Multiple observational human studies have linked elevated circulating preptin to metabolic dysfunction, including reports of elevated concentrations in obesity,(14, 17) T2DM,(12) gestational diabetes mellitus,(15) and polycystic ovarian syndrome.(13, 18, 19) Direct comparisons between observational human studies are complicated, as each study uses a different ELISA or radioimmunoassay protocol. Here, IGF2 is linked to obesity due to melanocortin 4 receptor deficiency.