Interleukin-18 promoter polymorphism in patients with rheumatoid arthritis

Proinflammatory Cytokines (IL-1, -6, -8, -15, -17, -18, -23, TNF-α) Single Nucleotide Polymorphisms in Rheumatoid Arthritis-A Literature Review

Conducted studies highlight that a mixture of genetic and environmental factors is responsible for rheumatoid arthritis (RA) development. This study aimed to analyze the available literature for the relationship between, on the one hand, single-nucleotide polymorphisms (SNPs) in the proinflammatory cytokines genes interleukin-1 (IL-1), -6, -8, -15, -17, -18, and -23, and tumor necrosis factor-alpha (TNF-α), and on the other hand, RA susceptibility, severity, and patients' response to applied treatment. The PubMed database was searched for sources. Preference was given to articles which were published within the past 20 years. Data indicate that the relationship between selected SNPs in proinflammatory cytokines genes and susceptibility to developing RA is inconclusive, and it depends on the ethnicity of the population. Although the allelic and genotypic frequencies of many SNPs in proinflammatory cytokines genes analyzed did not differ between RA patients and healthy controls, deeper analysis showed that these polymorphisms have a relationship with clinicopathological features of RA. SNPs in proinflammatory cytokines genes also "modify patients' response" to applied treatment. Further studies, on larger cohorts of subjects and in different populations, should be conducted to elucidate the role of SNPs in IL-1, -6, -8, -15, -17, -18, and -23, and TNF-α genes in RA patients.

Association of interleukin-18 gene polymorphisms with Takayasu arteritis in a Chinese Han population

Background:

Interleukin-18 (IL18) gene polymorphisms are related to many inflammatory and autoimmune diseases. However, a correlation analysis between IL18 −607C/A and −137G/C gene polymorphisms and Takayasu arteritis (TA) is lacking.

Methods:

This study enrolled 200 patients with TA as the case group and 334 region-, age-, and sex-matched healthy subjects as the control group. We genotyped alleles and genotypes at positions −607 and −137 of the IL18 gene and analyzed the distribution frequencies. Mann-Whitney U test, t test, Chi-squared test and Hardy-Weinberg equilibrium were performed.

Results:

After adjusting for risk factors, the adjusted odds ratios and 95% confidence intervals at position −607C/A were 0.533, 0.391 to 0.880 (P = 0.010); 0.266, 0.586 to 1.002 (P = 0.051); and 0.122, 0.552 to 1.420 (P = 0.613) under the dominant, additive, and recessive models, respectively. For the −137G/C polymorphism, the adjusted odds ratios and 95% confidence intervals were 1.571, 1.068 to 2.311 (P = 0.022); 1.467, 1.086 to 1.980 (P = 0.012); and 1.815, 0.901 to 3.656 (P = 0.095) under the dominant, additive, and recessive models, respectively. Moreover, regardless of the model used, we found no statistical difference in distribution frequency between the active and quiescent states of TA for the −607C/A (P = 0.355, 0.631, and 0.705, respectively) and −137G/C polymorphisms (P = 0.205, 0.385, and 0.208, respectively).

Conclusions:

The IL18 −607C/A gene polymorphism may decrease the risk of TA, and thus is a protective factor, whereas −137G/C may increase the risk of TA, and thus is a risk factor. However, neither polymorphism was related to activity (active vs. quiescent) of TA.

Interleukin-18 promoter polymorphisms and idiopathic Parkinson disease: an Egyptian study

