Association Of β-defensin(DEFB4) Gene Copy Number Variations With Ankylosing Spondylitis In Han Population

Objective1. To explore the association of β-defensin（DEFB4） gene copy number variations（CNVs） with Ankylosing Spondylitis（AS）.2. To explore the association of DEFB4 gene CNVs with disease activity, and explore the interaction between CNVs and suspected environment factors, and provide an important clues and evidence for exploring of the etiology of AS and clarifying the pathogenesis of AS.Methods1. Who was diagnosed in first affiliated hospital of Anhui Medical University from 2011 to 2014 in the department of rheumatology was participant in the patients group. And at the same time, chosen the health people from the first affiliated hospital of Anhui Medical University who was matched by age and gender. Questionnaire was used to collect the demographic data of patients and control, and clinical characters: age, gender, disease duration, BASDAI and BASFI, Erythrocyte sedimentation rate, C-reactive protein and HLA-B27. Acquisition 5ml peripheral venous blood of patients and controls.2. The modify salting out method was used to exact DNA, and the copy number of DEFB4 gene was measured by Accu CopyTM methods.3. Case control study and only-case study were designed. Logistic regression model was used to analysis the association of gene CNVs and AS, diseased activity and the interaction with environment factors. All data were analyzed by SPSS19.0 software, significance level was set at α=0.05.Results1. A total of 405 AS patients and 401 controls. With a mean age of 27.91±9.93 year and median disease duration was 2.08 year, and the positive rate of HLA-B27 was 64% in patients group. The mean age of control was 26.89±7.12 year. There was no statistically significant differences between the two groups with respect to age （t=1.77, P=0.076） and sex（χ2=1.13, P=0.288）.2. The ranges of DEFB4 gene CNV were 1 to 8 both in patients and control. In patients group, the common copy number were 2 to 4 in DEFB4₁ and 2 to 5 in DEFB4₂. In the control group, the most copy number of DEFB4₁ and DEFB4₂ were 3-copy（35.99%, 27.14%, respectively）. There were no statistical significant difference between case and control with respect to DEFB4₁（Z=0.63, P=0.528） and DEFB4₂（Z=1.27, P=0.111）.3. We divided the sample into 2 group（≤3 and ≥4）, the frequency distribution of DEFB4₂ with a significant difference between case and control（χ2=4.49, P=0.034）. ≥4 copy maybe the protect factor of AS: OR=0.74,95%CI（ 0.56,0.98）. After, we divided the samples into low（ two or fewer）, central（three） or high（ four or more）, the frequency distribution of DEFB4₂ with a significant difference between case and control（χ2=8.68, P=0.013）. The ≤2-copies and ≥4-copies conferred a 0.68 and 0.62 decrease risk of AS compared with 3-copy. Adjusted by age and sex, the ≤2-copies compared with 3-copy has not significant[OR=0.69,95%CI（0.47,1.03）, P=0.067].4. Univariate analysis showed that both DEFB4₁ and DEFB4₂ were associated with BASDAI, high-copies were decrease risk of the disease severity [OR=0.71, 95%CI（0.56, 0.90）, P=0.005; OR=0.75, 95%CI（0.60, 0.94）, P=0.013, respectively]. Adjusted by age, gender and disease duration, we found that CNVs of DEFB4 gene association with BASDAI were independent of age, sex and course. There is not association between CNVs and BASFI.5. Within the salt group, there also may be an interaction of G×E between median and light [OR=0.51,95%CI（0.28, 0.94）,P=0.032]. However, there was no interaction between CNVs and the other environmental factors in patients with AS.ConclusionThe results show that higher CNV（≥4） of DEFB4 gene were significantly associated with a decrease AS and BASDAI risk, and salt maybe a risk exposure factor to take combined actions with CNVs in AS patient. It suggest that CNVs of β-defensin gene may be a risk factor in the development of AS in a Chinese Han population.