positions.16
The DRB1*1402 and *1406 subtypes are found in most Yakima and Pima Indians,17 who have the highest reported
prevalence of RA in the world.18,19 Overall, the SE of HLA-DRB1 has been estimated to account for one third of the
genetic risk in RA.20 Genome-wide screening of multicase
families using microsatellite loci has confirmed linkage between RA and the HLA-DR region in European21-25 but
not Japanese26 subjects.
The HLA-DR genes are situated on chromosome 6p within the major histocompatibility complex (MHC), which consists of a large number of highly polymorphic genes. There is considerable linkage disequilibrium within the MHC, indicating that other genes, which are part of
extended SE-associated haplotypes, could to some degree explain disease associations with HLA alleles in the MHC class II region.
An extensive haplotype analysis of multicase families using markers distributed across the MHC by Jawaheer et al27 demonstrated linkage with markers in the class III
region, in addition to the known linkage with HLA-DRB1. The class III region markers were associated with the an-cestral A1-B8-DRB1*03 haplotype. Recently, HLA-DR3 was reported to be more frequent in patients with RA who lack antibodies directed against cyclic citrullinated pep-tides,28 whereas specific importance for HLA-DRB1*040129
and other SE alleles30,31 has been suggested for the immune
response to cyclic citrullinated peptides. In addition, a seg-ment in the class I region on some DRB1*0404 haplotypes was preferentially transmitted in families with RA. This suggests that other genes in the MHC modify the risk associated with HLA-DRB1 alleles. Furthermore, recent data implicate an independent susceptibility locus on chro-mosome 6p, telomeric to the HLA-DRB1 locus.32
Several non-HLA loci have been linked to RA in ge-nome-wide screening studies.21-26 However, only a few of
these have been replicated in independent samples (Table 1). Interestingly, of the regions with replicated linkage, several may be associated with other autoimmune disor-ders. 1p13,33 1q43,33 and 18q2134 have been linked to
sys-temic lupus erythematosus, and there is evidence of linkage of the 18q21 locus with type 1 diabetes mellitus35,36 and
Grave disease.37 These regions are relatively large, and
further mapping using dense sets of markers followed by analysis of candidate genes is necessary to identify the molecular basis for these associations.
The 18q21 region includes the TNFRSR11A gene, which encodes the receptor activator of nuclear factor κB (RANK). RANK, which binds the soluble or cell-bound RANK ligand (RANKL), has been shown to be involved in the differentiation of osteoclasts in inflamed synovium and is important for the development of bone resorption in people with arthritis.38 Thus, polymorphisms in this area
may influence susceptibility to erosive arthritis. In a recent survey of a cohort with early-onset RA, variant RANKL genotypes were associated with younger age at onset of RA in patients who have an HLA-DRB1 SE.39 This further
emphasizes the potential importance of genetic polymor-phisms for RANK-RANKL interactions and their impact on RA.
A meta-analysis of the first 4 genome searches for link-age with RA21,23,24,26 showed not only strong evidence for
linkage with the MHC region but also evidence for an RA susceptibility locus on 16.40 This region, which was not
identified as statistically significant in any of the individual genome searches that comprised the meta-analysis,
con-tains the CARD15 gene implicated as a susceptibility gene in Crohn disease.41 However, the CARD15 polymorphisms
associated with Crohn disease have not been shown to have any impact on the risk of RA.42 Other genes in this area may
be important both for RA and for Crohn disease.
In the combined data sets from the 2 US-based genome searches,24,25 the 8q13 locus was close to the predefined
level of significance for linkage with RA.25 This region is
close to the gene encoding corticotropin-releasing hormone (CRH). Specific CRH haplotypes have been implicated in familial and sporadic RA.43 The hypothalamic-pituitary
axis response to inflammatory stimuli is defective in pa-tients with RA,44 and CRH polymorphisms could influence
the risk of RA through effects on the regulation of the hypothalamic-pituitary axis. The CRHA2 allele has been associated with late onset seronegative RA in a cohort with a low frequency of RA-associated HLA-DRB1 alleles.45
Several other candidate genes for disease susceptibility have been suggested that have not been found to be consis-tently associated with RA, and others await replication. Discrepancies between different studies indicate that some primary associations were due to chance, but they may reflect ethnic heterogeneity or other differences in the se-lections of the populations studied. For example, the cytokine gene cluster in chromosome 5q31 has been linked to RA in Japanese subjects46 but not in studies of
Cauca-sians. Tokuhiro et al46 reported an association with RA for a
single nucleotide polymorphism (SNP) of the SLC22A4
TABLE 1. Loci With Significant Linkage With Rheumatoid Arthritis, Replicated in Independent Samples*
in Genome-Wide Screening of Multicase Families†
Suggested Reference Locus candidate genes Cornelis et al,21 1998 6p21.3 HLA-DRB1,
Jawaheer et al,24 2001 other MHC genes
MacKay et al,23 2002
Jawaheer et al,25 2003
Osorio et al,22 2004
Cornelis et al,21 1998 18q21 RANK
Jawaheer et al,24 2001
Jawaheer et al,25 2003
Cornelis et al,21 1998 1q43 Unknown, also
Jawaheer et al,24 2001 linkage with SLE
MacKay et al,23 2002
Jawaheer et al,25 2003
Jawaheer et al,24 2001 6q21 Unknown
MacKay et al,23 2002
Jawaheer et al,25 2003
Jawaheer et al,24 2001 1p13 Unknown
Jawaheer et al,25 2003
*Replicated in at least 2 independent samples; P<.005 in at least 1 sample. †MHC = major histocompatibility complex; RANK = receptor activator
gene located in this area. SCL22A4 encodes an organic cation transporter, which is present in lymphoid tissue and overexpressed in collagen-induced arthritis. In the same sample, a SNP in the RUNX1 transcriptor factor gene was associated with RA, and it was suggested that RUNX1 regulates expression of SCL22A4, with an effect partly dependent on genetic variants of SCL22A4.46
Generally speaking, for disease susceptibility studies, findings that have been replicated in several independent samples, and for which there is a plausible biologic expla-nation, are more likely to be of major relevance. Important studies of identified susceptibility genes with suggested underlying mechanisms are summarized in Table 2.