Etiology of sporadic Parkinson's disease (PD) is largely unknown. The contribution of genetic factors to the pathogenesis of PD is supported by the demonstration of high concordance in twins, increased risk among relatives of PD patients and existence of familial cases. This study aimed to examine the relation between interleukin 18 (IL-18) gene promoter polymorphisms and idiopathic PD, and its impact on clinical presentation and disease severity. 30 idiopathic PD patients and 15 age- and sex-matched healthy subjects were included. Disease severity was assessed using Unified Parkinson's Disease Rating Scale (UPDRS). Genetic testing for IL-18 gene promoter -607C/A single nucleotide polymorphisms (SNP) was done using real-time polymerase chain reaction (PCR) technique. A raised risk of PD development was found in patients with A/C and C/C genotypes of the site -607C/A (odds ratios = 1.83 and 1.98, respectively). The distribution of the genotypes showed no significant relation to gender or predominant clinical presentation. The age at onset of disease was significantly lower in C/C and A/A genotypes compared to A/C genotype (p = 0.001 and 0.04, respectively). Patients with A/A genotype showed significantly higher mentation score of UPDRS compared to patients with A/C and C/C genotypes (p = 0.003 and p = 0.002, respectively). Polymorphisms of IL-18 gene promoter increase the risk of developing idiopathic PD. The polymorphisms may affect phenotypic expression rather than being a direct cause of idiopathic PD.

Ethnicity-stratified analysis of the association between IL-18 polymorphisms and systemic lupus erythematosus in a European population: a meta-analysis

We performed a meta-analysis to identify the association between polymorphisms in the promoter of interleukin-18 (IL-18) and susceptibility for systemic lupus erythematosus (SLE) . Genotype data for three single-nucleotide polymorphisms (SNPs rs360719, rs1946518, and rs187238) in the IL-18 promoter were extracted from 20 studies of three different ethnicities (European, Asian, and South American). Data from each ethnicity group and their combinations were analyzed. We found distinct evidence of an association between rs360719 and SLE (P = 0.001) in the European/South American group [odds ratio (OR) 1.31 per C allele, 95% confidence interval (CI) 1.11-1.53]. Stratification analysis by ethnicity showed a significant association between rs360719 and SLE in the European population (OR 1.33 per C allele, 95% CI 1.11-1.61, P = 0.003) and a lesser effect in the same direction in the South American population (OR 1.18). A significant association was also identified between rs1946518 and SLE in the European population (OR 1.16 per A allele, 95% CI 1.03-1.30, P = 0.017), although there was no association in the Asian or the combined European/Asian population. We also examined genome-wide association study (GWAS) data from an Asian subpopulation (Chinese) for the association between rs1946518 and SLE, but found no association (P = 0.83). The third SNP, rs187238, was not significantly associated with SLE in any of the populations examined. In summary, this study identified a significant association between SLE and two SNPs within the IL-18 gene promoter region (rs360719 and rs1946518) in a European population, but not in populations of Asian origin.

Association of IL-18 promoter gene polymorphisms with rheumatoid arthritis: a meta-analysis

Interleukin-18(IL-18) plays a potential pathological role in rheumatoid arthritis (RA). The conclusions of the published reports on the relationship between single-nucleotide polymorphisms -607C/A (rs1946518) and -137G/C (rs187238) located in the IL-18 gene promoter and RA risk remain controversial. This meta-analysis was performed to evaluate the association between IL-18 gene promoter (-607A/C and -137C/G) polymorphisms and RA using (1) allele, (2) codominant, (3) dominant, and (4) recessive models. Literature search was conducted up to January, 2013, in PubMed, EMBASE, Spring-link, Web of Science, Wanfang (Chinese) and China National Knowledge Infrastructure (CNKI). A total of 10 studies from eight articles involving 2,662 cases and 2,168 controls for -607A/C polymorphism and 9 studies from six articles involving 1,331 cases and 1,468 controls for -137C/G polymorphism were considered in the meta-analysis. For the relationship of IL-18 -607A/C polymorphism with RA risk, significant association was observed in allele model (OR = 0.778, 95 % CI = 0.633-0.955) and dominant model (OR = 0.618, 95 % CI = 0.466-0.819). However, no significant association could be observed between -137C/G polymorphism and RA risk under all genetic models (allele model: OR = 0.940, 95 % CI = 0.777-1.138; codominant model: OR = 1.079, 95 % CI = 0.574-2.029; dominant model: OR = 0.913, 95 % CI = 0.779-1.069; recessive model: OR = 1.133, 95 % CI = 0.586-2.190). In the subgroup analysis by ethnicity, significant result was also found in Asian populations but not found in Caucasian populations for the relationship of IL-18 -607A/C polymorphism with RA risk; while no obvious association was found between IL-18 -137C/G polymorphism and RA risk. This meta-analysis indicates that IL-18 -607A/C polymorphism in promoter region may be associated with RA risk.

