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.
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.
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.