Nicotinamide phosphoribosyltransferase (NAMPT), also known as pre-B-cell colony-enhancing factor 1 (PBEF1) or visfatin, is an enzyme belonging to the family of glycosyltransferases, to be specific, the pentosyltransferases. This enzyme participates in nicotinate and nicotinamide metabolism. This enzyme catalyzes the condensation of nicotinamide with 5- phosphoribosyl-1- pyrophosphate to yield nicotinamide mononucleotide, one step in the biosynthesis of nicotinamide adenine dinucleotide. NAMPT is also considered as an essential enzyme mediating granulocyte colony-stimulating factor (G-CSF)-triggered granulopoiesis in healthy individuals and individuals with severe congenital neutropenia. Intracellular NAMPT and NAD+ amounts in myeloid cells, as well as plasma NAMPT and NAD+ levels, were increased by G-CSF treatment of both healthy volunteers and individuals with congenital neutropenia.