A gene located on chromosome 7p15.1 encodes a 36-amino acid protein designated NPY (Neuropeptide Y). NPY consists of a polyproline stretch followed by an amphipathic alpha-helix. NPY shares a 50% amino acid homology with pancreatic polypeptide gene (PP). The NPY hormone family consists of NPY, PP and peptide YY. NPY is expressed throughout the central and peripheral nervous system, particularly in the deep layers of the cortex and smaller cell bodies in the white matter. NPY interacts with the Y-receptor family of G-protein coupled receptors. NPY interacts with NPY receptor Y1 to increase corticotropin levels and decrease noradrenaline levels in the hypothalamus. Through interactions in the hypothalus, NPY plays important roles in the regulation of energy balance by stimulating food intake. NPY favors energy storage by increasing lipoprotein lipase activity in white adipose tissue. A leucine(7)-to- proline(7) polymorphism has been implicated in an increase in alcohol preference, and decrease in cholesterol metabolism.