Neutropenia or neutropaenia is an abnormally low concentration of neutrophils (a type of white blood cell) in the blood. Neutrophils make up the majority of circulating white blood cells and serve as the primary defense against infections by destroying bacteria, bacterial fragments and immunoglobulin-bound viruses in the blood. People with neutropenia are more susceptible to bacterial infections and, without prompt medical attention, the condition may become life-threatening (neutropenic sepsis).Neutropenia can be divided into congenital and acquired, with severe congenital neutropenia (SCN) and cyclic neutropenia being autosomal dominant and mostly caused by heterzygous mutations in the ELANE gene (neutrophil elastase). Neutropenia can be acute (temporary) or chronic (long lasting). The term is sometimes used interchangeably with "leukopenia" ("deficit in the number of white blood cells").