An update on the pathogenesis and diagnosis of Diamond-Blackfan anemia

Pituitary hemochromatosis in the clinical setting of secondary amenorrhea in a patient with Diamond-Blackfan anemia

Secondary amenorrhea is the absence of menses for more than 3 months in women who previously had regular menstrual cycles or 6 months for those with irregular cycles. Workup of secondary amenorrhea includes laboratory analysis to assess pituitary function, specifically luteinizing hormone (LH) and follicle stimulating hormone (FSH). If low, structural evaluation of the pituitary gland with MRI is recommended. We report a case of a 31-year-old female with history of transfusion-dependent Diamond-Blackfan anemia and type 2 diabetes that reported amenorrhea for 1 year following intrauterine device (IUD) removal. Due to low LH and FSH, the patient underwent an MRI of the pituitary gland. Imaging demonstrated complete absence of MRI signal within the pituitary parenchyma, which confirmed pituitary dysfunction from secondary hemochromatosis, presumably due to iron overload from multiple transfusions. As a result of her imaging and laboratory assessment, she was placed on an iron chelator and oral contraception.

Preclinical development of lentiviral vector gene therapy for Diamond-Blackfan anemia syndrome

Diamond-Blackfan anemia syndrome (DBAS) is an inherited bone marrow failure disorder caused by haploinsufficiency of ribosomal protein genes, most commonly RPS19. Limited access to patient hematopoietic stem and progenitor cells (HSPCs) is a major roadblock to developing novel therapies for DBAS. We developed a self-inactivating third-generation RPS19-encoding lentiviral vector (LV) called SJEFS-S19 for DBAS gene therapy. To facilitate LV design, optimize transduction, and assess potential therapeutic efficacy, we leveraged a human cellular model of DBAS based on heterozygous disruption of RPS19 in healthy donor CD34+ HSPCs. We show that SJEFS-S19 LV can rescue DBAS-associated defects in ribosomal RNA processing, erythropoiesis, and competitive bone marrow repopulation. Transduction of RPS19+/- CD34+ HSPCs with SJEFS-S19 LV followed by xenotransplantation into immunodeficient mice generated a polyclonal HSPC population with normal multilineage differentiation and a diverse integration site profile resembling that of clinically proven LVs. Overall, these preclinical studies demonstrate the safety and efficacy of SJEFS-S19, a novel LV for future DBAS gene therapy.

DNA damage repair in megakaryopoiesis: molecular and clinical aspects

INTRODUCTION

Endogenous DNA damage is a significant factor in the damage of hematopoietic cells. Megakaryopoiesis is one of the pathways of hematopoiesis that ends with the production of platelets and plays the most crucial role in hemostasis. Despite the presence of efficient DNA repair mechanisms, some endogenous lesions can lead to mutagenic alterations, disruption of pathways of hematopoiesis including megakaryopoiesis and potentially result in human diseases.

AREAS COVERED

The complex regulation of DNA repair mechanisms plays a central role in maintaining genomic integrity during megakaryopoiesis and influences platelet production efficiency and quality. Moreover, anomalies in DNA repair processes are involved in several diseases associated with megakaryopoiesis, including myeloproliferative disorders and thrombocytopenia.

EXPERT OPINION

In the era of personalized medicine, diagnosing diseases related to megakaryopoiesis can only be made with a complete assessment of their molecular aspects to provide physicians with critical molecular data for patient management and to identify the subset of patients who could benefit from targeted therapy.

Establishment of a Diamond-Blackfan anemia like model in zebrafish

BACKGROUND

Anemia is defined as a lack of erythrocytes, low hemoglobin levels, or abnormal erythrocyte morphology. Diamond-Blackfan anemia (DBA) is a rare and severe congenital hypoplastic anemia that occurs due to the dominant inheritance of a ribosomal protein gene mutation. Even rarer is a case described as Diamond-Blackfan anemia like (DBAL), which occurs due to a loss-of-function EPO mutation recessive inheritance. The effective cures for DBAL are bone marrow transfusion and treatment with erythropoiesis-stimulating agents (ESAs). To effectively manage the condition, construction of DBAL models to identify new medical methods or screen drugs are necessary.

RESULTS

Here, an epoa-deficient mutant zebrafish called epoaszy8 was generated to model DBAL. The epoa-deficiency in zebrafish caused developmental defects in erythroid cells, leading to severe congenital anemia. Using the DBAL model, we validated a loss-of-function EPO mutation using an in vivo functional analysis and explored the ability of ESAs to alleviate congenital anemia.

CONCLUSIONS

Together, our study demonstrated that epoa deficiency in zebrafish leads to a phenotype resembling DBAL. The DBAL zebrafish model was found to be beneficial for the in vivo assessment of patient-derived EPO variants with unclear implications and for devising potential therapeutic approaches for DBAL.

Normal Erythroid Precursors in Diamond-Blackfan Anemia: A Rare Case Highlighting Challenges That Remain

Diamond-Blackfan anemia (DBA) is a rare, inherited bone marrow failure syndrome that is both genetically and clinically heterogeneous. The diagnosis of DBA has changed over time, with advancements in our understanding of the varied genetic etiologies and phenotypic manifestations of the disease. We present a rare case of a patient who never developed erythroid precursor hypoplasia, adding to the understanding of atypical manifestations of DBA. Our patient had spontaneous remission followed by subsequent relapse, both atypical and poorly understood processes in DBA. We highlight important considerations in diagnostically challenging cases and review major outstanding questions surrounding DBA.

Hematopoietic cell transplantation and gene therapy for Diamond-Blackfan anemia: state of the art and science

Diamond-Blackfan anemia (DBA) is one of the most common inherited causes of bone marrow failure in children. DBA typically presents with isolated erythroid hypoplasia and anemia in infants. Congenital anomalies are seen in 50% of the patients. Over time, many patients experience panhematopoietic defects resulting in immunodeficiency and multilineage hematopoietic cytopenias. Additionally, DBA is associated with increased risk of myelodysplastic syndrome, acute myeloid leukemia and solid organ cancers. As a prototypical ribosomopathy, DBA is caused by heterozygous loss-of-function mutations or deletions in over 20 ribosomal protein genes, with RPS19 being involved in 25% of patients. Corticosteroids are the only effective initial pharmacotherapy offered to transfusion-dependent patients aged 1 year or older. However, despite good initial response, only ~20-30% remain steroid-responsive while the majority of the remaining patients will require life-long red blood cell transfusions. Despite continuous chelation, iron overload and related toxicities pose a significant morbidity problem. Allogeneic hematopoietic cell transplantation (HCT) performed to completely replace the dysfunctional hematopoietic stem and progenitor cells is a curative option associated with potentially uncontrollable risks. Advances in HLA-typing, conditioning regimens, infection management, and graft-versus-host-disease prophylaxis have led to improved transplant outcomes in DBA patients, though survival is suboptimal for adolescents and adults with long transfusion-history and patients lacking well-matched donors. Additionally, many patients lack a suitable donor. To address this gap and to mitigate the risk of graft-versus-host disease, several groups are working towards developing autologous genetic therapies to provide another curative option for DBA patients across the whole age spectrum. In this review, we summarize the results of HCT studies and review advances and potential future directions in hematopoietic stem cell-based therapies for DBA.

Anemia and Associated Risk Factors in Pediatric Patients

Anemia is the most common hematologic abnormality identified in children and represents a major global health problem. A delay in diagnosis and treatment might place patients with anemia at risk for the development of rare but serious complications, including chronic and irreversible cognitive impairment. Identified risk factors contributing to the development of anemia in children include the presence of nutritional deficiencies, environmental factors, chronic comorbidities, and congenital disorders of hemoglobin or red blood cells. Pediatricians, especially those in the primary care setting, serve a particularly critical role in the identification and care of those children affected by anemia. Prompt recognition of these risk factors is crucial for developing appropriate and timely therapeutic interventions and prevention strategies.

