RNA polymerase II pausing temporally coordinates cell cycle progression and erythroid differentiation.

Controlled release of promoter-proximal paused RNA polymerase II (RNA Pol II) is crucial for gene regulation. However, studying RNA Pol II pausing is challenging, as pause-release factors are almost all essential. In this study, we identified heterozygous loss-of-function mutations in SUPT5H, which encodes SPT5, in individuals with ß-thalassemia. During erythropoiesis in healthy human cells, cell cycle genes were highly paused as cells transition from progenitors to precursors. When the pathogenic mutations were recapitulated by SUPT5H editing, RNA Pol II pause release was globally disrupted, and as cells began transitioning from progenitors to precursors, differentiation was delayed, accompanied by a transient lag in erythroid-specific gene expression and cell cycle kinetics. Despite this delay, cells terminally differentiate, and cell cycle phase distributions normalize. Therefore, hindering pause release perturbs proliferation and differentiation dynamics at a key transition during erythropoiesis, identifying a role for RNA Pol II pausing in temporally coordinating the cell cycle and erythroid differentiation.

Significant haemoglobinopathies: A guideline for screening and diagnosis: A British Society for Haematology Guideline: A British Society for Haematology Guideline.

Antenatal screening/testing of pregnant women should be carried out according to the guidelines of the National Health Service (NHS) Sickle Cell and Thalassaemia Screening Programme. Newborn screening and, when necessary, follow-up testing and referral, should be carried out according to the guidelines of the NHS Sickle Cell and Thalassaemia Screening Programme. All babies under 1 year of age arriving in the United Kingdom should be offered screening for sickle cell disease (SCD). Preoperative screening for SCD should be carried out in patients from ethnic groups in which there is a significant prevalence of the condition. Emergency screening with a sickle solubility test must always be followed by definitive analysis. Laboratories performing antenatal screening should utilise methods that are capable of detecting significant variants and are capable of quantitating haemoglobins A2 and F at the cut-off points required by the national antenatal screening programme. The laboratory must ensure a provisional report is available for antenatal patients within three working days from sample receipt.

Diamond-Blackfan anemia in adults: In pursuit of a common approach for a rare disease.

Diamond-Blackfan anemia (DBA) is a rare bone marrow failure syndrome, usually caused by loss-of function variants in genes encoding ribosomal proteins. The hallmarks of DBA are anemia, congenital anomalies and cancer predisposition. Although DBA usually presents in childhood, the prevalence in later life is increasing due to an expanding repertoire of implicated genes, improvements in genetic diagnosis and increasing life expectancy. Adult patients uniquely suffer the manifestations of end-organ damage caused by the disease and its treatment, and transition to adulthood poses specific issues in disease management. To standardize and optimize care for this rare disease, in this review we provide updated guidance on the diagnosis and management of DBA, with a specific focus on older adolescents and adults. Recommendations are based upon published literature and our pooled clinical experience from three centres in the United Kingdom (U·K.). Uniquely we have also solicited and incorporated the views of affected families, represented by the independent patient organization, DBA U.K.

Direct correction of haemoglobin E ß-thalassaemia using base editors.

Haemoglobin E (HbE) ß-thalassaemia causes approximately 50% of all severe thalassaemia worldwide; equating to around 30,000 births per year. HbE ß-thalassaemia is due to a point mutation in codon 26 of the human HBB gene on one allele (GAG; glutamatic acid → AAG; lysine, E26K), and any mutation causing severe ß-thalassaemia on the other. When inherited together in compound heterozygosity these mutations can cause a severe thalassaemic phenotype. However, if only one allele is mutated individuals are carriers for the respective mutation and have an asymptomatic phenotype (ß-thalassaemia trait). Here we describe a base editing strategy which corrects the HbE mutation either to wildtype (WT) or a normal variant haemoglobin (E26G) known as Hb Aubenas and thereby recreates the asymptomatic trait phenotype. We have achieved editing efficiencies in excess of 90% in primary human CD34 + cells. We demonstrate editing of long-term repopulating haematopoietic stem cells (LT-HSCs) using serial xenotransplantation in NSG mice. We have profiled the off-target effects using a combination of circularization for in vitro reporting of cleavage effects by sequencing (CIRCLE-seq) and deep targeted capture and have developed machine-learning based methods to predict functional effects of candidate off-target mutations.