Interleukin-18 gene promoter--607 A/C polymorphism and the risk of immune thrombocytopenia

Interleukin-18 (IL-18) is a T helper 1 cytokine, which is postulated to play a role in immune thrombocytopenia (ITP). The aim of this study was to determine whether IL-18 promoter gene -607 A/C polymorphism was associated with ITP. Three-hundred and fifty-four Chinese ITP patients and 300 Chinese healthy individuals were enrolled. Genomic DNA was extracted from the peripheral blood. Polymerase chain reaction-restriction fragment length polymorphism (RFLP) was used to genotype the DNA samples for single nucleotide polymorphism (SNP)-607. Allelic and genotypic frequencies were compared between the case-control groups by the chi-square test. The results showed that the frequencies of the CC, CA and AA genotypes and C and A allele were 32.4, 47.8, 19.8, 56.4 and 43.6% in ITP patients and 32.3, 50.4, 17.3, 57.5 and 42.5% in the controls, respectively. There was no significant difference in either genotypes or allelic distribution between ITP patients and the controls. Furthermore, stratified analysis by the platelet count, age and disease course including ITP with severe thrombocytopenia (sITP), non-sITP, acute adult, chronic adult, acute childhood and chronic childhood revealed no significant difference in genotype and alleles distribution. In conclusion, this polymorphism was almost equally distributed between ITP patients and the controls. These data showed that this SNP may not be used as a stratification marker to predict the susceptibility to Chinese ITP.

Interleukin-4, interleukin-4 receptor, and interleukin-18 polymorphisms and rheumatoid arthritis: a meta-analysis

OBJECTIVE

The aim of this study was to determine whether the functional interleukin-4 (IL-4) -590 C/T, IL-4 receptor (IL-4R) 1902 G/A, IL-18 -607 C/A, and -137 G/C polymorphisms polymorphisms confer susceptibility to rheumatoid arthritis (RA).

METHODS

Meta-analysis was conducted on the associations between these IL-4, IL-4R, and IL-18 polymorphisms and RA.

RESULTS

A total of 12 comparative studies were included in this meta-analysis. Meta-analysis of the IL-4 -590 C/T polymorphism showed an association in all study subjects and Europeans (OR for the TT genotype = 2.280, 95% CI = 1.315-3.952, p = 0.003; OR = 2.139, 95% CI = 1.089-4.199, p = 0.027). However, meta-analysis showed no association between RA and the IL-4R 1902 G allele in all study subjects and Europeans. Meta-analysis showed no association between RA and the IL-18 -607 C allele (OR = 1.159, 95% CI = 0.967-1.387, p = 0.110). Meta-analysis of the IL-18 -137 G/C polymorphism revealed no association between RA and the IL-18 -137 G/C polymorphism.

CONCLUSIONS

This meta-analysis demonstrates that the IL-4 -590 T/C polymorphism is associated with susceptibility to RA in Europeans, but the IL-4R + 1902 G/A, IL-18 -607 C/A and -137 G/C polymorphisms are not associated with RA.

Association of interleukin-18 (-137G/C) polymorphism with rheumatoid arthritis and systemic lupus erythematosus: a meta-analysis

BACKGROUND

Recent studies have suggested that interleukin (IL)-18 gene (-137G/C) polymorphism is associated with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). However, other studies did not confirm this correlation.

OBJECTIVE

The objective of this study was to evaluate the relationships of IL-18 -137G/C and RA and SLE using a meta-analysis.

