Association Study Of The Genetic Variants In KIF21B And9Q34.3with Ankylosing Spondylitis In Han Chinese

Ankylosing spondylitis (AS), a form of the most common arthritis known as Spondylarthropathy, is a systemic and chronic autoimmune disease. AS may involve the axial skeleton, peripheral joints, the attachments of ligaments, eye, gut, aorta and other organs and patients often suffer from symptoms of sacroiliitis, anterior uveitis, spinal inflammation, psoriasis, enthesitis, back pain and over time some patients even develop spinal immobility and ankylosis.Many previous studies focusing on the pathogenesis of AS showed that AS is associated with interactions between genetic factors and environmental factors. Twin studies have shown that the heritability of AS has been determined to be>90%. Brown’s twin studies also showed that concordance of identical twins is63%while the concordance of dizygotic twins is only12.5%. Brown also showed that the recurrence risks in different degrees of relatives in Europeans were quite different,8.2%for the first degree relative,1.0%for the second degree relatives and0.7%for the third degree relatives. The prevalence of AS is0.2-0.54%among Chinese Han population which is similar to the prevalence in Europe and America. Familial aggregation in AS provide evidence that genetic factors play a vital role in AS, therefore, it is necessary to study the pathogenesis of this disease with genetic methods.There are approximately30,000genes in the human genome. Different gene mutations may cause different diseases. Linkage studies and association studies are principal methods used to identify these genes. However, linkage studies are limited in finding the susceptibility genes of complex diseases. Association study has a variety of approaches including case-control study which analyze the variance of different genotypes in unrelated individuals.HLA-B27is the first gene identified to be involved in the susceptibility to AS. Although about90%of Caucasians with AS carry the HLA-B27gene, not more than5%of HLA-B27-positive individuals develop AS, which means additional genes must be involved. For nearly40years, AS has been considered as a multifactorial genetic disease. Linkage studies and association studies have found genes on2p,2q,3p,6p22.3-p21.1,10q,16q,17p,21q were associated with AS and together with that were two gene desert regions2p15and21q22. With the application of the NGS (Next Generation Sequencing), more and more susceptible genes have been identified.KIF21B belongs to a family of kinesin motor proteins encoded by the gene on chromosome1. Kinesins are ATP-dependent microtubule-based motor proteins that are used for the intracellular transport of membranous organelles along axonal and dendritic microtubules by neurons. SNPs in this gene are associated with not only AS, inflammatory bowel disease (IBD) but also multiple sclerosis (MS) within Caucasians. For example a SNP, rs12122721, located in an intron of KIF21B was found to be associated with MS. It is still not clear if these genes are associated with AS in a Chinese Han population. Because of the genetic heterogeneity, we replicated the association of this gene with AS in Chinese Han population.A recent genome-wide association study (GWAS) by the Wellcome Trust Case Control Consortium (WTCCC) identified an association of2non-synonymous single nucleotide polymorphisms (SNP), rs4077515and rs3812571, on9q34.3(previously linked to AS) with AS (P<4.0×10-3and P<5.0x10-3, respectively) in Caucasians. The first SNP lies in a functional candidate gene, caspase recruitment domain-containing protein9(CARD9), and the latter in an adjacent gene, small nuclear RNA-activating complex polypeptide4(SNAPC4).A replication study supported that CARD9is a plausible susceptibility gene for AS. Another GWAS by the WTCCC found strong evidence of an association for an SNP across CARD9(rs10781500; P=1.1x10-6). CARD9has a vital role in mediating the innate immune response. As well, CARD9can couple innate to adaptive immunity by modulating the Th17pathway, which was previously linked to AS pathogenesis. Considerable evidence supports some degree of overlap between AS and inflammatory bowel disease (IBD) pathogenesis, and a study validated an association of CARD9(rs1080077) and ulcerative colitis and Crohn disease. SNAPC4is the largest subunit of the SNAP complex. The role of SNAPC4in autoimmune disorders has yet to be clarified. As SNAPC4is in strong linkage disequilibrium (LD) with CARD9, it is still difficult to tell which gene is really associated with AS.The aim of the present work was to determine whether polymorphisms in the KIF21B, CARD9and SNAPC4genes already known to be associated with MS, AS in white European ancestry would also contribute to the whole AS susceptibility in the Chinese Han population.We used case-control study with665patients with AS and1042healthy controls of Chinese Han population in Shandong province to study the association. Our results showed that two SNPs rs502658(allelic P=3.1x10-5, OR=0.60,95%CI=0.47-0.76), rs10494829(allelic P=5.0x10-4, OR=1.30,95%CI=1.12-1.52) were significantly associated with AS. Of the two SNPs rs502658and rs10494829a haplotype AT was strongly associated with AS and increased the risk of AS (χ2=4.013, P=0.045, OR=1.183,95%CI=1.004-1.395), while another genotype GC reduced the risk of AS (χ2=6.39, P=0.011, OR=0.715,95%CI=0.55-0.928).Our study focused on9q34.3containing SNAPC4and CARD9within1150patients with AS and1120healthy controls of Chinese Han population in Shandong province showed that rs3812555(P=6.0x10-3) in the CARD9,rs3812571(P=5.0×10-3) and rs11145835(P=1.0x10-3) in the SNAPC4were significantly associated with AS in our Chinese Han population. We replicatedthe results with490AS samples and380healthy controls from Ningxia Han Chinese and confirmed the association of rs11145835(P=2.0x10-3). RT-PCR results showed that AS patients had a lower expression of SNAPC4compared with controls. Individuals carrying the G allele of rs11145835was associated with increased risk of AS (OR=1.34,95%CI=1.12-1,59) and with decreased expression of CARD9(P=1.0×10-3) and SNAPC4(P=0.02) in leukocytes. Patients carrying the G allele of rs11145838had a lower expression of CARD9(P=1.0×10-3) and SNAPC4(P=0.02) compared with patients carrying the A allele, which meant that this SNP might be a functional variant.In summary, using case-control study conbining with gene expression analysis, we identified significant associations between KIF21B,9q34.3and AS in Chinese Han population. KIF21B, CARD9and SNAPC4genes may play an important role in the pathogenesis of AS in the Chinese population and it might be a new therapeutic target molecule for AS.