The human alpha globin gene cluster located on the short arm of chromosome 16 has seven alpha like globin genes. There are two hemoglobin alpha chain genes, HBA1 and HBA2. Almost all alpha thalassemias result from deletions of one or more of the alpha genes as well as deletions of both HBA2 and HBA1. Symptoms vary greatly, depending on how many genes are affected. Unlike Beta-thalssemia, which is found around the Meditrranean, alpha-thalassemias is more geographically widespread. Molecular genetic testing of HBA1 and HBA2 detects deletions in about 90% and point mutations in about 10% of affected individuals.
Testing is indicated for:
•Patients with symptoms of alpha-thalassemia or microcytic anemia.
•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 a coexistent hemoglobinopathy should be looked for, if anemia is present. Workup consists of laboratory evaluation, especially CBC, hemoglobin electrophoresis, and genetic testing.
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