Complex genetics of Wegener granulomatosis

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  • ePeter Jagielloa,*, Wolfgang L. Grossb, Jfrg T. Epplena

    Contents

    Wegener granulomatosis (WG) are characterized by a

    primary process of inflammation and damage of blood

    on the variety of clinical symptoms and the similar-

    ities in histology. So far, SV are differentiated by size

    of affected vessels, i.e. large vessels (e.g. Takayasu

    Wegener granulomatosis (WG) belongs to a heterogeneous group of systemic anti-neutrophil cytoplasmatic antibody

    (ANCA) associated vasculitides (AASV). WG is characterized by necrotizing granulomatous inflammation of the upper and

    lower respiratory tract, glomerulonephritis and vasculitis. As a multifactorial model disease, WG is hallmarked by the

    presence of specific ANCA-subtypes directed against a defined antigen. WG is more predominant among Caucasians and

    the genetic predisposition appears quite complex. Here, we provide a brief overview concerning genetic factors in the

    pathogenesis of WG and discuss intricacies of molecular genetic approaches.

    D 2004 Elsevier B.V. All rights reserved.

    Keywords: Wegener granulomatosis; Multifactorial disease; Predisposing genetic factor

    Autoimmunity Reviews 4 (2001. Conclusions and future directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

    Take-home messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

    References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

    Systemic vasculitides (SV) such as giant cell

    arteritis, Takayasu arteritis, Kawasaki disease and

    vessel walls [1]. Differentiation of defined entities in

    this enigmatic group of SV is often problematic, basedAbstractaDepartment of Human Genetics, Ruhr-University Bochum, Universitaetsstrasse 150, 44801 Bochum, GermanybRheumatology, Medizinische Universitatsklinik Lubeck and Rheumaklinik Bad Bramstedt, Germany

    Received 1 June 2004; accepted 23 June 2004

    Available online 26 July 2004Complex genetics of W1568-9972/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

    doi:10.1016/j.autrev.2004.06.003

    * Correspon

    3214196.

    E-mail address: peter.jagiello@rub.de (P. Jagiello).gener granulomatosis

    5) 4247

    www.elsevier.com/locate/autrev(e.g. Kawasaki disease)arteritis), intermediate vesselsding author. Tel.: +49 234 3223831; fax: +49 234and small vessels (e.g. WG, microscopic polyangiitis

    [MPA] or ChurgStrauss syndrome [CSS]). A feature

  • unityof the last-mentioned group concerns the presence of

    anti-neutrophil cytoplasmatic antibody (ANCA) that

    act as diagnostic markers positively correlating with

    disease activity [2]. Whereas ANCA against myelo-

    peroxidase (MPO-ANCA) occur in MPA and CSS,

    proteinase 3 (PRTN3-)ANCA are observed in patients

    suffering from WG [2].

    Several findings suggest genetic predisposition

    factors for WG [3]. Therefore, ANCA target genes

    were already extensively investigated. The membrane

    expression of the main ANCA target antigen PRTN3

    (previously designated as PR-3) is genetically deter-

    mined [4]. In addition, association of a promoter

    polymorphism in the PRTN3 gene with WG has been

    demonstrated affecting a putative SP1-transcription

    factor-binding site [5]. This polymorphism leads

    potentially to increased PRTN3 expression. PRTN3

    belongs to the serine proteinase family, which is

    inhibited by the serin protease inhibitors (serpins),

    their genes clustering (in addition to further loci) at

    chromosome 14q32.1. Interestingly, linkage disequi-

    librium in this gene cluster points to associated

    haplotypes with WG [6]. Moreover, association

    studies concerning the PRTN3 inhibitor alpha1-

    antitrypsin (a1-AT) gene showed that the frequencythe a1-AT deficiency allele PI*Z is increased in WGpatients. Yet, the carriers of this allele did not suffer

    from any vasculitis symptoms in a larger population

    of PI*Z+ individuals [7].

    Whenever ANCA are demonstrable, infectious

    aetiologies may be discussed and, therefore, a relation

    between (polymorphonuclear neutrophil [PMN]-medi-

    ated) host defence and ANCA induction appears

    conceivable. For example, PMN-derived antibiotic

    proteins represent a source of innate immune defence

    playing a role in recognition and neutralization of the

    proinflammatory surface components (e.g. endotoxins)

    of bacteria [8]. Interestingly, most of these molecules

    are target antigens for ANCA [9]. Yet, in 6% of ANCA

    associated vasculitides (AASV), bactericidal/perme-

    ability-increasing protein (BPI)-ANCA is detected.

    Therefore, in a further association study, the function-

    ally relevant Glu216Lys polymorphism of theBPI gene

    has been genotyped (Jagiello et al., unpublished data).