DISEASE SEVERITY GENES
The RA-associated SE subtypes have been found primarily in patients with severe disease, indicating that they not only affect disease susceptibility but also influence disease se-verity.49-51 At the same time, the utility of DR-typing in
cohorts with early-onset RA52 and in community-based RA
samples53 to predict outcome has been questioned. In a
recent study of a large US sample of patients with early-onset RA,54 the disorder was primarily associated with DRB1*0401, but there was no clear association between
the presence of SE subtypes and disability. In contrast, several meta-analyses of previous studies55,56 as well as
recent surveys of cohorts with new-onset RA57,58 have
indi-cated that double dose of HLA-DRB1*04 SE alleles is associated with disease severity in RA (Table 3).
There is considerable ethnic heterogeneity in the fre-quency of these alleles and their importance for the RA phenotype. For example, double dose of DRB1*04 SE alleles is associated with erosive disease55 and vasculitis56,57
in northern European Caucasians but has no significant
impact on disease outcome in Greek patients.56
Further-more, the relative importance of DRB1 genotypes com-pared to other clinical and genetic markers, and hence the clinical utility of HLA-DRB1 genotyping for prognostica-tion, remains unclear. In a recent study of early-onset RA by Goronzy et al,57 HLA-DRB1*04 SE double dose was one
of several predictors of progression of erosive disease in the univariate analysis, but only rheumatoid factor and the presence of baseline erosions remained significant in the multivariate model, indicating that these factors are more important prognostic markers in RA.
Data on the impact of HLA-DRB1 alleles on the need for joint surgery are conflicting,49,59 and the association
be-tween the SE and progressive joint damage seems to be attenuated in patients started on early and aggressive anti-rheumatic drug treatment.60 Preliminary data indicate that DRB1 SE alleles may predict mortality in RA,61 suggesting
that the relative importance of DRB1 genes is variable for different disease outcomes.
Given the role of HLA-DR in the maturation, selection, and activation of T cells, the association between the SE and RA, and in particular between DRB1*04 SE double dose and disease severity in RA, has been interpreted as reflecting the importance of T cells in RA.47,48 Patients with
RA and extra-articular organ involvement have extensive T-cell abnormalities.48,62 Other gene products with a role in
T-cell regulation may be important in disease severity in RA. HLA-C alleles63,64 and killer-like immunoglobulin-like
receptor gene variants,63 with suggested regulatory
func-tions for immunosenescent T cells in extra-articular RA,63
have been shown to be associated with vasculitis in patients with RA.
In addition, other HLA genes with a role in T-cell regu-lation may modify the effect of known disease severity factors. For example, in patients carrying HLA-DRB1*01
TABLE 2. Rheumatoid Arthritis Susceptibility Alleles Identified in Association Studies and Suggested Underlying Mechanisms*
Disease susceptibility
allele Gene product Suggested mechanism Reference
HLA-DRB1–shared HLA-DRβ chain T-cell selection and maturation 47, 48 epitope alleles Immune response to specific peptides 29
TNFSR11A RANK Osteoclast differentiation 38, 39
CRHA2 CRH Defective HPA response to inflammation 43-45
Slc2F2T SCL22A4 organic Regulates lymphocyte activation in 46 cation transporter secondary lymphoid organs and/or
contributes to local inflammation
Runx1 RUNX1 Regulates expression of SCL22A4 46
(Runt-related transcription factor)
*CRH = corticotropin-releasing hormone; HPA = hypothalamus-pituitary axis; RANK = receptor activator of nuclear factor kB.
alleles, HLA-DMA1*0103 and HLA-DMB1*0401 have been suggested to be associated with greater structural joint damage.65
The tumor necrosis factor (TNF) has been shown to be important in the pathogenesis of RA,66 and treatment with
TNF-blocking agents leads to amelioration of joint symp-toms and reduction of structural joint damage in many patients.67 The TNF is encoded within the class III region of
the MHC. A number of biallelic SNPs and 5 microsatellite markers in the TNF region have been identified.68 Several
of the SNPs are located in the enhancer/promoter region, but no clear evidence indicates that these polymorphisms explain individual variation in TNF expression.68
Sug-gested associations between the extent of joint damage in RA and the –238 GG genotype may instead be explained by linkage disequilibrium with other neighboring genes.69
An association between certain TNF-α microsatellite markers and susceptibility to RA independent of RA-associated haplotypes has been found in most studies.70,71
Although microsatellite markers do not seem to affect disease severity by themselves, interactions between the markers TNFa672 and TNFa1173 and SE genotypes have
been reported to be associated with radiographic damage and disability. The TNFa6-SE interaction may also pre-dict the development of rheumatoid nodules.74 Such
inter-actions could indicate that polymorphisms influencing TNF expression or function are important only in the presence of an immune system shaped by certain class II genes.
