Contrary to the above mentioned experimental studies, NASH, but not NAFL, was associated with lower circulating OPG compared to non-NAFLD participants [89], whereas two subsequent case-control studies with biopsy-proven NAFLD supported a gradual decrease of serum OPG levels from controls to patients with NAFL and then to NASH patients [90, 91]. The gene discussed is TNFRSF11B; the disease is non-alcoholic fatty liver.