NNMT and obesity due to melanocortin 4 receptor deficiency: Perturbations of polyamine synthesis have been linked to changes in adiposity (Jell et al. 2007; Pirinen et al. 2007), and mice expressing reduced levels of nicotinamide N-methyltransferase (NNMT), which influences polyamine synthesis, are obesity-resistant (Kraus et al. 2014).