Alternatively, the interactions could be attributed to other linked MHC genes. Various HLA-DRB1*04 sub-types are associated with specific TNF-lymphotoxin haplo-types,75 suggesting that these issues can be resolved only
through detailed typing of the MHC class II and III regions. Polymorphisms in other cytokine genes, such as interleu-kin (IL) 4 and IL-1β,76 IL-1α,77 and IL-1 receptor
antago-nist,78 may also affect radiographic progression and other
outcomes.
PHARMACOGENETICS
Individualized pharmacological therapy is a major goal of current research in the genetics of rheumatic diseases. This approach will ensure a safer and more efficacious applica-tion of drugs to manage complex diseases such as RA and in a nascent form is already being practiced in rheumatol-ogy. An example of this is the now routine determination of thiopurine methyltransferase (TPMT) enzyme levels be-fore azathioprine is prescribed. This example also high-lights the fact that it is currently generally easier to estab-lish an association between genetic type and potential drug toxicity than between genetic type and drug efficacy.
Lack of response to a given therapy may be due to many reasons, including drug-specific factors and genetically as-sociated resistance, coadministered drugs with competing metabolic pathways, and disease severity, including pres-ence of the SE as discussed previously.79, 80 Knowledge of
the likelihood of genetic resistance would prevent unneces-sary and potentially toxic drug exposure. Such factors are still unidentified, but it is clear that patients with advanced disease, regardless of their genetic background, may not respond because the disease is too advanced.
Currently, the most commonly used disease-modifying antirheumatic drug (DMARD) to manage RA is methotrex-ate, a folic acid analogue that inhibits the intracellular synthesis of purine and pyrimidine. Some of the anti-inflammatory effects of methotrexate are mediated by adenosine, a substrate in purine metabolism. In the cell, methotrexate undergoes polyglutamation, and this product inhibits aminoimidazole carboxamide ribonucleotide trans-formylase (AICAR-T). AICAR-T is important in purine synthesis, and blocking it leads to substrate accumulation
TABLE 3. Recent Studies With Evidence for Importance of HLA-DRB1*04 for Disease Severity in RA*
Reference Study design Main findings Goronzy et al,57 2004 Early-onset RA inception cohort with Increased risk of erosive disease in patients
analysis of multiple prognostic factors with double dose of HLA-DRB1*04 alleles Gorman et al,55 2004 Meta-analysis of 29 studies of erosive RA Association between SE and erosions overall but
published from 1987 to 1999 variability in different ethnic groups; erosions associated with DRB1*0401/0401 and 0401/0404 genotypes in northern European Caucasians Turesson et al,58 2005 Multicenter study of a large sample of Association of double dose of HLA-DRB1*04 alleles
patients with severe extra-articular RA with extra-articular RA overall, rheumatoid vasculitis, and Felty syndrome but not with other individual extra-articular RA manifestations Gorman et al,56 2004 Meta-analysis of 18 studies of rheumatoid HLA-DRB1*0401/0401, 0401/0404, and 0401/0101
vasculitis published from 1987 to 2003 genotypes were associated with vasculitis in RA *RA = rheumatoid arthritis; SE = shared epitope.
with increased adenosine release, effecting the anti-inflam-matory activity of methotrexate (Figure 1).
Another enzyme important in methotrexate metabolism is methylenetetrahydrofolate reductase (MTHFR), a cata-lyst for conversion of homocysteine to methionine. Defi-ciency of MTHFR is a cause of homocysteinemia and homocysteinuria, which can cause vasculopathy, thrombo-philia, and neurologic disease. About 10% of persons are homozygous, and another 40% are heterozygous for the C677T polymorphism of MTHFR, with corresponding re-duction in enzyme activity.81,82 Methotrexate-related bone
marrow toxicity has been linked to MTHFR polymor-phisms.81,82 Regarding efficacy, it has been suggested that
presence of a polymorphism in 1 of 3 enzymes important in methotrexate action thymidylate synthase (folate-depen-dent pyrimidine synthesis), AICAR-T, and RFCI (a protein that transports methotrexate into cells) is associated with increased methotrexate efficacy.83 Absence of members
of the functional multidrug resistance protein family that transport methotrexate out of the cell, plus the presence of reduced folate carrier, appears to be associated with signifi-cantly better responsiveness to methotrexate.84
Azathioprine is converted to 6-mercaptopurine and this metabolite to 6-thioguanine nucleotides and mercaptopu-rine metabolites (Figure 2). Xanthine oxidase and TPMT metabolize these products for excretion. Genetic polymor-phisms of TPMT are common, with about 10% of
Cauca-sians heterozygous for the wild-type gene and variants G460A and A719G, which are linked to diminished TPMT activity.85 This results in accumulation of thiopurine
me-tabolites, which cause bone marrow suppression.85 Patients
who are homozygous for the variant allele are at risk for severe bone marrow suppression with even standard doses of azathioprine. Levels of TPMT are now routinely used in clinical practice to predict this adverse effect, and azathio-prine-related adverse effects can be avoided in patients who have low TPMT levels.
