Thalassemia is an inherited blood disorder caused by a defect in a gene. The condition causes the body to produce abnormal hemoglobin, which in turn causes anemia. Symptoms include weakness, fatigue, feeling faint, dark urine, and more. After a diagnosis is made, your doctor may treat thalassemia with folic acid, blood transfusions, or other treatments. Follow the links below to find WebMD's comprehensive coverage about how thalassemia is caused, how to treat it, and much more.