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Biomedical subjects

Irene Roberts

Publications and source records attributed to Irene Roberts.

At least 19 recordsLinked to original sources
PubMed2006

Down myeloid disorders: a paradigm for childhood preleukaemia and leukaemia and insights into normal megakaryopoiesis.

Newborns and children with Down Syndrome are predisposed to a range of blood disorders, which include acute lymphoblastic leukaemia and acute megakaryocytic leukaemia (AMKL). Over the last four years there has been considerable progress in our understanding of DS AMKL. Like other childhood leukaemias DS AMKL is initiated in utero and can present in the neonatal period as a clinically overt preleukaemic condition, transient myeloproliferative disorder (TMD). In addition to trisomy 21, fetal haemopoietic progenitors acquire N-terminal truncating mutations in the key megakaryocyte-erythroid transcription factor GATA1. These are the minimum required events for TMD to develop. In approximately 30% of TMD patients, additional as yet unidentified (epi)genetic mutations are required for progression to AMKL. Thus, DS TMD and AMKL provide a unique model of childhood leukaemia where the preleukaemic and leukaemic phases are ascertainable and separable allowing distinct steps in leukaemogenesis to be studied individually. These findings also have implications for the clinical management of DS TMD and AMKL specifically and also of childhood leukaemia more generally.

Child↗
PubMed2006

Hypomorphic promoter mutation in PIGM causes inherited glycosylphosphatidylinositol deficiency.

Attachment to the plasma membrane by linkage to a glycosylphosphatidylinositol (GPI) anchor is a mode of protein expression highly conserved from protozoa to mammals. As a clinical entity, deficiency of GPI has been recognized as paroxysmal nocturnal hemoglobinuria, an acquired clonal disorder associated with somatic mutations of the X-linked PIGA gene in hematopoietic cells. We have identified a novel disease characterized by a propensity to venous thrombosis and seizures in which deficiency of GPI is inherited in an autosomal recessive manner. In two unrelated kindreds, a point mutation (c --> g) at position -270 from the start codon of PIGM, a mannosyltransferase-encoding gene, disrupts binding of the transcription factor Sp1 to its cognate promoter motif. This mutation substantially reduces transcription of PIGM and blocks mannosylation of GPI, leading to partial but severe deficiency of GPI. These findings indicate that biosynthesis of GPI is essential to maintain homeostasis of blood coagulation and neurological function.

Amino Acid Sequence↗
PubMed2006

Management of Evans syndrome.

Evans syndrome is an uncommon condition defined by the combination (either simultaneously or sequentially) of immune thrombocytopenia (ITP) and autoimmune haemolytic anaemia (AIHA) with a positive direct antiglobulin test (DAT) in the absence of known underlying aetiology. This condition generally runs a chronic course and is characterised by frequent exacerbations and remissions. First-line therapy is usually corticosteroids and/or intravenous immunoglobulin, to which most patients respond; however, relapse is frequent. Options for second-line therapy include immunosuppressive drugs, especially ciclosporin or mycophenolate mofetil; vincristine; danazol or a combination of these agents. More recently a small number of patients have been treated with rituximab, which induces remission in the majority although such responses are often sustained for <12 months and the long-term effects in children are unclear. Splenectomy may also be considered although long-term remissions are less frequent than in uncomplicated ITP. For very severe and refractory cases stem cell transplantation (SCT) offers the only chance of long-term cure. The limited data available suggest that allogeneic SCT may be superior to autologous SCT but both carry risks of severe morbidity and of transplant-related mortality. Cure following reduced-intensity conditioning has now been reported and should be considered for younger patients in the context of controlled clinical trials.

Anemia, Hemolytic, Autoimmune↗
PubMed2006

Correction of severe anaemia using immuno-regulated gene therapy is achieved by restoring the early erythroblast compartment.