METHODS

Pubmed, Embase and Cochrane library databases were systemically searched. Data were extracted by two independent reviewers and pooled odds ratio (OR) with 95% confidence interval (CI) was calculated.

RESULTS

In RA, the overall ORs and 95% CIs of -137C were 1.03, 0.88-1.22 (p=0.391); 1.22, 0.89-1.68 (p=0.020) and 1.06, 0.93-1.21 (p=0.110) in dominant, recessive, and additive models, respectively. Furthermore, in SLE, the overall ORs and 95% CIs of -137C were 1.10, 0.94-1.29 (p=0.980); 1.21, 0.91-1.60 (p=0.010) and 1.10, 0.97-1.24 (p=0.454) in dominant, recessive, and additive models, respectively. IL-18 -137G/C could increase the risk of RA and SLE. No publication bias was found in this meta-analysis. After population stratification analysis, under recessive model, the pooled ORs and 95% CIs of -137C were 1.14, 0.82-1.60 (p=0.008) and 1.01, 0.66-1.55 (p=0.004) in European RA patients and Asian SLE patients, respectively.

CONCLUSIONS

This meta-analysis showed that IL-18 -137G/C was a risk factor for RA and SLE, especially for RA in Europeans and SLE in Asians.

Interleukin-18 gene polymorphisms and rheumatoid arthritis: a meta-analysis

Interleukin-18 (IL-18) is a member of the IL-1 superfamily that enhances both innate and acquired immune responses. IL-18 is highly expressed in sera, synovial fluids and synovial tissues of patients with RA, and these IL-18 levels are correlated with RA disease activity, indicating an important role of IL-18 in the pathogenesis of RA. Several studies have examined the association of IL-18 gene polymorphisms with RA, but these studies have shown inconclusive and controversial results. To verify the association between IL-18 gene polymorphism and susceptibility to RA, we conducted a meta-analysis of all relevant reports cited in MEDLINE/PubMed before October 2012. A meta-analysis on the association between the IL-18 rs1946518 SNP and RA was performed for 2944 patients with RA and 2377 controls from 7 published studies and a meta-analysis on the association between the IL-18 rs187238 SNP and RA was performed for 1319 patients with RA and 1211 controls from 5 published studies. In addition, 2 studies involving 1873 RA patients and 1092 controls were considered in the meta-analysis of the association between the IL-18 rs360722 SNP and RA. No significant association was found between two IL-18 SNPs (rs1946518 and rs187238) and RA susceptibility in all subjects. In subgroup analysis stratified by ethnicity, there was still no significant association between these two IL-18 SNPs and RA susceptibility. However, the frequency of the T allele at rs360722 was found to be significantly lower in patients with RA compared with controls, although this finding was based on only 2 studies. The results of our meta-analysis suggest that IL-18 rs360722 SNP is only associated with RA susceptibility. However, due to only two studies included in our meta-analysis, large-scale well designed studies should be considered in future studies to confirm the exact role of IL-18 rs360722 SNP in RA susceptibility.

IL-18 105 A>C polymorphism contributes to renal manifestations in patients with SLE

Systemic lupus erythematosus (SLE) is a multisystem autoimmune connective tissue disorder characterized by various aberrations including increased production of IL-18. As IL-18 105 A>C polymorphic variants have been linked to increased production of this cytokine, we investigated the prevalence of IL-18 105 A>C (rs549908) polymorphic variants in SLE patients (n = 111) and controls (n = 152). There were no significant differences in the distribution of IL-18 105 A>C polymorphic variants in SLE patients and controls. However, there was a significant association between the IL-18 105 AA genotype (recessive model) and renal manifestations OR = 3.360 (1.523–7.415, P = 0.0039) and the P value remained statistically significant after Bonferroni correction (P corr = 0.0351).Our findings indicate that the IL-18 105 AA genotype variant can contribute to renal manifestations in patients with SLE.

