Compound heterozygosity for KLF1 mutations is associated with microcytic hypochromic anemia and increased fetal hemoglobin

Whole exome sequencing and rare variant association study to identify genetic modifiers, KLF1 mutations, and a novel double mutation in Thai patients with hemoglobin E/beta-thalassemia

OBJECTIVES

Clinical manifestations of patients with Hemoglobin E/beta-thalassemia vary from mild to severe phenotypes despite exhibiting the same genotype. Studies have partially identified genetic modifiers. We aimed to study the association between rare variants in protein-coding regions and clinical severity in Thai patients.

METHODS

From April to November 2018, a case-control study was conducted based on clinical information and DNA samples collected from Thai patients with hemoglobin E/beta-thalassemia over the age of four years. Cases were patients with severe symptoms, while patients with mild symptoms acted as controls. Whole exome sequencing and rare variant association study were used to analyze the data.

RESULTS

All 338 unrelated patients were classified into 165 severe and 173 mild cases. Genotypes comprised 81.4% of hemoglobin E/beta-thalassemia, 2.7% of homozygous or compound heterozygous beta-thalassemia, and 0.3% of (δβ)⁰ thalassemia Hb E while 15.7% of samples were not classified as beta-thalassemia. A novel cis heterozygotes of IVS I-7 (A > T) and codon 26 (G > A) was identified. Six genes (COL4A3, DLK1, FAM186A, PZP, THPO, and TRIM51) showed the strongest associations with severity (observed p-values of <0.05; significance lost after correction for multiplicity). Among known modifiers, KLF1 variants were found in four mild patients and one severe patient.

CONCLUSION

No rare variants were identified as contributors to the clinical heterogeneity of hemoglobin E/beta-thalassemia. KLF1 mutations are potential genetic modifiers. Studies to identify genetic factors are still important and helpful for predicting severity and developing targeted therapy.

Molecular and haematological characterisation of haemolytic anaemia associated with biallelic KLF1 mutations: a case series

AIMS

Krüppel-like factor 1 (KLF1) is an erythroid-specific transcription factor playing an important role in erythropoiesis and haemoglobin (Hb) switching. Biallelic KLF1 mutations can cause haemolytic anaemia with thalassaemia-like syndromes but are rarely reported. We explore the KLF1 mutations in Thai subjects with unexplainable haemolytic anaemia.

METHODS

The study was done on 57 subjects presented with haemolytic anaemia and elevated Hb F without β-thalassaemia diseases. Hb analysis was performed using capillary electrophoresis. Analyses of α-thalassaemia, β-thalassaemia and KLF1 genes were performed using PCR-based methods and DNA sequencing.

RESULTS

Thirteen subjects with compound heterozygous for a known and five new genetic KLF1 interactions were identified, including KLF1:c.519_525dupCGGCGCC/c.892G>C with class 3/2 (n=8), and each subject with new genetic interaction, including KLF1:c.-154C>T;643C>T/c.983G>A with class 3/2, KLF1:c.-154C>T;643C>T/c.809C>G with class 3/2, KLF1:c892G>C/c.983G>A with class 2/2, KLF1:c.892G>C/c.1001C>G with class 2/2 and KLF1:c.1001C>G/c.1003G>A with class 2/2. Most of them had anaemia with Hb levels ranging from 45 to 110 g/L, hypochromic microcytosis, aniso-poikilocytosis, increased Hb F levels (17.9%-47.4%), small amounts of Hb Bart's, regular blood transfusion, hyperbilirubinaemia, increased serum ferritin and nucleated red blood cell.

CONCLUSIONS

Biallelic KLF1 mutations associated with anaemia may not be uncommon in Thailand. Characteristics of haemolytic anaemia, abnormal red cell morphology with nucleated red blood cells and elevated Hb F, and presenting small amounts of Hb Bart's without thalassaemia diseases are useful markers to further investigation of the KLF1 gene.