Pharmacogenetic considerations also apply to other DMARDs used in the management of RA, although rel-evant enzyme assays are not as routinely available as they are for TPMT. About 62% of patients experiencing an adverse reaction such as myelosuppression and hepatotox-icity to sulfasalazine may be slow acetylators; thus, geno-typing of the N-acetyltransferase 2 gene could reduce the incidence of adverse events in these patients.86
Presence of the SE not only predicts disease severity but also may predict response to therapy. Patients with 2 copies of the SE are more likely to respond to DMARDs such as etanercept than are patients with no or only 1 copy.87
Genetic variation in TNF regions may be linked not only to RA susceptibility and severity but also to clinical re-sponse to anti-TNF agents.87,88 The TNF-308 SNP appears to
influence response to infliximab.89 Among 59 patients with FIGURE 1. Methotrexate and cellular metabolism. AICAR = aminoimidazole carboxamide ribonucleotide;
AICAR-T = AICAR transformylase; DHFR = dihydrofolate reductase; dTMP = deoxythymidine monophos-phate; dUMP = deoxyutidine monophosmonophos-phate; FAICAR = formyl aminoimidazole carboxamide ribonucle-otide; FPGS = folylpolyglutamate synthase; IMP = inosine monophosphate; MTHFR = methylenetetra-hydrofolate reductase; MTX = methotrexate; MTX-P-GIU = methotrexate polyglutamate; RFC1 = reduced folate carrier 1; THF = tetrahydrofolate; TS = thymidylate synthase. Adapted from Cronstein BN. Pharma-cogenetics in the rheumatic diseases. Ann Rheum Dis. 2004;63(suppl II):ii25-ii27, and reproduced with permission from the BMJ Publishing Group.
refractory RA, 42% with the TNF-308 AA or AG genotype had significant improvement with infliximab therapy com-pared with 81% of patients with the GG phenotype.89
Response to anti-TNF therapy may be governed by other genes in addition to those encoding TNF. These include genes for IL-10, transforming growth factor β1, and IL-1 receptor antagonist.90,91
SUMMARY
Rheumatoid arthritis is a complex disorder with consider-able genetic heterogeneity. Numerous HLA and non–HLA-associated gene regions appear to be involved in genetic predisposition to the disease. Some of these, such as the SE, appear to exert considerable influence on the disease phe-notype and possibly on the treatment response. Other genes exert only small effects, which may be markers of disease susceptibility and severity or perhaps even be protective. This genetic complexity demands that more and larger pop-ulations be studied to better characterize disease phenotypes and treatment response. Replicated findings with a plausible biologic explanation are more likely to be important.
Although genetic marker determination has not yet en-tered clinical practice, assays are clinically available for screening of enzymes such as TPMT that are important in metabolism of drugs used in the treatment of RA. More data are needed on genetic polymorphisms not only of drug-metabolizing enzymes but also of drug transporters and receptors. Cost-efficient enzyme testing and DNA chips and other assay kits need to be developed to expand the current knowledge of genetic disease and treatment
toxicity–related predispositions and to enhance the applica-bility of this knowledge to improve treatments and out-comes in RA.
There is great variability in the cost and response to treatment programs for RA. Genetic predictors of suscepti-bility to adverse effects of drugs and response to therapy have the potential for providing valuable information for therapeutic decisions, making it possible to better tailor individual treatment programs at the time of RA diagnosis, when the therapeutic intervention has the greatest chance of meaningfully altering the disease course. Even in pa-tients with established disease, improved understanding of these factors can enhance therapeutic strategies, avoiding predictable toxicities and improving outcomes. Most of the studies of the pharmacogenetics of RA to date have been performed in Caucasian populations. Further studies are necessary to extend the observations, to apply them to other populations and disease characteristics, and to define the specific genes or groups of genes and haplotypes that ac-count for these associations.
FIGURE 2. Metabolism of azathioprine. MP = mercaptopurine; TPMT = thiopurine methyltransferase; XO = xanthine oxidase. Adapted from Cronstein BN. Pharmacogenetics in the rheumatic diseases. Ann Rheum Dis. 2004;63(suppl II):ii25-ii27, and reproduced with permission from the BMJ Publishing Group.
REFERENCES
1. Aho K, Koskenvuo M, Tuominen J, Kaprio J. Occurrence of rheumatoid
arthritis in a nationwide series of twins. J Rheumatol. 1986;13:899-902.
2. Silman AJ, MacGregor AJ, Thomson W, et al. Twin concordance rates
for rheumatoid arthritis: results from a nationwide study. Br J Rheumatol. 1993;32:903-907.
3. Grant SF, Thorleifsson G, Frigge ML, et al. The inheritance of
rheuma-toid arthritis in Iceland. Arthritis Rheum. 2001;44:2247-2254.
4. MacGregor AJ, Snieder H, Rigby AS, et al. Characterizing the
quantita-tive genetic contribution to rheumatoid arthritis using data from twins.
Arthri-tis Rheum. 2000;43:30-37.
