Inheritance of the Bantu/Benin haplotype causes less severe hemolytic and oxidative stress in sickle cell anemia patients treated with hydroxycarbamide

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.

Molecular Analysis of Xmn1-Polymorphic Site ´5 to Gγ of the β-Globin Gene Cluster in a Saudi Population of Jazan Region in Correlation with Hb F Expression

The southern part of Saudi Arabia has an ethnically diverse population where sickle-cell anemia (sickle cell disease) is common, but little is known about its βs haplotypes. The goal of the current study is to ascertain the prevalence of the Hb S gene with analysis of Xmn1 ′5 to Gγ haplotype among the Saudi population in the Jazan area. Initially recorded findings of (1) Hb S gene and (2) hematological parameters with Hb F levels were collected from 5990 participants. Then, the second series of 70 different patients with established sickling disease and 30 healthy individuals as a control group was recruited, in which the genotype of Xmn1 ′5 to Gγ-SNP was performed by PCR-RFLP. In the first series, the prevalence of Hb types was AA at 86.8% (N = 5198), AS at 12.4% (N = 745), and SS at 0.8% (N = 47). Of the second series, three patients (4.3%) were (±) Xmn1 ′5 to Gγ and 67 (95.7%) were (−/−) in Xmn1 ′5 to Gγ. In the controls, the (±) Xmn1 ′5 to Gγ was observed in only one individual (3.3%), aged 30. These findings possibly represent a new Saudi haplotype, [±] Xmn1 ′5 to Gγ. Our results demonstrate that most patients with SCD in Jazan have [−/−] Xmn1 with higher levels of Hb F and positive Xmn1 ′5 to Gγ normally associated with a low level of Hb F.

Common disease-associated gene variants in a Saudi Arabian population

BACKGROUND

Screening programs for the most prevalent conditions occurring in a country is an evidence-based prevention strategy. The burden of autosomal recessive disease variations in Saudi Arabia is high because of the highly consanguineous population. The optimal solution for estimating the carrier frequency of the most prevalent diseases is carrier screening.

OBJECTIVES

Identify the most influential recessive alleles associated with disease in the Saudi population.

DESIGN

We used clinical whole-exome sequencing data from an in-house familial database to evaluate the most prevalent genetic variations associated with disease in a Saudi population.

SETTINGS

King Abdullah International Medical Research Center (KAIMRC) and King Abdulaziz Medical City.

METHODS

Whole exome sequencing data obtained from clinical studies of family members, a cohort of 1314 affected and unaffected individuals, were filtered using the in-house pipeline to extract the most prevalent variant in the dataset.

MAIN OUTCOME MEASURES

Most prevalent genetic variations associated with disease in the Saudi population.

SAMPLE SIZE

1314 affected and unaffected individuals.

RESULTS

We identified 37 autosomal recessive variants and two heterozygous X-linked variants in 35 genes associated with the most prevalent disorders, which included hematologic (32%), endocrine (21%), metabolic (11%) and immunological (10%) diseases.

CONCLUSION

This study provides an update of the most frequently occurring alleles, which support future carrier screening programs.

LIMITATIONS

Single center that might represent the different regions but may be biased. In addition, most of the families included in the database are part of the proband's genetic identification for specific phenotypes.

CONFLICT OF INTEREST

None.

Association between Oxidative Stress, Genetic Factors, and Clinical Severity in Children with Sickle Cell Anemia

OBJECTIVES

To investigate the associations between several sickle cell disease genetic modifiers (beta-globin haplotypes, alpha-thalassemia, and glucose-6-phosphate dehydrogenase deficiency) and the level of oxidative stress and to evaluate the association between oxidative stress and the rates of vaso-occlusive events.

STUDY DESIGN

Steady-state oxidative and nitrosative stress markers, biological variables, genetic modulators, and vaso-occlusive crisis events requiring emergency admissions were measured during a 2-year period in 62 children with sickle cell anemia (58 SS and 4 Sβ⁰). Twelve ethnic-matched children without sickle cell anemia also participated as healthy controls (AA) for oxidative and nitrosative stress level measurement.

RESULTS

Oxidative and nitrosative stress were greater in patients with sickle cell anemia compared with control patients, but the rate of vaso-occlusive crisis events in sickle cell anemia was not associated with the level of oxidative stress. The presence of alpha-thalassemia, but not glucose-6-phosphate dehydrogenase deficiency or beta-globin haplotype, modulated the level of oxidative stress in children with sickle cell anemia.

CONCLUSION

Mild hemolysis in children with alpha-thalassemia may limit oxidative stress and could explain the protective role of alpha-thalassemia in hemolysis-related sickle cell complications.