Among the high-frequency keywords, risk population, children, and prevalence stand out as representatives of the research hotspots in the field of β-thalassemia. Thalassemia is a group of genetic disorders of hemoglobin that were originally endemic in the tropics but are now found worldwide due to migration patterns[19]. Understanding the population at risk, particularly children is crucial in addressing the challenges associated with thalassemia. During the early stages of fetal development, different types of hemoglobins, such as β2ε2, α2ε2, and β2γ2, are formed in erythroid cells primarily located in the yolk sac. The erythropoiesis site shifts from the liver and spleen to the bone marrow during fetal development. This transition, known as "the switch of hemoglobin", involves a shift from γ-globin to β-globin expression and is completed by the time the baby reaches 6 months[20]. After this switch, hemoglobin A2 (Hb A2) and hemoglobin F (Hb F) constitute only a small percentage of hemoglobin, while the majority of hemoglobin in normal red blood cells is adult Hb A (α2β2). Severe forms of alpha thalassemia can lead to intrauterine death unless advanced measures are taken to save the fetus. In contrast, beta-thalassemia typically manifests in childhood due to "the switch of hemoglobin." In the past, due to limitations in diagnostic and therapeutic techniques, most affected children faced significant challenges in surviving into adulthood. However, with advancements in screening and prevention programs for thalassemia, the landscape has improved. These programs vary in their implementation, depending on regional distribution and cultural factors. As part of the management of thalassemia cases, nationwide screening programs are being implemented, as well as premarital and neonatal screenings. By focusing on the risk population, particularly children from low-income and middle-income countries, and addressing the prevalence of thalassemia, researchers and healthcare providers can contribute to the development of effective screening, prevention, and treatment strategies.
In terms of pathophysiological mechanisms, the high-frequency keywords in β-thalassemia research include iron overload, anemia, gene mutations, and ineffective erythropoiesis. These factors have been reported to contribute to the development of pathological β-thalassemia, with iron overload being a particularly important factor. Research has shown that unstable α-globin chain tetramers accumulate in erythroid cells in β-thalassemia, leading to premature cell death both inside and outside the bone marrow. This process also involves the formation of reactive oxygen species and structural membrane deformities, which result in the exposure of senescence antigens[21, 22]. Changes in the concentrations of several mediators involved in the control of erythropoiesis have also been noted in circumstances of inefficient erythropoiesis, in addition to changed signal pathways such overexpression of JAK/AKT/mTOR and SMAD2/3. Molecular regulators like HSP70 and the α-Hb stabilizing protein exert a protective role, according to recent study[23]. Medullary expansion, bone deformities, and a decrease in bone mass are caused by increased proliferation of erythroid precursors in the bone marrow. Additionally, compensatory hematopoietic points in the spleen, liver, and other tissues with hematopoietic potential are activated, resulting in splenomegaly and hepatomegaly[24]. Notably, ineffective erythropoiesis also leads to increased iron absorption and primary iron overload, mediated by the hepatic hormone hepcidin. Despite increased iron concentrations, ineffective erythropoiesis prevents the synthesis of hepatic hepcidin, which is regulated by a number of erythroid regulators, including GDF-15 and erythroferrone. Reticuloendothelial cells release more iron when hepcidin levels are lower because this promotes iron redistribution and dietary absorption. Ultimately, this leads to iron overload, causing cellular and organ damage[25, 26]. The non-transferrin-bound iron enters various cell types, such as cardiomyocytes, hepatocytes, pancreatic β cells, and anterior pituitary cells. The accumulation of iron generates reactive oxygen species, leading to damage to lipids, proteins, DNA, and subcellular organelles, as well as cellular dysfunction, apoptosis, necrosis, and toxicity in target organs[27].