Patients with chronic renal failure usually require exogenous erythropoietin (epo) to alleviate anaemia resulting from inadequate epo production by the kidneys. We have recently shown that severe anaemia in genetically manipulated epo-deficient mice (EpoTAg) can be corrected by adoptively transferred epo-producing lymphocytes. The aim of this study was to investigate the precise effects of human epo administration by this route on erythropoietic development in epo-deficient mice. The erythroblast compartments of untreated and treated EpoTAg mice were analysed in comparison with wild-type mice. The early erythroblast population was reduced in the bone marrow of epo-deficient mice, whilst the number of erythroid colony-forming units (CFU-E) was not significantly compromised. This paucity in marrow early erythroblasts was restored to normal values in treated mutant mice. In addition, the early erythroblast population was expanded in the spleens of treated animals. These findings show that the early erythroblasts are important targets of epo and that epo corrects anaemia of epo-deficient mice by restoring marrow function and splenic erythropoiesis.

Adoptive Transfer↗
PubMed2005

The role of mesenchymal stem cells in haemopoiesis.

The ontogeny of haemopoiesis during fetal life and the differentiation of blood cells in adult life depend upon a fully competent microenvironment to provide appropriate signals via production of soluble factors and cell contact interactions. The cellular constituents of the microenvironment, also defined as the haemopoietic niche, largely derive from a common progenitor of mesenchymal origin. Mesenchymal stem cells (MSC), initially identified in adult bone marrow, have also been described in fetal haemopoietic tissues where they accompany the migration of haemopoietic development. Their precise identity remains ill-defined because of the lack of specific markers. Their ability to self-renew and differentiate into tissues of mesodermal origin (osteocytes, adipocytes, chondrocytes) and their lack of expression of haemopoietic molecules are currently the main criteria for isolation. In the bone marrow the most important elements of the niche appear to be osteoblasts, whilst a less defined population of fibroblasts regulates the maturation of immature T cells in the thymus. Recently, MSC have been shown to exert a profound immunosuppressive effect on polyclonal as well as antigen-specific T cell responses by inducing a state of division arrest anergy. Thus, the multipotent capacity of MSC, their role in supporting haemopoiesis, and their immunoregulatory activity make MSC particularly attractive for therapeutic exploitation.

Animals↗
PubMed2005

GATA1 mutation and trisomy 21 are required only in haematopoietic cells for development of transient myeloproliferative disorder.

Trisomy 21 [Down's syndrome (DS)] and mutations in transcription factor GATA1 predispose neonates to a transient myeloproliferative disorder (TMD) and/or acute megakaryocytic leukaemia (AMKL). The role of trisomy 21 in their pathogenesis is unclear. We previously reported two rare neonates without DS who had TMD, one of whom progressed to AMKL. Trisomy 21 was detected only in blood cells at presentation with TMD/AMKL and disappeared with disease resolution. We now show that the blood cells at presentation of TMD harboured GATA1 genomic DNA mutations, suggesting a requirement for trisomy 21 in haematopoietic cells, rather than other cell types, for development of TMD/AMKL.

Base Sequence↗
PubMed2005

Bone involvement in sickle cell disease.

Bone involvement is the commonest clinical manifestation of sickle cell disease both in the acute setting such as painful vaso-occlusive crises, and as a source of chronic, progressive disability such as avascular necrosis. Management of these problems is often difficult because of the diagnostic imprecision of most laboratory and imaging investigations and because of the lack of evidence for most surgical procedures in sickle cell disease. This review first discusses the acute problems related to bone involvement in sickle cell disease, with particular reference to differentiating infection from infarction, and then describes the long-term effects of sickle cell disease on bone mineral density, growth, and chronic bone and joint damage.

Acute Disease↗
PubMed2005

The expression of minichromosome maintenance protein-2 in normal and abnormal megakaryocytes and comparison with the proliferative marker Ki-67.

The minichromosome maintenance (Mcm) and Cdc6 proteins are important regulators of eucaryotic DNA replication. In most normal tissues, a similar proportion of cells express Mcm-2 and Ki-67. The present study showed that in both normal and abnormal states, the proportion of megakaryocytes expressing Mcm-2 is roughly seven times as many as those that express Ki-67. This is likely to be related to the process of endomitosis and endoreduplication. We also demonstrated that a significantly lower proportion of megakaryocytes in myelodysplastic syndrome express Mcm-2. These findings provide new insights into megakaryocyte biology.

Bone Marrow↗
PubMed2004

Neonatal thrombocytopenia.

