Thalassemia is an inherited blood disorder through families in which the body makes an abnormal form of hemoglobin results in excessive destruction of red blood cells being destroyed, which leads to anemia. Thalassemia occurs when there is a defect in a gene that helps control production of one of these proteins. A blood disorder involves lower-than-normal amounts of an oxygen-carrying protein. Hemoglobin is the protein molecule in red blood cells that carries oxygen to all parts of the body. Due to a genetic mutation or missing gene, children do not produce enough of the protein in red blood cells that carries oxygen.