In the first decade of life, β-thalassemia major is fatal due to the complex pathophysiology underlying its symptoms. Understanding these pathophysiological mechanisms is crucial for developing effective therapeutic strategies and interventions to mitigate the impact of β-thalassemia on affected individuals. Additionally, chronic hemolytic anemia resulting from β-thalassemia can lead to acute complications, including cholelithiasis and adverse effects on growth, organ function, and vascular function[28]. Erythroid cells are exposed to senescence antigens such phosphatidylserine due to ineffective erythropoiesis, which has the potential to cause thrombosis. Patients with thalassemia have hypercoagulability and vascular symptoms such venous thrombosis and pulmonary hypertension as a result of dysfunctional platelets and coagulation systems[29]. Furthermore, recent research has uncovered an association between thalassemia and autoimmune diseases, implicating specific mutations and molecular pathways. Rheumatoid arthritis, multiple sclerosis, celiac disease, and autoimmune hemolytic anemia have all been linked to thalassemia[30]. The underlying cause of this hyperlink may be abnormalities in cellular immunity in thalassemia patients, including altered CD8+/CD4 + lymphocyte ratios, impaired innate effector activities of phagocytes, and suppression of lymphocyte development. These findings highlight the broader impact of β-thalassemia beyond its primary pathophysiological mechanisms, encompassing complications related to coagulation, vascular function, and the potential involvement of autoimmune processes. Understanding and addressing these aspects are essential for comprehensive management and care for individuals affected by thalassemia.
The keywords with the strongest citation bursts, as identified by CiteSpace, highlight several areas of hot research in the field of β-thalassemia. High-performance liquid chromatography (HPLC), polymerase chain reaction (PCR), and myocardial iron have emerged as important topics of investigation. Full blood count (FBC), reticulocytes, peripheral blood (PB) film for erythrocyte morphology study, hepatorenal function assessment, hemolysis indices evaluation, and iron, ferritin, transferrin levels are all used in thalassemia screening. The mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) derived from automated analyzers are useful for rapidly and cost-effectively identifying cases that require further investigation. Most carriers of β-thalassemia exhibit MCV < 79fl and MCH < 27pg. HPLC is a diagnostic technique used to assess HbA2, and HbF, and discover abnormal hemoglobins. It is frequently used in the diagnosis of -thalassemia and the detection of pathogenic variations[17]. To determine alpha and beta globin mutations, including alpha globin gene copy number analysis, PCR-based molecular analysis or DNA sequencing is used, validating the diagnosis and allowing genotype/phenotype correlations. Over 200 thalassemia-related mutations in the β-globin gene are currently known. These mutations range from silent mutations (silent β) to mild mutations that cause a slight reduction in the production of β-globin chains(β+), to severe mutations that completely prevent β-globin chain synthesis(β0). Less frequently do genes have deletions[31]. For validating the diagnosis, determining mutant hemoglobins, clarifying difficult cases, and enabling prenatal diagnosis, molecular techniques have emerged as the gold standard[32].
Among the treatment strategies, two prominent keywords that emerged were drug therapy and hematopoietic stem cell transplantation (HSCT). The longevity of patients with transfusion-dependent thalassemia (TDT) has been greatly improved by the introduction of iron-chelation treatment in conjunction with conventional blood transfusions. Currently, there are three available iron chelators: deferoxamine, which was the first clinically approved chelator and has been in use since the 1980s; oral deferasirox in tablet and film-coated tablet formats, as well as oral deferiprone in tablet or solution form. These chelators help in reducing iron overload, a major concern in thalassemia patients. Studies have also explored the potential of Janus kinase 2 (JAK2) as a target for treating ineffective erythropoiesis. Preclinical studies have shown promising results, and a clinical trial involving 30 TDT patients (NCT02049450) demonstrated that treatment with ruxolitinib, a JAK2 inhibitor, led to a sustained reduction in spleen size with manageable adverse reactions[33]. The only curative therapy available for people with β-thalassemia that does not entail modifying the patient's DNA is hematopoietic stem cell transplantation (HSCT) utilizing a related donor who is HLA-matched. However, the use of unrelated donors and umbilical cord blood as alternative sources of hematopoietic stem cells has been encouraged for patients who do not have a matched sibling donor[34]. However, graft vs. host disease and failure of grafts are some of the risks associated with HSCT, which is a risky and expensive procedure[35].
