The HAX1 gene encodes a protein called HS-1-associated protein X-1 (HAX-1) that is mainly localized in the mitochondria with a ubiquitous expression. The HAX-1 protein plays a role in neutrophil-specific apoptosis, promotes cell survival and potentiates cell migration. Defects in this protein have been associated with severe congenital neutropenia, a disease characterized by abnormally low levels of neutrophils (neutropenia), and onset of severe bacterial infections.