Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Alpha-thalassemia ?
    ### Response:
    Alpha-thalassemia is a blood disorder that reduces the body's production of hemoglobin. Affected people have anemia, which can cause pale skin, weakness, fatigue, and more serious complications. Two types of alpha-thalassemia can cause health problems: the more severe type is known as Hb Bart syndrome; the milder form is called HbH disease.
    