Classification of deletional α-thalassemia.
| Type of deletion . | Phenotype . | Number of examples recognized . | Examples . |
|---|---|---|---|
| *(α) indicates that the gene is present but non-functional. | |||
| †Loss of 16p13.3 may be the result of deletion, inversion plus deletion, formation of a ring chromosome 16 that lacks the a gene cluster or unbalanced inheritance of a derivative (16) lacking 16p13.3 from a parent who had a balanced translocation, eg, t(1;16), t(5;16) or t(16;20). | |||
| ‡(αα) indicates that both α genes are present but non-functional. | |||
| Reprinted with permission from Bain BJ. Haemoglobinopathy Diagnosis. 2nd ed. Malden, Mass.: Blackwell Publishing; 2006. | |||
| Deletion involving one or both α genes | |||
| Deletion of all or part of one α gene | α+ thalassemia | 7 | –α4.2, –α3.71, –α3.7H, –α3.7III, –α3.5, –α5.3*, –α2.7 |
| Deletion of all or part of both α genes, but without deletion of HS-40 | α0 thalassemia | 20 | – –SEA, – –THAI, – –MED, – –FIL, – –BRIT, – –SPAN, –(α)20.5*, –(α)5.2* |
| Deletion of both α genes and of HS-40 (100–250 kb) | α0 thalassemia | 8, without other phenotypic abnormality | – –DUTCH11 |
| Extensive loss of 16p13.3 (1–2 Mb) including both α genes and HS-40† | α0 thalassemia | 17, with mental retardation and dysmorphism | – –BO |
| Deletion of α1 gene and 18–20 kb downstream of α1 gene [17] | α0 thalassemia | 1 | (α)–ZF* |
| Deletion leaving α genes intact | |||
| Deletion of upstream major regulatory element (HS-40) without deletion of genes | α0 or very severe α+ thalassemia | 12 | (αα)RA,‡ (αα)TAT,‡ (αα)MM,‡ (αα)IJ‡ |
| Type of deletion . | Phenotype . | Number of examples recognized . | Examples . |
|---|---|---|---|
| *(α) indicates that the gene is present but non-functional. | |||
| †Loss of 16p13.3 may be the result of deletion, inversion plus deletion, formation of a ring chromosome 16 that lacks the a gene cluster or unbalanced inheritance of a derivative (16) lacking 16p13.3 from a parent who had a balanced translocation, eg, t(1;16), t(5;16) or t(16;20). | |||
| ‡(αα) indicates that both α genes are present but non-functional. | |||
| Reprinted with permission from Bain BJ. Haemoglobinopathy Diagnosis. 2nd ed. Malden, Mass.: Blackwell Publishing; 2006. | |||
| Deletion involving one or both α genes | |||
| Deletion of all or part of one α gene | α+ thalassemia | 7 | –α4.2, –α3.71, –α3.7H, –α3.7III, –α3.5, –α5.3*, –α2.7 |
| Deletion of all or part of both α genes, but without deletion of HS-40 | α0 thalassemia | 20 | – –SEA, – –THAI, – –MED, – –FIL, – –BRIT, – –SPAN, –(α)20.5*, –(α)5.2* |
| Deletion of both α genes and of HS-40 (100–250 kb) | α0 thalassemia | 8, without other phenotypic abnormality | – –DUTCH11 |
| Extensive loss of 16p13.3 (1–2 Mb) including both α genes and HS-40† | α0 thalassemia | 17, with mental retardation and dysmorphism | – –BO |
| Deletion of α1 gene and 18–20 kb downstream of α1 gene [17] | α0 thalassemia | 1 | (α)–ZF* |
| Deletion leaving α genes intact | |||
| Deletion of upstream major regulatory element (HS-40) without deletion of genes | α0 or very severe α+ thalassemia | 12 | (αα)RA,‡ (αα)TAT,‡ (αα)MM,‡ (αα)IJ‡ |