5. Symmons D, Harrison B. Early inflammatory polyarthritis: results from
development of inflammatory polyarthritis and rheumatoid arthritis.
Rheuma-tology (Oxford). 2000;39:835-843.
6. Silman AJ, Hochberg MC. Epidemiology of the Rheumatic Diseases.
Oxford, England: Oxford University Press; 1993.
7. Silman AJ, Newman J, MacGregor AJ. Cigarette smoking increases the
risk of rheumatoid arthritis: results from a nationwide study of disease-discor-dant twins. Arthritis Rheum. 1996;39:732-735.
8. Karlson EW, Lee IM, Cook NR, Manson JE, Buring JE, Hennekens CH.
A retrospective cohort study of cigarette smoking and risk of rheumatoid arthritis in female health professionals. Arthritis Rheum. 1999;42:910-917.
9. Wolfe F. The effect of smoking on clinical, laboratory, and radiographic
status in rheumatoid arthritis. J Rheumatol. 2000;27:630-637.
10. Saag KG, Cerhan JR, Kolluri S, Ohashi K, Hunninghake GW, Schwartz
DA. Cigarette smoking and rheumatoid arthritis severity. Ann Rheum Dis. 1997;56:463-469.
11. Turesson C, O’Fallon WM, Crowson CS, Gabriel SE, Matteson EL.
Extra-articular disease manifestations in rheumatoid arthritis: incidence trends and risk factors over 46 years. Ann Rheum Dis. 2003;62:722-727.
12. Padyukov L, Silva C, Stolt P, Alfredsson L, Klareskog L. A
gene-environment interaction between smoking and shared epitope genes in HLA-DR provides a high risk of seropositive rheumatoid arthritis. Arthritis Rheum. 2004;50:3085-3092.
13. Stastny P. Mixed lymphocyte cultures in rheumatoid arthritis. J Clin
Invest 1976;57:1148-1157.
14. Gibofsky A, Winchester RJ, Patarroyo M, Fotino M, Kunkel HG.
Dis-ease associations of the Ia-like human alloantigens: contrasting patterns in rheumatoid arthritis and systemic lupus erythematosus. J Exp Med. 1978;148: 1728-1732.
15. Gregersen PK, Silver J, Winchester RJ. The shared epitope hypothesis:
an approach to understanding the molecular genetics of susceptibility to rheu-matoid arthritis. Arthritis Rheum. 1987;30:1205-1213.
16. de Vries N, Tijssen H, van Riel PL, van de Putte LB. Reshaping the
shared epitope hypothesis: HLA-associated risk for rheumatoid arthritis is encoded by amino acid substitutions at positions 67-74 of the HLA-DRB1 molecule. Arthritis Rheum. 2002;46:921-928.
17. Williams RC, Jacobsson LT, Knowler WC, et al. Meta-analysis reveals
association between most common class II haplotype in full-heritage Native Americans and rheumatoid arthritis. Hum Immunol. 1995;42:90-94.
18. Beasley RP, Willkens RF, Bennett PH. High prevalence of rheumatoid
arthritis in Yakima Indians. Arthritis Rheum. 1973;16:743-748.
19. Del Puente A, Knowler WC, Pettitt DJ, Bennett PH. High incidence and
prevalence of rheumatoid arthritis in Pima Indians. Am J Epidemiol. 1989; 129:1170-1178.
20. Deighton CM, Walker DJ, Griffiths ID, Roberts DF. The contribution of
HLA to rheumatoid arthritis. Clin Genet. 1989;36:178-182.
21. Cornelis F, Faure S, Martinez M, et al, ECRAF. New susceptibility locus
for rheumatoid arthritis suggested by a genome-wide linkage study. Proc Natl
Acad Sci U S A. 1998;95:10746-10750.
22. Osorio YF, Bukulmez H, Petit-Teixeira E, et al. Dense genome-wide
linkage analysis of rheumatoid arthritis, including covariates. Arthritis Rheum. 2004;50:2757-2765.
23. MacKay K, Eyre S, Myerscough A, et al. Whole-genome linkage
analy-sis of rheumatoid arthritis susceptibility loci in 252 affected sibling pairs in the United Kingdom [published correction appears in Arthritis Rheum. 2002;46: 1406]. Arthritis Rheum. 2002;46:632-639.
24. Jawaheer D, Seldin MF, Amos CI, et al. A genomewide screen in
multiplex rheumatoid arthritis families suggests genetic overlap with other autoimmune diseases. Am J Hum Genet. 2001;68:927-936.
25. Jawaheer D, Seldin MF, Amos CI, et al, North American Rheumatoid
Arthritis Consortium. Screening the genome for rheumatoid arthritis suscepti-bility genes: a replication study and combined analysis of 512 multicase families. Arthritis Rheum. 2003;48:906-916.
26. Shiozawa S, Hayashi S, Tsukamoto Y, et al. Identification of the gene
loci that predispose to rheumatoid arthritis. Int Immunol. 1998;10:1891-1895.
27. Jawaheer D, Li W, Graham RR, et al. Dissecting the genetic complexity
of the association between human leukocyte antigens and rheumatoid arthritis.
Am J Hum Genet. 2002;71:585-594.
