The pathologic galaxy modulating the genotype and phenotype of inflammatory bowel disease: comorbidity, contiguity, and genetic and epigenetic factors

Abstract

The inflammatory bowel diseases (IBDs) are being seen as a gut inflammatory hub occurring: 1) with inflammatory spots in the eyes, skin, liver, joints (extra-intestinal manifestations); 2) with functionally contiguous disorders such as psoriasis and lung disease (barrier organ diseases); 3) as the consequence of genetic loss of non-redundant cell functions that are critical for gut homeostasis and defense (monogenic IBD). Recent multidisciplinary analysis, fostered by the input of genomic search, has helped hypothesize two pathogenetic models for the main phenotypes of IBDs. In ulcerative colitis, an increased mucosal permeability would prevail, allowing arousal of inflammation from the hyper-reactive underneath lymphoid tissue; an impaired bacterial sensing by innate immunity cells would by contrast place Crohn's disease (CD) in the chapter of the immune deficiency disorders, with the activity phases (the actual target of traditional immune suppressive strategies) representing just "zenith" phases in the continuously waxing-and-waning course of the attempts of the blunted inflammatory machinery to clear the invaders. Studying such errors of innate immunity, a few open-minded investigators have observed that they might not be a CD exclusivity at all: the proven evidence of CD-like pictures in a plethora of granulomatous disorders has thus been consolidated. This scenario calls for a concept of "syndrome" to best be accounted for, and to encourage the envisaging of the future therapy for IBD.