Information leaflet for patients and family membersIntroduction:
Thalassemia is one of the commonest genetic disorders worldwide with 100,000 affected children born each year. Thalassemia is the name given to a group of inherited disorders caused by an abnormality in the structure of haemoglobin.
Haemoglobin is a molecule present in all red blood cells and is important for the transport of oxygen to all parts of the body. There are two main protein chains in the structure of haemoglobin named alpha and beta globin. A defect in the production of alpha globin causes alpha thalassemia. A more serious medical problem is caused by a defect in beta globin chain, which causes beta thalassemia.
What is beta thalassemia?
Beta thalassemia is the name given to an inherited disorder where the individual does not make sufficient beta globin chains and therefore has a blood disorder called a haemoglobinopathy. This is caused by a defect in the pair of genes which make beta globin chains. There are three main types:
- Beta thalassemia major: here the beta globin chains are absent or very low. Children affected by this disorder need regular blood transfusions from the age of 6-8mths.
- Beta thalassemia intermedia: these individuals are more mildly affected and have variable amounts of beta globin production. They may also require blood transfusions to maintain their haemoglobin levels but not as often as those affected with thalassemia major. They may have enlargement of spleen and liver.
- Beta thalassemia minor (thalassemia trait): also called carriers, these individuals have one copy of the normal gene and one copy with a mutation. Carriers do not suffer from any disease but may have slightly lower haemoglobin levels all their life. When two carriers marry and have children, there is a 1 in 4 chance teach time that the child may have thalassemia major.
How is it inherited?
All humans have 46 chromosomes in every cell nucleus arranged in 23 pairs. One of each pair is inherited from the mother and the other from the father. Each chromosome is like a long string of genes. A single pair of genes is responsible for making beta globin protein. If there is a fault (mutation) in both copies of the beta globin gene, the affected individual will have thalassemia major (See figure below). This is also called autosomal recessive inheritance pattern.
(figure courtesy: Contact a family, UK)
What is the treatment?
For individuals with beta thalassemia, blood transfusions, either with whole blood or more preferably with packed red cells every 2-4 weeks is necessary to keep the blood counts and overall growth at a normal level.
The problem with regular transfusions is that the body accumulates an overload of iron from the transfused haemoglobin. This extra iron can be deposited in various organs and cause side effects. To reduce the iron levels from the body, newer medicines called iron chelators are also give concomitantly to all transfusion dependent individuals.
In a small number of patients, the spleen, an abdominal organ where damaged cells are removed from circulation, may get enlarged and start working overtime also destroying normal blood cells. This is known as hypersplenism. Individuals with hypersplenism may require their spleen to be removed surgically to maintain their blood counts.
Blood for regular transfusion must also be obtained from standard laboratories to avoid any chance of a blood borne infection in these individuals. At the start of transfusion therapy, the Hepatitis B and HIV status are ascertained. In individuals who are not immune, a full course of hepatitis B immunization is advised.
In a family where one child is affected with Thalassemia major, prenatal diagnosis is possible by gene testing from 11 weeks of pregnancy. This is done by a specialist in fetal medicine by (chorion villus sampling) CVS test in the unborn baby. It is important to contact your own doctor or your nearest genetics department in early pregnancy to arrange this test.
How is it beta thalassemia diagnosed?
In an individual in whom beta thalassemia is suspected, haemoglobin levels, a full blood count and a peripheral smear are first checked. Based on these results a test called haemoglobin electrophoresis is done to check the amount of different types of haemoglobin in the blood.If the pattern is indicative of beta thalassemia, a gene test is done to confirm the diagnosis. Identification of the gene changes in an affected individual is mandatory before offering other relatives at risk a confirmatory test. In a family where an affected individual is diagnosed, all siblings, children and parental siblings must be offered a carrier test.
Is there a cure for beta thalassemia?
In a small percentage of individuals with beta thalassemia, a permanent cure may be possible by bone marrow transplantation with matched bone marrow from a donor or stem cells from an unaffected sib. More information about this can be obtained from your local haematologist or genetics specialist.
Where can I get go to get more information or testing?
Information about testing may be available though your paediatrician, haematologist or a clinical genetics specialist. For more information about the testing a couple may need in pregnancy to determine risk to offspring, you may contact:
Dr Meenakshi Bhat,
Bangalore Fetal Medicine Centre, Bangalore