The Molecular and Genetic Mechanisms of Inherited Bone Marrow Failure Syndromes: The Role of Inflammatory Cytokines in Their Pathogenesis

Inherited bone marrow failure syndromes (IBMFSs) include Fanconi anemia, Diamond-Blackfan anemia, Shwachman-Diamond syndrome, dyskeratosis congenita, severe congenital neutropenia, and other rare entities such as GATA2 deficiency and SAMD9/9L mutations. The IBMFS monogenic disorders were first recognized by their phenotype. Exome sequencing has validated their classification, with clusters of gene mutations affecting DNA damage response (Fanconi anemia), ribosome structure (Diamond-Blackfan anemia), ribosome assembly (Shwachman-Diamond syndrome), or telomere maintenance/stability (dyskeratosis congenita). The pathogenetic mechanisms of IBMFSs remain to be characterized fully, but an overarching hypothesis states that different stresses elicit TP53-dependent growth arrest and apoptosis of hematopoietic stem, progenitor, and precursor cells. Here, we review the IBMFSs and propose a role for pro-inflammatory cytokines, such as TGF-β, IL-1β, and IFN-α, in mediating the cytopenias. We suggest a pathogenic role for cytokines in the transformation to myeloid neoplasia and hypothesize a role for anti-inflammatory therapies.

An RPS19-edited model for Diamond-Blackfan anemia reveals TP53-dependent impairment of hematopoietic stem cell activity

Diamond-Blackfan anemia (DBA) is a genetic blood disease caused by heterozygous loss-of-function mutations in ribosomal protein (RP) genes, most commonly RPS19. The signature feature of DBA is hypoplastic anemia occurring in infants, although some older patients develop multilineage cytopenias with bone marrow hypocellularity. The mechanism of anemia in DBA is not fully understood and even less is known about the pancytopenia that occurs later in life, in part because patient hematopoietic stem and progenitor cells (HSPCs) are difficult to obtain, and the current experimental models are suboptimal. We modeled DBA by editing healthy human donor CD34+ HSPCs with CRISPR/Cas9 to create RPS19 haploinsufficiency. In vitro differentiation revealed normal myelopoiesis and impaired erythropoiesis, as observed in DBA. After transplantation into immunodeficient mice, bone marrow repopulation by RPS19+/- HSPCs was profoundly reduced, indicating hematopoietic stem cell (HSC) impairment. The erythroid and HSC defects resulting from RPS19 haploinsufficiency were partially corrected by transduction with an RPS19-expressing lentiviral vector or by Cas9 disruption of TP53. Our results define a tractable, biologically relevant experimental model of DBA based on genome editing of primary human HSPCs and they identify an associated HSC defect that emulates the pan-hematopoietic defect of DBA.

Ribosome biogenesis in disease: new players and therapeutic targets

The ribosome is a multi-unit complex that translates mRNA into protein. Ribosome biogenesis is the process that generates ribosomes and plays an essential role in cell proliferation, differentiation, apoptosis, development, and transformation. The mTORC1, Myc, and noncoding RNA signaling pathways are the primary mediators that work jointly with RNA polymerases and ribosome proteins to control ribosome biogenesis and protein synthesis. Activation of mTORC1 is required for normal fetal growth and development and tissue regeneration after birth. Myc is implicated in cancer development by enhancing RNA Pol II activity, leading to uncontrolled cancer cell growth. The deregulation of noncoding RNAs such as microRNAs, long noncoding RNAs, and circular RNAs is involved in developing blood, neurodegenerative diseases, and atherosclerosis. We review the similarities and differences between eukaryotic and bacterial ribosomes and the molecular mechanism of ribosome-targeting antibiotics and bacterial resistance. We also review the most recent findings of ribosome dysfunction in COVID-19 and other conditions and discuss the consequences of ribosome frameshifting, ribosome-stalling, and ribosome-collision. We summarize the role of ribosome biogenesis in the development of various diseases. Furthermore, we review the current clinical trials, prospective vaccines for COVID-19, and therapies targeting ribosome biogenesis in cancer, cardiovascular disease, aging, and neurodegenerative disease.

Splice-site variant in the RPS7 5'-UTR leads to a decrease in the mRNA level and development of Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is an inherited bone marrow failure syndrome characterized by erythroid aplasia. Pathogenic variants in ribosomal protein (RP) genes, GATA1, TSR2, and EPO, are considered to be the etiology of DBA. Variants in 5'-untranslated regions (UTRs) of these genes are poorly studied and can complicate the variant interpretation. We investigated the functional consequences NM_001011.4:c.-19 + 1G > T variant in the donor splice-site of the RPS7 5'-UTR. This variant was found in a family where two sons with DBA were carriers. Father, who also had this variant, developed myelodysplastic syndrome, which caused his death. Search for candidate causal variants and copy number variations in DBA-associated genes left RPS7 variant as the best candidate. Trio whole exome sequencing analysis revealed no pathogenic variants in other genes. Functional analysis using luciferase expression system revealed that this variant leads to disruption of splicing. Also, a decrease in the levels of mRNA and protein expression was detected. In conclusion, the established consequences of 5'-UTR splice-site variant c.-19 + 1G > T in the RPS7 gene provide evidence that it is likely pathogenic.

[Prevalence and risk factors of obesity in children with Diamond-Blackfan anemia]

OBJECTIVES

To investigate the distribution of body mass index (BMI) and risk factors for obesity in children with Diamond-Blackfan Anemia (DBA).

METHODS

The children with DBA who attended National Clinical Research Center for Blood Diseases, Institute of Hematology & Blood Diseases Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, from January 2003 to December 2020 were enrolled as subjects. The related clinical data and treatment regimens were recorded. The height and weight data measured within 1 week before or after follow-up time points were collected to calculate BMI. The risk factors for obesity were determined by multivariate regression analysis in children with DBA.

RESULTS

A total of 129 children with DBA were enrolled, among whom there were 80 boys (62.0%) and 49 girls (38.0%), with a median age of 49 months (range 3-189 months). The prevalence rate of obesity was 14.7% (19/129). The multivariate logistic regression analysis showed that the absence of ribosomal protein gene mutation was closely associated with obesity in children with DBA (adjusted OR=3.63, 95%CI: 1.16-11.38, adjusted P=0.027). In children with glucocorticoid-dependent DBA, obesity was not associated with age of initiation of glucocorticoid therapy, duration of glucocorticoid therapy, and maintenance dose of glucocorticoids (P>0.05).

CONCLUSIONS

There is a high prevalence rate of obesity in children with DBA, and the absence of ribosomal protein gene mutation is closely associated with obesity in children with DBA.

Interactions between nuclear receptors glucocorticoid receptor α and peroxisome proliferator-activated receptor α form a negative feedback loop

Both nuclear receptors glucocorticoid receptor α (GRα) and peroxisome proliferator-activated receptor α (PPARα) are involved in energy and lipid metabolism, and possess anti-inflammation effects. Previous studies indicate that a regulatory loop may exist between them. In vivo and in vitro studies showed that glucocorticoids stimulate hepatic PPARα expression via GRα at the transcriptional level. This stimulation of PPARα by GRα has physiological relevance and PPARα is involved in many glucocorticoid-induced pathophysiological processes, including gluconeogenesis and ketogenesis during fasting, insulin resistance, hypertension and anti-inflammatory effects. PPARα also synergizes with GRα to promote erythroid progenitor self-renewal. As the feedback, PPARα inhibits glucocorticoid actions at pre-receptor and receptor levels. PPARα decreases glucocorticoid production through inhibiting the expression and activity of type-1 11β-hydroxysteroid dehydrogenase, which converts inactive glucocorticoids to active glucocorticoids at local tissues, and also down-regulates hepatic GRα expression, thus forming a complete and negative feedback loop. This negative feedback loop sheds light on prospective multi-drug therapeutic treatments in inflammatory diseases through a combination of glucocorticoids and PPARα agonists. This combination may potentially enhance the anti-inflammatory effects while alleviating side effects on glucose and lipid metabolism due to GRα activation. More investigations are needed to clarify the underlying mechanism and the relevant physiological or pathological significance of this regulatory loop.