28. Verpoort KN, van Gaalen FA, van der Helm-van Mil AH, et al.
Association of HLA-DR3 with anti-cyclic citrullinated peptide antibody-neg-ative rheumatoid arthritis. Arthritis Rheum. 2005;52:3058-3062.
29. Hill JA, Southwood S, Sette A, Jevnikar AM, Bell DA, Cairns E. Cutting
edge: the conversion of arginine to citrulline allows for a high-affinity peptide interaction with the rheumatoid arthritis-associated HLA-DRB1*0401 MHC class II molecule. J Immunol. 2003;171:538-541.
30. Auger I, Sebbag M, Vincent C, et al. Influence of HLA-DR genes on the
production of rheumatoid arthritis-specific autoantibodies to citrullinated fibrinogen. Arthritis Rheum. 2005;52:3424-3432.
31. Huizinga TW, Amos CI, van der Helm-van Mil AH, et al. Refining the
complex rheumatoid arthritis phenotype based on specificity of the HLA-DRB1 shared epitope for antibodies to citrullinated proteins. Arthritis Rheum. 2005;52:3433-3438.
32. Brintnell W, Zeggini E, Barton A, et al. Evidence for a novel rheumatoid
arthritis susceptibility locus on chromosome 6p. Arthritis Rheum. 2004;50: 3823-3830.
33. Gaffney PM, Kearns GM, Shark KB, et al. A genome-wide search for
susceptibility genes in human systemic lupus erythematosus sib-pair families.
Proc Natl Acad Sci U S A. 1998;95:14875-14879.
34. Shai R, Quismorio FP Jr, Li L, et al. Genome-wide screen for systemic
lupus erythematosus susceptibility genes in multiplex families. Hum Mol
Genet. 1999;8:639-644.
35. Davies JL, Kawaguchi Y, Bennett ST, et al. A genome-wide search for
human type 1 diabetes susceptibility genes. Nature. 1994;371:130-136.
36. Merriman T, Twells R, Merriman M, et al. Evidence by allelic
associa-tion-dependent methods for a type 1 diabetes polygene (IDDM6) on chromo-some 18q21. Hum Mol Genet. 1997;6:1003-1010.
37. Vaidya B, Imrie H, Perros P, et al. Evidence for a new Graves disease
susceptibility locus at chromosome 18q21. Am J Hum Genet. 2000;66:1710-1714.
38. Li J, Sarosi I, Yan XQ, et al. RANK is the intrinsic hematopoietic cell
surface receptor that controls osteoclastogenesis and regulation of bone mass and calcium metabolism. Proc Natl Acad Sci U S A. 2000;97:1566-1571.
39. Wu H, Khanna D, Park G, et al. Interaction between RANKL and
HLA-DRB1 genotypes may contribute to younger age at onset of seropositive rheuma-toid arthritis in an inception cohort. Arthritis Rheum. 2004;50:3093-3103.
40. Fisher SA, Lanchbury JS, Lewis CM. Meta-analysis of four rheumatoid
arthritis genome-wide linkage studies: confirmation of a susceptibility locus on chromosome 16. Arthritis Rheum. 2003;48:1200-1206.
41. Hugot JP, Chamaillard M, Zouali H, et al. Association of NOD2
leucine-rich repeat variants with susceptibility to Crohn’s disease. Nature. 2001;411: 599-603.
42. Steer S, Fisher SA, Fife M, et al. Development of rheumatoid arthritis is
not associated with two polymorphisms in the Crohn’s disease gene CARD15.
Rheumatology (Oxford). 2003;42:304-307.
43. Fife M, Steer S, Fisher S, et al. Association of familial and sporadic
rheumatoid arthritis with a single corticotropin-releasing hormone genomic region (8q12.3) haplotype. Arthritis Rheum. 2002;46:75-82.
44. Chikanza IC, Petrou P, Kingsley G, Chrousos G, Panayi GS. Defective
hypothalamic response to immune and inflammatory stimuli in patients with rheumatoid arthritis. Arthritis Rheum.1992;35:1281-1288.
45. Gonzalez-Gay MA, Hajeer AH, Garcia-Porrua C, et al.
Corticotropin-releasing hormone promoter polymorphisms in patients with rheumatoid ar-thritis from northwest Spain. J Rheumatol. 2003;30:913-917.
46. Tokuhiro S, Yamada R, Chang X, et al. An intronic SNP in a RUNX1
binding site of SLC22A4, encoding an organic cation transporter, is associated with rheumatoid arthritis. Nat Genet. 2003;35:341-348.
47. Weyand CM, Goronzy JJ. Functional domains on HLA-DR molecules:
implications for the linkage of HLA-DR genes to different autoimmune dis-eases. Clin Immunol Immunopathol. 1994;70:91-98.
48. Turesson C, Weyand CM, Matteson EL. Genetics of rheumatoid
arthri-tis: is there a pattern predicting extraarticular manifestations? Arthritis Rheum. 2004;51:853-863.
49. Weyand CM, Hicok KC, Conn DL, Goronzy JJ. The influence of
HLA-DRB1 genes on disease severity in rheumatoid arthritis. Ann Intern Med. 1992; 117:801-806.
50. Gough A, Faint J, Salmon M, et al. Genetic typing of patients with
inflammatory arthritis at presentation can be used to predict outcome. Arthritis
Rheum. 1994;37:1166-1170.
