MTOR and obesity due to melanocortin 4 receptor deficiency: The potential relevance of this mechanism in the context of obesity is outlined by the fact that plasma amino acid accumulation and mTOR activation has previously been detected in obese humans and in vivo animal models of obesity (Felig et al., 1969, Newgard et al., 2009, Tremblay et al., 2007, Wang et al., 2011).