    Comparison of allele frequencies and genotypes did not

    reveal differences between WG patients and healthy

    P. Jagiello et al. / Autoimmcontrols. In addition, alleles of an ad hoc designed in-

    tragenic microsatellite marker were not linked to WG.Binding of ANCA to antigens on the surface of

    PMN results in cellular activation as mediated by Fcgreceptors (FcgR) [10]. Most analyses of these highlypolymorphic genes did not show significant differences

    in genotype distributions or allele frequencies between

    patients and controls. Yet, a trend for increased

    homozygosity of the FcgRIIIb-NA1 allele was evidentwhich may have implications for disease susceptibility

    being significant in MPO-ANCA+ patients [11]. In

    addition, WG patients were more prone to disease

    relapse if they were homozygous for, both, the R131

    isoform of FcgRIIa and the F158 isoform ofFcggRIIIa. This fact might be related to chronic nasalcarriage of Staphylococcus aureus and the inability of

    the immune system to eliminate this bacterium,

    respectively [12]. Furthermore, adhesiveness of leuko-

    cytes to the endothelium is an important pathophysio-

    logical element of WG. Adhesion is augmented by

    expression of molecules like CD11, CD18, ICAM-1

    and E-selectin. Whereas studies did not reveal specific

    associations in the aforementioned genes as risk factors

    for WG, linkage was evidenced between given CD18

    alleles and MPO-ANCA vasculitides [13].

    Many autoimmune disorders are characterized by

    predominance of T helper 1 (Th1) cells, the cytokine

    pattern of which has also been observed in granulo-

    mata of WG patients [14]. As the cytotoxic T cell

    antigen 4 (CTLA4) has a role in inducing a Th1

    response also by suppressing Th2 cytokines, poly-

    morphisms in the CTLA4 gene were investigated. In a

    small WG cohort, an association of a simple AT repeat

    polymorphism in the 3V-untranslated region wasidentified [15]. In T cells from patients with myas-

    thenia gravis longer AT dinucleotide blocks cause

    reduced expression of CTLA-4 due to decreased

    mRNA stability [16]. A second single nucleotide

    polymorphism (SNP) in the promoter region revealed

    association with WG [17], but relevance for WG

    pathogenesis has still to be demonstrated, as this SNP

    is not comprised in any known consensus sequence,

    e.g. for transcription factor binding sites or other

    regulatory elements. Another SNP results in amino

    acid exchange (Y to A, position 49) without any

    association. Interestingly, linkage disequilibrium was

    demonstrated between the Y residue and the shortest

    allele of the AT microsatellite in controls but not in

    Reviews 4 (2005) 4247 43patients [17]. The functional significance of the

    genotypes for protection against WG remains elusive.

  • unityStudies on gene polymorphism in cytokines,

    chemokines and their receptors have also been carried

    out. In this context, SNPs in the tumor necrosis factor

    (TNF) genes were investigated whereby a TNFapromotor polymorphism at position 308 and anintronic SNP in the TNFh gene did not revealstatistically significant differences between patients

    and controls [18]. Yet concerning the clinical course

    of the disease, WG patients with a defined TNF 1/1

    phenotype were found to have a higher mean disease

    extension index than TNF 1/2 individuals [18]. In part

    these results were confirmed in a later study that, on

    the other hand, excluded certain interleukin 2 (IL2)

    and IL5 receptor (IL5R)a alleles as predisposinggenetic factors [19]. Furthermore, polymorphisms in

    the genes for IL1h and IL1Ra were examinedconcerning the clinical manifestation and outcome

    of AASV [20]. A distinct combination of these

    polymorphisms leads to a pro-inflammatory genotype

    increased in PRTN3-ANCA+ patients with end-stage-

    renal disease [20]. In a Swedish WG population

    variations in the IL4 and IL10 genes were investigated

    [21]. Both IL4 and IL10 belong to Th2 cytokine

    pattern and reduced levels of these anti-inflammatory

    cytokines might be related to WG manifestation.

    While IL4 variations did not reveal an association

    with WG, a so-called microsatellite polymorphism

    located in the promotor region of IL10 showed a

    significantly higher percentage of patients heterozy-

    gous for two specific alleles [21]. In addition, in

    another study on Caucasians, a significant shift

    toward the homozygous AA genotype of an IL10

    polymorphism was observed in WG patients. Fur-

    thermore, the latter study excluded the polymorphism

    in codon 25 of the transforming growth factor b1(TGFb1) gene as a genetic risk factor for WG [22].

    Human leukocyte antigen (HLA) genes are exceed-

    ingly polymorphic and numerous studies have implied

    factors in the major histocompatibility complex (MHC)

    for susceptibility to autoimmune diseases (see e.g. Ref.

