PER2 and obesity due to melanocortin 4 receptor deficiency: While one study reports that mice with a Per2 gene disruption are prone to obesity (Yang et al., 2009; Grimaldi et al., 2010), a recent study using mPer2Brdm1/Rev-Erbα−/− double mutant mice suggests that the Per2 gene is involved in hepatic glucose metabolism engaging a mechanism involving nuclear receptors (Schmutz et al., 2010).