Blood cells derive from hematopoietic stem cells through stepwise fating events. To characterize gene expression programs driving lineage choice, we sequenced RNA from eight primary human ...hematopoietic progenitor populations representing the major myeloid commitment stages and the main lymphoid stage. We identified extensive cell type-specific expression changes: 6711 genes and 10,724 transcripts, enriched in non-protein-coding elements at early stages of differentiation. In addition, we found 7881 novel splice junctions and 2301 differentially used alternative splicing events, enriched in genes involved in regulatory processes. We demonstrated experimentally cell-specific isoform usage, identifying nuclear factor I/B (NFIB) as a regulator of megakaryocyte maturation-the platelet precursor. Our data highlight the complexity of fating events in closely related progenitor populations, the understanding of which is essential for the advancement of transplantation and regenerative medicine.
Macrothrombocytopenia (MTP) is a heterogeneous group of disorders characterized by enlarged and reduced numbers of circulating platelets, sometimes resulting in abnormal bleeding. In most MTP, this ...phenotype arises because of altered regulation of platelet formation from megakaryocytes (MKs). We report the identification of DIAPH1, which encodes the Rho-effector diaphanous-related formin 1 (DIAPH1), as a candidate gene for MTP using exome sequencing, ontological phenotyping, and similarity regression. We describe 2 unrelated pedigrees with MTP and sensorineural hearing loss that segregate with a DIAPH1 R1213* variant predicting partial truncation of the DIAPH1 diaphanous autoregulatory domain. The R1213* variant was linked to reduced proplatelet formation from cultured MKs, cell clustering, and abnormal cortical filamentous actin. Similarly, in platelets, there was increased filamentous actin and stable microtubules, indicating constitutive activation of DIAPH1. Overexpression of DIAPH1 R1213* in cells reproduced the cytoskeletal alterations found in platelets. Our description of a novel disorder of platelet formation and hearing loss extends the repertoire of DIAPH1-related disease and provides new insight into the autoregulation of DIAPH1 activity.
•A gain-of-function variant in DIAPH1 causes macrothrombocytopenia and hearing loss and extends the spectrum of DIAPH1-related disease.•Our findings of altered megakaryopoiesis and platelet cytoskeletal regulation highlight a critical role for DIAPH1 in platelet formation.
To identify novel causes of hereditary thrombocytopenia, we performed a genetic association analysis of whole-genome sequencing data from 13 037 individuals enrolled in the National Institute for ...Health Research (NIHR) BioResource, including 233 cases with isolated thrombocytopenia. We found an association between rare variants in the transcription factor-encoding gene IKZF5 and thrombocytopenia. We report 5 causal missense variants in or near IKZF5 zinc fingers, of which 2 occurred de novo and 3 co-segregated in 3 pedigrees. A canonical DNA-zinc finger binding model predicts that 3 of the variants alter DNA recognition. Expression studies showed that chromatin binding was disrupted in mutant compared with wild-type IKZF5, and electron microscopy revealed a reduced quantity of α granules in normally sized platelets. Proplatelet formation was reduced in megakaryocytes from 7 cases relative to 6 controls. Comparison of RNA-sequencing data from platelets, monocytes, neutrophils, and CD4+ T cells from 3 cases and 14 healthy controls showed 1194 differentially expressed genes in platelets but only 4 differentially expressed genes in each of the other blood cell types. In conclusion, IKZF5 is a novel transcriptional regulator of megakaryopoiesis and the eighth transcription factor associated with dominant thrombocytopenia in humans.
•Mutations in the transcription factor IKZF5 cause autosomal dominant thrombocytopenia and a paucity of α granules.•Although IKZF5 is expressed across hematopoietic lineages, misregulation in IKZF5 cases is restricted to the megakaryocytic lineage.
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The last decade has seen large increases in the number of patients registered with heritable platelet disorders in national databases of bleeding disorders. Although individually rare, collectively ...they are a relatively common cause of heritable bleeding. This revolution has come about through the application of high-throughput sequencing strategies and efforts to standardize diagnostic testing. There is renewed interest in established parameters such as platelet volume and utilising simple tools such as blood smears. The diagnostic yield from peripheral blood smears can be improved with new microscopy techniques that could potentially assist in determining which patients need to be referred to tertiary centres for specialist testing. A better understanding of the other clinical features that can accompany abnormalities of platelet number or function, can lead to better clinical management and prevention of serious complications. There are challenges for clinicians who need to be aware of these developments, understand the limitations of new diagnostic techniques and keep abreast of strategies for incorporation into clinical practice. This review discusses some of these approaches, the limitations that clinicians need to be aware of and techniques that may enter clinical use in the future.
Abstract
Introduction
Gene therapy for haemophilia is in late-stage clinical development and has the potential to become a therapeutic option in clinical practice.
Aims
To enhance the understanding ...of the perspectives of people with haemophilia around gene therapy, and to highlight their concerns about and motivations for having gene therapy.
Method
Structured, qualitative interviews were conducted and recorded with six people who had received an investigational gene therapy product. The recordings were transcribed and thematically analysed.
Results
Most of those interviewed were under the age of 40, and the mean time out from their gene therapy infusion was 10 months. Adverse events were the main concerns pre-infusion, and impact on quality of life was the main motivating factor for choosing to go ahead. Pre-infusion, the treating centre and the health care professionals working there were the main source of information regarding gene therapy; only two participants looked elsewhere for information to support their decision. None of the respondents expressed concerns about the infusion day itself, and all found the infusion to be simple or uneventful. Post-infusion, four found the frequency of follow-up appointments difficult, with time and travel the main issues.
