Definition:

Neutropenias represents a series of potentially life-threatening disorders characterised by a reduction in circulating neutrophils. Since neutrophils play a major role in host defense against bacteria, neutropenia patients suffer from frequent episodes of opportunistic bacterial infections. Severe congenital neutropenia (SCN) is a rare neutropenia with a bone marrow maturation arrest of granulocytic differentiation. Kostmann syndrome is an autosomal recessive SCN. The characteristic maturation arrest and the lack of mature neutrophils in peripheral blood of patients with Kostmann syndrome can be explained by the deletion of an anti-apoptotic factor (HAX-1) in myeloid cells of these patients. Heterozygous mutations in the protooncogene growth factor-independent 1 (GFI1) gene are also associated with SCN. In patients with autosomal dominant cyclic neutropenia (CyN), a condition with oscillating neutrophil counts but less severe clinical symptoms, heterozygous mutations in ELA-2/ELANE were discovered. Patients with X-linked severe congenital neutropenia (SCN) have been reported with activating mutations in Wiskott-Aldrich syndrome protein (WASp) leading to a constitutively-active form of the protein, and unregulated actin polymerization.