B

nsulator

4. Ep-Thalassemia: Hemoglobin E (lysine ^ glutamic acid at 26) and P-chain genes deletion

5. Hb Lepore: A fusion globin due to unequal crossover of the P- and 5-globin genes (the globin is produced at a low level because it is under 5-globin regulation).

a-Thalassemia

1. Silent carrier a-thalassemia: Deletion of one a-globin gene

2. a-Thalassemia trait: Deletion of two a-globin genes

3. Hb Constant Spring: Abnormal a-chain variant produced in very small amounts, thereby mimicking deficiency of the gene

4. HbH disease: Deletion of 3 a-globin genes, resulting in significant reduction of a-chain synthesis

5. Hydrops fetalis: Deletion of all 4 a-globin genes; no normal adult or fetal hemoglobin production.

In many populations, a- and P-thalassemia and structural hemoglobin variants (hemoglobinopathies) exist together, resulting in a wide spectrum of clinical disorders. Tables 7-21 and 7-22 list some features of the heterozygous and homozygous or doubly heterozygous states, respectively, of P-thalassemia and its variants. Table 7-23 lists the a-thalassemia syndromes.

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