The discovery and development of the CRISPR-Cas9 gene-editing system in 2012 have revolutionized the field of gene editing and sparked numerous clinical trials. CRISPR-Cas9 offers a simple and programmable approach to modifying genes, and it has shown great promise in treating genetic disorders. CRISPR entered its first human clinical trial in 2020 to remove mutations causing Leber's congenital amaurosis, a major breakthrough[36]. Gene therapy for β-thalassemia is inserting a vector containing the healthy β-globin or γ-globin gene into hematopoietic stem cells to promote the formation of normal red blood cells. Several clinical trials have been conducted and are ongoing to explore the potential of gene therapy in treating β-thalassemia. A young male patient with transfusion-dependent βE/β0-thalassemia participated in the first clinical trial (LG001) in 2007. The HPV569 β-globin lentiviral vector, which expressed the globin variant T87Q, was used in the experiment. Hemoglobin levels in the patient ranged from 8.5 to 9g/dL one year later, when they were no longer dependent on blood transfusions[37]. Subsequent clinical trials, such as HGB-204 (NCT01745120) and HGB-205 (NCT02151526), sponsored by Bluebird Bio, utilized an improved vector called LentiGlobin BB305. These trials involved transducing the autologous CD34 + cells obtained from 22 transfusion-dependent-thalassemia (TDT) patients with the novel vector. The early results of these trials have shown promising efficacy and a favorable safety profile. In light of the positive outcomes and safety data, ZYNTEGLOTM (LentiGlobin BB305) was authorized and made accessible in the European Union for non-β0/β0 patients over the age of 12 in June 2019. This was a key pivotal moment for β-thalassemia gene therapy. The development of gene therapy techniques has the potential to offer patients with β-thalassemia long-term and curative therapeutic alternatives.
Techniques for editing the genome have been created to disrupt or directly correct certain genetic mutations found in the DNA of cells. Researchers are investigating into using genome editing to simulate mutations that cause hereditary persistence of fetal hemoglobin (HPFH), a disorder that may alleviate the symptoms of anemia in β-thalassemia patients [38, 39]. Targeting the BCL11A gene, making small deletions in the β-globin gene promoter region to prevent transcription factors from binding, introducing point mutations in the β-globin promoter region, and altering other transcription factors like KLF1, MYB, SOX6, and GATA-1 to make them less effective at suppressing β-globin gene expression and globin gene switching is just a handful of these[35]. For the treatment of β-thalassemia, clinical studies utilizing CRISPR-Cas9 gene editing have yielded encouraging results. In one such experiment, autologous CD34 + hematopoietic stem cells that had undergone CRISPR-Cas9 gene editing, or CTX001, were used. Transfusion independence as well as rises in levels of both total hemoglobin and fetal hemoglobin were seen in a trial of 15 individuals, including those with severe genotypes[40, 41]. In two patients with the most severe genotype of β-thalassemia, a second phase 1/2 trial conducted in China showed that gene editing was effective, producing high quantities of HbF, bringing hemoglobin levels back to normal, and enabling the patients to stop receiving blood transfusions[42]. Base editing is another emerging tool in genome editing that allows for specific editing of DNA sequences without the need for a DNA template or double-stranded breaks. The − 28 (A > G) mutation in β-thalassemia has been successfully corrected using base editing methods, which has also increased the synthesis of β-globin in hematopoietic stem and progenitor cells[43]. Similarly, base editing was used to carry out particular mutations that undermined the BCL11A and KLF1 binding sites, increasing the quantity of γ-globin[44, 45]. However, gene therapy and genome editing still face challenges and concerns. These include vector-triggered immune responses, off-target effects of gene editing, technological limitations, high costs, regulatory issues, and ethical considerations regarding the heritability of edited genes[46, 47]. These elements add to the uncertainty surrounding the development of gene editing and the widespread use of these treatments.
Among the top 20 burst keywords identified between 2013 and 2023, it is noteworthy that topics related to the novel coronavirus disease (COVID-19) pandemic have seen a significant surge since 2019. Patients with thalassemia may be more susceptible to infections as a result of conditions affecting the immune system, splenectomy, and adrenal hypofunction[48]. The COVID-19 epidemic has had a severe influence on various countries' critical healthcare systems, which has a direct or indirect impact on the lives of thalassemia patients. Due to transportation restrictions, patients have faced difficulties in accessing necessary medications and blood transfusions. Delays in referral to healthcare centers have been a cause for concern, particularly because regular blood transfusions are critical for the survival of patients with transfusion-dependent thalassemia (TDT). Furthermore, the economic hardships caused by the pandemic have worsened the financial situation of TDT patients, with job losses making it even more challenging for them to seek necessary treatment[49]. Long-term blood transfusion and iron chelation treatment patients during the COVID-19 pandemic continue to have to access medical care issues that are significant enough to warrant further study and debate.