Lack of association of interleukin-18 gene promoter -607 A/C polymorphism with susceptibility to autoimmune diseases: a meta-analysis

OBJECTIVE

Published data on the association between interleukin (IL)-18 gene promoter -607 A/C polymorphism and autoimmune diseases risk are inconclusive. To derive a more precise estimation of the relationship, a meta-analysis was performed.

METHODS

A total of 17 studies, including six studies on type 1 diabetes (T1D), four on rheumatoid arthritis (RA), five on systemic lupus erythematosus (SLE), three on Crohn's Disease (CD) and three on ulcerative colitis (UC), were available for the meta-analysis. Meta-analysis was performed for genotypes A/A (recessive effect), genotypes A/A + A/C (dominant effect), and A allele in fixed or random-effects models.

RESULTS

Overall, no significantly elevated autoimmune diseases risk was found in all genetic models when all studies were pooled into the meta-analysis. The overall odds ratios (ORs) and 95% confidence intervals (CIs) for A-allele were T1D (OR = 0.938, 95% CI = 0.757-1.162), RA (OR = 0.759, 95% CI = 0.540-1.067), SLE (OR = 0.858, 95% CI = 0.609-1.208), CD (OR = 1.159, 95% CI = 0.975-1.379) and UC (OR = 1.170, 95% CI = 0.977-1.402), respectively. In the subgroup analysis by ethnicity, there was still no significant association detected in all genetic models.

CONCLUSIONS

To date, there is still not enough evidence to indicate the association of IL-18 gene promoter -607 A/C polymorphism and the development of autoimmune diseases.

Interleukin-18 promoter polymorphisms and risk of Parkinson's disease in a Han Chinese population

The etiology of sporadic Parkinson's disease (PD) is not well established. Interleukin-18 (IL-18), a member of pro-inflammatory cytokines, might influence the risk of sporadic PD occurrence and development. In this study, two DNA polymorphisms at interleukin (IL)-18 promoter, -607C/A (rs1946518) and -137G/C (rs187238), were examined in sporadic PD patients in a Han Chinese population with 290 sporadic PD patients and 200 healthy controls. Direct sequencing was performed in 10% of the samples to validate the genotyping results. The results revealed that for -607C/A polymorphisms, there were significant differences in genotype distribution between PD and control in the total sample (P=0.017) and between LOPD and healthy-matched controls subgroup (P=0.011). For -137G/C polymorphisms, there were no significant differences in genotype distribution and gender and age-related differences between PD and control in the total sample (P=0.610). Results in this study revealed that the IL-18 607C/A polymorphism is a risk factor for sporadic LOPD in Han Chinese population, while IL-18 137G/C polymorphism is not a risk factor for sporadic PD in the Han Chinese population.

Interleukin-18 promoter polymorphisms in Japanese patients with rheumatoid arthritis: protective effect of the T allele and T/T genotype at rs360722

Rheumatoid arthritis (RA) is a chronic inflammatory disease with a strong genetic contribution to its pathogenesis. Among numerous candidate genes, cytokine gene polymorphisms have been implicated. Interleukin-18 (IL-18) induces production of tumor necrosis factor-α and promotes T helper (Th)1-type immune responses. This study investigates the association between IL-18 promoter polymorphisms and RA susceptibility. A total of 2471 Japanese case-control samples (1493 RA patients and 978 healthy controls) were examined. Three haplotype tag single-nucleotide polymorphisms, rs1946518A/C, rs360718T/G, and rs360722T/C, spanning from the 5'UTR to intron 1 were genotyped using allelic discrimination with the use of specific TaqMan probes, and three haplotypes (A-T-T, C-T-C, and A-G-C) were determined. Among these polymorphisms, the frequency of the T allele at rs360722, which tags the A-T-T haplotype, was significantly lower in the RA patient group compared with the normal subjects [0.46 versus 0.49, P = 0.0061, Fisher's exact probability test, odds ratio (OR) = 0.85, 95% confidence interval (CI) = 0.75-0.95]. Having the T/T genotype further increased the significance (0.20 versus 0.27, P = 0.0006, OR = 0.72, 95% CI = 0.58-0.86). Therefore, presence of the T allele and T/T genotype at rs360722 reduces the susceptibility of Japanese people to RA.