Decoding the pathogenesis of Diamond-Blackfan anemia using single-cell RNA-seq

Ribosomal protein dysfunction causes diverse human diseases, including Diamond-Blackfan anemia (DBA). Despite the universal need for ribosomes in all cell types, the mechanisms underlying ribosomopathies, which are characterized by tissue-specific defects, are still poorly understood. In the present study, we analyzed the transcriptomes of single purified erythroid progenitors isolated from the bone marrow of DBA patients. These patients were categorized into untreated, glucocorticoid (GC)-responsive and GC-non-responsive groups. We found that erythroid progenitors from untreated DBA patients entered S-phase of the cell cycle under considerable duress, resulting in replication stress and the activation of P53 signaling. In contrast, cell cycle progression was inhibited through induction of the type 1 interferon pathway in treated, GC-responsive patients, but not in GC-non-responsive patients. Notably, a low dose of interferon alpha treatment stimulated the production of erythrocytes derived from DBA patients. By linking the innately shorter cell cycle of erythroid progenitors to DBA pathogenesis, we demonstrated that interferon-mediated cell cycle control underlies the clinical efficacy of glucocorticoids. Our study suggests that interferon administration may constitute a new alternative therapeutic strategy for the treatment of DBA. The trial was registered at www.chictr.org.cn as ChiCTR2000038510.

Downregulation of SATB1 by miRNAs Reduces Megakaryocyte/Erythroid Progenitor Expansion in pre-clinical models of Diamond Blackfan Anemia

Diamond Blackfan Anemia (DBA) is an inherited bone marrow failure syndrome that is associated with anemia, congenital anomalies, and cancer predisposition. It is categorized as a ribosomopathy, because over 80% or patients have haploinsufficiency of either a small or large subunit-associated ribosomal protein (RP). The erythroid pathology is predominantly due to a block and delay in early committed erythropoiesis with reduced Megakaryocyte/Erythroid Progenitors (MEPs). To understand the molecular pathways leading to pathogenesis of DBA, we performed RNA-seq on mRNA and miRNA from RPS19-deficient human hematopoietic stem and progenitor cells (HSPCs) and compared an existing database documenting transcript fluctuations across stages of early normal erythropoiesis. We determined the chromatin regulator, SATB1 was prematurely downregulated through the coordinated action of upregulated miR-34 and miR-30 during differentiation in ribosomal-insufficiency. Restoration of SATB1 rescued MEP expansion, leading to a modest improvement in erythroid and megakaryocyte expansion in RPS19-insufficiency. However, SATB1 expression did not impact expansion of committed erythroid progenitors, indicating ribosomal insufficiency impacts multiple stages during erythroid differentiation.

Dedicated chaperones coordinate co-translational regulation of ribosomal protein production with ribosome assembly to preserve proteostasis

The biogenesis of eukaryotic ribosomes involves the ordered assembly of around 80 ribosomal proteins. Supplying equimolar amounts of assembly-competent ribosomal proteins is complicated by their aggregation propensity and the spatial separation of their location of synthesis and pre-ribosome incorporation. Recent evidence has highlighted that dedicated chaperones protect individual, unassembled ribosomal proteins on their path to the pre-ribosomal assembly site. Here, we show that the co-translational recognition of Rpl3 and Rpl4 by their respective dedicated chaperone, Rrb1 or Acl4, reduces the degradation of the encoding RPL3 and RPL4 mRNAs in the yeast Saccharomyces cerevisiae. In both cases, negative regulation of mRNA levels occurs when the availability of the dedicated chaperone is limited and the nascent ribosomal protein is instead accessible to a regulatory machinery consisting of the nascent-polypeptide-associated complex and the Caf130-associated Ccr4-Not complex. Notably, deregulated expression of Rpl3 and Rpl4 leads to their massive aggregation and a perturbation of overall proteostasis in cells lacking the E3 ubiquitin ligase Tom1. Taken together, we have uncovered an unprecedented regulatory mechanism that adjusts the de novo synthesis of Rpl3 and Rpl4 to their actual consumption during ribosome assembly and, thereby, protects cells from the potentially detrimental effects of their surplus production.

Living cells are packed full of molecules known as proteins, which perform many vital tasks the cells need to survive and grow. Machines called ribosomes inside the cells use template molecules called messenger RNAs (or mRNAs for short) to produce proteins. The newly-made proteins then have to travel to a specific location in the cell to perform their tasks. Some newly-made proteins are prone to forming clumps, so cells have other proteins known as chaperones that ensure these clumps do not form.

The ribosomes themselves are made up of several proteins, some of which are also prone to clumping as they are being produced. To prevent this from happening, cells control how many ribosomal proteins they make, so there are just enough to form the ribosomes the cell needs at any given time. Previous studies found that, in yeast, two ribosomal proteins called Rpl3 and Rpl4 each have their own dedicated chaperone to prevent them from clumping. However, it remained unclear whether these chaperones are also involved in regulating the levels of Rpl3 and Rpl4.

To address this question, Pillet et al. studied both of these dedicated chaperones in yeast cells. The experiments showed that the chaperones bound to their target proteins (either units of Rpl3 or Rpl4) as they were being produced on the ribosomes. This protected the template mRNAs the ribosomes were using to produce these proteins from being destroyed, thus allowing further units of Rpl3 and Rpl4 to be produced. When enough Rpl3 and Rpl4 units were made, there were not enough of the chaperones to bind them all, leaving the mRNA templates unprotected. This led to the destruction of the mRNA templates, which decreased the numbers of Rpl3 and Rpl4 units being produced.

The work of Pillet et al. reveals a feedback mechanism that allows yeast to tightly control the levels of Rpl3 and Rpl4. In the future, these findings may help us understand diseases caused by defects in ribosomal proteins, such as Diamond-Blackfan anemia, and possibly also neurodegenerative diseases caused by clumps of proteins forming in cells. The next step will be to find out whether the mechanism uncovered by Pillet et al. also exists in human and other mammalian cells.

The transcription factor Xrp1 orchestrates both reduced translation and cell competition upon defective ribosome assembly or function

Ribosomal Protein (Rp) gene haploinsufficiency affects translation rate, can lead to protein aggregation, and causes cell elimination by competition with wild type cells in mosaic tissues. We find that the modest changes in ribosomal subunit levels observed were insufficient for these effects, which all depended on the AT-hook, bZip domain protein Xrp1. Xrp1 reduced global translation through PERK-dependent phosphorylation of eIF2α. eIF2α phosphorylation was itself sufficient to enable cell competition of otherwise wild type cells, but through Xrp1 expression, not as the downstream effector of Xrp1. Unexpectedly, many other defects reducing ribosome biogenesis or function (depletion of TAF1B, eIF2, eIF4G, eIF6, eEF2, eEF1α1, or eIF5A), also increased eIF2α phosphorylation and enabled cell competition. This was also through the Xrp1 expression that was induced in these depletions. In the absence of Xrp1, translation differences between cells were not themselves sufficient to trigger cell competition. Xrp1 is shown here to be a sequence-specific transcription factor that regulates transposable elements as well as single-copy genes. Thus, Xrp1 is the master regulator that triggers multiple consequences of ribosomal stresses and is the key instigator of cell competition.

Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is an inherited bone marrow failure syndrome, characterized as a rare congenital bone marrow erythroid hypoplasia (OMIM#105650). Erythroid defect in DBA results in erythroblastopenia in bone marrow as a consequence of maturation blockade between the burst forming unit-erythroid and colony forming unit-erythroid developmental stages, leading to moderate to severe usually macrocytic aregenerative (<20 × 109/L of reticulocytes) anemia. Congenital malformations localized mostly in the cephalic area and in the extremities (thumbs), as well as short stature and cardiac and urogenital tract abnormalities, are a feature of 50% of the DBA-affected patients. A significant increased risk for malignancy has been reported. DBA is due to a defect in the ribosomal RNA (rRNA) maturation as a consequence of a heterozygous mutation in 1 of the 20 ribosomal protein genes. Besides classical DBA, some DBA-like diseases have been identified. The relation between the defect in rRNA maturation and the erythroid defect in DBA has yet to be fully defined. However, recent studies have identified a role for GATA1 either due to a specific defect in its translation or due to its defective regulation by its chaperone HSP70. In addition, excess free heme-induced reactive oxygen species and apoptosis have been implicated in the DBA erythroid phenotype. Current treatment options are either regular transfusions with appropriate iron chelation or treatment with corticosteroids starting at 1 year of age. The only curative treatment for the anemia of DBA to date is bone marrow transplantation. Use of gene therapy as a therapeutic strategy is currently being explored.

Mycoplasma genitalium Protein of Adhesion Promotes the Early Proliferation of Human Urothelial Cells by Interacting with RPL35

Mycoplasma genitalium is a newly recognized pathogen associated with sexually transmitted diseases (STDs). MgPa, the adhesion protein of Mycoplasma genitalium, is the main adhesin and the key factor for M. genitalium interacting with host cells. Currently, the long-term survival mechanism of M. genitalium in the host is not clear. In this study, a T7 phage-displayed human urothelial cell (SV-HUC-1) cDNA library was constructed, and the interaction of MgPa was screened from this library using the recombinant MgPa (rMgPa) as a target molecule. We verified that 60S ribosomal protein L35 (RPL35) can interact with MgPa using far-Western blot and co-localization analysis. According to the results of tandem mass tag (TMT) labeling and proteome quantitative analysis, there were altogether 407 differentially expressed proteins between the pcDNA3.1(+)/MgPa-transfected cells and non-transfected cells, of which there were 6 downregulated proteins and 401 upregulated proteins. The results of qRT-PCR demonstrated that interaction between rMgPa and RPL35 could promote the expressions of EIF2, SRP68, SERBP1, RPL35A, EGF, and TGF-β. 3-(4,5)-Dimethylthiahiazo(-z-y1)-3,5-di-phenytetrazoliumromide bromide (MTT) assays corroborated that the interaction between rMgPa and RPL35 could promote SV-HUC-1 cell proliferation. Therefore, our findings indicated that the interaction between rMgPa and RPL35 can enhance the expressions of transcription-initiation and translation-related proteins and thus promote cell proliferation. This study elucidates a new biological function of MgPa and can explain this new mechanism of M. genitalium in the host.

Regulation of RNA polymerase II activity is essential for terminal erythroid maturation

The terminal maturation of human erythroblasts requires significant changes in gene expression in the context of dramatic nuclear condensation. Defects in this process are associated with inherited anemias and myelodysplastic syndromes. The progressively dense appearance of the condensing nucleus in maturing erythroblasts led to the assumption that heterochromatin accumulation underlies this process, but despite extensive study, the precise mechanisms underlying this essential biologic process remain elusive. To delineate the epigenetic changes associated with the terminal maturation of human erythroblasts, we performed mass spectrometry of histone posttranslational modifications combined with chromatin immunoprecipitation coupled with high-throughput sequencing, Assay for Transposase Accessible Chromatin, and RNA sequencing. Our studies revealed that the terminal maturation of human erythroblasts is associated with a dramatic decline in histone marks associated with active transcription elongation, without accumulation of heterochromatin. Chromatin structure and gene expression were instead correlated with dynamic changes in occupancy of elongation competent RNA polymerase II, suggesting that terminal erythroid maturation is controlled largely at the level of transcription. We further demonstrate that RNA polymerase II "pausing" is highly correlated with transcriptional repression, with elongation competent RNA polymerase II becoming a scare resource in late-stage erythroblasts, allocated to erythroid-specific genes. Functional studies confirmed an essential role for maturation stage-specific regulation of RNA polymerase II activity during erythroid maturation and demonstrate a critical role for HEXIM1 in the regulation of gene expression and RNA polymerase II activity in maturing erythroblasts. Taken together, our findings reveal important insights into the mechanisms that regulate terminal erythroid maturation and provide a novel paradigm for understanding normal and perturbed erythropoiesis.

Diagnostic work-up for severe aplastic anemia in children: Consensus of the North American Pediatric Aplastic Anemia Consortium

The North American Pediatric Aplastic Anemia Consortium (NAPAAC) is a group of pediatric hematologist-oncologists, hematopathologists, and bone marrow transplant physicians from 46 institutions in North America with interest and expertise in aplastic anemia, inherited bone marrow failure syndromes, and myelodysplastic syndromes. The NAPAAC Bone Marrow Failure Diagnosis and Care Guidelines Working Group was established with the charge of harmonizing the approach to the diagnostic workup of aplastic anemia in an effort to standardize best practices in the field. This document outlines the rationale for initial evaluations in pediatric patients presenting with signs and symptoms concerning for severe aplastic anemia.

Untargeted metabolic profiling in dried blood spots identifies disease fingerprint for pyruvate kinase deficiency

The diagnostic evaluation and clinical characterization of rare hereditary anemia (RHA) is to date still challenging. In particular, there is little knowledge on the broad metabolic impact of many of the molecular defects underlying RHA. In this study we explored the potential of untargeted metabolomics to diagnose a relatively common type of RHA: Pyruvate Kinase Deficiency (PKD). In total, 1903 unique metabolite features were identified in dried blood spot samples from 16 PKD patients and 32 healthy controls. A metabolic fingerprint was identified using a machine learning algorithm, and subsequently a binary classification model was designed. The model showed high performance characteristics (AUC 0.990, 95%CI 0.981-0.999) and an accurate class assignment was achieved for all newly added control (13) and patient samples (6), with the exception of one patient (accuracy 94%). Important metabolites in the metabolic fingerprint included glycolytic intermediates, polyamines and several acyl carnitines. In general, the application of untargeted metabolomics in dried blood spots is a novel functional tool that holds promise for diagnostic stratification and studies on disease pathophysiology in RHA.

Enzymatic Changes in Red Blood Cells of Diamond-Blackfan Anemia

Diamond-Blackfan anemia is a congenital bone marrow failure syndrome characterized by red blood cell (RBC) aplasia with varied malformations in infants. Elevated activity of adenosine deaminase (ADA) has been considered as a useful biomarker of Diamond-Blackfan anemia, and ADA assay has been shown to be more sensitive than genetic diagnosis. Approximately, 80% of the examined patients showed elevated ADA activity, whereas genetic tests of ribosome subunit genes identified mutations in approximately 60% of the patients. We previously reported that reduced glutathione (GSH) levels in RBCs may serve as a biomarker of Diamond-Blackfan anemia. In this study, to confirm the universality of our data, we extended the analysis to seven RBC enzymes and GSH of 14 patients with Diamond-Blackfan anemia and performed a cross-analysis study using enzyme activity assay and recently reported proteome data. Statistical analysis revealed that both data exhibited high similarity, upregulation in the hexokinase and pentose-phosphate pathway, and downregulation in glycolytic enzymes such as phosphofructokinase and pyruvate kinase, in the RBCs obtained from the subjects with Diamond-Blackfan anemia. The only discrepancy between enzyme activity and proteome data was observed in glucose-6-phosphate dehydrogenase (G6PD), as increased G6PD activity showed no relation with the significant elevation in protein levels. These results suggest that our enzymatic activity data of Diamond-Blackfan anemia are universal and that the enzymatic activation of G6PD via a hitherto-unveiled mechanism is another metabolic feature of RBCs of Diamond-Blackfan anemia.

