MECOM is a transcription factor that plays critical roles in hematopoietic development and endothelial cell specification. The protein functions as a key regulator of hematopoietic stem cell (HSC) maintenance by binding to regulatory enhancers that control expression of genes essential for HSC self-renewal 1. MECOM serves as a signature marker distinguishing HSCs from progenitors throughout human gestation, with the HSC signature including RUNX1+HOXA9+MLLT3+MECOM+HLF+SPINK2+ 2. In endothelial lineage specification, MECOM acts as a leading regulator, with MECOM-positive cells being exclusively enriched in bona fide endothelial cell clusters 3. The protein regulates endothelial cell identity genes through chr3 loop formation and targets the VEGF signaling pathway 3. Additionally, MECOM functions as a transcription factor in heart valve cell differentiation and limb development, influencing fingerprint patterning 45. Clinically, MECOM deficiency causes a severe inherited bone marrow failure syndrome with early-onset pancytopenia, B-cell lymphopenia, and hypogammaglobulinemia 1. Patients may also present with extra-hematopoietic manifestations including skeletal, cardiac, and renal anomalies 16. The severity ranges from isolated thrombocytopenia to life-threatening bone marrow failure requiring HSC transplantation for survival 16.