Association of IL-18 promoter polymorphism with liver disease severity in HCV-infected patients

INTRODUCTION

Interleukin (IL)-18 plays an important dual role in Th1 polarization and viral clearance, as well as in the development of liver fibrosis. Single-nucleotide promoter polymorphisms influence the transcription of IL-18 mRNA. Promoter polymorphisms are linked to delayed virus clearance and disease susceptibility in many diseases. However, there is no information about their role in hepatitis C virus (HCV) infection.

AIM

To investigate the association between -607 or -137 polymorphism with susceptibility and severity of HCV infection.

PATIENTS AND METHODS

Two hundred and four serologically proven patients with chronic HCV infection and 350 matched healthy controls were included in this study. Patients were segregated in 2 groups: group A with mild liver disease and group B with severe liver disease on the basis of histological activity index (HAI </=5 or >5) and hepatic fibrosis score (</=2 or >2). IL-18 promoter genotyping was performed with sequence-specific primers.

RESULTS

There was no significant difference in the frequencies of -607 and -137 allelic distribution in patients and controls. The -607 A/A allele was more common in group A patients with mild liver disease than in patients with severe liver disease on the basis of HAI (38.6% vs. 21%, P = 0.05; odds ratio [OR] = 0.424, confidence interval [CI] = 0.233-0.773; R (2) = 0.631) and stage of fibrosis (38.7% vs. 16.7%, P = 0.008; OR = 0282, CI = 0.134-0.596; R (2) = 0.434).

CONCLUSIONS

IL-18 promoter polymorphism at -607 position with A/A allele is a potential protective marker, as it is associated with milder liver disease in patients with chronic HCV infection.

A/C polymorphism in the interleukin-18 coding region among Taiwanese systemic lupus erythematosus patients

Interleukin-18 (IL-18) is associated with chronic inflammation, autoimmune diseases and various cancers and infectious diseases. An IL-18 genetic A/C polymorphism at coding position 105 (rs549908) has been linked with asthma and rheumatoid arthritis. We tested a hypothesis that the IL-18 genetic polymorphism confers systemic lupus erythematosus (SLE) susceptibility. Study participants were Taiwanese SLE patients and a healthy control group. Our results indicate (1) a significantly higher A allele frequency in SLE patients (P = 0.003; OR = 1.97; 95% CI = 1.26-3.08) and (2) a significantly higher A allele frequency in SLE patients with a central nervous system disorder (P = 0.027; OR = 7.18; 95% CI = 0.95-54.28). Our results suggest that the A/C polymorphism contributes to SLE pathogenesis.

Polymorphism of interleukin-18 promoter influences the onset of kidney graft function after transplantation

It has been well recognized that the promoter polymorphisms of interleukin-18 (IL-18) influence the level of cytokine expression. In our previously published data, we showed constitutive IL-18 expression in the epithelium of renal distal tubules in patients after kidney transplantation and significantly elevated IL-18 expression during acute rejection. In this study, we evaluated the clinical significance of two functional promoter polymorphisms of the IL-18 gene at positions -607 A/C (rs1946518) and -137 C/G (rs187238) in patients after kidney transplantation and looked for associations with the onset of graft function and the incidence of rejection episodes. Promoter polymorphisms in 124 patients and 103 unrelated controls were evaluated by sequence-specific primer polymerase chain reaction and the allele, genotype and haplotype frequencies were statistically correlated. We found a statistically different distribution of the allele frequency of -607 A/C polymorphism between patients with immediate or delayed onset of kidney graft function. Data showed that the C allele, which contributes to higher IL-18 expression, is more frequent in patients with delayed onset of function (P = 0.03, odds ratio = 1.93; 95% confidence interval = 1.15-3.25). A/C single nucleotide polymorphisms of the IL-18 promoter at position -607 may influence the onset of early kidney allograft function.

