SYT4 and obesity due to melanocortin 4 receptor deficiency: In accordance with these observations, mice modified genetically to have a reduced PVN oxy signaling, such as single-minded 1 gene (SIM1) haploinsufficient mice (Xi et al., 2012) or synaptotagmin 4 (SYT4) null mice (Zhang et al., 2011), are characterized by a reduction in energy expenditure, hyperphagia and obesity.