Ribosomal proteins and human diseases: molecular mechanisms and targeted therapy

Ribosome biogenesis and protein synthesis are fundamental rate-limiting steps for cell growth and proliferation. The ribosomal proteins (RPs), comprising the structural parts of the ribosome, are essential for ribosome assembly and function. In addition to their canonical ribosomal functions, multiple RPs have extra-ribosomal functions including activation of p53-dependent or p53-independent pathways in response to stress, resulting in cell cycle arrest and apoptosis. Defects in ribosome biogenesis, translation, and the functions of individual RPs, including mutations in RPs have been linked to a diverse range of human congenital disorders termed ribosomopathies. Ribosomopathies are characterized by tissue-specific phenotypic abnormalities and higher cancer risk later in life. Recent discoveries of somatic mutations in RPs in multiple tumor types reinforce the connections between ribosomal defects and cancer. In this article, we review the most recent advances in understanding the molecular consequences of RP mutations and ribosomal defects in ribosomopathies and cancer. We particularly discuss the molecular basis of the transition from hypo- to hyper-proliferation in ribosomopathies with elevated cancer risk, a paradox termed "Dameshek's riddle." Furthermore, we review the current treatments for ribosomopathies and prospective therapies targeting ribosomal defects. We also highlight recent advances in ribosome stress-based cancer therapeutics. Importantly, insights into the mechanisms of resistance to therapies targeting ribosome biogenesis bring new perspectives into the molecular basis of cancer susceptibility in ribosomopathies and new clinical implications for cancer therapy.

The active component of ginseng, ginsenoside Rb1, improves erythropoiesis in models of Diamond-Blackfan anemia by targeting Nemo-like kinase

Nemo-like kinase (NLK) is a member of the mitogen-activated protein kinase family of kinases and shares a highly conserved kinase domain with other mitogen-activated protein kinase family members. The activation of NLK contributes to the pathogenesis of Diamond–Blackfan anemia (DBA), reducing c-myb expression and mechanistic target of rapamycin activity, and is therefore a potential therapeutic target. Unlike other anemias, the hematopoietic effects of DBA are largely restricted to the erythroid lineage. Mutations in ribosomal genes induce ribosomal insufficiency and reduced protein translation, dramatically impacting early erythropoiesis in the bone marrow of patients with DBA. We sought to identify compounds that suppress NLK and increases erythropoiesis in ribosomal insufficiency. We report that the active component of ginseng, ginsenoside Rb1, suppresses NLK expression and improves erythropoiesis in in vitro models of DBA. Ginsenoside Rb1–mediated suppression of NLK occurs through the upregulation of miR-208, which binds to the 3′-UTR of NLK mRNA and targets it for degradation. We also compare ginsenoside Rb1–mediated upregulation of miR-208 with metformin-mediated upregulation of miR-26. We conclude that targeting NLK expression through miRNA binding of the unique 3′-UTR is a viable alternative to the challenges of developing small-molecule inhibitors to target the highly conserved kinase domain of this specific kinase.

Impact of Next-Generation Sequencing on the Diagnosis and Treatment of Congenital Anemias

Congenital anemias are a wide spectrum of diseases including hypoproliferative anemia syndromes, dyserythropoietic anemias, sideroblastic anemias, red blood cell membrane and enzymatic defects, hemoglobinopathies, and thalassemia syndromes. The various congenital anemia syndromes may have similar clinical and laboratory presentations, making the diagnosis challenging. The traditional work-up, which includes a complete blood count, blood smears, bone marrow studies, flow cytometry, and the osmotic fragility test, does not always lead to the diagnosis. Specialized tests such as red blood cell enzyme activity and ektacytometry are not widely available. In addition, red blood cell transfusions may mask some of the laboratory characteristics. Therefore, genetic testing is crucial for accurate diagnosis of patients with congenital anemias. However, gene-by-gene testing is labor intensive because of the large number of genes involved. Thus, targeted next-generation sequencing using custom-made gene panels has been increasingly utilized, with a high success rate of diagnosis. Accurate genetic diagnosis is important for determining specific therapeutic modalities, as well as for avoiding splenectomy when contraindicated. In addition, molecular diagnosis can allow for genetic counseling and prenatal diagnosis in severe cases. We suggest a work-up scheme for patients with congenital anemias, including early incorporation of targeted next-generation sequencing panels.

Complex Modes of Inheritance in Hereditary Red Blood Cell Disorders: A Case Series Study of 155 Patients

Hereditary erythrocytes disorders include a large group of conditions with heterogeneous molecular bases and phenotypes. We analyzed here a case series of 155 consecutive patients with clinical suspicion of hereditary erythrocyte defects referred to the Medical Genetics Unit from 2018 to 2020. All of the cases followed a diagnostic workflow based on a targeted next-generation sequencing panel of 86 genes causative of hereditary red blood cell defects. We obtained an overall diagnostic yield of 84% of the tested patients. Monogenic inheritance was seen for 69% (107/155), and multi-locus inheritance for 15% (23/155). PIEZO1 and SPTA1 were the most mutated loci. Accordingly, 16/23 patients with multi-locus inheritance showed dual molecular diagnosis of dehydrated hereditary stomatocytosis/xerocytosis and hereditary spherocytosis. These dual inheritance cases were fully characterized and were clinically indistinguishable from patients with hereditary spherocytosis. Additionally, their ektacytometry curves highlighted alterations of dual inheritance patients compared to both dehydrated hereditary stomatocytosis and hereditary spherocytosis. Our findings expand the genotypic spectrum of red blood cell disorders and indicate that multi-locus inheritance should be considered for analysis and counseling of these patients. Of note, the genetic testing was crucial for diagnosis of patients with a complex mode of inheritance.

Proerythroblast Cells of Diamond-Blackfan Anemia Patients With RPS19 and CECR1 Mutations Have Similar Transcriptomic Signature

Diamond Blackfan Anemia (DBA) is an inherited bone marrow (BM) failure syndrome, characterized by a paucity of erythroid differentiation. DBA is mainly caused by the mutations in ribosomal protein genes, hence classified as ribosomopathy. However, in approximately 30% of patients, the molecular etiology cannot be discovered. RPS19 germline mutations caused 25% of the cases. On the other hand, CECR1 mutations also cause phenotypes similar to DBA but not being a ribosomopathy. Due to the blockade of erythropoiesis in the BM, we investigated the transcriptomic profile of three different cell types of BM resident cells of DBA patients and compared them with healthy donors. From BM aspirates BM mononuclear cells (MNCs) were isolated and hematopoietic stem cells (HSC) [CD71^–CD34⁺ CD38^mo/lo], megakaryocyte–erythroid progenitor cells (MEP) [CD71^–CD34⁺ CD38^hi] and Proerythroblasts [CD71⁺ CD117⁺ CD38⁺] were sorted and analyzed with a transcriptomic approach. Among all these cells, proerythroblasts had the most different transcriptomic profile. The genes associated with cellular stress/immune responses were increased and some of the transcription factors that play a role in erythroid differentiation had altered expression in DBA proerythroblasts. We also showed that gene expression levels of ribosomal proteins were decreased in DBA proerythroblasts. In addition to these, colony formation assay (CFU-E) provided functional evidence of the failure of erythroid differentiation in DBA patients. According to our findings that all patients resembling both RPS19 and CECR1 mutations have common transcriptomic signatures, it may be possible that inflammatory BM niche may have a role in DBA pathogenesis.

