MTOR and obesity due to melanocortin 4 receptor deficiency: Although global deletion of mTOR, Raptor, and Rictor results in embryonic lethality, cell-specific deletion strategies show that mTOR is implicated in the pathogenesis of various diseases, including cancer, obesity, and cardiovascular disease (Murakami et al., 2004; Guertin et al., 2006; Shiota et al., 2006).