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Thalassemia

Can it be prevented in your next child?

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What is thalassemia?

Thalassemia is an inherited blood disorder that causes mild or severe anemia. The anemia is due to reduced hemoglobin and fewer red blood cells than normal. Hemoglobin is the protein in red blood cells that carries oxygen to all parts of the body.

In people with thalassemia, the genes that code for hemoglobin are missing or variant (different than the normal genes). Severe forms of thalassemia are usually diagnosed in early childhood and are lifelong conditions.

The two main types of thalassemia, alpha and beta, are named for the two protein chains that make up normal hemoglobin. The genes for each type of thalassemia are passed from parents to their children. Alpha and beta thalassemias have both mild and severe forms.

Alpha thalassemia occurs when one or more of the four genes needed for making the alpha globin chain of hemoglobin are variant or missing. Moderate to severe anemia results when more than two genes are affected. The most severe form of alpha thalassemia is known as alpha thalassemia major. It can result in miscarriage.

Beta thalassemia occurs when one or both of the two genes needed for making the beta globin chain of hemoglobin are variant. The severity of illness depends on whether one or both genes are affected and the nature of the abnormality. If both genes are affected, anemia can range from moderate to severe. The severe form of beta thalassemia is also known as Cooley's anemia.

 20081016103515_thalassemia_blood     20081016103515_thalassemia_beta 
 Normal red blood cells  Beta thalassemia
 

What is the chance of being thalassemia carrier?

Unfortunately, thalassemia is a lot more common than most people think, especially in parts of South East Asia including Thailand. Up to 40% of Thais will be a carrier of a thalassemia trait or of HbE. Carrier rates are also high in people from some other ethnic groups, for example the Mediterranean, while the carrier rate is much lower in other ethnic groups. For example a thalassemia gene is found in only 1 in 1000 people from Northern Europe. Just over 1% of Thai couples will have a child affected by thalassemia

20081016103515_carriers

If you have a family history of thalassemia, the chance that you are a carrier will be higher. However, some children born with thalassemia do not have a family history of the disease.

When two carriers of beta thalassemia have a child, there is a 1 in 4 chance (25%) their child will have thalassemia, a 1 in 2 chance (50%) that their child will be a carrier like them, and a 1 in 4 chance the child will have normal genes. See diagram.

It follows that just because a couple has had one or more non-thalassemia children. It does not mean that they are not carriers of a thalassemia gene and that future children will not be affected.

Thalassemia may be curable by stem cell or bone marrow transplantation, but it is preventable by screening and PGD

The key to preventing thalassemia lies in genetic screening and the first step is quick and simple. From a blood sample, scientists can determine if you are a thalassemia carrier.

For any untested Thai couple without a family history of thalassemia, the risk of carrying a thalassemia gene error is about 40% for each person or about 16% for both of the couple. The chance of having an affected child is about 1 in 100. Screening can help to more accurately assess your risk. We think it is important for you to have the option for testing if you are considering a pregnancy.

If a thalassemia mutation is identified, your doctor will discuss with you the risk of having a baby with thalassemia, and may arrange for you to have genetic counseling. Because the thalassemia gene is inherited, your blood relatives will have a high chance of also carrying the gene error. Your relatives may also want to have thalassemia screening.

In the case where both parents test positive as thalassemia carriers, there are several options. Couples can have a baby naturally and take the risk of having an affected child, couples can have prenatal testing at around 12-14 weeks of pregnancy and choose to terminate the pregnancy if foetus is affected, or couples can have PGD, preimplantation genetic diagnosis, and transfer an embryo not affected by thalassemia.


References

US Department of Health and Human Services (Dec 07).

Dr. Nancy Ferguson

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