Identifying genetic variants and pathways associated with extreme levels of fetal hemoglobin in sickle cell disease in Tanzania

Transcriptional regulators of fetal hemoglobin

Sickle cell anemia is a hereditary disease caused by sickle-shaped red blood cells that can lead to vaso-occlusive crises. Treatment options are currently limited, highlighting the need to develop new clinical approaches. Studies demonstrated that elevated levels of fetal hemoglobin (Hb F) are associated with a reduction of mortality and morbidity in sickle cell anemia patients. In light of this, researchers have been trying to elucidate the transcriptional regulation of Hb F to develop new therapeutic interventions. The present study aimed to present the main transcription factors of Hb F and discuss the clinical feasibility of these molecular targets. Two search strategies were used in the PubMed, SciELO, and LILACS databases between July and August 2023 to conduct this review. Manual searches were also conducted by checking references of potentially eligible studies. Eligibility criteria consisted of clinical trials and cohort studies from the last five years that investigated transcription factors associated with Hb F. The transcription factors investigated in at least four eligible studies were included in this review. As a result, 56 eligible studies provided data on the BCL11A, LRF, NF-Y, GATA1, KLF1, HRI, ATF4, and MYB factors. The studies demonstrated that Hb F is cooperatively regulated by transcription factors with the BCL11A factor appearing to be the most specific target gene for γ-globin induction. Although these data are promising, there are still significant gaps and intervention limitations due to the adverse functions of the target genes. New studies that clarify the aspects and functionalities of Hb F regulators may enable new clinical approaches for sickle cell anemia patients.

Genetic Variation and Sickle Cell Disease Severity: A Systematic Review and Meta-Analysis

Importance

Sickle cell disease (SCD) is a monogenic disorder, yet clinical outcomes are influenced by additional genetic factors. Despite decades of research, the genetics of SCD remain poorly understood.

Objective

To assess all reported genetic modifiers of SCD, evaluate the design of associated studies, and provide guidelines for future analyses according to modern genetic study recommendations.

Data Sources

PubMed, Web of Science, and Scopus were searched through May 16, 2023, identifying 5290 publications.

Study Selection

At least 2 reviewers identified 571 original, peer-reviewed English-language publications reporting genetic modifiers of human SCD phenotypes, wherein the outcome was not treatment response, and the comparison was not between SCD subtypes or including healthy controls.

Data Extraction and Synthesis

Data relevant to all genetic modifiers of SCD were extracted, evaluated, and presented following STREGA and PRISMA guidelines. Weighted z score meta-analyses and pathway analyses were conducted.

Main Outcomes and Measures

Outcomes were aggregated into 25 categories, grouped as acute complications, chronic conditions, hematologic parameters or biomarkers, and general or mixed measures of SCD severity.

Results

The 571 included studies reported on 29 670 unique individuals (50% ≤ 18 years of age) from 43 countries. Of the 17 757 extracted results (4890 significant) in 1552 genes, 3675 results met the study criteria for meta-analysis: reported phenotype and genotype, association size and direction, variability measure, sample size, and statistical test. Only 173 results for 62 associations could be cross-study combined. The remaining associations could not be aggregated because they were only reported once or methods (eg, study design, reporting practice) and genotype or phenotype definitions were insufficiently harmonized. Gene variants regulating fetal hemoglobin and α-thalassemia (important markers for SCD severity) were frequently identified: 19 single-nucleotide variants in BCL11A, HBS1L-MYB, and HBG2 were significantly associated with fetal hemoglobin (absolute value of Z = 4.00 to 20.66; P = 8.63 × 10-95 to 6.19 × 10-5), and α-thalassemia deletions were significantly associated with increased hemoglobin level and reduced risk of albuminuria, abnormal transcranial Doppler velocity, and stroke (absolute value of Z = 3.43 to 5.16; P = 2.42 × 10-7 to 6.00 × 10-4). However, other associations remain unconfirmed. Pathway analyses of significant genes highlighted the importance of cellular adhesion, inflammation, oxidative and toxic stress, and blood vessel regulation in SCD (23 of the top 25 Gene Ontology pathways involve these processes) and suggested future research areas.

Conclusions and Relevance

The findings of this comprehensive systematic review and meta-analysis of all published genetic modifiers of SCD indicated that implementation of standardized phenotypes, statistical methods, and reporting practices should accelerate discovery and validation of genetic modifiers and development of clinically actionable genetic profiles.

