Table 3.1.
Common genotypes and basic classification of alpha thalassemia
| Genotype | α-globin gene numbera | Name | Phenotype |
|---|---|---|---|
| αα/αα | 4 | Normal state | None |
| αα/α– | 3 | Silent carrier | None (values for Hb and MCV may be near the lower limits of normal) |
| – –/αα or α–/α– | 2 | Thalassemia trait | Thalassemia minor: asymptomatic, mild microcytic anemia |
| – –/α– | 1 | Hb H disease | Thalassemia intermedia: mild to moderate microcytic anemia |
| – –/αCSα | 1 | Hb H-Constant Spring | Thalassemia intermedia: moderate to severe microcytic anemia |
| – –/– – | 0 | Alpha thalassemia major | Thalassemia major: hydrops fetalis |
a
Number of normal alpha globin genes
Abbreviations: αα a chromosome with a normal complement (2) of α-globin genes, α– a chromosome with 1 of the 2 α-globin genes deleted, – – a chromosome with both α-globin genes deleted, αα a chromosome with the thalassemic Hb Constant Spring mutation affecting 1 of the 2 α-globin genes