In which of the following disease normal structure of hemoglobin but their blood volume reduced in?

Thalassemia describes a group of inherited disorders characterized by reduced or absent amounts of hemoglobin, the oxygen-carrying protein inside the red blood cells. There are two basic groups of thalassemia disorders: alpha thalassemia and beta thalassemia. These conditions cause varying degrees of anemia, which can range from insignificant to life-threatening.Ref: Ganong&;s Review of Medical Physiology; 24th edition