    [23,24]). HLA genes encode cell surface molecules

    initiating acquired immune responses to invading

    pathogens (potentially also S. aureus for WG). Poly-

    morphic HLA genes were extensively studied in order

    to determine possible associations with WG. Different

    alleles were increased in frequency in WG patients like

    P. Jagiello et al. / Autoimm44HLA-B8, -B50, -DR9, -DR1, -DR2, -DQw7 and the

    haplotype HLA-DR4DQ7 [2429], respectively,whereas a decrease of HLA-DR3 alleles and HLA-

    DR13DR6 heterozygotes among WG or SV patients

    has also been observed [29,30]. Most of these studies

    revealed no consistent or, better, exclusively spurious

    associations, largely depending on the number of

    patients investigated. In a recent systematic association

    screen with 202 microsatellites certain alleles within

    chromosome region 6p21.3 were significantly associ-

    ated with WG [31]. HLA-DPB1 genotyping of this

    comparatively large cohort of 150 patients revealed an

    increased frequency of the DPB1*0401 allele. In

    contrast, the frequency of the *0301 allele was

    significantly decreased. These results were confirmed

    in an independent WG patient cohort [31]. Although

    these genes present veritable candidates, WG predis-

    position based on adjacent factors is difficult to be

    differentiated due to extensive linkage disequilibrium

    (LD). Genotyping of SNPs spanning 200 kb of the

    abovementioned region differed significantly between

    patients and controls, as well, clustering at the HLA-

    DPB1 and retinoid X receptor b (RXRB) genes. Amongother functions RXRB protein forms heterodimers with

    vitamin D receptors (VDR) and dimerization with

    VDR plays an important role in forming the soluble

    vitamin D3 metabolite, 1,25-dihydroxyvitamin D3

    [32]. This metabolite harbours anti-inflammatory

    effects due to inhibition of cytokine transcription

    required for Th1 differentiation [33,34]. In addition,

    haplotypes spanning the HLA-DPB1 and RXRB genes

    reinforced the association ofDPB1 and RXRB markers,

    thus presenting a predisposing and a protective

    haplotype [31]. In conclusion, this genomic region

    appears as the major risk factor for WG.

    Furthermore, two additional loci (Casp14 and re-

    ceptor (TNFRSF)-interacting serine-threonine kinase

    1 [Ripk1]) represent good candidates for WG predis-

    position. Polymorphisms in these genes may cause

    subtle shifts in the balance of apoptosis [31]. Apoptosis

    appears critically involved in (auto)immune reactions

    in terms of deither too little or too muchT [35,36].Firstly, autoreactive immune cells are eliminated and

    inactivated by apoptosis. This process might be dis-

    rupted by decreased apoptosis leading to loss of self-

    tolerance. On the other hand, augmented apoptosis in

    cells surrounding WG foci might enhance pro-inflam-

    matory responses and finally the self-sustaining in-

    Reviews 4 (2005) 4247flammatory process (references in Ref. [31]). Whereas

    the expression of Casp14 is keratinocyte specific [37]

  • and a relationship to WG appears doubtful, Ripk1 is

    directly involved in apoptosis through interacting with

    TNFRSF1A-associated via death domain (TRADD).

    This interaction recruits RIPK1 to TNFR1, which

    triggers pathways leading to apoptosis and activation

    the nuclear factor of n light chain gene enhancer in Bcells [38]. Yet, the relevance of these findings remain to

    be ascertained on the functional level.

    1. Conclusions and future directions

    The pathophysiology of complex diseases has not

    yet been deciphered in detail and, like in WG,

    candidates for genetic predisposition are truly abun-

    dant. In WG such candidates represent genes of diverse

    dfunctional systemsT comprising molecules involved in

    e.g. T cell or PMN activation, Th1 or Th2 response,

    host defence and apoptosis. In general, each individual

    observed genetic variation is neither necessary nor

    sufficient to explain the pathogenetic mechanisms for

    WG manifestation and development. Apparently,

    environmental plus a number of genetic predisposition

    factors influence the manifestation of WG (Fig. 1).

    Additional predisposing genes will be investigated

    by diverse genotyping methods potentially revealing

    further genetic variations associated with WG. In this

    scenario, it appears timely to focus on diligent

    evaluation of combinations and/or interactions

    between polymorphisms, both of statistically signifi-

    cant major effects but also of genetic factors harbouring

    no or minimal main effects by themselves. Existing

    variations have to be confirmed in distinct WG

    populations, which must be homogenous in clinical

    egen

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    P. Jagiello et al. / Autoimmunity Reviews 4 (2005) 4247 45Fig. 1. Phenotypes of WG patients as determined theoretically by gen

    variations are related to the manifestation of the WG phenotypes. (

    symptoms of WG (e.g. HLA-DPB1). Several genetic variations can a

    (2) Variations of multiple loci (specific genotypes) apparently have c

    alone might not differ significantly when compared between patie

    sequence variations is thought to be due to epistasis, so-called ge

    symptoms. The equilibrium of the genes concerted actions is d

    physiological homeostases. Consequently imbalanced expression o

    resulting potentially in WG phenotypes, finally. (C) WG phenotypesrather they are distributed continuously as influenced by delicate combinati

    effects of several genes plus environmental factors.e and by geneenvironment interactions. (A) Several genetic factors/

    jor independent effects may predict the WG phenotype or distinct

    henever N1 is involvedin either additive or non-additive manner.ed effects on the WG phenotype. Respective alleles...