| A severe form of alpha-thalassemia that is mostly lethal, and associated with severe long-term outcome and lifelong transfusions in survivors. It is characterized by fetal onset of generalized edema, pleural and pericardial effusions, and severe hypochromic anemia. Caused by deletion or inactivation of all four alpha-globin alleles leading to a severe deficiency in alpha-globin chains of Hb, and to the production of gamma-4 tetramers (Hb Bart's) during fetal life, and beta-4 tetramers (HbH) postnatally. Hb Bart's and HbH have increased oxygen affinity resulting in ineffective tissue oxygen delivery. The disease is mostly the result of combined, biallelic deletions in the HBA1 and HBA2 genes (16p13.3). The pattern of inheritance is autosomal recessive. |
