Interestingly, OPG is also known as a biomarker for inflammatory bowel diseases (IBD), namely, Crohn’s disease and ulcerative colitis18,19; this suggests that an imbalance of RANKL–OPG may contribute to the pathogenesis of IBD by affecting gut immunity in a manner separate from its function in osteoimmunology. This evidence concerns the gene TNFRSF11B and inflammatory bowel disease.