MC4R and obesity due to melanocortin 4 receptor deficiency: In particular, double knockout of synapse-associated protein 90/postsynaptic density-95-associated protein-3 (Sapap3), a key gene involved in anxiety-like behaviors, and Mc4r, one of the most frequent obesogenic genes in humans, completely rescues anxiety-like behaviors seen in Sapap3 knockouts and obesity in Mc4r knockouts (Xu et al., 2013), demonstrating an intimate interaction between the two seemingly unrelated genes.