Association Study Of Genetic Polymorphisms And Their Interaction Involved In NF-κB Signaling Pathway With Systemic Lupus Erythematosus

Background Systemic lupus erythematosus (SLE), a complex autoimmune disease arising from the action of multiple genetic and environmental risk factors, is characterized by the production of a wide range of auto-antibodies and multiple organs involvement. The etiology of SLE has not been completely demonstrated, but genetic factors have been suggested to play a vital role in the development and progression of this disease. Recently, genome-wide association studies (GWASs) and large-scale candidate gene studies have led to the discovery and validation of multiple susceptible genes/loci for SLE. However, the heritability of SLE could not be fully explained by all these disclosed genetic factors. With regard to this point, one important explanation for the "missing heritability" might be the genetic interaction. Recently, multiple genetic associations have been found between genetic polymorphisms within genes involved in nulear factor-KB (NF-κB) signaling pathway [NFKB1rs28362491, REL rs13031237, REL rs842647, nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor-like1(NFKBIL1) rs2071592, inhibitor of kappa light polypeptide gene enhancer in B-cells, kinase beta (IKBKB) rs12676482, TNF receptor-associated factor6(TRAF6) rs4755453, TRAF6rs5030437, tumor necrosis factor alpha-induced protein3(TNFAIP3) rs2230926, TNFAIP3-interacting protein1(TNIF1)rs10036748and TNIP1rs3792783] and SLE and/or other autoimmune disorders. NF-κB is a transcription factor family that is widely expressed in multiple kinds of cell. As an important transcription factor family, NF-κB regulates the expression of a wide range of pro-inflammatory cytokines, chemokines, adhesion molecules and matrix metalloproteinases. Abnormal activation of NF-κB has been associated with several inflammatory diseases and autoimmune diseases, including SLE. Autoimmune diseases are complex chronic conditions caused by loss of immunologic tolerance to self-antigens, leading to immune-mediated tissue destruction. Shared genetic background has been suggested by the observation of co-occurrence of multiple autoimmune diseases within individuals and families. This has also been validated by the recent floods of meta-analysis and investigations following up susceptible genes of one autoimmune disorder for another. Interaction analysis is dependent on the selection of interaction model, thus additive and multiplicative interactions were to be analyzed simultaneously. In addition, the highway interaction would be explored by multifactor dimensionality reduction (MDR) software.Objective This study was undertaken to examine the associations between the above-mentioned genetic polymorphisms within genes involved in NF-κB signaling pathway and genetic susceptibility to SLE and clinical features of SLE, and further test for genetic interaction among these genetic polymorphisms in SLE in a Chinese population.Methods Ten genetic polymorphisms (NFKB1rs28362491, REL rs13031237, REL rs842647, NFKBIL1rs2071592, IKBKB rs12676482, TRAF6rs4755453, TRAF6rs5030437, TNFAIP3rs2230926, TNIP1rs10036748and TNIP1rs3792783) were genotyped in883Chinese patients with SLE and979healthy controls by Sequenom MassArray technology. Patients with SLE were recruited from the First Affiliated Hospital of Anhui Medical University and Anhui Provincial Hospital. The diagnosis of SLE was based on the presence of the combination of at least four criteria of1997American College of Rheumatology (ACR) revised criteria for the classification of SLE. The normal control subjects without any signs or symptoms of autoimmune diseases were enrolled in the present study, and this group consisted of subjects attending health-check center in the First Affiliated Hospital of Anhui Medical University, and teaching staff and students from Anhui Medical University. Data was inputted by EpiData3.02software. Chi-square test was applied to compare allele and genotype frequencies between cases and controls. Fisher’s exact test was employed when necessary. Estimated odds ratios (ORs) and95%confidence intervals (95%CIs) were calculated. Hardy-Weinberg equilibrium (HWE) was assessed in control subjects by STATA10.0software. Statistical power was determined by the free-download software-Power and Sample Size Calculation Software. Additive and multiplicative interactions were analyzed sequentially. Highway genetic interaction was analyzed by MDR software. Statistical analysis was performed using SPSS10.01software. A two-tailed P value less than0.05was considered significant. Bonferroni adjustment was applied for multiple comparisons.Results Based on the consideration of genetic interaction, only subjects with all genetic polymorphisms successfully genotyped were included in the final analysis, and a total of845SLE patients and950normal controls were eligible for final analysis. Clinical feature data was available from769SLE patients, and453had arthritis (58.9%),342malar rash (44.5%),320renal disorder (41.6%),152oral ulcer (19.8%),112neurological disorder (14.6%),87photosensitivity (11.3%),81discoid rash (10.5%) and41serositis (5.3%). Associations of TNFAIP3rs2230926and TNIP1rs10036748with SLE were replicated in our study (TNFAIP3rs2230926, G vs. T:X2=10.172, P=0.001, OR=1.557,95%CI1.184-2.048; G/G+G/T vs. T/T:X2=10.042, P=0.002, OR=1.585,95%CI1.190-2.111; TNIP1rs10036748, T vs. C:X2=8.140,P=0.004, OR=1.261,95%CI1.075-1.478; T/T vs. T/C+C/C:X2=12.594, P=3.870×10-4, OR=1.412,95%CI1.167-1.708). Two other polymorphisms, NFKB1rs28362491and NFKBIL1rs2071592, showed nominal evidence for association (NFKB1rs28362491, del vs. ins:X2=3.944, P=0.047, OR=1.144,95%CI1.002-1.307; NFKBIL1rs2071592, A vs. T:X2=7.580, P=0.006, OR=1.205,95%CI1.055-1.376; A/A+T/A vs. T/T:X2=6.235,P=0.013, OR=1.362,95%CI1.068-1.736; A/A vs. T/A+T/T:X2=4.175, P=0.041, OR=1.228, 95%CI1.008-1.495) but these were not significant after applying Bonferroni correction. NFKB1rs28362491was found to be associated with arthritis (del vs. ins:X2=6.901, P=0.009, OR=1.318,95%CI1.072-1.619) and NFKBIL1rs2071592was detected to be associated with serositis (A vs. T:X2=5.474, P=0.019, OR=0.590,95%CI0.378-0.922). Additive interaction analysis revealed significant interaction between NFKB1rs28362491and TNFAIP3rs2230926[The relative excess risk due to interaction (RERI)=0.98,95%CI=0.02-1.93, attributable proportion due to interaction (AP)=43.2%,95%CI=0.12-0.74]. Multiplicative interaction between NFKBl rs28362491and TNIP1rs3792783(P=0.03) was observed. No best candidate model with significant evidence was detected by MDR analysis.Conclusion Our results provide evidence for genetic associations and genetic interactions, which further support the important role of NF-κB signaling pathway in the development of SLE.