Analysis of deficiency of adenosine deaminase 2 pathogenesis based on single-cell RNA sequencing of monocytes

Deficiency of adenosine deaminase 2 (DADA2) is a rare autosomal recessive disease caused by loss-of-function variants in the ADA2 gene. DADA2 typically presents in childhood and is characterized by vasculopathy, stroke, inflammation, immunodeficiency, as well as hematologic manifestations. ADA2 protein is predominantly present in stimulated monocytes, dendritic cells, and macrophages. To elucidate molecular mechanisms in DADA2, CD14⁺ monocytes from 14 patients and 6 healthy donors were analyzed using single-cell RNA sequencing (scRNA-seq). Monocytes were purified by positive selection based on CD14 expression. Subpopulations were imputed from their transcriptomes. Based on scRNA-seq, monocytes could be classified as classical, intermediate, and nonclassical. Further, we used gene pathway analytics to interpret patterns of up- and down-regulated gene transcription. In DADA2, the frequency of nonclassical monocytes was higher compared with that of healthy donors, and M1 macrophage markers were up-regulated in patients. By comparing gene expression of each monocyte subtype between patients and healthy donors, we identified upregulated immune response pathways, including IFNα/β and IFNγ signaling, in all monocyte subtypes. Distinctively, the TNFR2 noncanonical NF-κB pathway was up-regulated only in nonclassical monocytes. Patients' plasma showed increased IFNγ and TNFα levels. Our results suggest that elevated IFNγ activates cell signaling, leading to differentiation into M1 macrophages from monocytes and release of TNFα. Immune responses and more general response to stimuli pathways were up-regulated in DADA2 monocytes, and protein synthesis pathways were down-regulated, perhaps as stress responses. Our identification of novel aberrant immune pathways has implications for therapeutic approaches in DADA2 (registered at clinicaltrials.gov NCT00071045).

AQP0 is a novel surface marker for deciphering abnormal erythropoiesis

Background

Hematopoiesis occurs in the bone marrow, producing a complete spectrum of blood cells to maintain homeostasis. In addition to light microscopy, chromosome analysis, and polymerase chain reaction, flow cytometry is a feasible and fast method for quantitatively analyzing hematological diseases. However, because sufficient specific cell markers are scarce, dyserythropoietic diseases are challenging to identify through flow cytometry.

Methods

Bone marrow samples from C57BL/B6 mice and one healthy donor were analyzed using traditional two-marker (CD71 and glycophorin A) flow cytometry analysis. After cell sorting, the gene expressions of membrane proteins in early and late erythropoiesis precursors and in nonerythroid cells were characterized using microarray analysis.

Results

Among characterized gene candidates, aquaporin 0 (AQP0) expressed as a surface protein in early- and late-stage erythropoiesis precursors and was not expressed on nonerythroid cells. With the help of AQP0 staining, we could define up to five stages of erythropoiesis in both mouse and human bone marrow using flow cytometry. In addition, because patients with dyserythropoiesis generally exhibited a reduced population of APQ0^high cells relative to healthy participants, the analysis results also suggested that the levels of APQ0^high cells in early erythropoiesis serve as a novel biomarker that distinguishes normal from dysregulated erythropoiesis.

Conclusions

AQP0 was successfully demonstrated to be a marker of erythroid differentiation. The expression levels of AQP0 are downregulated in patients with dyserythropoiesis, indicating a critical role of AQP0 in erythropoiesis. Accordingly, the level of AQP0^high in early erythroid precursor cells may serve as a reference parameter for diagnosing diseases associated with dyserythropoiesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02343-4.

Genotype-phenotype association and variant characterization in Diamond-Blackfan anemia caused by pathogenic variants in RPL35A

Diamond Blackfan anemia (DBA) is predominantly an autosomal dominant inherited red cell aplasia primarily caused by pathogenic germline variants in ribosomal protein genes. DBA due to pathogenic RPL35A variants has been associated with large 3q29 deletions and phenotypes not common in DBA. We conducted a multi-institutional genotypephenotype study of 45 patients with DBA associated with pathogenic RPL35A germline variants and curated the variant data on 21 additional cases from the literature. Genotype-phenotype analyses were conducted comparing patients with large deletions versus all other pathogenic variants in RPL35A. Twenty-two of the 45 cases had large deletions in RPL35A. After adjusting for multiple tests, a statistically significant association was observed between patients with a large deletion and steroid-resistant anemia, neutropenia, craniofacial abnormalities, chronic gastrointestinal problems, and intellectual disabilities (P<0.01) compared with all other pathogenic variants. Non-large deletion pathogenic variants were spread across RPL35Awith no apparent hot spot and 56% of the individual family variants were observed more than once. In this, the largest known study of DBA patients with pathogenic RPL35A variants, we determined that patients with large deletions have a more severe phenotype that is clinically different from those with non-large deletion variants. Genes of interest also deleted in the 3q29 region that could be associated with some of these phenotypic features include LMLN and IQCG. Management of DBA due to large RPL35A deletions may be challenging due to complex problems and require comprehensive assessments by multiple specialists including immunological, gastrointestinal, and developmental evaluations to provide optimal multidisciplinary care.

Diamond-Blackfan Anemia: 2 Cases With a Twist

BACKGROUND

Diamond-Blackfan anemia is a rare inherited bone marrow failure disease. Typical findings include hypoplastic macrocytic anemia, congenital anomalies, and a predisposition to cancer. The molecular basis of the disease is heterozygous mutations of ribosomal proteins without a strict correlation between genotype and phenotype.

OBSERVATION

We present 2 cases of Diamond-Blackfan anemia diagnosed during infancy with interesting clinical, molecular, and family characteristics.

CONCLUSIONS

A thorough evaluation of all family members is imperative to identify possible 'silent carriers' who are those with no physical stigmata and minor or absent hematologic manifestations. New mutations could add in the map of the disease.

Deciphering the mutational signature of congenital limb malformations

Congenital limb malformations (CLMs) affect 1 in 500 live births. However, the value of exome sequencing (ES) for CLM is lacking. The purpose of this study was to decipher the mutational signature of CLM on an exome level. We enrolled a cohort of 66 unrelated probands (including 47 families) with CLM requiring surgical correction. ES was performed for all patients and available parental samples. A definite molecular diagnosis was achieved in 21 out of 66 (32%) patients. We identified 19 pathogenic or likely pathogenic single-nucleotide variants and three copy number variants, of which 11 variants were novel. We identified four variants of uncertain significance. Additionally, we identified RPL9 and UBA2 as novel candidate genes for CLM. By comparing the detailed phenotypic features, we expand the phenotypic spectrum of diastrophic dysplasia and chromosome 6q terminal deletion syndrome. We also found that the diagnostic rate was significantly higher in patients with a family history of CLM (p = 0.012) or more than one limb affected (p = 0.034). Our study expands our understanding of the mutational and phenotypic spectrum of CLM and provides novel insights into the genetic basis of these syndromes.

Unique Combination of Diamond-Blackfan Anemia and Lynch Syndrome in Adult Female: A Case Report

We present an extremely rare clinical case of a 38-year-old Russian patient with multiple malignant neoplasms of the uterus and colon caused by genetically confirmed two hereditary diseases: Diamond-Blackfan anemia and Lynch syndrome. Molecular genetic research carried out by various methods (NGS, Sanger sequencing, aCGH, and MLPA) revealed a pathogenic nonsense variant in the MSH6 gene: NM_000179.2: c.742C>T, p.(Arg248Ter), as well as a new deletion of the chromosome 15's locus with the capture of 82,662,932-84,816,747 bp interval, including the complete sequence of the RPS17 gene. The lack of expediency of studying microsatellite instability in endometrial tumors using standard mononucleotide markers NR21, NR24, NR27, BAT25, BAT26 was demonstrated. The estimated prevalence of patients with combination of Diamond-Blackfan anemia and Lynch syndrome in the world is one per 480 million people.

Shock in the Setting of Diamond-Blackfan Anemia Relapse

Adult intensivists have increasing exposure to individuals with congenital diseases surviving into adulthood. Solid knowledge bases and early recognition of the possible sequelae of congenital disorders are crucial in caring for these patients. We present a challenging case of shock and relapse of Diamond-Blackfan anemia in a 42-year-old man lost to follow-up for 18 years and highlighted the importance of healthcare transitions into adulthood and the challenges faced by health care systems to develop new strategies successfully transitioning complex pediatric patients to adult care.

