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• This study describes the molecular basis and genetic interactions of deletional high Hb F determinants in a large cohort of Thai individuals. • Eight different DNA deletions including a novel one causing HPFH and δβ0-thalassemia were described. • Genotype-phenotype interactions were reported. • Multiplex gap-PCR assays were described to detect these high Hb F determinants in routine setting. • Updated data on prevalence, molecular heterogeneity, and various genetic interactions were reported. High hemoglobin F determinants can be classified into hereditary persistence of fetal hemoglobin (HPFH) and δβ-thalassemia with different phenotype. We report the molecular basis and hematological features in a large cohort of deletional high Hb F determinants in Thailand. Subjects (n = 28,177) encountered during 2015–2022 were reviewed, and those with phenotypically suspected of having high Hb F determinants were selected. Combined PCR, multiplex ligation-dependent probe amplification, next-generation sequencing, and DNA sequencing were used to identify the mutations. Among 28,177 subjects investigated, 300 (1.06 %) were found to carry deletional high Hb F determinants in a total of 302 alleles, including heterozygote, compound heterozygote with β-hemoglobinopathies, and homozygote. DNA analysis identified eight different DNA deletions, including δβ0-thalassemia (12.6 kb deletion) (73.8 %), HPFH-6 (14.9 %), Indian deletion-inversion Aγδβ0-thalassemia (3.6 %), Thai deletion-inversion-insertion Aγδβ0-thalassemia (3.0 %), SEA-HPFH (3.0 %), Chinese Aγδβ0-thalassemia (1.0 %), Thai δβ0-thalassemia (11.3 kb deletion) (0.3 %), and a novel δβ0-thalassemia (137.1 kb deletion) (0.3 %). In addition, three novel genetic interactions, including Chinese Aγδβ0-thalassemia/Hb E, δβ0-thalassemia/Indian deletion-inversion Aγδβ0-thalassemia, and homozygous δβ0-thalassemia were found. Hematological features and Hb analysis results of 20 different genotypes were recorded. Multiplex gap-PCR assays for detection of these genetic determinants were described. Deletional high Hb F determinants are common and heterogeneous in Thailand. Data on the prevalence, molecular spectrum, phenotypic expression, and complex interactions of these genetic determinants should prove useful in the study and a prevention and control program of hemoglobinopathies in the region. [ABSTRACT FROM AUTHOR]

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Abstract: Background: Deletions represent about 5% of the mutations in the β-globin gene cluster. We report here the screening for such deletions in the two French urban areas of Paris and Lyon between 2003 and 2010. Methods: Semi-quantitative PCR methods were used for the first screening of deletions. Thereafter, a specific gap-PCR, eventually followed by DNA sequencing, was used for precise identification. Results: 285 patients bore a deletion or recombination event in the β-globin gene cluster. Hbs Lepore or anti-Lepore were detected in 99 patients. Among the remaining 186 patients, 132 bore a deletion that could be fully identified. The most prevalent deletions were the Ghanaian HPFH-2 (n=46), the Sicilian (δβ)0-thal (n=22) and the Spanish (δβ)0-thal (n=12). The other characterized deletions were the: HPFH-3, HPFH-1, Filipino, Senegalese, Corfu, Kabilian, −1.39kb, Indian −619bp and −468bp. Interestingly, three new deletions were fully characterized: a −7719bp deletion, a −27,825bp deletion with a 25bp insertion and a −125bp deletion. Conclusions: The present study emphasizes the importance to detect deletions in the β-globin gene cluster, particularly for at risk couples. The new −27,825bp deletion illustrates the complexity to understand the transcriptional regulation of fetal to adult hemoglobin switch. [Copyright &y& Elsevier]

