Severe congenital neutropenia (SCN) is characterized by a selective decrease in circulating neutrophils, bone marrow maturation arrest at the promyelocyte stage, and occurrence of infections. Typical infections include omphalitis, pneumonia, sinusitis and gingivitis caused by resident bacteria of the skin, mouth, and oropharynx. While all types of severe congenital neutropenia are sometimes called Kostmann disease, the extended family actually described in detail by Kostmann had a recessive disorder now known to be caused by mutations in HAX1. A recent observation is that some, but not all, HAX1 mutations are associated with neurological disorders. Mutations in HAX1 are not known to cause any type of cyclic or periodic neutropenia.