300 Longwood Avenue Boston, MA 02115 (617) 355-6000 Clinical Services (Thalassemia Program): Thalassemia Types There are two main types of thalassemia - "alpha" and "beta." The names refer to the part of the hemoglobin molecule that is missing or mutated. Alpha thalassemia is caused by a defect in or absence of two or more of the four "alpha" chains of the hemoglobin molecule. The alpha chains are located on chromosome 16. This type of thalassemia is divided into four categories: Silent carrier Alpha thalassemia trait "Hemoglobin H" disease Alpha thalassemia major Beta thalassemia is caused by a mutation on one or both of the two genes on the "beta" chain of the hemoglobin molecule. The beta chain is found on chromosome 11. Unlike alpha thalassemia, beta genes are usually not missing, but are mutated. The hundreds of possible mutations make beta thalassemia more diverse than alpha thalassemia. There are three main types of beta thalassemia. Beta thalassemia minor, or trait Beta thalassemia intermedia Beta thalassemia major The information on this website should not be taken as medical advice, which can only be given to you by your personal health care professional. Copyright © Children's Hospital Boston. All rights reserved.