Causes - Thalassemias - What Causes Thalassemias?
Your body makes three types of blood cells: red blood cells, white blood cells, and platelets (PLATE-lets). Red blood cells contain hemoglobin, an iron-rich protein that carries oxygen from your lungs to all parts of your body. Hemoglobin also carries carbon dioxide (a waste gas) from your body to your lungs, where it's exhaled.
Hemoglobin has two kinds of protein chains: alpha globin and beta globin. If your body doesn't make enough of these protein chains or they're abnormal, red blood cells won't form correctly or carry enough oxygen. Your body won't work well if your red blood cells don't make enough healthy hemoglobin.
Genes control how the body makes hemoglobin protein chains. When these genes are missing or altered, thalassemias occur.
Thalassemias are inherited disorders—that is, they're passed from parents to children through genes. People who inherit faulty hemoglobin genes from one parent but normal genes from the other are called carriers. Carriers often have no signs of illness other than mild anemia. However, they can pass the faulty genes on to their children.
People who have moderate to severe forms of thalassemia have inherited faulty genes from both parents.
You need four genes (two from each parent) to make enough alpha globin protein chains. If one or more of the genes is missing, you'll have alpha thalassemia trait or disease. This means that your body doesn't make enough alpha globin protein.
- If you're only missing one gene, you're a "silent" carrier. This means you won't have any signs of illness.
- If you're missing two genes, you have alpha thalassemia trait (also called alpha thalassemia minor). You may have mild anemia.
- If you're missing three genes, you likely have hemoglobin H disease (which a blood test can detect). This form of thalassemia causes moderate to severe anemia.
Very rarely, a baby is missing all four genes. This condition is called alpha thalassemia major or hydrops fetalis. Babies who have hydrops fetalis usually die before or shortly after birth.
Example of an Inheritance Pattern for Alpha Thalassemia
You need two genes (one from each parent) to make enough beta globin protein chains. If one or both of these genes are altered, you'll have beta thalassemia. This means that your body won’t make enough beta globin protein.
- If you have one altered gene, you're a carrier. This condition is called beta thalassemia trait or beta thalassemia minor. It causes mild anemia.
- If both genes are altered, you'll have beta thalassemia intermedia or beta thalassemia major (also called Cooley's anemia). The intermedia form of the disorder causes moderate anemia. The major form causes severe anemia.