HAX1 and severe congenital neutropenia: Familial forms of SCN or CN are caused by mutations within the neutrophil elastase (ELANE), growth factor independence 1 transcription repressor (GFI1), HCLS1-associated protein X-1 (HAX1), glucose-6-phosphatase 3 (G6PC3), Wiskott-Aldrich syndrome protein (WAS), and vacuolar protein sorting 45 homolog (VPS45) genes [5].