Identification of a genomic DNA sequence that quantitatively modulates KLF1 transcription factor expression in differentiating human hematopoietic cells

The onset of erythropoiesis is under strict developmental control, with direct and indirect inputs influencing its derivation from the hematopoietic stem cell. A major regulator of this transition is KLF1/EKLF, a zinc finger transcription factor that plays a global role in all aspects of erythropoiesis. Here, we have identified a short, conserved enhancer element in KLF1 intron 1 that is important for establishing optimal levels of KLF1 in mouse and human cells. Chromatin accessibility of this site exhibits cell-type specificity and is under developmental control during the differentiation of human CD34+ cells towards the erythroid lineage. This site binds GATA1, SMAD1, TAL1, and ETV6. In vivo editing of this region in cell lines and primary cells reduces KLF1 expression quantitatively. However, we find that, similar to observations seen in pedigrees of families with KLF1 mutations, downstream effects are variable, suggesting that the global architecture of the site is buffered towards keeping the KLF1 genetic region in an active state. We propose that modification of intron 1 in both alleles is not equivalent to complete loss of function of one allele.

Krüppel-Like Factor 1: A Pivotal Gene Regulator in Erythropoiesis

Krüppel-like factor 1 (KLF1) plays a crucial role in erythropoiesis. In-depth studies conducted on mice and humans have highlighted its importance in erythroid lineage commitment, terminal erythropoiesis progression and the switching of globin genes from γ to β. The role of KLF1 in haemoglobin switching is exerted by the direct activation of β-globin gene and by the silencing of γ-globin through activation of BCL11A, an important γ-globin gene repressor. The link between KLF1 and γ-globin silencing identifies this transcription factor as a possible therapeutic target for β-hemoglobinopathies. Moreover, several mutations have been identified in the human genes that are responsible for various benign phenotypes and erythroid disorders. The study of the phenotype associated with each mutation has greatly contributed to the current understanding of the complex role of KLF1 in erythropoiesis. This review will focus on some of the principal functions of KLF1 on erythroid cell commitment and differentiation, spanning from primitive to definitive erythropoiesis. The fundamental role of KLF1 in haemoglobin switching will be also highlighted. Finally, an overview of the principal human mutations and relative phenotypes and disorders will be described.

Thalassemia and erythroid transcription factor KLF1 mutations associated with borderline hemoglobin A2 in the Thai population

INTRODUCTION

Elevated hemoglobin (Hb) A₂ is an important diagnostic marker for β-thalassemia carriers. However, diagnosis of cases with borderline Hb A₂ may be problematic. We described the molecular characteristics found in a large cohort of Thai subjects with borderline Hb A₂.

MATERIAL AND METHODS

Examination was done on 21,657 Thai subjects investigated for thalassemia at Khon Kaen University, Thailand. A total of 202 subjects with borderline Hb A₂ (3.5-4.0%) were selectively recruited and hematological parameters were recorded. DNA variants in α-, β-, δ-globin, and Krüppel-like factor 1 (KLF1) genes were examined using PCR.

RESULTS

Among 202 subjects, DNA analysis identified carriers of α⁺-thalassemia (n = 48; 23.8%), β-thalassemia (n = 22; 10.9%) and KLF1 mutations (n = 48; 23.8%). No molecular defect was observed in the remaining 84 (41.5%) subjects. Interaction of KLF1 and α-thalassemia was observed in 10 cases. Of the 22 β-thalassemia carriers, five β⁺-thalassemia mutations were identified with lower MCV and higher Hb A₂. Seven KLF1 mutations were detected in 10 genotypes in subjects with higher MCV and Hb F. No β⁰-thalassemia, α-globin gene triplication or δ-globin gene mutation was detected.

CONCLUSIONS

A large proportion of subjects with borderline Hb A₂ are not β-thalassemia carriers and for those with β-thalassemia, only mild β⁺-thalassemia mutations were detected. Evaluation of the patients using Hb A₂, Hb F and MCV values will help in selecting cases for further molecular analysis. The results should explain the unusual phenotype of the cases and facilitate a thalassemia screening program in the region.

Experimental Babesia rossi infection induces hemolytic, metabolic, and viral response pathways in the canine host

Background

Babesia rossi is a leading cause of morbidity and mortality among the canine population of sub-Saharan Africa, but pathogenesis remains poorly understood. Previous studies of B. rossi infection were derived from clinical cases, in which neither the onset of infection nor the infectious inoculum was known. Here, we performed controlled B. rossi inoculations in canines and evaluated disease progression through clinical tests and whole blood transcriptomic profiling.

