Among them, it is worth highlighting the following: (1) SLIT3, reported in the UK Twins Dataset [40] as associated with unclassified Clostridiaceae [41], linked to MetaCyc pathways involved in plant-derived steroid degradation, and whose expression is upregulated in colon crypts during the conventionalization of germ-free mice [42]; (2) SLC39A8, a gene with a pleiotropic missense variant related with Crohn’s disease and the composition of human gut microbiome [43]; and (3) NOS1, for which a pleiotropic association with body fatness and gut microbiota composition in mice had been shown [44]. This evidence concerns the gene SLC39A8 and Crohn disease.