51. Combe B, Dougados M, Goupille P, et al. Prognostic factors for
radio-graphic damage in early rheumatoid arthritis: a multiparameter prospective study. Arthritis Rheum. 2001;44:1736-1743.
52. Eberhardt K, Fex E, Johnson U, Wollheim FA. Associations of
HLA-DRB and -DQB genes with two and five year outcome in rheumatoid arthritis.
Ann Rheum Dis. 1996;55:34-39.
53. Suarez-Almazor ME, Tao S, Moustarah F, Russell AS, Maksymowych
W. HLA-DR1, DR4, and DRB1 disease related subtypes in rheumatoid arthri-tis: association with susceptibility but not severity in a city wide community based study. J Rheumatol. 1995;22:2027-2033.
54. Fries JF, Wolfe F, Apple R, et al. HLA-DRB1 genotype associations in
793 white patients from a rheumatoid arthritis inception cohort: frequency, severity, and treatment bias. Arthritis Rheum. 2002;46:2320-2329.
55. Gorman JD, Lum RF, Chen JJ, Suarez-Almazor ME, Thomson G,
Criswell LA. Impact of shared epitope genotype and ethnicity on erosive disease: a meta-analysis of 3,240 rheumatoid arthritis patients. Arthritis
Rheum. 2004;50:400-412.
56. Gorman JD, David-Vaudey E, Pai M, Lum RF, Criswell LA. Particular
HLA-DRB1 shared epitope genotypes are strongly associated with rheumatoid vasculitis. Arthritis Rheum. 2004;50:3476-3484.
57. Goronzy JJ, Matteson EL, Fulbright JW, et al. Prognostic markers of
radiographic progression in early rheumatoid arthritis. Arthritis Rheum. 2004; 50:43-54.
58. Turesson C, Schaid DJ, Weyand CM, et al. The impact of HLA-DRB1
genes on extra-articular disease manifestations in rheumatoid arthritis.
Arthri-tis Res Ther. 2005;7:R1386-R1393.
59. Gossec L, Bettembourg-Brault I, Pham T, Dougados M. HLA DRB1*01
and DRB1*04 phenotyping does not predict the need for joint surgery in rheumatoid arthritis: a retrospective quantitative evaluation of 300 French patients. Clin Exp Rheumatol. 2004;22:462-464.
60. Lard LR, Boers M, Verhoeven A, et al. Early and aggressive treatment of
rheumatoid arthritis patients affects the association of HLA class II antigens with progression of joint damage. Arthritis Rheum. 2002;46:899-905.
61. Mattey D, Thomson W, Ollier WER, Koduri G, Young A. Association of
the HLA-DRB1 shared epitope with mortality in rheumatoid arthritis [ab-stract]. Arthritis Rheum. 2004;50(suppl):S381. Abstract 936.
62. Goronzy JJ, Weyand CM. Aging, autoimmunity and arthritis: T-cell
senescence and contraction of T-cell repertoire diversity - catalysts of autoim-munity and chronic inflammation. Arthritis Res Ther. 2003;5:225-234.
63. Yen JH, Moore BE, Nakajima T, et al. Major histocompatibility complex
class I-recognizing receptors are disease risk genes in rheumatoid arthritis. J
Exp Med. 2001;193:1159-1167.
64. Turesson C, Schaid DJ, Weyand CM, et al. Association of HLA-C3 and
smoking with vasculitis in patients with rheumatoid arthritis [abstract].
Arthri-tis Rheum. 2004;50(suppl):S162. Abstract 294.
65. Morel J, Roch-Bras F, Molinari N, Sany J, Eliaou JF, Combe B.
HLA-DMA*0103 and HLA-DMB*0104 alleles as novel prognostic factors in rheu-matoid arthritis. Ann Rheum Dis. 2004;63:1581-1586.
66. Feldmann M, Brennan FM, Maini RN. Role of cytokines in rheumatoid
arthritis. Annu Rev Immunol. 1996;14:397-440.
67. Lipsky PE, van der Heijde DM, St Clair EW, et al, Anti-Tumor Necrosis
Factor Trial in Rheumatoid Arthritis with Concomitant Therapy Study Group. Infliximab and methotrexate in the treatment of rheumatoid arthritis. N Engl J
Med. 2000;343:1594-1602.
68. Kaijzel EL, Bayley JP, van Krugten MV, et al. Allele-specific
quantification of tumor necrosis factor alpha (TNF) transcription and the role of promoter polymorphisms in rheumatoid arthritis patients and healthy individuals. Genes Immun. 2001;2:135-144.
69. Kaijzel EL, van Krugten MV, Brinkman BM, et al. Functional analysis
of a human tumor necrosis factor alpha (TNF-alpha) promoter polymorphism related to joint damage in rheumatoid arthritis. Mol Med. 1998;4:724-733.
70. Meyer JM, Han J, Moxley G. Tumor necrosis factor markers show
sex-influenced association with rheumatoid arthritis. Arthritis Rheum. 2001;44: 286-295.
71. Castro F, Acevedo E, Ciusani E, Angulo JA, Wollheim FA,
Sandberg-Wollheim M. Tumour necrosis factor microsatellites and DRB1*, HLA-DQA1*, and HLA-DQB1* alleles in Peruvian patients with rheumatoid arthri-tis. Ann Rheum Dis. 2001;60:791-795.
