Hemoglobin, alpha 2

The human alpha globin gene cluster is located on chromosome 16 and spans about 30 kb, including seven alpha like globin genes and pseudogenes: 5'- HBZ - HBZP1 - HBM - HBAP1 - HBA2 - HBA1 - HBQ1 -3'. The HBA2 (α₂) and HBA1 (α₁) coding sequences are identical. These genes differ slightly over the 5' untranslated regions and the introns, but they differ significantly over the 3' untranslated regions.

Two alpha chains plus two beta chains constitute HbA, which in normal adult life accounts for about 97% of the total hemoglobin; alpha chains combine with delta chains to constitute HbA-2, which with HbF (fetal hemoglobin), composed of alpha and gamma chains, make up the remaining 3% of adult hemoglobin.

Alpha-thalassemias most commonly result from deletions of any of the four alpha alleles, although some alpha thalassemias have been reported that are due to mutations other than deletion. Deletion of 1 or 2 alleles is clinically silent. Deletion of 3 alleles causes HbH disease, resulting in anemia and hepatosplenomegaly. Deletion of all 4 alleles is lethal because it renders the body unable to make fetal hemoglobin (HbF), adult hemoglobin (HbA) or adult variant hemoglobin (HbA2), and results in hydrops fetalis.