Hb Calgary (HBB: c.194G>T): A Highly Unstable Hemoglobin Variant with a ß-Thalassemia Major Phenotype.

We describe two unrelated patients, both heterozygous for an unstable hemoglobin (Hb) variant named Hb Calgary (HBB: c.194G>T) that causes severe hemolytic anemia and dyserythorpoietic, resulting in transfusion dependence and iron overload. The molecular pathogenesis is a missense variation on the ß-globin gene, presumed to lead to an unstable Hb. The phenotype of Hb Calgary is particularly severe presenting as transfusion-dependent anemia in early infancy, precluding phenotypic diagnosis and highlighting the importance of early genetic testing in order to make an accurate diagnosis.

Recapitulation of erythropoiesis in congenital dyserythropoietic anaemia type I (CDA-I) identifies defects in differentiation and nucleolar abnormalities.

The investigation of inherited disorders of erythropoiesis has elucidated many of the principles underlying the production of normal red blood cells and how this is perturbed in human disease. Congenital Dyserythropoietic Anaemia type 1 (CDA-I) is a rare form of anaemia caused by mutations in two genes of unknown function: CDAN1 and CDIN1 (previously called C15orf41), whilst in some cases, the underlying genetic abnormality is completely unknown. Consequently, the pathways affected in CDA-I remain to be discovered. To enable detailed analysis of this rare disorder we have validated a culture system which recapitulates all of the cardinal haematological features of CDA-I, including the formation of the pathognomonic 'spongy' heterochromatin seen by electron microscopy. Using a variety of cell and molecular biological approaches we discovered that erythroid cells in this condition show a delay during terminal erythroid differentiation, associated with increased proliferation and widespread changes in chromatin accessibility. We also show that the proteins encoded by CDAN1 and CDIN1 are enriched in nucleoli which are structurally and functionally abnormal in CDA-I. Together these findings provide important pointers to the pathways affected in CDA-I which for the first time can now be pursued in the tractable culture system utilised here.

Genetic and functional insights into CDA-I prevalence and pathogenesis.

BACKGROUND: Congenital dyserythropoietic anaemia type I (CDA-I) is a hereditary anaemia caused by biallelic mutations in the widely expressed genes CDAN1 and C15orf41. Little is understood about either protein and it is unclear in which cellular pathways they participate. METHODS: Genetic analysis of a cohort of patients with CDA-I identifies novel pathogenic variants in both known causative genes. We analyse the mutation distribution and the predicted structural positioning of amino acids affected in Codanin-1, the protein encoded by CDAN1. Using western blotting, immunoprecipitation and immunofluorescence, we determine the effect of particular mutations on both proteins and interrogate protein interaction, stability and subcellular localisation. RESULTS: We identify six novel CDAN1 mutations and one novel mutation in C15orf41 and uncover evidence of further genetic heterogeneity in CDA-I. Additionally, population genetics suggests that CDA-I is more common than currently predicted. Mutations are enriched in six clusters in Codanin-1 and tend to affect buried residues. Many missense and in-frame mutations do not destabilise the entire protein. Rather C15orf41 relies on Codanin-1 for stability and both proteins, which are enriched in the nucleolus, interact to form an obligate complex in cells. CONCLUSION: Stability and interaction data suggest that C15orf41 may be the key determinant of CDA-I and offer insight into the mechanism underlying this disease. Both proteins share a common pathway likely to be present in a wide variety of cell types; however, nucleolar enrichment may provide a clue as to the erythroid specific nature of CDA-I. The surprisingly high predicted incidence of CDA-I suggests that better ascertainment would lead to improved patient care.

Whole-genome sequencing of patients with rare diseases in a national health system.

Most patients with rare diseases do not receive a molecular diagnosis and the aetiological variants and causative genes for more than half such disorders remain to be discovered1. Here we used whole-genome sequencing (WGS) in a national health system to streamline diagnosis and to discover unknown aetiological variants in the coding and non-coding regions of the genome. We generated WGS data for 13,037 participants, of whom 9,802 had a rare disease, and provided a genetic diagnosis to 1,138 of the 7,065 extensively phenotyped participants. We identified 95 Mendelian associations between genes and rare diseases, of which 11 have been discovered since 2015 and at least 79 are confirmed to be aetiological. By generating WGS data of UK Biobank participants2, we found that rare alleles can explain the presence of some individuals in the tails of a quantitative trait for red blood cells. Finally, we identified four novel non-coding variants that cause disease through the disruption of transcription of ARPC1B, GATA1, LRBA and MPL. Our study demonstrates a synergy by using WGS for diagnosis and aetiological discovery in routine healthcare.

