Epigenomic analysis of KLF1 haploinsufficiency in primary human erythroblasts

Haploinsufficiency for the erythroid-specific transcription factor KLF1 is associated with hereditary persistence of fetal hemoglobin (HPFH). Increased HbF ameliorates the symptoms of β-hemoglobinopathies and downregulation of KLF1 activity has been proposed as a potential therapeutic strategy. However, the feasibility of this approach has been challenged by the observation that KLF1 haploinsufficient individuals with the same KLF1 variant, within the same family, display a wide range of HbF levels. This phenotypic variability is not readily explained by co-inheritance of known HbF-modulating variants in the HBB, HBS1L-MYB and/or BCL11A loci. We studied cultured erythroid progenitors obtained from Maltese individuals in which KLF1 p.K288X carriers display HbF levels ranging between 1.3 and 12.3% of total Hb. Using a combination of gene expression analysis, chromatin accessibility assays and promoter activity tests we find that variation in expression of the wildtype KLF1 allele may explain a significant part of the variability in HbF levels observed in KLF1 haploinsufficiency. Our results have general bearing on the variable penetrance of haploinsufficiency phenotypes and on conflicting interpretations of pathogenicity of variants in other transcriptional regulators such as EP300, GATA2 and RUNX1.

Characterization of β-Globin Gene Cluster Deletions Using Multiplex-Gap Polymerase Chain Reaction (PCR) and Multiplex Ligation-Dependent Probe Amplification (MLPA)

Background : Deletions in the β-globin gene cluster are usually rare, problematic to detect, and subsequently possess a challenge in many diagnostic laboratories. They are normally related to the heterozygous of the delta beta (δβ) thalassemia, hereditary persistence of fetalhemoglobin (HPFH) and some of the hemoglobin variants. These disorders are typically presented by elevated levels of hemoglobin F (Hb F), but with low to normal hemoglobin A2 (Hb A2). However, despite their existence, there is still a limited number of studies focusing on this area, hence no definitive diagnosis could be conclusively established. Therefore, this pilot study was carried out to fill this knowledge gap. Methods: In this study, screening of the selected deletional mutations in the β-globin gene cluster among patients with Hb F (>1%) and Hb A2 (<4%) were performed using multiplex Gap-PCR and multiplex ligation-dependent probe amplification (MLPA). Results: The results showed that out of 54 samples tested using multiplex Gap-PCR against four target deletions; Thai (δβ)°-thalassemia, HPFH-6, Siriraj J and HbLepore, one sample was found positive with Thai (δβ)°-thalassemia. Further findings from the MLPA screening on 12 randomly selected samples revealed that another patient was positive with double deletions within the region of the β-globin gene cluster. These deletions occur at the gamma-globin gene 1 (HBG1) and gamma-globin gene 2 (HBG2) in exon 3. Conclusions: In conclusion, this study highlighted the importance of these deletions’ characterization using multiplex Gap-PCR and MLPA which helps in establishing a definitive diagnosis among this selected group of patients. Bangladesh Journal of Medical Science Vol.20(3) 2021 p.618-624

Physiological and Aberrant γ-Globin Transcription During Development

The expression of the fetal Gγ- and Aγ-globin genes in normal development is confined to the fetal period, where two γ-globin chains assemble with two α-globin chains to form α2γ2 tetramers (HbF). HbF sustains oxygen delivery to tissues until birth, when β-globin replaces γ-globin, leading to the formation of α2β2 tetramers (HbA). However, in different benign and pathological conditions, HbF is expressed in adult cells, as it happens in the hereditary persistence of fetal hemoglobin, in anemias and in some leukemias. The molecular basis of γ-globin differential expression in the fetus and of its inappropriate activation in adult cells is largely unknown, although in recent years, a few transcription factors involved in this process have been identified. The recent discovery that fetal cells can persist to adulthood and contribute to disease raises the possibility that postnatal γ-globin expression could, in some cases, represent the signature of the fetal cellular origin.

