# Delta-beta thalassemia

**Delta-beta thalassemia** (δβ-thalassemia) is a beta-thalassemia variant in which production of the delta- and beta-globin chains is reduced or absent, prompting a compensatory rise in fetal gamma-chain output; consequently, fetal hemoglobin (HbF, α₂γ₂) stays elevated into adulthood.<sup>[1](https://www.orpha.net/en/disease/detail/231237)</sup> It is usually caused by deletions of the entire delta and beta gene sequences in the β-globin gene cluster on chromosome 11, with production of only gamma-globin and formation of HbF.<sup>[1](https://www.orpha.net/en/disease/detail/231237)</sup>

| Key fact | Detail |
|---|---|
| Definition | Decreased or absent δ- and β-globin chain synthesis with compensatory increase in γ-chain (HbF) expression<sup>[1](https://www.orpha.net/en/disease/detail/231237)</sup> |
| Molecular cause | Most commonly gross deletions removing the δ and β genes while preserving the γ genes<sup>[1](https://www.orpha.net/en/disease/detail/231237)</sup><sup> • </sup><sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK190571/)</sup> |
| Inheritance | Autosomal recessive; onset in the neonatal period or infancy<sup>[1](https://www.orpha.net/en/disease/detail/231237)</sup> |
| Heterozygote phenotype | Clinically asymptomatic, mild microcytosis, no elevation of HbA₂, HbF about 5%–20% distributed heterocellularly<sup>[1](https://www.orpha.net/en/disease/detail/231237)</sup><sup> • </sup><sup>[3](https://www.akhav.org.tr/upload/THALASSEMIA-AND-HEMOGLOBINOPATHY.pdf)</sup> |
| Homozygote phenotype | Mild clinical presentation resembling thalassemia intermedia<sup>[1](https://www.orpha.net/en/disease/detail/231237)</sup><sup> • </sup><sup>[3](https://www.akhav.org.tr/upload/THALASSEMIA-AND-HEMOGLOBINOPATHY.pdf)</sup> |
| Distribution | Found in many ethnic groups but most common in Greece and Italy; prevalence unknown<sup>[1](https://www.orpha.net/en/disease/detail/231237)</sup> |
| Classification codes | ICD-10 D56.2; ICD-11 3A50.3; OMIM 141749<sup>[1](https://www.orpha.net/en/disease/detail/231237)</sup> |

## Molecular basis

Unlike typical β-thalassemia, in which the great majority of alleles are point mutations affecting the β-globin gene or its immediate flanking sequences, δβ- and γδβ-thalassemias most commonly result from gross gene deletions.<sup>[4](https://pubmed.ncbi.nlm.nih.gov/2675099/)</sup> The deletion removes both the δ- and β-globin genes but preserves the γ genes, which continue to be expressed after the normal fetal-to-adult hemoglobin switch.<sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK190571/)</sup><sup> • </sup><sup>[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC11842922/)</sup> The persistent γ-chain production pairs with excess α chains to form HbF, reducing the α/non-α globin chain imbalance that drives the pathophysiology of β-thalassemia.<sup>[6](https://perspectivesinmedicine.cshlp.org/content/3/2/a011684.full)</sup>

Deletional δβ-thalassemia alleles vary in size and ethnic origin. The Asian Indian inversion deletion, designated Gγ(Aγδβ)⁰-thalassemia, abolishes expression from the Aγ, δ, and β genes while leaving the Gγ gene intact.<sup>[7](https://www.tandfonline.com/doi/full/10.1080/10245332.2018.1458934)</sup> Named deletions reported in Southeast Asia include the Gγ(Aγδβ)⁰-thalassemia Siriraj I deletion of about 118 kb and the δβ⁰-thalassemia Thai deletion of about 12.5 kb.<sup>[8](https://d-nb.info/1382887272/34)</sup> In Sardinians, one nondeletion δβ-thalassemia has been reported together with elevated Aγ-globin synthesis; molecular analysis revealed that the affected chromosome carried two separate mutations: a β-globin gene nonsense change at codon 39 plus an Aγ promoter change at position −196.<sup>[9](https://ashpublications.org/blood/article-pdf/70/5/1470/365472/1470.pdf)</sup>

## Clinical picture

**Heterozygotes.** The heterozygous form is clinically asymptomatic, with mild microcytosis and no elevation of HbA₂, the adult hemoglobin fraction that rises in classical β-thalassemia trait.<sup>[1](https://www.orpha.net/en/disease/detail/231237)</sup> Carriers of a δβ-thalassemia allele have HbF levels of about 5% to 20%, distributed heterocellularly, meaning the HbF-containing cells are unevenly spread through the red cell population.<sup>[3](https://www.akhav.org.tr/upload/THALASSEMIA-AND-HEMOGLOBINOPATHY.pdf)</sup>

**Homozygotes and compound heterozygotes.** The few reported homozygous patients have a mild clinical presentation.<sup>[1](https://www.orpha.net/en/disease/detail/231237)</sup> When a δβ-thalassemia allele is inherited together with heterozygous classical β-thalassemia, patients usually show the thalassemia intermedia phenotype, although the more severe thalassemia major phenotype has been described in some cases.<sup>[1](https://www.orpha.net/en/disease/detail/231237)</sup> The raised HbF from the δβ-thalassemia deletion attenuates the severity of co-inherited β-chain disorders, a mechanism also seen when deletional δβ-thalassemia or HPFH determinants accompany the sickle cell (βˢ) gene.<sup>[10](https://pubmed.ncbi.nlm.nih.gov/1713909/)</sup>