Results

Two subjects were administered a low inoculum (10⁴ parasites) while three received a high (10⁸ parasites). Subjects were monitored for 8 consecutive days; anti-parasite treatment with diminazene aceturate was administered on day 4. Blood was drawn prior to inoculation as well as every experimental day for assessment of clinical parameters and transcriptomic profiles. The model recapitulated natural disease manifestations including anemia, acidosis, inflammation and behavioral changes. Rate of disease onset and clinical severity were proportional to the inoculum. To analyze the temporal dynamics of the transcriptomic host response, we sequenced mRNA extracted from whole blood drawn on days 0, 1, 3, 4, 6, and 8. Differential gene expression, hierarchical clustering, and pathway enrichment analyses identified genes and pathways involved in response to hemolysis, metabolic changes, and several arms of the immune response including innate immunity, adaptive immunity, and response to viral infection.

Conclusions

This work comprehensively characterizes the clinical and transcriptomic progression of B. rossi infection in canines, thus establishing a large mammalian model of severe hemoprotozoal disease to facilitate the study of host-parasite biology and in which to test novel anti-disease therapeutics. The knowledge gained from the study of B. rossi in canines will not only improve our understanding of this emerging infectious disease threat in domestic dogs, but also provide insight into the pathobiology of human diseases caused by Babesia and Plasmodium species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07889-4.

Severe neonatal haemolytic anaemia caused by compound heterozygous KLF1 mutations: report of four families and literature review

Mutations in the KLF1 gene, which encodes a transcription factor playing a role in erythropoiesis, have recently been demonstrated to be a rare cause of hereditary haemolytic anaemia. We described the genotypic and phenotypic spectra of four unrelated families with compound heterozygous class 2/class 3 KLF1 mutations. All patients had p.G176RfsX179 on one allele and either p.A298P, p.R301H or p.G335R on the other allele. All presented on the first day of life with severe haemolytic anaemia with abnormal red blood cell morphology, markedly increased nucleated red blood cells and hyperbilirubinaemia. Three patients later became transfusion-dependent. All parents with heterozygous KLF1 mutation without co-inherited thalassaemia had normal to borderline mean corpuscular volume (MCV) and normal to slightly elevated Hb F. Fifteen previously reported cases of biallelic KLF1 mutations were identified from a literature review. All except one presented with severe haemolytic anaemia in the neonatal period. Our finding substantiates that compound heterozygous KLF1 mutations are associated with severe neonatal haemolytic anaemia and expands the haematologic phenotypic spectrum. In carriers, the previously suggested findings of low MCV, high Hb A₂ and high Hb F are inconsistent; thus this necessitates molecular studies for the identification of carriers.

Compound Heterozygosity for KLF1 Mutations Causing Hemolytic Anemia in Children: A Case Report and Literature Review

Background

Anemia is one of the most common diseases affecting children worldwide. Hereditary forms of anemia due to gene mutations are difficult to diagnose because they only rely on clinical manifestations. In regions with high prevalence of thalassemia such as southern China, pediatric patients with a hereditary hemolytic anemia (HHA) phenotype are often diagnosed with β-thalassemia. However, HHA can be caused by other gene defects. Here, a case previously diagnosed with thalassemia in a local hospital was sent to our laboratory for further genetic diagnosis. Preliminary molecular testing did not identify any mutations in globin genes.

Methods

All blood samples were collected after informed consent had been obtain from the proband’s parents. Both clinical and genetic analyses were conducted for the patient and her family members, including clinical data collection and sequencing of the KLF1 gene. Relevant literature was reviewed, including genetically confirmed cases with well-documented clinical summaries.

Results

Based on the detailed clinical data for this case, we diagnosed the patient with severe HHA. Sanger sequencing confirmed that there was a mutation on each KLF1 allele in the proband, which is missense mutation c.892G > C (p.Ala298Pro) inherited from father and frameshift mutation c.525_526insCGGCGCC (p.Gly176Argfs^∗179) from the mother, respectively. A summary of the KLF1 mutation spectrum and a clarification of genotype–phenotype correlation were performed through a combined analysis of the case and literature studies.