Single-cell O2 exchange imaging shows that cytoplasmic diffusion is a dominant barrier to efficient gas transport in red blood cells.

Disorders of oxygen transport are commonly attributed to inadequate carrying capacity (anemia) but may also relate to inefficient gas exchange by red blood cells (RBCs), a process that is poorly characterized yet assumed to be rapid. Without direct measurements of gas exchange at the single-cell level, the barriers to O2 transport and their relationship with hematological disorders remain ill defined. We developed a method to track the flow of O2 in individual RBCs by combining ultrarapid solution switching (to manipulate gas tension) with single-cell O2 saturation fluorescence microscopy. O2 unloading from RBCs was considerably slower than previously estimated in acellular hemoglobin solutions, indicating the presence of diffusional barriers in intact cells. Rate-limiting diffusion across cytoplasm was demonstrated by osmotically induced changes to hemoglobin concentration (i.e., diffusive tortuosity) and cell size (i.e., diffusion pathlength) and by comparing wild-type cells with hemoglobin H (HbH) thalassemia (shorter pathlength and reduced tortuosity) and hereditary spherocytosis (HS; expanded pathlength). Analysis of the distribution of O2 unloading rates in HS RBCs identified a subpopulation of spherocytes with greatly impaired gas exchange. Tortuosity imposed by hemoglobin was verified by demonstrating restricted diffusivity of CO2, an acidic gas, from the dissipative spread of photolytically uncaged H+ ions across cytoplasm. Our findings indicate that cytoplasmic diffusion, determined by pathlength and tortuosity, is a major barrier to efficient gas handling by RBCs. Consequently, changes in RBC shape and hemoglobin concentration, which are common manifestations of hematological disorders, can have hitherto unrecognized and clinically significant implications on gas exchange.

Protecting vulnerable patients with inherited anaemias from unnecessary death during the COVID-19 pandemic.

With the developing COVID-19 pandemic, patients with inherited anaemias require specific advice regarding isolation and changes to usual treatment schedules. The National Haemoglobinopathy Panel (NHP) has issued guidance on the care of patients with sickle cell disease, thalassaemia, Diamond Blackfan anaemia (DBA), congenital dyserythropoietic anaemia (CDA), sideroblastic anaemia, pyruvate kinase deficiency and other red cell enzyme and membrane disorders. Cascading of accurate information for clinicians and patients is paramount to preventing adverse outcomes, such as patients who are at increased risk of fulminant bacterial infection due to their condition or its treatment erroneously self-isolating if their fever is mistakenly attributed to a viral cause, delaying potentially life-saving antibiotic therapy. Outpatient visits should be minimised for most patients, however some, such as first transcranial dopplers for children with sickle cell anaemia should not be delayed as known risk of stroke will outweigh the unknown risk from COVID-19 infection. Blood transfusion programmes should be continued, but specific changes to usual clinical pathways can be instituted to reduce risk of patient exposure to COVID-19, as well as contingency planning for possible reductions in blood available for transfusions. Bone marrow transplants for these disorders should be postponed until further notice. With the current lack of evidence on the risk and complications of COVID-19 infection in these patients, national data collection is ongoing to record outcomes and eventually to identify predictors of disease severity, particularly important if further waves of infection travel through the population.

The pathogenesis, diagnosis and management of congenital dyserythropoietic anaemia type I.

Congenital dyserythropoietic anaemia type I (CDA-I) is one of a heterogeneous group of inherited anaemias characterised by ineffective erythropoiesis. CDA-I is caused by bi-allelic mutations in either CDAN1 or C15orf41 and, to date, 56 causative mutations have been documented. The diagnostic pathway is reviewed and the utility of genetic testing in reducing the time taken to reach an accurate molecular diagnosis and avoiding bone marrow aspiration, where possible, is described. The management of CDA-I patients is discussed, highlighting both general and specific measures which impact on disease progression. The use of interferon alpha and careful management of iron overload are reviewed and suggest the most favourable outcomes are achieved when CDA-I patients are managed with a holistic and multidisciplinary approach. Finally, the current understanding of the molecular and cellular pathogenesis of CDA-I is presented, highlighting critical questions likely to lead to improved therapy for this disease.