β thalassemia major or Cooley's Anemia (CA) has been difficult to model in mice due to their lack of a fetal hemoglobin gene equivalent. This summary describes novel preclinical humanized mouse models of CA that survive on human fetal hemoglobin at birth and are blood-transfusion dependent for life upon completion of their human fetal-to-adult hemoglobin switch after birth. These CA models are the first to recapitulate the temporal onset of the disease in human patients. These novel humanized CA disease models are useful for the study of the regulation of globin gene expression, synthesis, and switching; examining the onset of disease pathology; development of transfusion and iron chelation therapies; induction of fetal hemoglobin synthesis; and the testing of novel genetic and cell-based therapies for the correction of thalassemia. [ABSTRACT FROM AUTHOR]

The human β globin locus consists of an upstream LCR and functional genes arranged sequentially in the order of their expression during development: 5′- HBE1, HBG2, HBG1, HBD, HBB-3′. Haemoglobin switching entails the successive recruitment of these genes into an active chromatin hub (ACH). Here we show that the transcription factor Ikaros plays a major role in the formation of the β-globin ACH, and in haemoglobin switching. In Plastic mice, where the DNA-binding region of Ikaros is disrupted by a point mutation, there is concomitant marked down-regulation of HBB, and up-regulation of HBG expression. We show for the first time Ikaros and its family member Eos, bind to critical cis elements implicated in haemoglobin switching and deletional hereditary persistence of fetal haemoglobin (HPFH). Chromatin conformation capture (3C) data demonstrated that Ikaros facilitates long-distance DNA looping between the LCR and a region upstream of HBD. This study provides new insights into the mechanism of stage-specific assembly of the β-globin ACH, and HPFH. [ABSTRACT FROM AUTHOR]

Background: Several previous studies reported that the Venezuelan Warao Indians presented unusual genetic characteristics. Aim: The present study checked previous reports of a high frequency of hereditary persistence of fetal hemoglobin (HPFH) and examined other hematological traits. Subjects and methods: Standard hematology, electrophoresis on cellulose acetate, fetal hemoglobin alkali denaturation, γ-globin chain, DNA amplification and sequencing, and denaturing gradient gel electrophoresis determinations were performed in 269 individuals living in two localities of the Orinoco River Delta. Results: Two βs genes, in apparently non-related individuals, were found. HPFH, detected in this same population of Warao Indians 25 years ago, was present in heterozygous form in five individuals from a large kindred, with hemoglobin F levels ranging from 3.7% to 8%, and with a pancellular distribution. The HPFH mutation was of the deletional type. β-globin gene haplotypes were determined by direct counting (through family studies) in 150 chromosomes; 26% of the 150 examined cluster presented haplotype 2, 22% haplotype 6, and 13% a new, Warao haplotype. Haplotype 3, of probable African origin, was also found with a frequency of 5%. Conclusions: The presence of the HPFH mutation was confirmed, and the new β-globin gene haplotype together with the presence of other rare variants indicates that the Warao are very distinctive in relation to other Native Americans. Evidence was also found of a slight admixture from Africa-derived subjects (Layrisse et al. 1988). [ABSTRACT FROM AUTHOR]

Abstract: The genetic mechanisms underlying the continued expression of the γ-globin genes during the adult stage in deletional hereditary persistence of fetal hemoglobin (HPFH) and δβ-thalassemias are not completely understood. Herein, we investigated the possible involvement of transcription factors, using the suppression subtractive hybridization (SSH) method as an initial screen to identify differentially expressed transcripts in reticulocytes from a normal and a HPFH-2 subject. Some of the detectable transcripts may participate in globin gene regulation. Quantitative real-time PCR (qRT-PCR) experiments confirmed the downregulation of ZHX2, a transcriptional repressor, in two HPFH-2 subjects and in a carrier of the Sicilian δβ-thalassemia trait. The chromatin remodeling factors ARID1B and TSPYL1 had a very similar pattern of expression with an incremental increase in HPFH and decreased expression in δβ-thalassemia. These differences suggest a mechanism to explain the heterocellular and pancellular distribution of fetal hemoglobin in δβ-thalassemia and deletional HPFH, respectively. Interestingly, α-globin mRNA levels were decreased, similar to β-globin in all reticulocyte samples analyzed. [Copyright &y& Elsevier]