Conclusion

This study corrected the misdiagnosis and identified the etiology in a Chinese patient with HHA. Identification of the disease-causing gene is important for the treatment and care of the patient and prevention of another affected childbirth in her family. In addition, this study provided insight to better distinguish HHA patients with β-thalassemia mutations from those with KLF1 mutations.

Hemoglobin switching in mice carrying the Klf1Nan variant

Haploinsufficiency for transcription factor KLF1 causes a variety of human erythroid phenotypes, such as the In(Lu) blood type, increased HbA2 levels, and hereditary persistence of fetal hemoglobin. Severe dominant congenital dyserythropoietic anemia IV (OMIM 613673) is associated with the KLF1 p.E325K variant. CDA-IV patients display ineffective erythropoiesis and hemolysis resulting in anemia, accompanied by persistent high levels of embryonic and fetal hemoglobin. The mouse Nan strain carries a variant in the orthologous residue, KLF1 p.E339D. Klf1Nan causes dominant hemolytic anemia with many similarities to CDA-IV. Here we investigated the impact of Klf1Nan on the developmental expression patterns of the endogenous beta-like and alpha-like globins, and the human beta-like globins carried on a HBB locus transgene. We observe that the switch from primitive, yolk sac-derived, erythropoiesis to definitive, fetal liver-derived, erythropoiesis is delayed in Klf1wt/Nan embryos. This is reflected in globin expression patterns measured between E12.5 and E14.5. Cultured Klf1wt/Nan E12.5 fetal liver cells display growth- and differentiation defects. These defects likely contribute to the delayed appearance of definitive erythrocytes in the circulation of Klf1wt/Nan embryos. After E14.5, expression of the embryonic/fetal globin genes is silenced rapidly. In adult Klf1wt/Nan animals, silencing of the embryonic/fetal globin genes is impeded, but only minute amounts are expressed. Thus, in contrast to human KLF1 p.E325K, mouse KLF1 p.E339D does not lead to persistent high levels of embryonic/fetal globins. Our results support the notion that KLF1 affects gene expression in a variant-specific manner, highlighting the necessity to characterize KLF1 variant-specific phenotypes of patients in detail.

Congenital Nonspherocytic Hemolytic Anemia Caused by Krüppel-Like Factor 1 Gene Variants: Another Case Report

In this study, we report on a compound heterozygote for variants in the key erythroid transcription factor Krüppel-like factor 1 (KLF1) gene in a patient who presented with severe, transfusion-dependent hemolytic anemia. The red cells were normochromic and normocytic, and resembled those seen in patients with congenital nonspherocytic hemolytic anemia (CNSHA). Next generation sequencing (NGS) revealed that the patient was a compound heterozygote for the KLF1 frameshift variant c.519_525dup (p.Gly176ArgfsTer179) and a missense variant c.1012C>A (p.Pro338Thr). This report adds to the wide clinical spectrum of KLF1 gene variants. We suggest that loss of KLF1 should be considered in otherwise unexplained cases of congenital hemolytic anemia.

LOVD-DASH: A comprehensive LOVD database coupled with diagnosis and an at-risk assessment system for hemoglobinopathies

Hemoglobinopathies are the most common monogenic disorders worldwide. Substantial effort has been made to establish databases to record complete mutation spectra causing or modifying this group of diseases. We present a variant database which couples an online auxiliary diagnosis and at-risk assessment system for hemoglobinopathies (DASH). The database was integrated into the Leiden Open Variation Database (LOVD), in which we included all reported variants focusing on a Chinese population by literature peer review-curation and existing databases, such as HbVar and IthaGenes. In addition, comprehensive mutation data generated by high-throughput sequencing of 2,087 hemoglobinopathy patients and 20,222 general individuals from southern China were also incorporated into the database. These sequencing data enabled us to observe disease-causing and modifier variants responsible for hemoglobinopathies in bulk. Currently, 371 unique variants have been recorded; 265 of 371 were described as disease-causing variants, whereas 106 were defined as modifier variants, including 34 functional variants identified by a quantitative trait association study of this high-throughput sequencing data. Due to the availability of a comprehensive phenotype-genotype data set, DASH has been established to automatically provide accurate suggestions on diagnosis and genetic counseling of hemoglobinopathies. LOVD-DASH will inspire us to deal with clinical genotyping and molecular screening for other Mendelian disorders.

