NPY and obesity due to melanocortin 4 receptor deficiency: Ngn3 is a developmental regulator of energy homeostasis systems in the hypothalamus, pancreas, and intestine, whereas Pomc+ and Npy+ hypothalamic neurons shape a central microcircuitry for the integration of peripheral signals providing feedback on energy status and for the control of feeding and energy expenditure; disruptions or deficits in any of these systems have been associated with hyperphagia, obesity, and obesity-related type 2 diabetes (Yaswen et al., 1999; Gradwohl et al., 2000; Anthwal et al., 2013; Bouret, 2017; Vohra et al., 2022).