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.

The HAX1 gene was mapped to chromosome 1q21.3; it consists of seven coding exons and encodes a 279 amino acid protein, with a molecular weight of 35 kDa.  This gene has two alternatively spliced transcript variants.  More than 10 different mutations have been identified in the HAX1 gene in patients with severe congenital neutropenia.  These mutations result in a nonfunctional protein that leads to the premature death of neutrophils.