Corrupted DNA-binding specificity and ectopic transcription underpin dominant neomorphic mutations in KLF/SP transcription factors

Background

Mutations in the transcription factor, KLF1, are common within certain populations of the world. Heterozygous missense mutations in KLF1 mostly lead to benign phenotypes, but a heterozygous mutation in a DNA-binding residue (E325K in human) results in severe Congenital Dyserythropoietic Anemia type IV (CDA IV); i.e. an autosomal-dominant disorder characterized by neonatal hemolysis.

Results

To investigate the biochemical and genetic mechanism of CDA IV, we generated murine erythroid cell lines that harbor tamoxifen-inducible (ER™) versions of wild type and mutant KLF1 on a Klf1^−/− genetic background. Nuclear translocation of wild type KLF1 results in terminal erythroid differentiation, whereas mutant KLF1 results in hemolysis without differentiation. The E to K variant binds poorly to the canonical 9 bp recognition motif (NGG-GYG-KGG) genome-wide but binds at high affinity to a corrupted motif (NGG-GRG-KGG). We confirmed altered DNA-binding specificity by quantitative in vitro binding assays of recombinant zinc-finger domains. Our results are consistent with previously reported structural data of KLF-DNA interactions. We employed 4sU-RNA-seq to show that a corrupted transcriptome is a direct consequence of aberrant DNA binding.

Conclusions

Since all KLF/SP family proteins bind DNA in an identical fashion, these results are likely to be generally applicable to mutations in all family members. Importantly, they explain how certain mutations in the DNA-binding domain of transcription factors can generate neomorphic functions that result in autosomal dominant disease.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5805-z) contains supplementary material, which is available to authorized users.

Genetic disarray follows mutant KLF1-E325K expression in a congenital dyserythropoietic anemia patient

Congenital dyserythropoietic anemia type IV is caused by a heterozygous mutation, Glu325Lys (E325K), in the KLF1 transcription factor. Molecular characteristics of this disease have not been clarified, partly due to its rarity. We expanded erythroid cells from a patient's peripheral blood and analyzed its global expression pattern. We find that a large number of erythroid pathways are disrupted, particularly those related to membrane transport, globin regulation, and iron utilization. The altered genetics lead to significant deficits in differentiation. Glu325 is within the KLF1 zinc finger domain at an amino acid critical for site specific DNA binding. The change to Lys is predicted to significantly alter the target site recognition sequence, both by subverting normal recognition and by enabling interaction with novel sites. Consistent with this, we find high level ectopic expression of genes not normally present in the red cell. These altered properties explain patients' clinical and phenotypic features, and elucidate the dominant character of the mutation.

Exploring Impact of Rare Variation in Systemic Lupus Erythematosus by a Genome Wide Imputation Approach

The importance of low frequency and rare variation in complex disease genetics is difficult to estimate in patient populations. Genome-wide association studies are therefore, underpowered to detect rare variation. We have used a combined approach of genome-wide-based imputation with a highly stringent sequence kernel association (SKAT) test and a case-control burden test. We identified 98 candidate genes containing rare variation that in aggregate show association with SLE many of which have recognized immunological function, but also function and expression related to relevant tissues such as the joints, skin, blood or central nervous system. In addition we also find that there is a significant enrichment of genes annotated for disease-causing mutations in the OMIM database, suggesting that in complex diseases such as SLE, such mutations may be involved in subtle or combined phenotypes or could accelerate specific organ abnormalities found in the disease. We here provide an important resource of candidate genes for SLE.

Investigation of the variable In(Lu) phenotype caused by KLF1 variants

INTRODUCTION

KLF1 is an essential transcriptional activator that drives erythropoiesis. KLF1 variants can result in the Inhibitor of Lutheran, or In(Lu), phenotype where red blood cells (RBCs) have reduced BCAM (LU) and CD44 (IN). Other RBC surface molecules also have changed expression; however, there is controversy in the literature regarding which are truly impacted. We aimed to investigate KLF1 variants in the Australian population.