## Distinction from hereditary persistence of fetal hemoglobin

Delta-beta thalassemia must be distinguished from hereditary persistence of fetal hemoglobin (HPFH), a related deletion or point-mutation condition in which γ-globin production persists into adult life; HPFH is frequently considered within the spectrum of δβ-thalassemia, although strictly it is not a form of β-thalassemia because it lacks significant α to non-α globin chain imbalance.<sup>[6](https://perspectivesinmedicine.cshlp.org/content/3/2/a011684.full)</sup> The two conditions differ measurably in heterozygotes: carriers of δβ-thalassemia have 5%–20% HbF with a heterocellular distribution, whereas heterozygotes for HPFH mutations have 17%–30% HbF with a pancellular distribution, meaning HbF is present in essentially every red cell.<sup>[3](https://www.akhav.org.tr/upload/THALASSEMIA-AND-HEMOGLOBINOPATHY.pdf)</sup> Homozygous HPFH is an asymptomatic, benign hemoglobinopathy, while δβ-thalassemia homozygotes have a phenotype like thalassemia intermedia.<sup>[3](https://www.akhav.org.tr/upload/THALASSEMIA-AND-HEMOGLOBINOPATHY.pdf)</sup>

The molecular basis for the different γ-globin output has been mapped to the deletion endpoints. Comparison of δβ-thalassemia and HPFH deletions in Mediterranean patients suggested that a region centered on a cluster of repetitive sequences approximately 3.5 kilobases 5′ to the δ-globin gene may be critical for the higher, persistent γ-globin expression seen in HPFH compared with δβ-thalassemia.<sup>[11](https://air.unimi.it/handle/2434/176167)</sup> The same study documented ethnic variation in the Gγ/Aγ ratio within HbF among δβ-thalassemia heterozygotes, from approximately 0.07 in Sardinian to approximately 0.15 in Sicilian and approximately 0.35 in Spanish patients.<sup>[11](https://air.unimi.it/handle/2434/176167)</sup>

## Diagnosis

The δβ-thalassemia, HPFH, Hb Lepore, and Hb Kenya deletion mutations were originally characterized by restriction enzyme mapping with the [Southern blot](https://www.edgepedia.org/southern-blot) technique; gap-PCR and/or MLPA are now used for their detection.<sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK190571/)</sup> Gap-PCR diagnoses most of the common δβ-thalassemia and HPFH alleles, including Hb Kenya, and provides a quick genotype screening method for distinguishing HPFH trait from δβ-thalassemia trait in Asian Indian, African, and Mediterranean individuals with raised HbF levels.<sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK190571/)</sup> MLPA detects all deletion alleles, but unlike gap-PCR it reports only a result consistent with a particular known deletion rather than defining the breakpoint.<sup>[2](https://www.ncbi.nlm.nih.gov/books/NBK190571/)</sup>

## Significance as a genetic modifier

δβ⁰-thalassemia caused by deletions of variable size in the HBB gene cluster is listed among the genetic determinants that increase fetal hemoglobin output and can ameliorate the clinical severity of β-thalassemia by reducing α/non-α globin chain imbalance.<sup>[12](https://www.ncbi.nlm.nih.gov/books/NBK1426/)</sup> For this reason δβ-thalassemia appears among the recognized determinants of mild β-thalassemia forms, alongside α-thalassemia coinheritance and nondeletion HPFH.<sup>[4](https://pubmed.ncbi.nlm.nih.gov/2675099/)</sup>

## References

1. [Delta-beta-thalassemia, Orphanet (ORPHA:231237)](https://www.orpha.net/en/disease/detail/231237)
2. [Molecular Diagnosis, in Prevention of Thalassaemias and Other Haemoglobin Disorders, NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK190571/)
3. [Thalassemia and Hemoglobinopathy practical management text, Turkish Red Crescent](https://www.akhav.org.tr/upload/THALASSEMIA-AND-HEMOGLOBINOPATHY.pdf)
4. [Cao A, Murru S (1989). Molecular pathology and detection of beta-thalassemias. Prog Clin Biol Res 309:3-11.](https://pubmed.ncbi.nlm.nih.gov/2675099/)
5. [Challenges in diagnosis of thalassemia syndromes, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC11842922/)
6. [Classification of the Disorders of Hemoglobin, Cold Spring Harbor Perspectives in Medicine](https://perspectivesinmedicine.cshlp.org/content/3/2/a011684.full)
7. [Contrasting co-inheritance of alpha and beta mutations in delta beta thalassemia and hereditary persistence of fetal hemoglobin: a study from India, Hematology](https://www.tandfonline.com/doi/full/10.1080/10245332.2018.1458934)
8. [Molecular spectrum and carrier frequency of deletional HPFH and delta-beta thalassemia in Malaysia, Blood Research (2025)](https://d-nb.info/1382887272/34)
9. [Nondeletion δβ-thalassemia in Sardinians, Blood 70(5):1470 (1987)](https://ashpublications.org/blood/article-pdf/70/5/1470/365472/1470.pdf)
10. [Bollekens JA, Forget BG (1991). Delta beta thalassemia and hereditary persistence of fetal hemoglobin. Hematol Oncol Clin North Am 5(3):399-422.](https://pubmed.ncbi.nlm.nih.gov/1713909/)
11. [Ottolenghi S and colleagues (1982). Molecular comparison of delta beta-thalassemia and HPFH DNAs: evidence of a regulatory area? PNAS 79(7):2347-2351.](https://air.unimi.it/handle/2434/176167)
12. [Beta-Thalassemia, GeneReviews, NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK1426/)

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*Topic: Encyclopedia › Life and health › Human health and medicine › Diseases and injuries › Cardiovascular and blood conditions › Blood disorders (hematologic conditions) › Hemoglobinopathies › Compound and interacting hemoglobinopathies*

*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 11, 2026; Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*

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