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

Challenges and opportunities for conceiving genetically diverse sickle cell mice

A milestone in sickle cell disease (SCD) therapeutics was achieved in December 2023 with the FDA-approved gene therapy for patients aged 12 years and older. However, these therapies may only suit a fraction of patients because of cost or health risks. A better understanding of SCD outcome heterogeneity is needed to propose patient-specific pharmacological interventions. To achieve this, humanized and genetically diverse mouse models are essential for associating candidate genotypes with specific hematological traits, organ function, and disease resilience. Here, we discuss the challenges and opportunities in developing genetically diverse sickle cell mice (GDS mice). These models are expected to complement current approaches in SCD research and enhance our understanding of SCD heterogeneity and anemia.

Unraveling the Complex Genomic Interplay of Sickle Cell Disease Among the Saudi Population: A Case-Control GWAS Analysis

Sickle cell disease (SCD) is a severe inherited blood disorder characterized by abnormal hemoglobin (HbS) that leads to varying degrees of severity, including chronic hemolysis, episodic vaso-occlusion, and damage to multiple organs, causing significant morbidity and mortality. While SCD is a monogenic disease, its complications are influenced by polygenic factors. SCD prevalence is notably high in regions including the Middle East, with Saudi Arabia reporting significant cases, particularly in the Eastern Province. Most genetic factors associated with SCD outcomes have been identified in populations predominantly from Africa or of African ancestry. This study aims to identify genetic variants that characterize Saudi SCD patients with the potential to influence disease outcomes in this population. A multicenter case-control genome-wide association study (GWAS) was conducted involving 350 adult Saudi SCD patients and 202 healthy controls. Participants were genotyped using the Affymetrix Axiom array, covering 683,030 markers. Rigorous quality control measures were applied to ensure data integrity. Fisher's exact was used to identify genetic variants with a significant difference in allele frequency (p < 5 × 10-8). Functional annotations and regulatory functions of variants were determined using the Ensembl Variant Effect Predictor (VEP) and RegulomeDB databases. The GWAS identified numerous significant genetic variants characterizing SCD cases in the Saudi population. These variants, distributed across multiple chromosomes, were found in genes with known functional consequences. A substantial proportion of the markers were detected in the olfactory receptor cluster, TRIM family, and HBB locus genes. Many of the identified genes were reported in previous studies showing significant associations with various SCD outcomes, including hemoglobin regulation, inflammation, immune response, and vascular function. The findings highlight the genetic complexity underlying SCD and its clinical manifestations. The identified variants suggest potential molecular biomarkers and therapeutic targets, enhancing our understanding of the molecular basis of SCD in the Saudi population. This is the first genetic analysis characterizing SCD patients compared to healthy individuals, uncovering genetic markers that could serve as diagnostic biomarkers and therapeutic targets. Given the known molecular mechanisms of the detected genetic loci, these provide a foundation for precision medicine in SCD management, highlighting the need for further studies to validate these results and explore their clinical implications.

Novel clinical care models for patients with sickle cell disease

This educational program outlines the importance of evolving clinical care models in response to increased life expectancy and variability in individual patient experiences, particularly in the context of sickle cell disease (SCD). It emphasizes the need for personalized and adaptive care models, in which the patient should play a central role, and the need for collaborative networks of physicians and caregivers, taking into account the multisystemic nature of the disease. The proposal also discusses the role of personalized medicine and technological advances, highlighting the need for a shared medical record; the balance between rare center expertise and widespread dissemination of knowledge; and the challenges in high- and low-income countries. It emphasizes the need to move toward personalized medicine, given the significant interindividual variability in both follow-up and treatment, and the introduction of more appropriate biomarkers and predictive algorithms to aid decision-making. The proposal includes real-world examples of successful adaptation in clinical care models. It concludes with a summary of the importance and benefits of evolving clinical care models and a future outlook on the evolution of clinical care in response to demographic changes. These proposals are intended to provide a comprehensive overview of the current state and future directions of clinical care models for SCD.

Inflammatory pathways and anti-inflammatory therapies in sickle cell disease

Sickle cell disease (SCD) is a monogenic disease, resulting from a single-point mutation, that presents a complex pathophysiology and high clinical heterogeneity. Inflammation stands as a prominent characteristic of SCD. Over the past few decades, the role of different cells and molecules in the regulation of the inflammatory process has been elucidated. In conjunction with the polymerization of hemoglobin S (HbS), intravascular hemolysis, which releases free heme, HbS, and hemoglobin-related damage-associated molecular patterns, initiates multiple inflammatory pathways that are not yet fully comprehended. These complex phenomena lead to a vicious cycle that perpetuates vaso-occlusion, hemolysis, and inflammation. To date, few inflammatory biomarkers can predict disease complications; conversely, there is a plethora of therapies that reduce inflammation in SCD, although clinical outcomes vary widely. Importantly, whether the clinical heterogeneity and complications are related to the degree of inflammation is not known. This review aims to further our understanding of the roles of main immune cells, and other inflammatory factors, as potential prognostic biomarkers for predicting clinical outcomes or identifying novel treatments for SCD.

