Alternative Names
Alpha-thal; Hemoglobin H disease; Hydrops fetalis; Alpha-thalassmia (Major or Minor); Hemoglobin H - Constant Spring; Hemoglobinopathy
Symptoms & Characteristics
Thalassemia is a genetic condition that involves abnormalities in hemoglobin (the molecule in red blood cells that transports oxygen throughout the body) which may lead to an ineffective production or increased destruction of red blood cells as well as reduced oxygen transport. Hemoglobin is mostly made up of two types of proteins (or chains), called alpha and beta globin. Defects in these proteins cause alpha-thalassemia and beta-thalassemia, respectively.
There are (at least) five main types of alpha-thalassemia with symptoms that range from mild to severe. Alpha-globin is produced by four genes, two genes from each parent. The severity of the condition correlates with how many of the four genes are damaged or missing. Here are the five main types:
- Silent carrier is when a person has one damaged (or missing) alpha-globin gene and is a carrier. These people typically do not have any symptoms.
- Alpha-thalassemia minor is when a person has two damaged (or missing) alpha-globin genes and is a carrier. These people typically do not have any major health problems, but may have mild anemia.
- Hemoglobin H disease is when a person has three damaged (or missing) alpha-globin genes. Affected people typically have mild to moderate anemia and regular treatment is needed.
- Hemoglobin H - Constant Spring is when a person has three damaged (or missing) alpha-globin genes, one of which has a specific mutation called Constant Spring. Affected people typically have moderate to severe anemia and often develop complications. Regular treatment is needed.
- Alpha-thalassemia major is when a person has four damaged (or missing) alpha-globin genes. Affected fetuses typically have severe anemia, heart failure, and a buildup of fluid (edema) in the body (called hydrops fetalis). They usually are stillborn or pass away within the first couple of hours of life.
Management & Treatment
In some types of alpha-thalassemia, early diagnosis, routine surveillance, and treatment may help to manage some of the symptoms and sometimes prevent related problems. Alpha-thalassemia major currently has no effective treatment.
How Common Is It?
Alpha-thalassemia is most common in people of Southeast Asian, Indian, southern Chinese, Middle Eastern and African ancestry.
Genetics & Inheritance
Alpha-thalassemia is caused by mutations in the alpha-globin gene cluster on the chromosome 16 at the location pter-p13.3.
As discussed previously, the severity of the condition increases with the number of damaged (or missing) genes. People with one or two damaged genes are carriers, while people with three or four damaged genes are affected. Alpha-thalassemia has autosomal recessive inheritance.
- Both parents of an affected person are always obligate carriers of one or two damaged genes.
- The odds of having an affected child will depend on how many damaged genes each parent has and if the damaged genes are located on the same chromosome (called in cis) or on separate chromosomes (called in trans).
- Without a family history, the chance to be a carrier is determined by a person's ethnic background. For example, about 1 in 20 people of Southeast Asian descent have alpha-thalassemia minor.
There are many genetic and non-genetic conditions, which have symptoms that overlap with alpha-thalassemia. As such, a genetic consultation with a trained genetic professional may be beneficial for a complete evaluation and accurate diagnosis.
Genetic Testing
Clinical genetic testing for alpha-thalassemia can be broken down into two categories: diagnostic testing and carrier testing.
- Diagnostic testing may be used to confirm or rule out a diagnosis in a person suspected to have alpha-thalassemia.
- Carrier testing for alpha-thalassemia is available for people of high-risk ethnic groups.
Clinical genetic testing for alpha-thalassmia is available through genetic consultation. A trained genetic professional can discuss the benefits and limitations of genetic testing, coordinate testing and interpret results in the context of personal and family medical history.
- A board-certified genetic counselor is available by telephone.
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