Genomics of fetal haemoglobin: a targeted approach for reticulocyte transcriptome study

Background

Fetal haemoglobin (HbF) remains a major sickle cell disease modifier. The mechanism of HbF synthesis has been studied for several decades with the intention of increasing interventions for sickle cell disease (SCD), including drugs. However, the complex mechanism of HbF synthesis is influenced by multiple genetic factors interacting with environmental factors. In order to capture useful genetic information, especially with limited resources, one has to carefully design the study. This includes choosing the relevant participants, the correct phenotyping, the choice of samples, and the right genomic assays. This paper describes the approach undertaken as part of preparations for a reticulocyte transcriptome study intended to discover genes associated with HbF decline in newborns in Tanzania.

Results

Of the 152 newborns enrolled in the larger study, 40 babies were selected for the reticulocyte transcriptome study based on their HbF levels at birth and later stage of life. Of these, 30 individuals were included under the category of high HbF levels ranging from 72.6-90% and the remaining 10 under the category of low HbF levels ranging from 5.9 - 10.3%. The reticulocyte enrichment recovery purity ranged from 85% - 97%. The total RNA concentrations obtained were >250 ng total RNA, with the average purity of 1.9 (A 260/280) respectively. The total concentration obtained was sufficient for the transcriptome and other downstream assays.

Conclusion

We have documented important steps and factors to consider in identifying the relevant participants and required laboratory sample processes prior to the final stage, which involves total reticulocyte RNA sequencing.

Prevalence of Hemoglobin-S and Baseline Level of Knowledge on Sickle Cell Disease Among Pregnant Women Attending Antenatal Clinics in Dar-Es-Salaam, Tanzania

Background: Sickle cell disease (SCD) is the single most important genetic cause of childhood mortality globally. Newborn screening (NBS) is the recommended intervention aimed at early identification of babies with SCD and their linkage to care. To ensure success of NBS, pregnant women need to have the required knowledge on SCD and therefore motivation to screen their babies. Objective: The aim of this study was to determine the prevalence of hemoglobin-S and assess the baseline level of knowledge on SCD among pregnant women attending antenatal clinics in urban settings in Dar-es-Salaam, Tanzania. Methods: This cross-sectional study was conducted between August 2020 and February 2021, involving 600 pregnant women at 20-28 weeks of gestation attending antenatal clinics at Buguruni Health Center, Mbagala Hospital, and Sinza Hospital in Dar-es-Salaam, Tanzania. We administered a structured questionnaire to all participants to assess socio-demographic characteristics and baseline level of knowledge on SCD, where those scoring 7 or higher out of 10 questions were considered to have good knowledge. We screened for SCD a total of 300 participants from two centers (Buguruni Health Center and Mbagala Hospital) by using Sickle SCAN point-of-care test (BioMedomics Inc., United States). We used SPSS version 23 to analyze the data. On determining the association between level of knowledge and socio-demographic factors, we used Pearson's Chi-square and multivariate logistic regression in ascertaining the strength of associations. Results: Of the 600 participants, the majority were of the age between 26 and 35 years (51%), with the parity of 1-3 children (55.8%) and secondary level of education (43%), while 56% were self-employed. Only 14.7% had good knowledge on SCD. The majority of the participants had ever heard of SCD (81.3%), most of them heard from the streets (42.4%), and only 2.4% heard from hospitals. Of all 600 study participants, only 2 (0.3%) knew their SCD status while 7.7% declared having a family history of SCD. A proficient level of knowledge on SCD is associated with a high level of education, occupation, and knowing personal status of SCD. Among 300 participants who were screened for SCD, 252 were Hb-AA (84%), 47 were Hb-AS (15.7%), and 1 (0.3%) was Hb-SS. Conclusion: Despite the high prevalence of hemoglobin-S among pregnant women attending antenatal clinics in urban settings in Tanzania, there is a poor level of knowledge on SCD and personal knowledge of SCD status. Maternal screening and health education on SCD should be included as part of the comprehensive package for health promotion at antenatal clinics.

Developing a Sustainable Cardiovascular Disease Research Strategy in Tanzania Through Training: Leveraging From the East African Centre of Excellence in Cardiovascular Sciences Project

Introduction

Cardiovascular disease (CVD) contribute the largest mortality burden globally, with most of the deaths (80% of all deaths) occurring in low and middle-income countries (LMICs), including Tanzania. Despite the increasing burden, to date, CVD research output is still limited in Tanzania, as it is for many sub-Saharan Africa (SSA) countries. This trend hinders the establishment of locally informed CVD management and policy changes. Here, we aim to review the existing gaps while highlighting the available opportunities for a sustainable CVD research strategy in Tanzania.

