JAGN1 is an endoplasmic reticulum transmembrane protein essential for neutrophil development and function 1. As part of the early secretory pathway, JAGN1 mediates vesicle-dependent transport and regulates granulocyte colony-stimulating factor (G-CSF) receptor signaling 2. The protein shares structural features with known cargo transporters and likely facilitates protein trafficking at the endoplasmic reticulum-Golgi interface 3. JAGN1 critically regulates neutrophil glycosylation, migration, and cytotoxic granule formation necessary for fungal defense 4. Biallelic JAGN1 mutations cause severe congenital neutropenia (SCN), characterized by absent or severely reduced neutrophils and recurrent infections 5. Pathologically, mutant JAGN1 triggers aberrant calcium- and calpain-dependent cell death in myeloid cells rather than apoptosis 5. SCN-associated JAGN1 mutations also cause syndromic features including facial dysmorphism, short stature, and neurodevelopmental delay 2. A zebrafish model confirmed that Jagn1 is critical for G-CSF receptor signaling and steady-state granulopoiesis 6. Clinically, granulocyte colony-stimulating factor provides partial benefit, while allogeneic hematopoietic stem cell transplantation remains the definitive treatment for therapy-refractory cases 2.