Copy Number Variations of Complement Component C4 Are Associated With Behçet's Disease but Not With Ankylosing Spondylitis Associated With Acute Anterior Uveitis

Abstract

Objective. Complement component C4 copy number variations are associated with various inflammatory diseases. This study was undertaken to investigate whether copy number variations of C4 are also involved in the pathogenesis of Behçet's disease (BD).Methods. Gene expression was examined by enzyme-linked immunosorbent assay (ELISA) or realtime polymerase chain reaction (PCR). Copy number variations of C4 isotypes (C4A and C4B) were detected by real-time PCR in 905 patients with BD, 205 patients with ankylosing spondylitis (AS) and acute anterior uveitis, and 1,238 controls. The activation of CD4؉ T cells was analyzed by flow cytometry, and cytokine production was detected by ELISA.Results. Protein expression of total C4 in serum was significantly increased in patients with active BD compared with those with inactive BD or controls (Bonferroni corrected P [P corr ] ‫؍‬ 1.64 ؋ 10 ؊4 and P corr ‫؍‬ 0.037, respectively), but not in patients with AS and acute anterior uveitis. Copy number variation analysis identified a significantly increased frequency of more than 2 copies of C4A in BD patients (P ‫؍‬ 1.65 ؋ 10 ؊7 , odds ratio [OR] 2.84). HLA-B51, which is located on the same chromosome as C4, showed a strong association with BD in the Han Chinese population (P ‫؍‬ 8.90 ؋ 10 ؊65 , OR 5.05), but logistic regression showed that C4A copy number variation was an independent risk factor for BD. A significantly increased expression of C4A was observed in the high copy number groups (>2 copies or 2 copies) versus the low copy number group (P corr ‫؍‬ 0.019 and P corr ‫؍‬ 0.044, respectively). Increased production of interleukin-6 (IL-6) was also observed in the high C4A copy number group (P corr ‫؍‬ 0.037). No effect of C4 copy number variation on the expression of T cell activation markers was detected.Conclusion. Our findings indicate that a high copy number of C4A confers risk for BD by modulating the expression of C4A and enhancing IL-6 production.

Genetic Variations of IL17F and IL23A Show Associations with Behçet’s Disease and Vogt-Koyanagi-Harada Syndrome

“…In addition to the association of IL17F and IL23A with uveitis, many other genes are shown to be associated with uveitis, such as CNVs in complement component 4 13,25 and polymorphisms in HLA, 23,26,27 IL23R, 23 STAT4, 27,28 CCR1-CCR3, 29 UBAC2, 30 SUMO4, 31,32 and PDGFRL. 33 Additionally, although the actual number of BD patients in our study is barely higher than the number of controls in the more than 2 copies group of IL17F, the significant difference of the frequency of having more than 2 copies for IL17F and the relatively low frequency of IL17F cases with more than 2 copies between BD patients and controls (9.75% vs. 4.65%) led to the high P value.…”

“…Evidence is accumulating that CNVs have phenotypic consequences and play important roles in human diseases, including BD, 12,13 systemic lupus erythematosus (SLE), 14 and leprosy. 15 The association of CNV with Th17 cellrelated genes recently was addressed in patients with SLE.…”

Association of T-Bet, GATA-3, RORC, and FOXP3 Copy Number Variations With Acute Anterior Uveitis With or Without Ankylosing Spondylitis in Chinese Han

“…Gene copy number variations have been shown earlier to affect the predisposition to a variety of diseases and our study expands earlier observations concerning the association of CNVs with uveitis including IL-17F, IL-23A, and complement component C4. 46 Interestingly, an earlier study on the association of CNVs with other types of uveitis, such as VKH syndrome and BD, observed that high CNVs of RORC predispose to BD. 44 This discrepancy with AAU, where no effect of RORC could be shown, may be due to the different mechanisms involved in the pathogenesis of these uveitis entities.…”

Molecular Genetic Advances in Uveitis

“…A high copy number of C4 was positively associated with the expression level of C4A and the production of IL-6. 15 However, another study showed that the expression of total C4 in serum was significantly decreased in patients with VKH when compared with controls. CNV analysis showed a significantly decreased frequency of more than two copies of C4A or more than four copies of total C4 in VKH patients relative to controls.…”

“…Recent studies showed that total serum complement component 4 (C4) level was increased in patients with active BD as compared with controls, but not in AAU patients. 15 Copy number variation analysis identified a significant association between the presence of more than two copies of C4A with BD. While HLA-B51, which is located on the same chromosome as C4, also showed a strong association with BD in the Chinese Han population, logistic regression showed that the C4A copy number variation was an independent risk factor for BD from HLA-B51.…”