Which of the following types of anemia is characterized by a defect in the synthesis of the globin chains of hemoglobin, leading to a buildup of alpha-globin chains?

Alpha-thalassemia major, also known as Hb Bart's hydrops fetalis, is a severe form of thalassemia characterized by a defect in the synthesis of the alpha-globin chains of hemoglobin. This leads to a buildup of gamma-globin chains (in fetal life) or beta-globin chains (in adult life), resulting in severe anemia and other complications.