NNMT and obesity due to melanocortin 4 receptor deficiency: The NNMT pathway has been linked to lifespan and aging [66–69], to sirtuin protein stabilization in positive a feedback loop to the pathway in Fig. 6b involved in energy regulation and obesity [52, 70, 71] and to epigenetics in cancer and stem cell status [52, 72–74] (reviewed by [75]).