Figure 1. The genetic basis of VEO IBD.

A schematic diagram illustrating the contributions to the development of IBD. Environmental effects are most pronounced in polygenic disease where the effect size of any individual gene is low and collectively, the genetic contribution to disease is less than what is seen for single gene causality. Environment and microbiome are nearly always a contribution, in the monogenic cases of VEO IBD, their relative contribution is less than what is seen in polygenic disease. Age of onset somewhat tracks with single gene causality but increasingly adults are being recognized with significant inborn errors of immunity causing IBD.