Study Of A Novel And Potential Susceptibility Gene To Crohn’s Disease In A Chinese Family By Exome Sequencing And Bioinformatics Methods

Objective Genetic variants make some contributions to inflammatory bowel disease (IBD). including Crohn’s disease (CD) and ulcerative colitis (UC). More than100susceptibility loci were identified in Western IBD studies, but susceptibility gene has not been found in Chinese IBD patients till now. We aimed to describe the clinical characteristics and epidemiologic features of10IBD patients in4Han Chinese families, and explore environmental and genetic risk factors. We focused on a Han Chinese CD family, to identify high-risk variants and potentially novel loci using whole exome sequencing technique.Methods Pedigrees of4IBD families were analyzed. Clinical characteristics of lOfamilial subjects were compared with general Chinese IBD and western familial patients. Risk factors of IBD were evaluated.7reported mutations (IL10RAThr84Ile、 IL10RAGly141Arg、IL10RBTrp159X、XIAPCyS203Tyr、NOD2Arg702Trp NOD2Gly908Arg、NOD2Leu1007fsinsC) in Caucasian population were tested by Sanger sequencing on101BD patients. Exome sequence data from4familial individuals were analyzed using bioinformatics methods to narrow down the variants associated with CD. The potential risk genes were further analyzed by genotyping and Sanger sequencing in additional401healthy controls (HC),278sporadic CD patients,123UC cases, a pair of monozygotic CD twins and another Han Chinese CD family.Results8CD patients were found in3families, and other2UC sisters were belonging to a same family. The ratio of patients with IBD family history at our centre was1.25%. The median age at onset (CD29, UC35.5years) or diagnosis (CD29.6, UC37years) was relatively young. Siblings had a high concordance for phenotype. The prevalence of extraintestinal manifestations and complications of IBD and surgical interventions were comparatively less. Immigration was a significant risk factor of IBD (OR4.667, P=0.021). Neither of10familial patients carried any of7reported mutations. From the CD family in which the father and daughter were affected, we identified a novel single nucleotide variant (SNV) c.374T>C (p.1125T) in exon4of discs large homolog1(DLG1), a gene has been reported to play mutiple roles in cell proliferation, T cell polarity and T cell receptor signaling. We found that only one sporadic CD case and no HC carried this variant. By examining all of the exons of DLG1in25young and intractable CD patients, we found two cases who carried another variant in DLG1(exon9, c.833G>A. p.R278Q). We traced these two cases and their families, and found that two cousin sisters and one brother (Case CJ4) of Case4unexpectedly had ulcers identified at the terminal ileum by endoscopy. and a biopsy showed non-specific chronic inflammation. Cases CJ2, CJ3and CJ4were all confirmed to be carriers of mutation R278Q (c.833G>A) by Sanger sequencing. We found4unaffected carriers (CJ5, CJ6, CJ7and CJ8) of this variant after sequencing the other15members of family B. Neither of the monozygotic CD twins or UC sisters carried any mutation in all25exons of DLG1.Conclusions Commonalities and differences both exist between4Chinese IBD families and the western population. A pattern of polygenetic or multifactorial inheritance and autosomal recessive inheritance maybe contribute in Chinese IBD families. Environmental factor of a stressful life event was probably a significant risk factor of IBD. We have discovered novel genetic variants in the coding regions of DLG1gene, the results support that DLG1is a novel potential susceptibility gene for CD in Chinese patients.