Conclusion
Although participants' perspectives on gene therapy were generally positive, there remains a need for education and support. Nurses will play an important role in the delivery of gene therapy for haemophilia, but all staff within the haemophilia treatment centre should be armed with the knowledge and confidence to answer questions about gene therapy.
The necessity of a multidisciplinary team (MDT) approach in haemophilia care is well recognised globally, with international guidelines advocating this. Prior to the coronavirus disease 2019 ...pandemic, virtual MDT haemophilia care was gaining support worldwide. However, the pandemic necessitated the rapid implementation of innovative virtual solutions to ensure continued access to multidisciplinary care. A multidisciplinary panel of healthcare professionals who specialise in haemophilia care in the United Kingdom gathered to discuss the following: the current landscape of haemophilia MDT care and best practices, the benefits, challenges, and opportunities for virtual MDT care, managing bleeds remotely, virtual paediatric care, and the future of virtual MDT care. The consensus was that virtual MDT care is widely used, however formats vary depending on the healthcare setting, available resources, MDT preferences, and local policy. Advisors agreed that virtual MDT care has several benefits, such as improved convenience/choice for their patients and wider patient reach. However, many patient-specific and logistical challenges exist. Hybrid care models may provide an opportunity to overcome these challenges. The decision on how bleeds are managed (virtually versus face-to-face) depends on provider preference, the patient-provider relationship, and the patient’s disease severity, history, and ability to self-manage. As such, this should be assessed on a case-by-case basis. Virtual tracking tools cannot be solely relied upon for MDT decisionmaking as patient accuracy cannot be ascertained. The MDT composition for paediatric care should be tailored to the patients’ and their parents’/caregivers’ needs. Lastly, hybridised care will likely be adopted for future haemophilia management and will facilitate the advancement of MDT care.
Next-generation sequencing is transforming our understanding of human genetic variation but assessing the functional impact of novel variants presents challenges. We analyzed missense variants in the ...integrin αIIbβ3 receptor subunit genes ITGA2B and ITGB3 identified by whole-exome or -genome sequencing in the ThromboGenomics project, comprising ∼32,000 alleles from 16,108 individuals. We analyzed the results in comparison with 111 missense variants in these genes previously reported as being associated with Glanzmann thrombasthenia (GT), 20 associated with alloimmune thrombocytopenia, and 5 associated with aniso/macrothrombocytopenia. We identified 114 novel missense variants in ITGA2B (affecting ∼11% of the amino acids) and 68 novel missense variants in ITGB3 (affecting ∼9% of the amino acids). Of the variants, 96% had minor allele frequencies (MAF) < 0.1%, indicating their rarity. Based on sequence conservation, MAF, and location on a complete model of αIIbβ3, we selected three novel variants that affect amino acids previously associated with GT for expression in HEK293 cells. αIIb P176H and β3 C547G severely reduced αIIbβ3 expression, whereas αIIb P943A partially reduced αIIbβ3 expression and had no effect on fibrinogen binding. We used receiver operating characteristic curves of combined annotation-dependent depletion, Polyphen 2-HDIV, and sorting intolerant from tolerant to estimate the percentage of novel variants likely to be deleterious. At optimal cut-off values, which had 69–98% sensitivity in detecting GT mutations, between 27% and 71% of the novel αIIb or β3 missense variants were predicted to be deleterious. Our data have implications for understanding the evolutionary pressure on αIIbβ3 and highlight the challenges in predicting the clinical significance of novel missense variants.
Significance Next-generation sequencing is identifying millions of novel gene variants, presenting challenges to researchers and clinicians. Variations in the genes ITGA2B and ITGB3 affect integrin αIIbβ3, leading to the bleeding disorder Glanzmann thrombasthenia. We analyzed novel missense variants on ∼32,000 alleles of ITGA2B and ITGB3 and found missense variants affecting ∼10% of the amino acids in each protein in ∼1.3% of the population. Almost all variants are rare, indicating recent entry into the population. Two novel variants we predicted would be deleterious profoundly affected recombinant protein expression. At cut-off values that correctly predicted at least 69% of the known Glanzmann thrombasthenia mutations as deleterious, three variant prediction algorithms predicted that at least 27% of the novel variants are deleterious.
Investigation of 3 families with bleeding symptoms demonstrated a defect in the collagen-binding activity of von Willebrand factor (VWF) in association with a normal VWF multimeric pattern. Genetic ...analysis showed affected persons to be heterozygous for mutations in the A3 domain of VWF: S1731T, W1745C, and S1783A. One person showed compound heterozygosity for W1745C and R760H. W1745C and S1783A have not been reported previously. The mutations were reproduced by site-directed mutagenesis and mutant VWF expressed in HEK293T cells. Collagen-binding activity measured by immunosorbent assay varied according to collagen type: W1745C and S1783A were associated with a pronounced binding defect to both type I and type III collagen, whereas the principal abnormality in S1731T patients was a reduction in binding to type I collagen only. The multimer pattern and distribution of mutant proteins were indistinguishable from wild-type recombinant VWF, confirming that the defect in collagen binding resulted from the loss of affinity at the binding site and not impairment of high-molecular-weight multimer formation. Our findings demonstrate that mutations causing an abnormality in the binding of VWF to collagen may contribute to clinically significant bleeding symptoms. We propose that isolated collagen-binding defects are classified as a distinct subtype of von Willebrand disease.
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