Thalassemias
Definition
Thalassemia is a group of inherited disorders which is associated with hemoglobin defects. The disorder results in excessive destruction of red blood cells leading to anemia.
Types of Thalassemia
There are two main types of Thalassemia based on the chain of hemoglobin it affects. These are the following:
- Beta Thalassemia or Cooley’s anemia – defect in the beta-chain of hemoglobin is present.
- Alpha Thalassemia – defect in the alpha-chain of hemoglobin is present.
Forms of Thalassemia
Both the alpha and beta thalassemia include the following forms:
- Major - threatening disease characterized by severe anemia, hemolysis and ineffective erythropoiesis
- Minor - a mild form of anemia. The affected individual has only one defective gene and is asymptomatic.
Incidence
Aplha thalassemias occur frequently among Southeast Asians,Middle East Asians, Chinese and Africans.
Beta Thalassemias occur frequently to those of Mediterranean origin and lesser to Chinese, other Asians and African Americans.
Review of Related Anatomy and Physiology
Red blood cells or erythrocytes carry oxygen to the different parts of the body. Different from other cells, RBC’s do not contain a nucleus (anucleated). These small cells are circular and flattened with depressed centers on both sides resembling to that of a doughnut when viewed under a microscope. Their size and shape provides a large surface area for carrying oxygen in relation to their volume. The normal RBC count is 4-6 million/mm3. RBC’s has the life span of 120 days.
Hemoglobin is a form of protein that contains iron which is responsible for transporting oxygen that is carried in blood. Adult hemoglobin contains a beta chain (HBB) while a fetus’ hemoglobin has a gamma chain. Hemoglobin is comprised of four protein (amino acid) components. It has two beta-globin and two alpha-globin. The subunit beta-globin is located inside the RBCs. These amino acids carry an iron-bearing molecule called heme. Heme molecules, which are only found in mature RBC’s, enables the erythrocytes to pick oxygen from the lungs and transport it throughout the body. Once oxygen attaches to hemoglobin it gives the blood its bright red pigment.
The more hemoglobin molecules the RBC contain, a higher amount of oxygen will they be able to carry. If the hemoglobin is defective, the erythrocyte will also malfunction. A red blood cell is just a vessel; the one that performs the oxygen transportation is the hemoglobin. Normal hemoglobin is 13-18 grams/100 ml of blood in males and 12-16 grams in females.
Pathophysiology
Risk Factors
- Family history
- Asian, Chinese, Mediterranean or African American ethnicity
Causes
- Thalassemia is an inherited disorder that follows an autosomal recessive pattern.
Thalassemias are inherited disorders of hemoglobin synthesis that result from a change in globin chain production. Beta-globin normally joins to alpha-globin component of hemoglobin. When beta-protein is lacking, alpha-globin accumulates and causes destructive membrane effects and vice versa. This leads to destruction of red blood cells. Not only that it causes membrane damage and cell destruction but it also suppresses the mitosis in stem cells, thus RBC production falls. The result of impaired hemoglobin synthesis is a microcytic, hypochromic anemia.