STUDY DESIGN AND METHODS

In(Lu) samples were sourced through screening and through the RBC reference laboratory. Blood donor samples (8036) were screened to identify weakened/absent Lu^b antigen. Samples were genotyped by massively parallel sequencing, while surface carbohydrates and blood group molecules were assessed by flow cytometry. Hemoglobin (Hb) types were analyzed by high-performance liquid chromatography.

RESULTS

Four of 8036 donors were identified to be In(Lu), and two previously identified In(Lu) samples were provided from the RBC reference laboratory. Five different KLF1 variants were identified; two were novel: c.954G>C/p.Trp318Cys and c.421C>T/p.Arg141*. BCAM and CD44 were reduced in all samples, consistent with previous reports. As a group, In(Lu) RBCs had reduced CD35 (KN), ICAM4 (LW), and CD147 (OK), and demonstrated increased binding of lectins ECA and SNAI. One In(Lu) sample had elevated HbF and another elevated HbA2.

CONCLUSION

Different KLF1 variants may potentially produce variable phenotypes. A framework for investigating KLF1 variants and their phenotypic impact has been provided. In the future, given available international databases, further testing algorithms (as advocated here) will allow for correlation of phenotype with genotype and therefore accurately document this variability between KLF1 variants.

miR-326 regulates HbF synthesis by targeting EKLF in human erythroid cells

Haploinsufficiency of erythroid Krüppel-like factor (EKLF/KLF1) has been shown recently to ameliorate the clinical severity of β-thalassemia by increased expression levels of fetal hemoglobin (HbF). The underlying mechanisms for role of EKLF in regulating HbF are of great interest but remain incompletely understood. In this study, we used a combination of in silico, in vitro, and in vivo approaches to identify microRNAs (miRs) involved in EKLF regulation and to validate the role of miR-326 in HbF modification. We found that miR-326 suppresses EKLF expression directly by targeting its 3' untranslated region. miR-326 overexpression in K562 cells or CD34⁺ hematopoietic progenitor cells resulted in reduced EKLF protein levels and was associated with elevated expression of γ-globin, whereas inhibition of physiological miR-326 levels increased EKLF and thus reduced γ-globin expression. Moreover, miR-326 expression is positively correlated with HbF levels in β-thalassemia patients. Our results suggest that miR-326 plays a key role in regulating EKLF expression and in modifying the HbF level, which may provide a new strategy for activating HbF in individuals with β-thalassemia or sickle cell disease.

Neomorphic effects of the neonatal anemia (Nan-Eklf) mutation contribute to deficits throughout development

Transcription factor control of cell-specific downstream targets can be significantly altered when the controlling factor is mutated. We show that the semi-dominant neonatal anemia (Nan) mutation in the EKLF/KLF1 transcription factor leads to ectopic expression of proteins that are not normally expressed in the red blood cell, leading to systemic effects that exacerbate the intrinsic anemia in the adult and alter correct development in the early embryo. Even when expressed as a heterozygote, the Nan-EKLF protein accomplishes this by direct binding and aberrant activation of genes encoding secreted factors that exert a negative effect on erythropoiesis and iron use. Our data form the basis for a novel mechanism of physiological deficiency that is relevant to human dyserythropoietic anemia and likely other disease states.

An Unusual Hydrops Fetalis Associated with Compound Heterozygosity for Krüppel-like Factor 1 mutations