Thrombocytopenia occurs in up to a third of preterm neonates admitted to intensive care units. In these babies, thrombocytopenia typically presents in one of two patterns: early-onset thrombocytopenia occurring within 72 h of birth and late-onset thrombocytopenia which develops after 72 h. Early-onset thrombocytopenia is most commonly caused by disorders associated with placental insufficiency (e.g. maternal hypertension), is mild-moderate, self-limiting and requires no treatment; it is caused by reduced platelet production. Late-onset thrombocytopenia is usually due to bacterial sepsis or necrotising enterocolitis; it is often severe (platelets <50 x 10(9)/l), prolonged and requires treatment with platelet transfusions. In term babies, neonatal thrombocytopenia is usually severe and most commonly caused by bacterial sepsis, perinatal asphyxia or neonatal alloimmune thrombocytopenia. There is a lack of evidence-based guidelines for treatment of neonatal thrombocytopenia. The most important future developments will depend upon studies aimed at determining optimal platelet transfusion schedules for term and preterm neonates.

Humans↗
PubMed2003

Natural history of GATA1 mutations in Down syndrome.

Acquired mutations in megakaryocyte transcription factor GATA1 have recently been reported in Down syndrome (DS), transient myeloproliferative disorder (TMD), and acute megakaryoblastic leukemia (AMKL). To provide novel insight into GATA1 mutations in DS, genomic DNA was assayed from 12 AMKL and 4 TMD cases (including neonatal, prediagnosis samples in 4 of 16), neonatal blood spots from 21 DS children without clinically evident TMD or AMKL, and 62 non-DS cord blood samples, using techniques not previously employed with such samples. GATA1 mutations were present in all TMD and AMKL cases and at birth in 3 of 4 children without known clinical TMD, who later developed AMKL. They were present at birth in 2 of 21 DS neonates, who have not yet, but could still, develop AMKL (now 26 and 31 months). GATA1 mutations were not detected in 62 non-DS cord blood samples. In 4 AMKL patients multiple independent GATA1 mutations were observed. These data show GATA1 mutations occur in utero in most DS TMD and AMKL, that they may occur without clinical signs of disease, and that multiple separate GATA1 mutant clones can occur in an individual. The findings have implications for pathogenesis of DS TMD and AMKL and highlight parallels between DS AMKL and other childhood leukemias.

Child, Preschool↗
PubMed2003

Characterization of first trimester fetal erythroblasts for non-invasive prenatal diagnosis.

Isolating fetal erythroblasts from first trimester maternal blood offers a promising non-invasive alternative for prenatal diagnosis. The aim of this study was to characterize the biological properties of first trimester primitive erythroblasts to facilitate their enrichment from first trimester maternal blood. Primitive erythroblasts were the predominant cell type until 12 weeks gestation, after which time their numbers declined steeply; 100% were epsilon-globin-positive versus <0.06% definitive erythroblasts. Buoyant densities of first trimester fetal erythroblasts ranged from 1.077 to 1.130 g/ml, and optimal recoveries were obtained with Percoll 1118. Although primitive erythroblasts carried a negative surface charge and were resistant to NH(4)Cl lysis, these properties had only a limited role in fetal cell enrichment. Immunophenotyping showed that primitive, like definitive, erythroblasts were GPA+, CD47+, CD45- and CD35-, whereas CD71 expression was weak/undetectable on primitive erythroblasts but strongly positive on 100% of definitive erythroblasts; primitive erythroblasts were also CD36- whereas definitive erythroblasts were CD36+. We therefore used CD45/GPA selection of Percoll 1118-separated cells to demonstrate successful enrichment of male epsilon-globin-positive fetal erythroblasts from model mixtures, and as proof of principle from some first trimester maternal blood samples. Fetal cell enrichment protocols based on first trimester epsilon-globin-positive primitive erythroblasts may allow reliable enrichment of fetal cells from maternal blood for early non-invasive prenatal diagnosis of genetic disorders.

Ammonium Chloride↗
PubMed2002

Related umbilical cord blood transplantation in patients with thalassemia and sickle cell disease.