A Fresh Breath of Oxygen: Red Blood Cell Exchange Transfusion in Sickle Cell and COVID-19

We present the first documented case of a 69 year-old female with history of sickle cell anemia with hereditary persistence of fetal hemoglobin that presented due to joint pains and COVID-19 infection. The red blood cell exchange transfusion may play an important factor in preventing intubations and longer hospital stays.

β-Hemoglobinopathies: The Test Bench for Genome Editing-Based Therapeutic Strategies

Hemoglobin is a tetrameric protein composed of two α and two β chains, each containing a heme group that reversibly binds oxygen. The composition of hemoglobin changes during development in order to fulfill the need of the growing organism, stably maintaining a balanced production of α-like and β-like chains in a 1:1 ratio. Adult hemoglobin (HbA) is composed of two α and two β subunits (α2β2 tetramer), whereas fetal hemoglobin (HbF) is composed of two γ and two α subunits (α2γ2 tetramer). Qualitative or quantitative defects in β-globin production cause two of the most common monogenic-inherited disorders: β-thalassemia and sickle cell disease. The high frequency of these diseases and the relative accessibility of hematopoietic stem cells make them an ideal candidate for therapeutic interventions based on genome editing. These strategies move in two directions: the correction of the disease-causing mutation and the reactivation of the expression of HbF in adult cells, in the attempt to recreate the effect of hereditary persistence of fetal hemoglobin (HPFH) natural mutations, which mitigate the severity of β-hemoglobinopathies. Both lines of research rely on the knowledge gained so far on the regulatory mechanisms controlling the differential expression of globin genes during development.

Fetal Hemoglobin in Sickle Hemoglobinopathies: High HbF Genotypes and Phenotypes

Fetal hemoglobin (HbF) usually consists of 4 to 10% of total hemoglobin in adults of African descent with sickle cell anemia. Rarely, their HbF levels reach more than 30%. High HbF levels are sometimes a result of β-globin gene deletions or point mutations in the promoters of the HbF genes. Collectively, the phenotype caused by these mutations is called hereditary persistence of fetal hemoglobin, or HPFH. The pancellularity of HbF associated with these mutations inhibits sickle hemoglobin polymerization in most sickle erythrocytes so that these patients usually have inconsequential hemolysis and few, if any, vasoocclusive complications. Unusually high HbF can also be associated with variants of the major repressors of the HbF genes, BCL11A and MYB. Perhaps most often, we lack an explanation for very high HbF levels in sickle cell anemia.

Prevalence of Hemoglobinopathies in Tribal Region of India: A Retrospective Observational Study

Hemoglobinopathies are the common inherited diseases around the world. Thalassemia & sickle cell disease are the important challenges for tribal populations in India. Many study demonstrated the prevalence of haemoglobinopathies in India & among tribes of India but limited data available from Baster tribal region. This study will further lightens the haemoglobinopathies among Baster region of Chhattisgarh state of India. Methods: It was an retrospective observational study, carried out in Late. BRKM Government Medical College, Dimrapal, Jagdalpur which was located at baster region of Chhattisgarh state of India aims to determine the prevalence of various hemoglobinopathies in Baster. Out of 421 suspected patient’s screened for hemoglobinopathies by Capillary electrophoresis. Statistical Package for Social Sciences (SPSS) used for descriptive analysis. Results: Out of 421 cases, 276 were diagnosed with various type of hemoglobinopathies {49% has HbAS (sickle cell anaemia trait), 3% HbSS (sickle cell disease), 6% sickled beta-thalassemia & 8% HPFH (hereditary persistence of foetal hemoglobin)}. Non-tribal population has higher trends of sickled beta thalassemia 14 (8.28%), Hereditary persistence of foetal hemoglobin 26 (15.38%) and HbAS 122 (72.19%) as compare to tribal population but there was similar prevalence of HbSS among both of these groups. Conclusion: In India, hemoglobin disorders are the great threat for tribal population. As <10% of tribes residing in India and many were extinct. The non-tribal community has more prevent than tribal communities.