Table 2 Noteworthy novel candidate genes

ATG9A : ATG9A encodes autophagy related protein 9A. Autophagy plays an import role in host defense by eliminating pathogens. ATG-family member ATG16L1 has previously been associated with Crohn’s disease [29].

BATF : Basic leucine zipper transcription factor ATF-like (BATF) belongs to the activator protein 1 family that is involved in transcription regulation in all immune cells. Batf-deficient mice do not develop Th17 cells and do not produce IL17. Furthermore, BATF regulates cell type specific gene expression in Th2 cells, germinal center B-cells, and T-follicular helper cells [30].

CD46/CD55 : CD46 (also known as MCP) and CD55 (also known as DAF) are regulatory proteins expressed on surface membranes. These proteins protect the host from autologous complement-mediated injury upon activation of the complement cascade. Daf-deficient mice show increased epithelial damage upon induction of colitis, delayed healing, and elevated expression of proinflammatory cytokines [31].

IL10RA : The IL10-receptor consists of the two subunits IL10RA and IL10RB. Sequence variants in genes encoding these two subunits are known to cause severe very early onset IBD in a monogenic fashion [32]. While the association of IL10RB with the complex form of IBD was reported by GWASs, the link with IL10RA was so far missing.

SMAD5: SMAD5 is a downstream effector in BMP signaling. SMAD5 expression was found to be downregulated in intestinal cells of IBD patients. Furthermore, conditional depletion of Smad5 in mice results in increased susceptibility for development of colitis upon DSS-induction (dextran sulfate sodium) [34].