Haemolysis in sickle cell anaemia: effects of polymorphisms in α-globin gene regulatory elements

Effects of Senegal haplotype (Xmn1-rs7412844), alpha-thalassemia (3.7kb HBA1/HBA2 deletion), NPRL3-rs11248850 and BCL11A-rs4671393 variants on sickle cell nephropathy

OBJECTIVE

Sickle cell anemia (SCA) can cause substantial kidney dysfunction resulting in sickle cell nephropathy, which may be affected by the presence of modifier genes. This study evaluates the effects of some modifier genes on sickle cell nephropathy.

METHODS

Patients living with SCA were recruited. Alpha-thalassemia (3.7kb HBA1/HBA2 deletion) was genotyped using gap PCR multiplex. Senegal haplotype (Xmn1-rs7412844), BCL11A-rs4671393 and NPRL3-rs11248850 were genotyped using Mass Array. The effects of variants on kidney dysfunction were then evaluated using multivariate analysis.

RESULTS

The number of patients living with SCA included in this study was 162 with a median age of 20 years [minimum-maximum: 4-57] and a female frequency of 53.21%. Senegal haplotype, BCL11A-rs4671393 variant were protective factors against albuminuria stage A2 with an odds ratio (OR) of 0.22 (95% CI 0.05-0.90) and 0.27 (95% CI 0.08-0.96) respectively. The combination NPRL3-rs11248850 variant - 3.7kb HBA1/HBA2 deletion was a protective factor against albuminuria stage A2 (OR = 0.087, 95% Cl 0.01-0.78) but it was a risk factor for glomerular hyperfiltration (OR = 17.69, 95% CI 1.85-169.31).

CONCLUSIONS

All four variants displayed a protective effect against albuminuria stage A2. The combination alpha-thalassemia - NPRL3-rs11248850 variant is a risk factor for glomerular hyperfiltration.

Regulatory Mutation Study in Cases with Unsolved Hypochromic Microcytic Anemia and α-Major Regulatory Element Haplotype Analysis in Iran

α-Thalassemia (α-thal) is an inherited blood disorder with different clinical manifestations. Although genetic causes of anemia are identified routinely in the majority of α-thal cases, a pathogenic variant in a few cases remains undiagnosed. In this study, some reported regulatory mutations have been investigated in five unsolved α-thal carriers. α-Major regulatory element (α-MRE) haplotype analysis has also been performed in Iran for the first time. Four regions, including the HBA2 core promoter, the highly conserved sequence of hypersensitive-40 (HS-40), a region containing regulatory single nucleotide polymorphism (SNP) CR062116, and a region containing rs7203560, were screened for changes by Sanger sequencing in a total of five unsolved suspected α-thal carriers. The frequencies of α-MRE haplotypes B and C were also determined in control samples with normal hematological indices. No pathogenic variant was found in the investigated regions. Haplotype frequencies observed for B and C haplotypes fell into the range of frequencies observed in previous studies. The investigated genotypes in the control group were in the Hardy-Weinberg equilibrium. This study can provide evidence that there is no association between the B haplotype and microcytic hypochromic anemia. The cause of anemia remains a mystery in our unsolved cases, which demonstrates the need for further studies on the causes of hypochromic microcytic anemia in individuals with intact α- and β-globin genes without iron deficiency.

MZF1 regulates α-globin gene transcription via long-range interactions in erythroid differentiation

Precise spatiotemporal gene expression regulation is crucial for human erythropoiesis. However, dramatic changes in the chromatin structure and transcriptome involved in α-globin gene expression during erythropoiesis still not fully understand. To identify candidate regulators for α-globin gene regulation, we carried out an integrated approach by integrating publicly available transcriptomic and epigenomic data. We computed active enhancers by overlapping enriched regions marked with H3K4me1 and H3K27ac and correlated their activity with mRNA expression. Next, we cataloged potential transcription factors via de novo motif analysis. We highlighted the discovery of potential novel transcription factor MZF1 of the α-globin gene in erythroid differentiation. To validate the role of MZF1, we quantified the expression level of MZF1 and α-globin gene in HSPCs, early erythroid progenitors and late erythroid precursors cells. Both the mRNA and protein expression patterns of MZF1 were consistent with the α-globin gene. Also, the qPCR result showed that the expression of the α-globin gene was significantly increased by the MZF1 overexpression. To further investigate the role of MZF1 regulating α-globin gene transcriptional activity during erythroid differentiation, we performed ChIP-qPCR at the α-globin locus. Our results showed that MZF1 recruitment both at 4 upstream HS sites and α-globin gene promoter in erythroid precursor cells. To determine the importance of the MZF1 to enhancer-promoter interaction at the α-globin locus, we compared interaction frequency before and after knockdown of MZF1 by chromosome conformation capture (3C) assay. Upon MZF1 depletion, both the expression of the α-globin gene and all 3C signals were significantly decreased. Taken together, MZF1 plays an important role in regulating α-globin gene expression by binding to long-region enhancers and α-globin gene promoter and facilitates the organization of specific 3D chromatin architecture in erythroid differentiation.

Sickle cell disease in the era of precision medicine: looking to the future

Introduction

Sickle cell anemia is a mendelian disease that is noted for the heterogeneity of its clinical expression. Because of this, providing an accurate prognosis has been a longtime quest.

Areas covered

Reviewed are the benefits and shortcomings of testing for the major modulators of the severity of disease, like fetal hemoglobin and α thalassemia, along with studies that have attempted to link genetic variation with sub-phenotypes of disease in a predictive fashion. Induced pluripotent stem cells driven to differentiate into erythroid precursor cells provide another area for potential patient-specific drug testing.

Expert opinion

Fetal hemoglobin is the strongest modulator of sickle cell anemia but simply measuring its blood levels is an insufficient means of forecasting an individual's prognosis. A more precise method would be to know the distribution of fetal hemoglobin levels across the population of red cells, an assay not yet available. Prognostic measures have been developed using genetic and other signatures, but their predictive value is suboptimal. Widely applicable assays must be developed to allow a tailored approach to using the several new treatments that are likely to be available in the near future.