Genetic Predisposition to Myelodysplastic Syndromes: A Challenge for Adult Hematologists

Myelodysplastic syndromes (MDS) arising in the context of inherited bone marrow failure syndromes (IBMFS) differ in terms of prognosis and treatment strategy compared to MDS occurring in the adult population without an inherited genetic predisposition. The main molecular pathways affected in IBMFS involve telomere maintenance, DNA repair, biogenesis of ribosomes, control of proliferation and others. The increased knowledge on the genes involved in MDS pathogenesis and the wider availability of molecular diagnostic assessment have led to an improvement in the detection of IBMFS genetic predisposition in MDS patients. A punctual recognition of these disorders implies a strict surveillance of the patient in order to detect early signs of progression and promptly offer allogeneic hematopoietic stem cell transplantation, which is the only curative treatment. Moreover, identifying an inherited mutation allows the screening and counseling of family members and directs the choice of donors in case of need for transplantation. Here we provide an overview of the most recent data on MDS with genetic predisposition highlighting the main steps of the diagnostic and therapeutic management. In order to highlight the pitfalls of detecting IBMFS in adults, we report the case of a 27-year-old man affected by MDS with an underlying telomeropathy.

Genetics and Genomics Approaches for Diagnosis and Research Into Hereditary Anemias

The hereditary anemias are a relatively heterogeneous set of disorders that can show wide clinical and genetic heterogeneity, which often hampers correct clinical diagnosis. The classical diagnostic workflow for these conditions generally used to start with analysis of the family and personal histories, followed by biochemical and morphological evaluations, and ending with genetic testing. However, the diagnostic framework has changed more recently, and genetic testing is now a suitable approach for differential diagnosis of these patients. There are several approaches to this genetic testing, the choice of which depends on phenotyping, genetic heterogeneity, and gene size. For patients who show complete phenotyping, single-gene testing remains recommended. However, genetic analysis now includes next-generation sequencing, which is generally based on custom-designed targeting panels and whole-exome sequencing. The use of next-generation sequencing also allows the identification of new causative genes, and of polygenic conditions and genetic factors that modify disease severity of hereditary anemias. In the research field, whole-genome sequencing is useful for the identification of non-coding causative mutations, which might account for the disruption of transcriptional factor occupancy sites and cis-regulatory elements. Moreover, advances in high-throughput sequencing techniques have now resulted in the identification of genome-wide profiling of the chromatin structures known as the topologically associating domains. These represent a recurrent disease mechanism that exposes genes to inappropriate regulatory elements, causing errors in gene expression. This review focuses on the challenges of diagnosis and research into hereditary anemias, with indications of both the advantages and disadvantages. Finally, we consider the future perspectives for the use of next-generation sequencing technologies in this era of precision medicine.

Oxidative DNA Damage, Inflammatory Signature, and Altered Erythrocytes Properties in Diamond-Blackfan Anemia

Molecular pathophysiology of Diamond-Blackfan anemia (DBA) involves disrupted erythroid-lineage proliferation, differentiation and apoptosis; with the activation of p53 considered as a key component. Recently, oxidative stress was proposed to play an important role in DBA pathophysiology as well. CRISPR/Cas9-created Rpl5- and Rps19-deficient murine erythroleukemia (MEL) cells and DBA patients' samples were used to evaluate proinflammatory cytokines, oxidative stress, DNA damage and DNA damage response. We demonstrated that the antioxidant defense capacity of Rp-mutant cells is insufficient to meet the greater reactive oxygen species (ROS) production which leads to oxidative DNA damage, cellular senescence and activation of DNA damage response signaling in the developing erythroblasts and altered characteristics of mature erythrocytes. We also showed that the disturbed balance between ROS formation and antioxidant defense is accompanied by the upregulation of proinflammatory cytokines. Finally, the alterations detected in the membrane of DBA erythrocytes may cause their enhanced recognition and destruction by reticuloendothelial macrophages, especially during infections. We propose that the extent of oxidative stress and the ability to activate antioxidant defense systems may contribute to high heterogeneity of clinical symptoms and response to therapy observed in DBA patients.

Special pre- and posttransplant considerations in inherited bone marrow failure and hematopoietic malignancy predisposition syndromes

Advances in the diagnosis and treatment of inherited bone marrow failure syndromes (IBMFS) have provided insight into the complexity of these diseases. The diseases are heterogeneous and characterized by developmental abnormalities, progressive marrow failure, and predisposition to cancer. A correct diagnosis allows for appropriate treatment, genetic counseling, and cancer surveillance. The common IBMFSs are Fanconi anemia, dyskeratosis congenita, and Diamond-Blackfan anemia. Hematopoietic cell transplantation (HCT) offers curative treatment of the hematologic complications of IBMFS. Because of the systemic nature of these diseases, transplant strategies are modified to decrease immediate and late toxicities. HCT from HLA-matched related or unrelated donors offers excellent survival for young patients in aplasia. Challenges include the treatment of adults with marrow aplasia, presentation with myeloid malignancy regardless of age, and early detection or treatment of cancer. In this article, I will describe our approach and evaluation of patients transplanted with IBMFS and review most frequent complications before and after transplant.

Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) was the first ribosomopathy described and is a constitutional inherited bone marrow failure syndrome. Erythroblastopenia is the major characteristic of the disease, which is a model for ribosomal diseases, related to a heterozygous allelic variation in 1 of the 20 ribosomal protein genes of either the small or large ribosomal subunit. The salient feature of classical DBA is a defect in ribosomal RNA maturation that generates nucleolar stress, leading to stabilization of p53 and activation of its targets, resulting in cell-cycle arrest and apoptosis. Although activation of p53 may not explain all aspects of DBA erythroid tropism, involvement of GATA1/HSP70 and globin/heme imbalance, with an excess of the toxic free heme leading to reactive oxygen species production, account for defective erythropoiesis in DBA. Despite significant progress in defining the molecular basis of DBA and increased understanding of the mechanistic basis for DBA pathophysiology, progress in developing new therapeutic options has been limited. However, recent advances in gene therapy, better outcomes with stem cell transplantation, and discoveries of putative new drugs through systematic drug screening using large chemical libraries provide hope for improvement.

Expansion of germline RPS20 mutation phenotype to include Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is a ribosomopathy of variable expressivity and penetrance characterized by red cell aplasia, congenital anomalies, and predisposition to certain cancers, including early-onset colorectal cancer (CRC). DBA is primarily caused by a dominant mutation of a ribosomal protein (RP) gene, although approximately 20% of patients remain genetically uncharacterized despite exome sequencing and copy number analysis. Although somatic loss-of-function mutations in RP genes have been reported in sporadic cancers, with the exceptions of 5q-myelodysplastic syndrome (RPS14) and microsatellite unstable CRC (RPL22), these cancers are not enriched in DBA. Conversely, pathogenic variants in RPS20 were previously implicated in familial CRC; however, none of the reported individuals had classical DBA features. We describe two unrelated children with DBA lacking variants in known DBA genes who were found by exome sequencing to have de novo novel missense variants in RPS20. The variants affect the same amino acid but result in different substitutions and reduce the RPS20 protein level. Yeast models with mutation of the cognate residue resulted in defects in growth, ribosome biogenesis, and polysome formation. These findings expand the phenotypic spectrum of RPS20 mutation beyond familial CRC to include DBA, which itself is associated with increased risk of CRC.

