HAX1 and severe congenital neutropenia: In addition, rare causes of neonatal neutropenia include severe congenital neutropenia due to gene mutations, such as ELANE, HAX1, and G6PC3 [41,42,43,44], as well as neonatal alloimmune neutropenia caused primarily by maternally derived anti-neutrophil antibodies [45,46,47,48].