MONDO_0015579 (Hb Bart's hydrops fetalis) is alpha thalassemia caused by variation in all four copies of the alpha hemoglobin genes (e.g., homozygous deletion encompassing HBA1 and HBA2). Also known as: Alpha-thalassemia major, HBA1;HBA2 digenic quadallelic Hb Bart’s hydrops fetalis, Haemoglobin Bart's hydrops fetalis, Hb Bart’s hydrops fetalis caused by quadallelic variation in HBA1;HBA2, Hb Bart’s hydrops fetalis related to quadallelic variation in HBA1 and HBA2, Hemoglobin Bart's hydrops fetalis, alpha-thalassemia hydrops fetalis, homozygous alpha0-thalassemia.