Thalassemia Alpha is a blood disorder that reduces the production of hemoglobin. Hemoglobin is the protein in red blood cells that carries oxygen to cells throughout the body.
In people with the characteristics of thalassemia alpha, the reduced amount of hemoglobin prevents enough oxygen from reaching the tissues of the body. Affected individuals also experience a shortage of red blood cells (anemia), which can lead to pale skin, weakness, fatigue and more serious complications.
There are two types of thalassemia alpha that can cause health problems. The more severe type is known as hemoglobin Bart's fetal edema syndrome, also known as hemoglobin Bart's syndrome or thalassemia alpha major. The milder type is known as HbH disease.
Hb Bart syndrome is characterized by hydrops fetalis, a condition in which excess fluid accumulates in the body before birth. Other signs and symptoms may include severe anemia, enlargement of the liver and spleen (hepatosplenomegaly), heart defects, and abnormalities of the urinary system or genitalia. Because of these serious health problems, most babies with this disorder are stillborn or die shortly after birth.Hb Bart syndrome may also cause serious complications during a woman's pregnancy, including dangerously high blood pressure with swelling (preeclampsia), preterm labor, and abnormal bleeding.
HbH disease causes mild to moderate anemia, enlargement of the liver and spleen, and yellowing of the eyes and skin (jaundice). Some affected individuals also develop skeletal changes such as an overgrown maxilla and an abnormally prominent forehead. features of HbH disease usually appear in early childhood, and affected individuals usually live into adulthood.
What is the probability of having thalassemia alpha?
Thalassemia alpha is a fairly common blood disorder worldwide. Thousands of infants with Hb Bart syndrome and HbH disease are born each year, particularly in Southeast Asia. Alpha thalassemia also occurs frequently in people from Mediterranean countries, Africa, the Middle East, India, and Central Asia.
What are the causes of thalassemia alpha?
Thalassemia alpha typically results from deletions involving the HBA1 and HBA2 genes. Both of these genes provide instructions for making a protein called alpha-globin, which is a component (subunit) of hemoglobin.
People have two copies of the HBA1 gene and two copies of the HBA2 gene in each cell. Each copy is called an allele. For each gene, one allele is inherited from a person's father, and the other is inherited from a person's mother. As a result, there are four alleles that produce alpha-globin. The different types of thalassemia alpha result from the loss of some or all of these alleles.
Hb Bart syndrome, the most severe form of thalassemia alpha, results from the loss of all four alpha-globin alleles. HbH disease is caused by a loss of three of the four alpha-globin alleles. In these two conditions, a shortage of alpha-globin prevents cells from making normal hemoglobin. Instead, cells produce abnormal forms of hemoglobin called hemoglobin Bart (Hb Bart) or hemoglobin H (HbH). These abnormal hemoglobin molecules cannot effectively carry oxygen to the body's tissues. The substitution of Hb Bart or HbH for normal hemoglobin causes anemia and the other serious health problems associated with thalassemia alpha.
Two additional variants of thalassemia alpha are related to a reduced amount of alpha-globin. Because cells still produce some normal hemoglobin, these variants tend to cause few or no health problems. A loss of two of the four alpha-globin alleles results in thalassemia alpha trait. People with thalassemia alpha trait may have unusually small, pale red blood cells and mild anemia. A loss of one alpha-globin allele is found in thalassemia alpha silent carriers. These individuals typically have no thalassemia-related signs or symptoms.
What are the genetic causes of thalassemia alpha?
The inheritance of thalassemia alpha is complex. Each person inherits two alpha-globin alleles from each parent. If both parents are missing at least one alpha-globin allele, their children are at risk of having Hb Bart syndrome, HbH disease, or alpha thalassemia trait. The precise risk depends on how many alleles are missing and which combination of the HBA1 and HBA2 genes is affected.
What Else Should I Know About Thalassemia Alpha?
If your child has thalassemia alpha, it can be a challenge for your family to manage the medical care and the thoughts and feelings that come with the illness. It can help to find support through:
- your child's care team, especially the social worker or psychologist
- other families who have a child with thalassemia alpha
- friends and family
Help your child see the opportunities they have, not the limitations. And manage your own stress level by taking care of yourself and doing things that you enjoy.
Include siblings of the child with thalassemia alpha. Show them that they can have a role, such as keeping their sibling company during transfusions or just being there to listen.
You also can learn more about thalassemia alpha online at:
- Thalassemia.org (The Cooley's Anemia Foundation Website)
- Centers for Disease Control and Prevention (CDC)
- Thalassaemia International Federation
References
1. Alpha Thalassemia Reviewed by: Corinna L. Schultz, MD
2. Alpha thalassemia: MedlinePlus Genetics
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