Allogeneic bone marrow transplantation (BMT) from HLA-identical siblings is an accepted treatment for both thalassemia and sickle cell disease (SCD). However, it is associated with decided risk of both transplant-related mortality (TRM) and chronic graft-versus-host disease (GVHD). We analyzed 44 patients (median age, 5 years; range, 1-20 years) given an allogeneic related cord blood transplant for either thalassemia (n = 33) or SCD (n = 11). Thirty children were given cyclosporin A (CsA) alone as GVHD prophylaxis, 10 received CsA and methotrexate (MTX), and 4 patients received other combinations of immunosuppressive drugs. The median number of nucleated cells infused was 4.0 x 10(7)/kg (range, 1.2-10 x 10(7)/kg). No patient died and 36 of 44 children remain free of disease, with a median follow-up of 24 months (range, 4-76 months). Only one patient with SCD did not have sustained donor engraftment as compared with 7 of the 33 patients with thalassemia. Three of these 8 patients had sustained donor engraftment after BMT from the same donor. Four patients experienced grade 2 acute GVHD; only 2 of the 36 patients at risk developed limited chronic GVHD. The 2-year probability of event-free survival is 79% and 90% for patients with thalassemia and SCD, respectively. Use of MTX for GVHD prophylaxis was associated with a greater risk of treatment failure. Related CBT for hemoglobinopathies offers a good probability of success and is associated with a low risk of GVHD. Optimization of transplantation strategies could further improve these results.

Acute Disease↗
PubMed2002

RBC T activation and hemolysis in a neonatal intensive care population: implications for transfusion practice.

BACKGROUND: Reports of transfusion-associated hemolysis in infants with T-activated RBCs have led to the suggestion that infants should be screened and provided with low-titer anti-T blood components. T-activated RBCs react with the lectins Arachis hypogea and Glycine soja; variants of T (Th and Tx) and Tk also react with A. hypogea, but not G. soja. Although Tk is not a true variant of T, for the purposes of this study, all RBCs that are reactive with A. hypogea but are not reactive with G. soja are called "T variants." STUDY DESIGN AND METHODS: A prospective study was carried out to examine T and T variant activation and transfusion-associated hemolysis in a neonatal intensive care population and to determine if antibodies to T and T variant are detectable in donor plasma. A total of 2041 samples from 375 infants were tested for T and T variant activation utilizing a lectin panel. Three hundred donor plasma samples were tested for antibodies to T and T variant. RESULTS: Forty-eight of 375 infants (12.8%) had T- and T-variant-activated RBCs. Of these, 13 of 48 (27%) developed at least one episode of sepsis and 9 of 48 (19%) developed necrotizing enterocolitis (NEC) at some point during their inpatient stay. T activation was not always temporally associated with the onset of NEC or sepsis. The remaining 26 of 48 (54%) were healthy infants receiving convalescent care in the neonatal intensive care units and showed no evidence of either NEC or sepsis. Twelve (of 375) additional infants (3.2%) who developed NEC and 100 (27%) who developed sepsis showed no RBC T activation. Twenty-three of 48 (48%) infants with T-activated RBCs received standard blood components, but no transfusion-associated hemolysis occurred. Donor plasma samples contained T but not T variant antibodies. CONCLUSION: T variant activation of RBCs occurs in healthy neonates as well as in infants with NEC and sepsis, but T activation appears rare. Transfusion- associated hemolysis was not seen. The provision of specially prepared blood components for infants with NEC is unnecessary.

Antibodies↗
PubMed2002

High transduction efficiency of circulating first trimester fetal mesenchymal stem cells: potential targets for in utero ex vivo gene therapy.

We recently reported the existence of fetal mesenchymal stem cells in first trimester fetal blood. Here we demonstrate that fetal mesenchymal stem cells from as early as eight weeks of gestation can be retrovirally transduced with 99% efficiency without selection. Circulating fetal mesenchymal stem cells are known to readily expand and differentiate into multiple tissue types both in vitro and in vivo, and might be suitable vehicles for prenatal gene delivery. With advances in early fetal blood sampling techniques, we suggest that genetic disorders causing irreversible damage before birth could be treated in utero in the late first/early second trimester by genetically manipulated autologous fetal stem cells.

Female↗