Correlation between the stage and severity of neutrophil development impairment and responsiveness to G-CSF therapy. SCN1 and SCN3, which display a severe maturation arrest at an early stage (between promyelocyte and myelocyte) during BM neutrophil development, show a poor response to G-CSF. CyN, WHIM, and SBDS, where BM neutrophil development is disrupted at a late stage, unaffected, or partially interrupted, respond well to G-CSF therapy. An ‘×’ indicates a developmental block or migration defect; The line thickness reflects the degree of normal neutrophil development.