72. Mattey DL, Hassell AB, Dawes PT, Ollier WE, Hajeer A. Interaction
between tumor necrosis factor microsatellite polymorphisms and the HLA-DRB1 shared epitope in rheumatoid arthritis: influence on disease outcome.
Arthritis Rheum. 1999;42:2698-2704.
73. Mu H, Chen JJ, Jiang Y, King MC, Thomson G, Criswell LA. Tumor
necrosis factor a microsatellite polymorphism is associated with rheumatoid arthritis severity through an interaction with the HLA-DRB1 shared epitope.
Arthritis Rheum. 1999;42:438-442.
74. Mattey DL, Dawes PT, Fisher J, et al. Nodular disease in rheumatoid
arthritis: association with cigarette smoking and HLA-DRB1/TNF gene inter-action. J Rheumatol. 2002;29:2313-2318.
75. Newton J, Brown MA, Milicic A, et al. The effect of HLA-DR on
susceptibility to rheumatoid arthritis is influenced by the associated lympho-toxin alpha-tumor necrosis factor haplotype. Arthritis Rheum. 2003;48:90-96.
76. Genevay S, Di Giovine FS, Perneger TV, et al. Association of
inter-leukin-4 and interleukin-1B gene variants with Larsen score progression in rheumatoid arthritis. Arthritis Rheum. 2002;47:303-309.
77. Jouvenne P, Chaudhary A, Buchs N, Giovine FS, Duff GW, Miossec P.
Possible genetic association between interleukin-1alpha gene polymorphism and the severity of chronic polyarthritis. Eur Cytokine Netw. 1999;10:33-36.
78. Cvetkovic JT, Wallberg-Jonsson S, Stegmayr B, Rantapaa-Dahlqvist S,
Lefvert AK. Susceptibility for and clinical manifestations of rheumatoid arthri-tis are associated with polymorphisms of the TNF-alpha, IL-1beta, and IL-1Ra genes. J Rheumatol. 2002;29:212-219.
79. Nesher G, Mates M, Zevin S. Effect of caffeine consumption on the
efficacy of methotrexate in rheumatoid arthritis. Arthritis Rheum. 2003;48: 571-572.
80. Lee M, Min DI, Ku YM, Flanigan M. Effect of grapefruit juice on
pharmacokinetics of microemulsion cyclosporine in African American sub-jects compared with Caucasian subsub-jects: does ethnic difference matter? J Clin
Pharmacol. 2001;41:317-323.
81. Kumagai K, Hiyama K, Oyama T, Maeda H, Kahno N. Polymorphisms
in the thymidylate synthase and methylenetetrahydrofolate reductase genes and sensitivity to the low-dose methotrexate therapy in patients with rheuma-toid arthritis. Int J Mol Med. 2003;11:593-600.
82. van Ede AE, Laan RF, Blom JH, et al. The C677T mutation in the
methylenetetrahydrofolate reductase gene: a genetic risk factor for methotrex-ate-related elevation of liver enzymes in rheumatoid arthritis patients. Arthritis
Rheum. 2001;44:2525-2530.
83. Dervieux T, Lein DO, Park G, et al. Single nucleotide polymorphisms
(SNPs) in the folate/purine synthesis pathway predict methotrexate’s effects in rheumatoid arthritis [abstract]. Arthritis Rheum. 2003;48(suppl):S438. Ab-stract 1093.
84. Wolf J, Stranzl T, Filipits M, et al. Expression of resistance markers to
methotrexate predicts clinical improvement in patients with rheumatoid arthritis. Ann Rheum Dis. 2005;64:564-568.
85. Clunie GP, Lennard L. Relevance of thiopurine methyltransferase status
in rheumatology patients receiving azathioprine. Rheumatology (Oxford). 2004;43:13-18.
86. Tanaka E, Taniguchi A, Urano W, et al. Adverse effects of sulfasalazine
in patients with rheumatoid arthritis are associated with diplotype con-figuration at the N-acetyltransferase 2 gene. J Rheumatol. 2002;29:2492-2499.
87. Criswell LA, Lum RF, Turner KN, et al. The influence of genetic
variation in the HLA-DRB1 and LTA-TNF regions on the response to treat-ment of early rheumatoid arthritis with methotrexate or etanercept. Arthritis
Rheum. 2004;50:2750-2756.
88. Field M. Tumour necrosis factor polymorphisms in rheumatic diseases.
QJM. 2001;94:237-246.
89. Prevoo ML, van’t Hof MA, Kuper HH, van Leeuwen MA, van de Putte
LB, van Riel PL. Modified disease activity scores that include twenty-eight-joint counts: development and validation in a prospective longitudinal study of patients with rheumatoid arthritis. Arthritis Rheum. 1995;38:44-48.
90. Padyukov L, Lampa J, Heimburger M, et al. Genetic markers for the
efficacy of tumour necrosis factor blocking therapy in rheumatoid arthritis.
Ann Rheum Dis. 2003;62:526-529.
91. Schotte H, Schlüter B, Drynda S, et al. Interleukin 10 promoter
micro-satellite polymorphisms are associated with response to long term treatment with etanercept in patients with rheumatoid arthritis. Ann Rheum Dis. 2005; 64:575-581.