Sickle Cell Disease

Background

Sickle cell disease (SCD) is among the most frequent hereditary disorders globally and its prevalence in Europe is increasing due to migration movements.

Summary

The basic pathophysiological event of SCD is polymerization of deoxygenated sickle hemoglobin, resulting in hemolysis, vasoocclusion, and multiorgan damage. While the pathophysiological cascade offers numerous targets for treatment, currently only two disease-modifying drugs have been approved in Europe and transfusion remains a mainstay of both preventing and treating severe complications of SCD. Allogeneic stem cell transplantation and gene therapy offer a curative option but are restricted to few patients due to costs and limited availability of donors.

Key Message

Further efforts are needed to grant patients access to approved treatments, to explore drug combinations and to establish new treatment options.

Association of ZBTB38 gene polymorphism (rs724016) with height and fetal hemoglobin in individuals with sickle cell anemia

Objectives

Our study evaluated the association of the polymorphism rs724016 in the ZBTB38 gene, previously associated with height in other populations, with predictors of height, clinical outcomes, and laboratory parameters in sickle cell anemia (SCA).

Methods

Cross-sectional study with individuals with SCA and aged between 3 and 20 years. Clinical, laboratory, molecular, and bone age (BA) data were evaluated. Levels of IGF-1 and IGFBP-3 were adjusted for BA, target height (TH) was calculated as the mean parental height standard deviation score (SDS), and predicted adult height (PAH) SDS was calculated using BA.

Results

We evaluated 80 individuals with SCA. The homozygous genotype of the G allele of rs724016 was associated with a lower height SDS (p < 0.001) and, in a additive genetic model, was negatively associated with HbF levels (p = 0.016). Lower adjusted IGF-1 levels were associated with co-inheritance of alpha-thalassemia and with the absence of HU therapy. Elevated HbF levels were associated with a lower deficit in adjusted growth potential (TH minus PAH).

Conclusion

Our analysis shows that SNP rs724016 in the ZBTB38 is associated with shorter height and lower HbF levels, an important modifier of SCA.

Impact of α-Globin Gene Expression and α-Globin Modifiers on the Phenotype of β-Thalassemia and Other Hemoglobinopathies: Implications for Patient Management

In this short review, we presented and discussed studies on the expression of globin genes in β-thalassemia, focusing on the impact of α-globin gene expression and α-globin modifiers on the phenotype and clinical severity of β-thalassemia. We first discussed the impact of the excess of free α-globin on the phenotype of β-thalassemia. We then reviewed studies focusing on the expression of α-globin-stabilizing protein (AHSP), as a potential strategy of counteracting the effects of the excess of free α-globin on erythroid cells. Alternative processes controlling α-globin excess were also considered, including the activation of autophagy by β-thalassemia erythroid cells. Altogether, the studies reviewed herein are expected to have a potential impact on the management of patients with β-thalassemia and other hemoglobinopathies for which reduction in α-globin excess is clinically beneficial.

Vaso-Occlusive Crises in Sickle Cell Trait Patients With Blood Loss Anemia: A Report of Two Cases

This report of two cases confronts the longstanding perception of Sickle Cell Trait (SCT) as a clinically benign condition, highlighting its complex and severe clinical manifestations, particularly in the context of blood loss anemia and vaso-occlusive crises (VOCs). The hallmark of sickle cell disease is the severe pain caused by acute vaso-occlusion of the microvasculature that leads to bone marrow infarction. We report two cases of patients with SCT and severe anemia in the setting of blood loss secondary to uterine fibroids subsequently causing VOCs with likely bone sequestration. The occurrence of VOCs in SCT, while infrequent, can be serious and demands a high index of suspicion, particularly when patients appear in significant distress and cardiac or vascular etiologies are ruled out as a source. Reversal of anemia in this case provided quick resolution to symptoms, and we recommend other clinicians not disregard a differential of VOC in SCT carriers, and urge to treat patients as they would if they had sickle cell disease. This report challenges the conventional view of SCT as a condition of clinical benignity, calling for a recalibration in the clinical understanding, management strategies, and focus on this genetic trait under similar circumstances.