Impact of Genetic Variations on Thromboembolic Risk in Saudis with Sickle Cell Disease

BACKGROUND

Sickle cell disease (SCD) is a Mendelian disease characterized by multigenic phenotypes. Previous reports indicated a higher rate of thromboembolic events (TEEs) in SCD patients. A number of candidate polymorphisms in certain genes (e.g., FVL, PRT, and MTHFR) were previously reported as risk factors for TEEs in different clinical conditions. This study aimed to genotype these genes and other loci predicted to underlie TEEs in SCD patients.

METHODOLOGY

A multi-center genome-wide association study (GWAS) involving Saudi SCD adult patients with a history of TEEs (n = 65) and control patients without TEE history (n = 285) was performed. Genotyping used the 10× Affymetrix Axiom array, which includes 683,030 markers. Fisher's exact test was used to generate p-values of TEE associations with each single-nucleotide polymorphism (SNP). The haplotype analysis software tool version 1.05, designed by the University of Göttingen, Germany, was used to identify the common inherited haplotypes.

RESULTS

No association was identified between the targeted single-nucleotide polymorphism rs1801133 in MTHFR and TEEs in SCD (p = 0.79). The allele frequency of rs6025 in FVL and rs1799963 in PRT in our cohort was extremely low (<0.01); thus, both variants were excluded from the analysis as no meaningful comparison was possible. In contrast, the GWAS analysis showed novel genome-wide associations (p < 5 × 10-8) with seven signals; five of them were located on Chr 11 (rs35390334, rs331532, rs317777, rs147062602, and rs372091), one SNP on Chr 20 (rs139341092), and another on Chr 9 (rs76076035). The other 34 SNPs located on known genes were also detected at a signal threshold of p < 5 × 10-6. Seven of the identified variants are located in olfactory receptor family 51 genes (OR51B5, OR51V1, OR51A1P, and OR51E2), and five variants were related to family 52 genes (OR52A5, OR52K1, OR52K2, and OR52T1P). The previously reported association between rs5006884-A in OR51B5 and fetal hemoglobin (HbF) levels was confirmed in our study, which showed significantly lower levels of HbF (p = 0.002) and less allele frequency (p = 0.003) in the TEE cases than in the controls. The assessment of the haplotype inheritance pattern involved the top ten significant markers with no LD (rs353988334, rs317777, rs14788626882, rs49188823, rs139349992, rs76076035, rs73395847, rs1368823, rs8888834548, and rs1455957). A haplotype analysis revealed significant associations between two haplotypes (a risk, TT-AA-del-AA-ins-CT-TT-CC-CC-AA, and a reverse protective, CC-GG-ins-GG-del-TT-CC-TT-GG-GG) and TEEs in SCD (p = 0.024, OR = 6.16, CI = 1.34-28.24, and p = 0.019, OR = 0.33, CI = 0.13-0.85, respectively).

CONCLUSIONS

Seven markers showed novel genome-wide associations; two of them were exonic variants (rs317777 in OLFM5P and rs147062602 in OR51B5), and less significant associations (p < 5 × 10-6) were identified for 34 other variants in known genes with TEEs in SCD. Moreover, two 10-SNP common haplotypes were determined with contradictory effects. Further replication of these findings is needed.

MTHFR C677T, Prothrombin G20210A, and Factor V Leiden (G1691A) Polymorphism and Beta-Thalassemia Risk: A Meta-Analysis

Background Beta (β)-thalassemia major patients frequently suffer from many vascular problems. Thrombophilia is a blood disorder that comprises imbalances in the blood coagulating factor due to ecological and hereditary components. Previous evidence shows that thrombosis is the commonest risk in beta-thalassemia patients. Several studies have examined that MTHFR C677T, prothrombin G20210A (PT G20210A), and Factor V Leiden G1691A (FVL G1691A) polymorphism play a crucial role in the development of β-thalassemia major, yet the result was questionable and uncertain. Therefore, in this study, we executed the correlation between these gene polymorphisms with β-thalassemia major patients. Methods Suitable keywords were used to search related articles in PubMed, Google Scholar, and Web of Science. In this random-effects meta-analysis, we analyzed the odds ratio (OR) for the estimation of risk. Results A total of nine research articles with 645 β-thalassemia major patients and 989 healthy controls were incorporated in this meta-analysis. The pooled OR was assessed in MTHFR C677T, PT G20210A, and FVL G1691A polymorphism. This random-effects meta-analysis demonstrated that MTHFR C677T, PT G20210A, and FVL G1691A gene polymorphism did not significantly associate with β-thalassemia major. Moreover, the heterogeneity was significantly found in genotype CC vs CT+TT C677T (I²=61%) and allele C vs T (I²=71%) of MTHFR and genotype GG vs GA (I²=95%), GG vs GA+AA (I²=95%), GA vs GG+AA (I²=95%), and allele G vs A (I²=93%) of FVL G1691A. Conclusion The results of this meta-analysis show that MTHFR C677T, prothrombin G20210A, and Factor V Leiden (G1691A) gene polymorphism are not a risk factor for β-thalassemia major.

