In hydrops Fetalis (or Homozygous Alpha Thalassemia) all the 4 a genes are abnormal. There is no a chain production hence no HbF production and death in utero. At autopsy the cord blood shows severe anemia, less than 60g/L. There is no HbA or HbF on electrophoresis, most of the hemoglobin is hemoglobin Bart´swhich consists of 4 gamma chains.
The classic alpha-thalassemia clinical syndromes studied extensively in Southeast Asians include hydrops fetalis due to homozygous alpha-thalassemia, hemoglobin H disease, alpha-thalassemia trait, and the silent carrier form of alpha- thalassemia.