MYSM1 maintains ribosomal protein gene expression in hematopoietic stem cells to prevent hematopoietic dysfunction

Ribosomopathies are congenital disorders caused by mutations in the genes encoding ribosomal and other functionally related proteins. They are characterized by anemia, other hematopoietic and developmental abnormalities, and p53 activation. Ribosome assembly requires coordinated expression of many ribosomal protein (RP) genes; however, the regulation of RP gene expression, especially in hematopoietic stem cells (HSCs), remains poorly understood. MYSM1 is a transcriptional regulator essential for HSC function and hematopoiesis. We established that HSC dysfunction in Mysm1 deficiency is driven by p53; however, the mechanisms of p53 activation remained unclear. Here, we describe the transcriptome of Mysm1-deficient mouse HSCs and identify MYSM1 genome-wide DNA binding sites. We establish a direct role for MYSM1 in RP gene expression and show a reduction in protein synthesis in Mysm1-/- HSCs. Loss of p53 in mice fully rescues Mysm1-/- anemia phenotype but not RP gene expression, indicating that RP gene dysregulation is a direct outcome of Mysm1 deficiency and an upstream mediator of Mysm1-/- phenotypes through p53 activation. We characterize a patient with a homozygous nonsense MYSM1 gene variant, and we demonstrate reduced protein synthesis and increased p53 levels in patient hematopoietic cells. Our work provides insights into the specialized mechanisms regulating RP gene expression in HSCs and establishes a common etiology of MYSM1 deficiency and ribosomopathy syndromes.

Moxibustion with deferasirox results in safe, accelerated, and sustained cardiac iron chelation for a young Diamond Blackfan Anemia patient: An integrative case report

Diamond Blackfan Anemia (DBA) is a rare blood disorder of bone marrow failure typically identified in the first year of life. Due to treatment limitations, nearly all DBA patients are reliant upon chronic red cell infusion for some period of their lives. Repeat blood transfusion invariably leads to iron overload, which creates significant and life-threatening side effects. In this case report, a female child of 2 years and 8 months with DBA was diagnosed via T2* MRI imaging with potentially emergent levels of cardiac iron overload as a result of chronic red cell infusion. According to Chinese, Japanese, and integrative medicine principles, moxibustion was applied externally in conjunction with the prescribed oral chelation agent, deferasirox (DFX), over a period of six months. Analysis of repeat imaging at six months showed complete removal of cardiac iron and a one-third decrease in hepatic iron. In addition, there was no evidence of known risks to high-dose chelation, including renal, aural, or ocular damage. Follow-up examination two years after initial imaging showed no evidence of cardiac iron deposition with hepatic iron levels below minimum levels recommended for chelation despite the medical necessity of continued red cell infusion. This case study suggests that an integrative medical approach combining DFX with moxibustion may safely accelerate and sustain iron chelation for transfusion-dependent DBA patients. Recommendations for a successful approach to integrative iron chelation are provided in the case discussion.

Diamond Blackfan anemia is mediated by hyperactive Nemo-like kinase

Diamond Blackfan Anemia (DBA) is a congenital bone marrow failure syndrome associated with ribosomal gene mutations that lead to ribosomal insufficiency. DBA is characterized by anemia, congenital anomalies, and cancer predisposition. Treatment for DBA is associated with significant morbidity. Here, we report the identification of Nemo-like kinase (NLK) as a potential target for DBA therapy. To identify new DBA targets, we screen for small molecules that increase erythroid expansion in mouse models of DBA. This screen identified a compound that inhibits NLK. Chemical and genetic inhibition of NLK increases erythroid expansion in mouse and human progenitors, including bone marrow cells from DBA patients. In DBA models and patient samples, aberrant NLK activation is initiated at the Megakaryocyte/Erythroid Progenitor (MEP) stage of differentiation and is not observed in non-erythroid hematopoietic lineages or healthy erythroblasts. We propose that NLK mediates aberrant erythropoiesis in DBA and is a potential target for therapy.

Diamond Blackfan Anemia (DBA) is a congenital bone marrow failure syndrome that is associated with anemia. Here, the authors examine the role of Nemo-like kinase (NLK) in erythroid cells in the pathogenesis of DBA and as a potential target for therapy.

Hematopoietic cell transplantation for Diamond Blackfan anemia: A report from the Pediatric Group of the Brazilian Bone Marrow Transplantation Society

OBJECTIVES

The aim of this study was to analyze the outcomes of children with Diamond-Blackfan anemia (DBA) treated in Brazil with hematopoietic cell transplantation (HCT).

METHODS

We performed a retrospective analysis of 44 pediatrics patients transplanted between 1990 and 2018. The median age of patients was 5 years, and 57% were male. Twenty-five received their first HCT from an HLA-matched sibling donor (MSD), 12 from a HLA matched unrelated bone marrow donor (MUD 10/10, n = 12) and 7 other HLA mismatched donors (MMD).

RESULTS

After a median follow-up of 4 years, estimate 5-year overall survival (OS) for the entire cohort was 70%, 80% for MSD group, 73% for MUD, and 29% for MMD. Thirty-eight out of the 44 evaluable patients engrafted successfully. Primary and secondary graft failure was observed in five and three patients, respectively. Rates of grade II-IV and III-IV acute graft-versus-host disease (aGVHD) were 25% and 18%, respectively. Nine patients developed chronic GVHD (cGVHD).

CONCLUSION

Overall survival rates observed after HLA matched donors transplant for DBA were comparable to those reported from higher-income countries and international registries.

Nonsense Suppression Therapy: New Hypothesis for the Treatment of Inherited Bone Marrow Failure Syndromes

Inherited bone marrow failure syndromes (IBMFS) are a group of cancer-prone genetic diseases characterized by hypocellular bone marrow with impairment in one or more hematopoietic lineages. The pathogenesis of IBMFS involves mutations in several genes which encode for proteins involved in DNA repair, telomere biology and ribosome biogenesis. The classical IBMFS include Shwachman–Diamond syndrome (SDS), Diamond–Blackfan anemia (DBA), Fanconi anemia (FA), dyskeratosis congenita (DC), and severe congenital neutropenia (SCN). IBMFS are associated with high risk of myelodysplastic syndrome (MDS), acute myeloid leukemia (AML), and solid tumors. Unfortunately, no specific pharmacological therapies have been highly effective for IBMFS. Hematopoietic stem cell transplantation provides a cure for aplastic or myeloid neoplastic complications. However, it does not affect the risk of solid tumors. Since approximately 28% of FA, 24% of SCN, 21% of DBA, 20% of SDS, and 17% of DC patients harbor nonsense mutations in the respective IBMFS-related genes, we discuss the use of the nonsense suppression therapy in these diseases. We recently described the beneficial effect of ataluren, a nonsense suppressor drug, in SDS bone marrow hematopoietic cells ex vivo. A similar approach could be therefore designed for treating other IBMFS. In this review we explain in detail the new generation of nonsense suppressor molecules and their mechanistic roles. Furthermore, we will discuss strengths and limitations of these molecules which are emerging from preclinical and clinical studies. Finally we discuss the state-of-the-art of preclinical and clinical therapeutic studies carried out for IBMFS.

Ubiquitously Expressed Proteins and Restricted Phenotypes: Exploring Cell-Specific Sensitivities to Impaired tRNA Charging

Aminoacyl-tRNA synthetases (ARS) are ubiquitously expressed, essential enzymes that charge tRNA with cognate amino acids. Variants in genes encoding ARS enzymes lead to myriad human inherited diseases. First, missense alleles cause dominant peripheral neuropathy. Second, missense, nonsense, and frameshift alleles cause recessive multisystem disorders that differentially affect tissues depending on which ARS is mutated. A preponderance of evidence has shown that both phenotypic classes are associated with loss-of-function alleles, suggesting that tRNA charging plays a central role in disease pathogenesis. However, it is currently unclear how perturbation in the function of these ubiquitously expressed enzymes leads to tissue-specific or tissue-predominant phenotypes. Here, we review our current understanding of ARS-associated disease phenotypes and discuss potential explanations for the observed tissue specificity.