Hemoglobin, alpha 2
also known as HBA2 is a
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
that in humans codes for the alpha globin chain of
hemoglobin
Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...
.
Function
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
Hemoglobin subunit alpha, Hemoglobin, alpha 1, is a hemoglobin protein that in humans is encoded by the ''HBA1'' gene.
Gene
The human alpha globin gene cluster located on chromosome 16 spans about 30 kb and includes seven loci: 5'- zeta - pseu ...
-
HBQ1 -3'. The HBA2 (α
2) and
HBA1
Hemoglobin subunit alpha, Hemoglobin, alpha 1, is a hemoglobin protein that in humans is encoded by the ''HBA1'' gene.
Gene
The human alpha globin gene cluster located on chromosome 16 spans about 30 kb and includes seven loci: 5'- zeta - pseu ...
(α
1) 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.
Protein
Two alpha chains plus two beta chains constitute HbA, which in normal adult life comprises about 97% of the total
hemoglobin
Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...
; alpha chains combine with delta chains to constitute
HbA-2, which with
HbF (fetal hemoglobin) makes up the remaining 3% of adult hemoglobin.
Clinical significance
Alpha-thalassemia
Alpha-thalassemia (α-thalassemia, α-thalassaemia) is a form of thalassemia involving the genes '' HBA1'' and '' HBA2''. Thalassemias are a group of inherited blood conditions which result in the impaired production of hemoglobin, the molecule ...
s 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
Hydrops foetalis or hydrops fetalis is a condition in the fetus characterized by an accumulation of fluid, or edema, in at least two fetal compartments. By comparison, hydrops allantois or hydrops amnion is an accumulation of excessive fluid in ...
.
References
Further reading
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External links
GeneReviews/NCBI/NIH/UW entry on Alpha-Thalassemia OMIM entries on Alpha-Thalassemia
{{Hemeproteins
Hemoglobins