Integration of genomics and transcriptomics to investigate biological pathways in very early onset IBD

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ABSTRACT The genomic contribution to the development of very early onset inflammatory bowel disease (VEO-IBD), IBD diagnosed at <6 years of age, remains understudied, yet elucidation of genetic risk factors would undoubtedly enhance our understanding of pathogenesis and suggest novel therapeutic approaches. The aggressive phenotype, often refractory to conventional therapy, early onset, and strong family history points to an enrichment of monogenic defects. Indeed, we and others have identified causal variants in VEO-IBD that has changed care for these children. Whole exome sequencing has radically changed our approach to VEO-IBD, however, it has only been successful in ~18% of cases, despite evidence highly suggestive of an underlying genetic defect. In addition, linking the identified variant to the development of the VEO-IBD phenotype remains difficult. The goal of this proposal is to widen our genetic analysis through whole genome sequencing (WGS) and leverage transcriptome modifications to enhance our capacity in identifying causal variants. Our central hypothesis is that a proportion of VEO-IBD is a monogenic disease, a subset of which will alter gene transcription, and transcriptome analysis, including single cell analysis, will allow us to more rapidly and accurately identify such mutations among the detected candidate variants. Using a novel innovative method, based on WGS, we will expand our repertoire of causal defects in VEO-IBD. We will integrate these findings with RNA-seq and scRNA-seq data, which can generate a more sensitive and specific approach to detect causal variants and characterize their mechanism of action. In addition, when WGS cannot identify a clear causal variant, RNA-seq and scRNA-seq can provide insight into the underlying disease mechanism, supporting the implication of candidate mutations. To test our central hypothesis, in Specific Aim 1 we will expand our dataset of potential causal mutations in VEO- IBD through WGS. We will validate candidate genes in additional VEO-IBD cases. In Specific Aim 2, we will test the ability of transcriptional profiling of colonic tissue and PBMCs to enhance the identification of novel causal variants of VEO-IBD. Finally, in Specific Aim 3, using scRNA sequencing, we will assess the colonic and immune cell heterogeneity and characterize genes and pathways associated with infantile onset IBD using transcriptional profiling of individual cells from colonic tissue and PBMCs. Completion of this project will result in the identification of novel genetic causes of VEO-IBD, providing a fertile source of biologic processes to pursue to better understand the basic mechanisms of disease, with the ultimate goal of translating this knowledge into improved care for children with VEO-IBD through individualized and targeted therapy.