The increased level of ROS and NO in the first-order neurons into arcuate nucleus, and the aberrant functioning of orexigenic Agouti-related protein (AgRP)/Neuropeptide Y (NPY), anorexigenic pro-opiomelanocortin (POMC)/cocaine- and amphetamine-regulated transcript (CART) can lead to obesity. The gene discussed is NPY; the disease is obesity due to melanocortin 4 receptor deficiency.