Low OPG expression, elevated OPG expression (in the presence of low RANKL), and a low OPG/RANKL ratio have been associated with post-menopausal osteoporosis [64] and fragility fractures; elevated OPG has also been associated with atherosclerosis [65], coronary artery disease [66], heart failure [67], microvascular changes in diabetes mellitus and chronic kidney disease [68,69], and primary biliary cirrhosis [70]. The gene discussed is TNFSF11; the disease is osteoporosis.