The human alpha gene is found on the short arm of chromosome 16 and there are two hemoglobin alpha chain genes, HBA1 and HBA2. Almost all alpha thalassemias result from a loss of one or more of the alpha genes; the more genes dropped, the more severe is the disease. Unlike Beta-thalssemia, which is found around the Mediterranean, alpha-thalassemias is more geographically widespread and can be found in the descendents of people from Africa and Asia, as well as the Mediterranean. . Molecular genetic testing of HBA1 and HBA2 detects loss of genes in about 90% and point mutations inside a gene in about 10% of affected individuals.
Testing is indicated for:
•Patients with symptoms of alpha-thalassemia or anemia with smaller read cell size.
•Family members of an affected patient who are at risk to be carriers of alpha-thalassemia.
•Carrier screening for individuals of Asian, African, and Mediterranean background.
Individuals with beta thalassssemia trait rarely have anemia and another coexistent gemoglobin mutation should be looked for, if anemia is present. Workup consists of laboratory evaluation, especially CBC, hemoglobin electrophoresis, and genetic testing.
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