Alpha-thalassemia is an inherited disorder that affects the blood's ability to carry oxygen. There are two types of alpha-thalassemia, hemoglobin H (HbH) disease and hemoglobin Bart hydrops fetalis (Hb Bart) syndrome. The milder type, HbH disease, causes moderate anemia (too few red blood cells), weakness, fatigue, spleen and liver problems, as well as characteristic bone changes in the forehead or upper jaw. Symptoms typically appear in childhood and survival is into adulthood. Some individuals with HbH disease may not require any special medical treatment and some may require regular blood transfusions. The more severe type, Hb Bart syndrome, is generally diagnosed during pregnancy because it causes fluid to build up in the body before birth. It also causes severe anemia and problems with the liver and heart. Babies with Hb Bart syndrome are stillborn or die soon after birth. Alpha-thalassemia is caused by pathogenic variants on the HBA1 and HBA2 genes.