Hydrops fetalis is commonly due to Hb Bart's (γ4) disease in South East Asia. Here, we report an unusual case of hydrops fetalis due to congenital dyserythropoietic anemia (CDA) associated with compound heterozygosity for Krüppel-like factor 1 (KLF1) gene mutations. Fetal cardiomegaly was first detected on routine mid-trimester scan in a pregnant woman with normal mean corpuscular volume (MCV) and Rhesus positive status. The fetus subsequently developed hydrops fetalis, and cordocentesis showed severe fetal anemia with a hemoglobin (Hb) level of 3.4 g/dL. Common causes of fetal anemia including Hb Bart's disease, parvovirus infection, and red cell antibodies were excluded. In view of the marked increase in erythroblasts at various stages of erythropoiesis, the diagnosis of CDA was suspected. We screened the couple for previously reported KLF1 gene mutations, showing that the mother was heterozygous for the c.525_526insCGGCGCC, p.Gly176Argfs*179 mutation, and her husband heterozygous for c.1012C>A, p.Pro338Thr mutation. The fetus was a compound heterozygote for these two KLF1 mutations. After counseling, repeated intrauterine transfusions were given at 27, 29, and 34 weeks' gestation; the hydrops fetalis was resolved. The baby was delivered at 34 weeks' gestation and required monthly blood transfusions but was otherwise thriving. Bone marrow aspiration at 10 months of age showed the features of ineffective erythropoiesis, compatible with CDA. In conclusion, hydrops fetalis can rarely be due to CDA associated with a compound heterozygous mutation for KLF1 gene mutations, and be managed by repeated intrauterine transfusions. Our present report adds to the wide clinical spectrum of KLF1 mutations.

Activation of KLF1 Enhances the Differentiation and Maturation of Red Blood Cells from Human Pluripotent Stem Cells

Blood transfusion is widely used in the clinic but the source of red blood cells (RBCs) is dependent on donors, procedures are susceptible to transfusion-transmitted infections and complications can arise from immunological incompatibility. Clinically-compatible and scalable protocols that allow the production of RBCs from human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) have been described but progress to translation has been hampered by poor maturation and fragility of the resultant cells. Genetic programming using transcription factors has been used to drive lineage determination and differentiation so we used this approach to assess whether exogenous expression of the Erythroid Krüppel-like factor 1 (EKLF/KLF1) could augment the differentiation and stability of iPSC-derived RBCs. To activate KLF1 at defined time points during later stages of the differentiation process and to avoid transgene silencing that is commonly observed in differentiating pluripotent stem cells, we targeted a tamoxifen-inducible KLF1-ERT2 expression cassette into the AAVS1 locus. Activation of KLF1 at day 10 of the differentiation process when hematopoietic progenitor cells were present, enhanced erythroid commitment and differentiation. Continued culture resulted the appearance of more enucleated cells when KLF1 was activated which is possibly due to their more robust morphology. Globin profiling indicated that these conditions produced embryonic-like erythroid cells. This study demonstrates the successful use of an inducible genetic programing strategy that could be applied to the production of many other cell lineages from human induced pluripotent stem cells with the integration of programming factors into the AAVS1 locus providing a safer and more reproducible route to the clinic. Stem Cells 2017;35:886-897.

Fetal haemoglobin in sickle-cell disease: from genetic epidemiology to new therapeutic strategies

Sickle-cell disease affects millions of individuals worldwide, but the global incidence is concentrated in Africa. The burden of sickle-cell disease is expected to continue to rise over the coming decades, adding to stress on the health infrastructures of many countries. Although the molecular cause of sickle-cell disease has been known for more than half a century, treatment options remain greatly limited. Allogeneic haemopoietic stem-cell transplantation is the only existing cure but is limited to specialised clinical centres and remains inaccessible for most patients. Induction of fetal haemoglobin production is a promising strategy for the treatment of sickle-cell disease. In this Series paper, we review scientific breakthroughs in epidemiology, genetics, and molecular biology that have brought reactivation of fetal haemoglobin to the forefront of sickle-cell disease research. Improved knowledge of the regulation of fetal haemoglobin production in human beings and the development of genome editing technology now support the design of innovative therapies for sickle-cell disease that are based on fetal haemoglobin.

Krüppeling erythropoiesis: an unexpected broad spectrum of human red blood cell disorders due to KLF1 variants

Until recently our approach to analyzing human genetic diseases has been to accurately phenotype patients and sequence the genes known to be associated with those phenotypes; for example, in thalassemia, the globin loci are analyzed. Sequencing has become increasingly accessible, and thus a larger panel of genes can be analyzed and whole exome and/or whole genome sequencing can be used when no variants are found in the candidate genes. By using such approaches in patients with unexplained anemias, we have discovered that a broad range of hitherto unrelated human red cell disorders are caused by variants in KLF1, a master regulator of erythropoiesis, which were previously considered to be extremely rare causes of human genetic disease.