University of Groningen Genetic and prognostic factors in lupus Martens, Henk Allard IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2009 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Martens, H. A. (2009). Genetic and prognostic factors in lupus Groningen: s.n. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 19-12-2017
Chapter 1 Introduction, aim and outline of the thesis 9
Chapter 1 General introduction Systemic lupus erythematosus (SLE) is a multisystem disorder characterized by the production of autoantibodies directed against self-antigens. These autoantibodies, together with other immune effector mechanisms, can affect several organs or organ systems and cause a broad spectrum of clinical and immunological manifestations. Most of these organ- and immunological manifestations are mentioned in the SLE classification criteria according to the American College of Rheumatology (ACR). 1 The pathogenesis of SLE is largely unknown, but genetic predisposition is thought to play an important role. Genetics are not only influential for disease susceptibility, they also might contribute to prognosis and development of specific disease manifestations in SLE. One of these manifestations is renal disease: lupus nephritis (LN). In this thesis we describe the results of the analysis of genetic and prognostic factors in SLE, with a focus on LN. This thesis has three aims: 1. Are (functional) genetic factors associated with susceptibility for SLE and LN? 2. Are genetic factors associated with disease severity and outcome in SLE and LN? 3. Do results of renal hemodynamic tests have a prognostic value in proliferative LN? Genetics in SLE and lupus nephritis SLE is an autoimmune disease with heterogeneous clinical manifestations. It is a very complex disease and its exact pathogenesis is not known. Several factors are thought to play a role in the pathogenesis of SLE, one of these is genetic predisposition. This is demonstrated in patients harbouring hereditary deficiencies in complement factors such as C1q deficiency. Over 90% of patients presenting with C1q deficiency develop a clinical syndrome that closely resembles SLE. These hereditary conditions, however, are very rare. Most of the SLE cases do not have a monogenic defect, so, in almost all patients, SLE is a polygenic disease. Genetic factors alone, however, are not sufficient to develop clinical disease. 2 In monozygotic twins, for instance, the rate of concordance for SLE is 24-58%. 3 Therefore, other factors such as environmental factors, probably contribute to the pathogenesis of SLE as well. Over the past years, several genetic loci have been found to be associated with SLE. The strongest association with SLE has been described for the HLA locus 10
Introduction, aim and outline on chromosome 6. 4-13 SLE susceptibility loci have first been detected by (familybased) linkage studies and fine mapping. The DNA for analysis in our studies was obtained in the years 2000-2001. The data was analyzed in the period before data became available of genome wide association studies (GWAS). By then, 8 loci had been confirmed to show significant linkage to SLE. 2 At that time, the HLA region on chromosome 6p11-21 already was the most prominent susceptibility locus for SLE. Other loci included the 1q23, 1q25-31 and 1q41-42 regions on chromosome 1. The 1q 23 region contains the genes encoding CRP and the Fcγ-receptors, the 1q41-42 region contains the gene encoding the enzyme poly(adp-ribose) polymerase 1 (PARP1). In addition, linkage of the chromosome 2q35-37 region (programmed cell death gene 1), the chromosome 4p16-15.2 region (SLEB3 gene), the chromosome 12q24 region and the chromosome 16q12 region with SLE had been established. Later on, highly significant associations were found for the STAT4 gene 14;15 and IRF5. 16-18 In the more recent years, GWAS have revealed more SLE susceptibility loci. 7;8;19;20 In these studies, DNA of large numbers of SLE patients is scanned by the determination of thousands of single nucleotide polymorphisms (SNPs) throughout the entire genome. These studies revealed highly significant association of SLE with known loci such as the HLA locus on chromosome 6, but also with other genes that were not found previously. These new genes include the gene encoding B lymphoid tyrosine kinase (BLK) and C8orf13 on chromosome 8p23.1 and ITGAM-ITAX (encoding the integrins alpha M and alpha X) on chromosome 16. In general, those loci being involved in SLE, are also involved in LN. In total, for more than 20 genes, robust associations with SLE have now been identified and confirmed. 7 Prognostic factors in SLE and lupus nephritis Although survival of SLE patients has remarkably increased over the past years, long-term prognosis is still reduced. LN was the major cause of morbidity and mortality of SLE patients in the past. In recent years other causes, in particular cardiovascular disease and infection, have been responsible for the increased morbidity and mortality in SLE. 21 These causes are at least in part attributable to side effects of immunosuppressive drugs. Other prognostic factors include age, sex, race, immunological and socioeconomic factors. 21-23 One of the most common and severe manifestations is renal disease, also known as lupus nephritis (LN). The different forms of LN have been described in the International Society of Nephrology/Renal Pathology Society 11
