Any given individual has two β globin alleles:
| Name |
Description |
Alleles |
|---|
| β thalassemia minor (sometimes called β thalassemia trait) |
If only ''one'' β globin allele bears a mutation. This is a mild microcytic anemia. Detection usually involves measuring the mean corpuscular volume (size of red blood cells) and noticing a slightly decreased mean volume than normal. The patient will have an increased fraction of Hemoglobin A2 (>3.5%) and a decreased fraction of Hemoglobin A (<97.5%). |
β+/β or βo/β |
| Thalassemia intermedia | A condition intermediate between the major and minor forms. Affected individuals can often manage a normal life but may need occasional transfusions e.g. at times of illness or pregnancy, depending on the severity of their anemia. | β+/β+ or βo/β |
| β thalassemia major or Cooley's anemia |
If ''both'' alleles have thalassemia mutations. This is a severe microcytic, hypochromic anemia. Untreated, it causes anaemia, splenomegaly and severe bone deformities. It progresses to death before age twenty. Treatment consists of periodic blood transfusion; splenectomy if splenomegaly is present, and treatment of transfusion-caused iron overload. Cure is possible by bone marrow transplantation. Cooley's anemia is named after Thomas Benton Cooley. |
β+/βo or βo/βo |
Note that βo/β can be associated with β thalassemia minor or β thalassemia intermedia.
The genetic mutations present in β thalassemias are very diverse, and a number of different mutations can cause reduced or absent β globin synthesis. Two major groups of mutations can be distinguished:
- Nondeletion forms: These defects generally involve a single base substitution or small deletion or inserts near or upstream of the β globin gene. Most commonly, mutations occur in the promoter regions preceding the beta-globin genes. Less often, abnormal splice variants are believed to contribute to the disease.
- Deletion forms: Deletions of different sizes involving the β globin gene produce different syndromes such as (βo) or hereditary persistence of fetal hemoglobin syndromes.
Further Reading
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"Beta-thalassemia"
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