Frequency of the MTHFR C677T Polymorphism in Yemeni Children with Sickle Cell Disease

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.

Relevance of Plasma Homocysteine and Methylenetetrahydrofolate Reductase 677TT Genotype in Sickle Cell Disease: A Systematic Review and Meta-Analysis

We evaluated the relevance of plasma homocysteine (HC) and the TT genotype of the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism (rs1801133) in sickle cell disease (SCD) and associated vaso-occlusive crisis (VOC) and ischemic stroke (IS). We identified in Embase and Medline 22 studies on plasma HC and 22 on MTHFR genotypes. Due to age-related HC differences, adult and paediatric SCD were separated: 879 adult SCD and 834 controls (CTR) yielded a neutral effect size; 427 paediatric SCD and 625 CTR favoured SCD (p = 0.001) with wide heterogeneity (I2 = 95.5%) and were sub-grouped by country: six studies (Dutch Antilles n = 1, USA n = 5) yielded a neutral effect size, four (India n = 1, Arab countries n = 3) favoured SCD (p < 0.0001). Moreover, 249 SCD in VOC and 419 out of VOC yielded a neutral effect size. The pooled prevalence of the MTHFR TT genotype in 267 SCD equalled that of 1199 CTR (4.26% vs. 2.86%, p = 0.45), and in 84 SCD with IS equalled that of 86 without IS (5.9% vs. 3.7%, p = 0.47); removal of one paediatric study yielded a significant effect size (p = 0.006). Plasma HC in paediatric SCD from Middle East and India was higher, possibly due to vitamin deficiencies. Despite its low prevalence in SCD, the MTHFR TT genotype relates to adult IS.

Methylenetetrahydrofolate reductase polymorphisms as genetic markers to predict homocysteinemia and clinical severity in sickle cell disease

Aim: The present study observed the relationship between the methylenetetrahydrofolate reductase genotypes and clinical outcome in children with sickle cell disorder. Methodology: A total of 249 children were recruited for the study and evaluated clinically for calculating severity score, homocysteine levels and C677T and A1298C genotyping. Results: The frequencies of variant genotypes were 28.1% CT/TT677 and 69.1% AC/CC1298. Plasma homocysteine was significantly elevated in variant groups (p < 0.001). Both the genotypes accorded significant association with homocysteinemia (p < 0.001). Vascular crisis (p = 0.04), frequency of hospitalization (p < 0.001) and severity score (p = 0.02) revealed association with C677T and not with A1298C. The CT/TT677 genotypes showed 3.39-times (p = 0.032) increase in a higher score for severity. Conclusion: C677T depicted significant association with clinical severity in study population.

Association between MTHFR 677C>T polymorphism and vascular complications in sickle cell disease: A meta-analysis

Sickle cell disease (SCD) is considered as a vascular disease due to its chronic vascular manifestations such as leg ulcers, priapism, acute chest syndrome (ACS), stroke, retinopathy, renal insufficiency, pulmonary hypertension, avascular necrosis of the femoral head (AVNF) and splenic infarction. Emerging evidence has shown that the MTHFR 677C>T variant allele is associated with vascular complications (VC) in patients with SCD; however, results from individual studies are inconclusive. The aim of this meta-analysis is to evaluate the association between the MTHFR 677C>T polymorphism and the susceptibility for VC in SCD patients. Articles published in English were collected from Medline, PubMed, Embase, and Web of Science databases. As a result, 11 studies in different populations including 614 SCD patients with VC, and 559 patients without VC were selected. Meta-analysis in fixed effect model showed that mutant genotypes (CT+TT vs. CC) of the MTHFR 677C>T polymorphism is associated with increased risk of vascular complication (OR=1.81, 95% CI=1.37-2.40, P<0.001). This study did not demonstrate publication bias or between-study heterogeneity. Our meta-analysis establishes that the MTHFR 677C>T polymorphism as a high-penetrant risk factor for VC in SCD patients. Further research is needed to support the clinical utility of MTHFR genetic testing for predicting VC in patients with sickle cell disease.

Utility of plasma transferrin receptor, ferritin and inflammatory markers in children with sickle cell disease

BACKGROUND

Soluble transferrin receptor (sTfR) is generally unaffected by inflammatory status, whereas ferritin increases along with acute-phase proteins. The utility of these iron biomarkers in relation to inflammatory markers in children with sickle cell disease (SCD) with differing grades of severity is unclear.

OBJECTIVES

To describe iron biomarker profiles and inflammatory responses in relation to disease severity in children with SCD.

METHODS

This cross-sectional study describes plasma levels of sTfR, ferritin, C-reactive protein (CRP) and serum amyloid A (SAA) among 102 Yemeni children with SCD in relation to clinical profiles and disease severity.

RESULTS

Median (IQR) sTfR was 58·5 mg/L (38-81), and concentration was positively correlated with reticulocyte count (r = +0·31, P = 0·002) and splenic enlargement (r = +0·20, P = 0·04), and was negatively correlated with Hb (r = -0·28, P = 0·004). Subcategories of children in a steady state were identified using ferritin and CRP cut-off values to discriminate iron status. In children in a steady state, the prevalence of iron deficiency was 25%, iron repletion 48% and marginal or normal status 27%. Ferritin concentration correlated positively with Hb and 23% of iron-deficient children had severe anaemia. CRP and SAA were increased in the steady state and were higher with acute disease complications (P<0·05 and <0·001, respectively). There was no association between sTfR or sTfR-ferritin index and inflammatory markers or disease severity score.

CONCLUSION

In SCD, elevated sTfR is related to hypererythropoietic activity and does not correlate with inflammatory status or disease severity. Iron deficiency prevalence was estimated to be 25%. A classification of iron status is proposed.