Hormones related to lipid and glucose metabolism, including adipokines (leptin, resistin, and adiponectin) and fibroblast growth factor 21 (FGF21), can be biomarkers for NAFLD, but with low specificity since they are also associated with other disorders, including MetS.56 Serum biomarkers are easy to measure, but their low specificity and sensitivity have limited their wide application. This evidence concerns the gene RETN and metabolic syndrome.