HLA-DRB1⁎04 gene polymorphisms and expressions profiles of interleukin-18 and interleukin-18 binding protein following in vitro stimulation in human peripheral blood mononuclear cells of healthy individuals and patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic arthritic condition that can lead to deformities and disabilities. Interleukin-18 (IL-18) is a proinflammatory cytokine known to play a role in the acute and chronic inflammatory phases of RA. IL-18 binding protein is the natural antagonist of IL-18 protein. We aim to identify the effect of HLA-DRB1*04 gene polymorphisms on IL-18 and IL-18BP gene expressions profiles as well as the time-course profiles following in vitro stimulation with mitogens. Peripheral blood mononuclear cells from 16 RA patients and 21 healthy controls were cultured for 1, 4, 8, 12, 24, 48 and 72 h following stimulation with either LPS or PHA. mRNA expression of IL-18 and IL 18BP were determined by quantitative real-time PCR using a comparative Ct (threshold cycle) method. IL-18 levels in supernatants were measured by enzyme-linked immunosorbent assay. Basal mRNA (4.5-fold) and protein levels of IL-18 were increased and IL-18BP mRNA expression was decreased (8-fold) in RA patients when compared to controls. Similarly, increased IL-18 levels were observed in active RA patients, whereas IL-18BP expression was increased in inactive patients. There was an increase in mRNA and protein levels of IL-18 in RA patients that peaked at 4 h and 8 h respectively following LPS stimulation. A similar profile was observed for IL-18BP; however, the expression level was higher in controls than RA patients. Persistent high production of IL-18 in RA is associated with disease progression and IL-18 BP seems to inhibit this activity.

Disease association of the interleukin-18 promoter polymorphisms in Taiwan Chinese systemic lupus erythematosus patients

Interleukin (IL)-18, an important mediator of innate and adaptive immunity, plays multiple roles in chronic inflammation, in autoimmune diseases, in a variety of cancers and in number of infectious diseases. IL-18 promoter polymorphisms have been also noted associated with various inflammatory diseases. We investigated the association of IL-18 promoter polymorphisms (-656T/G, -607A/C and -137C/G) with systemic lupus erythematosus (SLE) in Taiwan Chinese patients and controls. Six haplotypes (hts) were identified from the three promoter polymorphisms. The genotype distribution of the ht1 (GCC), ht2 (TAC), ht4 (GAC) and ht5 (TCC) were different in patients and controls (P<0.002). Moreover, the haplotype and genotype frequencies of ht1 were significantly increased in patients with discoid rash (P=0.045, odds ratio (OR): 2.01, 95% confidence interval (CI): 1.01-4.00; P=0.027, OR: 5.13, 95% CI: 1.41-18.68). In addition, the homozygous genotype ht1/ht1 was significant increased in patients with serositis (P=0.015, OR: 9.78, 95% CI: 1.55-61.73). These observations suggest that the three promoter polymorphisms contribute to the genetic background of SLE pathogenesis.

Interleukin-18 genetics and inflammatory disease susceptibility

IL18 was mapped to 11q22.2-22.3 in 1998. Owing to interleukin (IL)-18's important and novel role in immunomodulation, the gene itself has been subject to scrutiny, with the aim of discovering variants that may impact on disease susceptibility and/or progression. Despite being sequenced numerous times in different populations, no non-synonymous variants have been found. However, a number of polymorphisms within the proximal promoter have been verified that may interfere with transcription-factor-binding sites. Much of the subsequent association analyses have centred on these variants, but have yielded no consistent results, despite numerous different study populations being genotyped. IL18 has recently been resequenced in its entirety, enabling the tagging-single-nucleotide polymorphism (tSNP) methodology to be adopted. This approach has yielded interesting results, with genetic variation being shown to affect protein levels, and risk. This review aims to compile and reflect on the association data of interest published to date, with a focus on the diseases related to aberrant inflammatory control.