of Genetic Terms
Definitions for genetic terms used on this page.
Learning About Thalassemia
What do we know about heredity and thalassemia?
Thalassemia is actually a group of inherited diseases of the blood that affect a person's ability to produce hemoglobin, resulting in anemia. Hemoglobin is a protein in red blood cells that carries oxygen and nutrients to cells in the body. About 100,000 babies worldwide are born with severe forms of thalassemia each year. Thalassemia occurs most frequently in people of Italian, Greek, Middle Eastern, Southern Asian and African Ancestry.
The two main types of thalassemia are called "alpha" and "beta," depending on which part of an oxygen-carrying protein in the red blood cells is lacking. Both types of thalassemia are inherited in the same manner. The disease is passed to children by parents who carry the mutated thalassemia gene. A child who inherits one mutated gene is a carrier, which is sometimes called "thalassemia trait." Most carriers lead completely normal, healthy lives.
A child who inherits two thalassemia trait genes - one from each parent - will have the disease. A child of two carriers has a 25 percent chance of receiving two trait genes and developing the disease, and a 50 percent chance of being a thalassemia trait carrier.
Most individuals with alpha thalassemia have milder forms of the disease, with varying degrees of anemia. The most severe form of alpha thalassemia, which affects mainly individuals of Southeast Asian, Chinese and Filipino ancestry, results in fetal or newborn death.
A child who inherits two copies of the mutated gene for beta thalassemia will have beta thalassemia disease. The child can have a mild form of the disease, known as thalassemia intermedia, which causes milder anemia that rarely requires transfusions.
Thalassemia Major: A Serious Disorder
The more severe form of the disease is thalassemia major, also called Cooley's Anemia. It is a serious disease that requires regular blood transfusions and extensive medical care.
Those with thalassemia major usually show symptoms within the first two years of life. They become pale and listless and have poor appetites. They grow slowly and often develop jaundice. Without treatment, the spleen, liver and heart soon become greatly enlarged. Bones become thin and brittle. Heart failure and infection are the leading causes of death among children with untreated thalassemia major.
The use of frequent blood transfusions and antibiotics has improved the outlook for children with thalassemia major. Frequent transfusions keep their hemoglobin levels near normal and prevent many of the complications of the disease. But repeated blood transfusions lead to iron overload - a buildup of iron in the body - that can damage the heart, liver and other organs. Drugs known as "iron chelators" can help rid the body of excess iron, preventing or delaying problems related to iron overload.
Thalassemia has been cured using bone marrow transplants. However, this treatment is possible only for a small minority of patients who have a suitable bone marrow donor. The transplant procedure itself is still risky and can result in death.
Gene Therapy Offers Hope for a Cure
Scientists are working to develop a gene therapy that may offer a cure for thalassemia. Such a treatment might involve inserting a normal beta globin gene (the gene that is abnormal in this disease) into the patient's stem cells, the immature bone marrow cells that are the precursors of all other cells in the blood.
Another form of gene therapy could involve using drugs or other methods to reactivate the patient's genes that produce fetal hemoglobin - the form of hemoglobin found in fetuses and newborns. Scientists hope that spurring production of fetal hemoglobin will compensate for the patient's deficiency of adult hemoglobin.
Is there a test for thalassemia?
Blood tests and family genetic studies can show whether an individual has thalassemia or is a carrier. If both parents are carriers, they may want to consult with a genetic counselor for help in deciding whether to conceive or whether to have a fetus tested for thalassemia.
Prenatal testing can be done around the 11th week of pregnancy using chorionic villi sampling (CVS). This involves removing a tiny piece of the placenta. Or, the fetus can be tested with amniocentesis around the 16th week of pregnancy. In this procedure, a needle is used to take a sample of the fluid surrounding the baby for testing.
Assisted reproductive therapy is also an option for carriers who don't want to risk giving birth to a child with thalassemia. A new technique, pre-implantation genetic diagnosis (PGD), used in conjunction with in vitro fertilization, may enable parents who have thalassemia or carry the trait to give birth to healthy babies. Embryos created in-vitro are tested for the thalassemia gene before being implanted into the mother, allowing only healthy embryos to be selected.
Current Clinical Research on Thalassemia
Currently, NHGRI is not conducting studies on thalassemia.
Other studies on thalassemia are being conducted at other research facilities or educational institutions:
- Stem Cell Transplant in Sickle Cell Disease and Thalassemia
- Stem Cell Transplant in Patients With Thalassemia
- Reduced Intensity Transplant Conditioning Regimen for Severe Thalassemia
- Iron Overload and Growth Velocity in Thalassemia and Sickle Cell Anemia
- Detection of ? Thalassemia Carriers by Red Cell Parameters Obtained From the H2 Automatic Counter
- Current NHGRI Clinical Studies
- Search ClinicalTrials.gov [clinicaltrials.gov]
- Clinical Research FAQ
Additional Resources for Thalassemia
- Thalassemia [nhlbi.nih.gov]
From the National Heart, Lung, and Blood Institute
- Thalassemia [nlm.nih.gov.gov]
From Medline Plus
- Thalassemia [nlm.nih.gov.gov]
From Medline Plus Medical Encyclopedia
- Beta thalassemia [ghr.nlm.nih.gov]
Summary FAQ from the Genetics Home Reference at the National Library of Medicine.
A comprehensive site with information on thalassemia, including detailed information about genetics and testing. Hosted by Children's Hospital and Research Center, Oakland, CA.
- Thalassemia [rarediseases.info.nih.gov]
Information from the Genetics and Rare Diseases Information Center.
- Finding Reliable Health Information Online
A listing of information and links for finding comprehensive genetics health information online.
Last Updated: December 27, 2013