Chapter 1 classification criteria. 24 LN occurs in 50 to 75% of SLE patients during the course of the disease. 25 As we mentioned before, in the past, LN was a major cause of morbidity and mortality in SLE patients. Before the introduction of treatment with immunosuppressive agents it often led to loss of renal function and, ultimately, death. After the introduction of high dose corticosteroid treatment, prognosis of LN improved dramatically. 26 Further improvement was achieved when treatment with corticosteroids was combined with cytostatic drugs. 27;28 Nowadays, renal survival in LN, defined as survival without dialysis, ranges from 83 to 92% after five years and 74 to 84% after ten years. Still, renal survival is mainly determined by the severity of renal involvement. 23;29 In particular, patients with diffuse proliferative LN are at risk for the development of end stage renal disease (11 to 33% within five years). 23 Several factors are involved in the prognosis of LN, such as genetic, immunological, histopathological and demographic factors. One of the strongest predicting factors is decrease in renal function at the initial presentation. 23;30 In addition, Houssiau et al. found that (persistent) proteinuria after six months of treatment is associated with poorer outcome in LN. 31 Outline of the thesis The gene encoding the enzyme poly(adp-ribose) polymerase 1 (PARP1) has been associated with susceptibility for SLE, but results have been conflicting. In chapter 2 we describe the results of the analysis of the 1q41-42 region, containing the PARP1 gene, in a population of 103 SLE patients. DNA from family members of these patients was also available for analysis. This gave us the opportunity to provide additional data on the inheritance of markers in the 1q41-42 region. In previous studies, the human leucocyte antigen (HLA) region has been associated with susceptibility for SLE. In this region, however, strong linkage disequilibrium (LD) is present. This makes it difficult to discriminate associations due to LD from true associations. Chapter 3 describes the results of an extensive screen of the HLA region in 103 caucasian SLE patients and their family members. An additional test (additional disease locus test; ADLT) was applied to discriminate true causal associations from associations due to LD. Several findings link SLE with C1q, the first molecule of the classical complement pathway. Genetical analysis already has revealed mutations in the C1q gene in individuals with hereditary C1q deficiency. Whether the C1q gene 12
Introduction, aim and outline is involved in SLE has not been investigated before. In chapter 4, we describe the analysis of the C1q gene in 103 SLE patients and their family members. In addition to the association of the C1q gene with susceptibility for SLE, we also analyzed the association with SLE phenotypes, C1q and CH50 levels. The c-c chemokine receptor 5 (CCR5) plays an important role in inflammation. A 32-basepair ( 32) deletion in the CCR5 gene leads to a non-functional receptor. In Chapter 5 we review the literature on the role of CCR5 32 basepair deletion in RA and SLE. In chapter 6, we analyze the role of the CCR5 32 basepair deletion in a population of 405 RA patients, 97 SLE patients, 113 LN patients and 431 healthy controls. In addition to association with disease susceptibility, we analyzed the role of the 32 basepair deletion on outcome parameters in RA and LN. Several factors have shown to play a role in the pathogenesis of chronic inflammation in SLE and RA, amongst them advanced glycation end products (AGE s). AGE s may contribute to inflammatory and destructive processes by ligation to their receptor (RAGE). In literature, the gene encoding for RAGE is known also as AGE-R. In chapter 7 we analyze the role of AGE-R polymorphisms in susceptibility for SLE, RA and LN. In addition, we analyzed the role of AGE-R polymorphisms in outcome of RA and LN. Previous studies have demonstrated that renal hemodynamic parameters, such as effective renal plasma flow (ERPF) and glomerular filtration rate (GFR), are altered in active proliferative LN. In chapter 8 we describe the prognostic value of renal hemodynamic function tests on renal outcome in 37 SLE patients with a proliferative form of LN. Finally, the results and conclusions of the thesis are summarized in chapter 9. 13
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