Reticular dysgenesis associates AR T-B-NK- SCID and severe congenital neutropenia (arrest of myeloid maturation at the promyelocyte stage) with total leukocytes < 400/μL ("aleukocytosis"), fatal neonatal sepsis, no response to granulocyte colony-stimulating factor (G-CSF), and severe sensorineural deafness in babies surviving after successful HSCT. Here, CSF3 is linked to severe congenital neutropenia.