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Expert
Reviews in Molecular Medicine: http://www.expertreviews.org/
Accession information: Vol. 8; Issue 10; 9 May 2006 Abstract
PDF
a-Thalassaemia
Fabrizia Urbinati, Catherine Madigan and Punam Malik
| Table 2. a-Thalassaemia | |||
|
Type |
Genetic defecta | Phenotype | Hb electrophoresisb |
| a-Thalassaemia
silent carrier (a+- thalassaemia) |
Single a-gene deletion (–a/aa) |
Asymptomatic; no haematological abnormalities |
Normal |
| a-Thalassaemia
minor (a0- thalassaemia) |
Two a-gene
deletions Trans (–a/–a) or cis (– –/aa) deletions |
Asymptomatic; erythrocytosis, microcytosis, hypochromia |
Normal |
| HbH disease | Three a-gene deletions | Mild to moderate microcytic, hypochromic anaemia, chronic haemolysis, episodic severe anaemia |
Hb Bart’s (g4) |
| Hb Bart’s hydrops
fetalis |
Four a-gene deletion | Hydrops fetalis | HbH, Hb Bart’s |
| a
a+- Thalassaemia
refers to deletion of one of the four a-globin
genes; a0-
thalassaemia refers to two a-globin gene deletions,
either in trans (deletions of one a-globin on
each of the two different alleles) or in cis (deletion of two a-globin
on the same allele). The symptomatic forms of a-thalassaemia
result from three or four a-globin gene deletions.
b Types of haemoglobin (Hb) found on electrophoresis. When there is a paucity or total lack of a-globin chains, the complementary unpaired g-globin or b-globin chains form tetramers and precipitate as Hb Bart’s (g4) or HbH (b4), respectively, both detectable as distinct species. |
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