Methods

A rapid review of available literature on CVD research in SSA was conducted, with emphasis on the contribution of Tanzania in the world literature of CVD. Through available literature, we identify strategic CVD research priorities in Tanzania and highlight challenges and opportunities for sustainable CVD research output.

Findings

Shortage of skilled researchers, inadequate research infrastructure, limited funding, and lack of organized research strategies at different levels (regional, country, and institutional) are among the existing key bottlenecks contributing to the low output of CVD research in Tanzania. There is generally strong global, regional and local political will to address the CVD epidemic. The establishment of the East African Centre of Excellence in Cardiovascular Sciences (EACoECVS) offers a unique opportunity for setting strategies and coordinating CVD research and training for Tanzania and the East African region.

Conclusion

There is a light of hope for long-term sustainable CVD research output from Tanzania, taking advantage of the ongoing activities and plans for the evolving EACoECVS. The Tanzanian experience can be taken as a lesson for other SSA countries.

HSC and miRNA Regulation with Implication for Foetal Haemoglobin Induction in Beta Haemoglobinopathies

Sickle cell disease (SCD) is one of the most common haemoglobinopathies worldwide, with up to 70 % of global SCD annual births occurring in sub-Saharan Africa. Reports have shown that 50 to 80 % of affected children in these countries die annually. Efforts geared towards understanding and controlling HbF production in SCD patients could lead to strategies for effective control of globin gene expression and therapeutic approaches that could be beneficial to individuals with haemoglobinopathies. Hemopoietic stem cells (HSCs) are characterized by a specific miRNA signature in every state of differentiation. The role of miRNAs has become evident both in the maintenance of the "stemness" and in the early induction of differentiation by modulation of the expression of the master pluripotency genes and during early organogenesis. miRNAs are extra regulatory mechanisms in hematopoietic stem cells (HSCs) via influencing transcription profiles together with transcript stability. miRNAs have been reported to be used to reprogram primary somatic cells toward pluripotency. Their involvement in cell editing holds the potential for therapy for many genetic diseases. This review provides a snapshot of miRNA involvement in cell fate decisions, haemoglobin induction pathway, and their journey as some emerge prime targets for therapy in beta haemoglobinopathies.

Molecular Pathways Involved in the Development of Congenital Erythrocytosis

Patients with idiopathic erythrocytosis are directed to targeted genetic testing including nine genes involved in oxygen sensing pathway in kidneys, erythropoietin signal transduction in pre-erythrocytes and hemoglobin-oxygen affinity regulation in mature erythrocytes. However, in more than 60% of cases the genetic cause remains undiagnosed, suggesting that other genes and mechanisms must be involved in the disease development. This review aims to explore additional molecular mechanisms in recognized erythrocytosis pathways and propose new pathways associated with this rare hematological disorder. For this purpose, a comprehensive review of the literature was performed and different in silico tools were used. We identified genes involved in several mechanisms and molecular pathways, including mRNA transcriptional regulation, post-translational modifications, membrane transport, regulation of signal transduction, glucose metabolism and iron homeostasis, which have the potential to influence the main erythrocytosis-associated pathways. We provide valuable theoretical information for deeper insight into possible mechanisms of disease development. This information can be also helpful to improve the current diagnostic solutions for patients with idiopathic erythrocytosis.

Inauguration of the Tanzania Society of Human Genetics: Biomedical Research in Tanzania with Emphasis on Human Genetics and Genomics

Human genetics research and applications are rapidly growing areas in health innovations and services. African populations are reported to be highly diverse and carry the greatest number of variants per genome. Exploring these variants is key to realize the genomic medicine initiative. However, African populations are grossly underrepresented in various genomic databases, which has alerted scientists to address this issue with urgency. In Tanzania, human genetics research and services are conducted in different institutions on both communicable and noncommunicable diseases. However, there is poor coordination of the research activities, often leading to limited application of the research findings and poor utilization of available resources. In addition, contributions from Tanzanian human genetics research and services are not fully communicated to the government, national, and international communities. To address this scientific gap, the Tanzania Society of Human Genetics (TSHG) has been formed to bring together all stakeholders of human genetics activities in Tanzania and to formally bring Tanzania as a member to the African Society of Human Genetics. This article describes the inauguration event of the TSHG, which took place in November 2019. It provides a justification for its establishment and discusses presentations from invited speakers who took part in the inauguration of the TSHG.