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.

Factor V Leiden G1691A and prothrombin G20210A mutations among Palestinian patients with sickle cell disease

Background

Vascular thrombosis is an important pathophysiological aspect of sickle cell disease (SCD). This study aimed to investigate the prevalence and clinical impact of factor V Leiden G1691A (FVL) and prothrombin G20210A mutations among Palestinian sickle cell disease (SCD) patients.

Methods

A total of 117 SCD patients, including 59 patients with sickle cell anemia (SS), 33 patients with sickle β-thalassemia and 25 individuals with sickle cell trait (AS) were studied. The control group consisted of 118 healthy individuals. FVL and prothrombin G20210A mutations were determined by RFLP PCR.

Results

Analysis of the clinical history of SCD patients revealed that seven patients have had vascular complications such as ischemic stroke or deep vein thrombosis. In SCD patients, the inheritance of the FVL mutation showed a significantly higher incidence of pain in joints, chest and abdomen as well as regular dependence on blood transfusion compared to SCD with the wild type. Age- and sex-adjusted logistic regression analysis revealed a significant association between FVL and sickle cell anemia with an odds ratio (OR) of 5.6 (95% confidence intervals [CI] of 1.91–39.4, P = 0.039) in SS patients. However, increased prevalence of the FVL in AS subjects and sickle β-thalassemia patients was not statistically significant compared to controls (OR 3.97, 95% CI 0.51–28.6, P = 0.17 and OR 3.59, 95% CI 0.35–41.6, P = 0.26, respectively). The distribution of prothrombin G20210A mutation among SCD patients compared to controls was not significantly different, thus our findings do not support an association of this mutation with SCD.

Conclusions

FVL was more prevalent among SS patients compared to controls and it was associated with higher incidence of disease complications among SCD patients.

Prevalence of Factor V Leiden-G1691A and MTHFR-C677T Thrombosis Gene Modifier in Iron Deficiency Anemia: A Pathophysiological Effect in Indian Isolates

Normal iron levels are required to prevent thrombocytosis by inhibiting thrombopoiesis. Thrombocytosis is usually associated with a mild iron deficiency and is the result of a lack of inhibition of thrombopoiesis. Study participants were 430 iron deficiency anemia (IDA) patients. Ten (10) mL of venous blood were collected for the subjects. Ferritin analysis was done by ELISA method while Hemogram analysis was done by auto-analyzer. Factor V Leiden, PRTG20210A, and MTHFR C677T genotype analysis was performed by PCR-RFLP method. Among the patients, 9 were heterozygous (G>A) and 2 were homozygous (A>A) carrier of FV Leiden; while 20 were heterozygous (C>T) and 3 were homozygous (T>T) for MTHFR polymorphism. None of the patient was identified with PT mutation. Patients with thrombosis gene marker had lower hemoglobin, mean corpuscular volume, mean corpuscular haemoglobin levels, and mean corpuscular hemoglobin concentration than patients without thrombosis gene marker. Serum ferritin was elevated in subject with the absence of thrombosis gene markers. Our data suggest a high impact of inherited hypercoagulability risk factors in the pathogenesis of IDA and its complications.

The Prevalence of Factor V Leiden (G1691A) and Methylenetetrahydrofolate Reductase C677T Mutations in Sickle Cell Disease in Western India

The prevalence of the Factor V Leiden (FVL; G1691A) mutation and the methylenetetrahydrofolate reductase (MTHFR; C677T) mutation was determined in 180 patients with sickle cell (SS) disease (126 sickle homozygous and 54 sickle β-thalassaemia—age 1-47 years) and in 130 healthy controls. The FVL mutation in the heterozygous state was present in only 3 patients with SS disease and was absent in the controls. Genotyping of MTHFR 677C > T revealed increased frequency of the C allele than the T allele in patients as well as in controls. This suggests that these genetic markers may not be major risk factors for a hypercoagulable state in Indian patients with SS disease.