Veerle Labarque

GNAS defects identified by stimulatory G protein alpha-subunit signalling studies in platelets.

CONTEXT GNAS is an imprinted region that gives rise to several transcripts, antisense transcripts, and noncoding RNAs, including transcription of RNA encoding the alpha-subunit of the stimulatory G protein (Gsalpha). The complexity of the GNAS cluster results in ubiquitous genomic imprints, tissue-specific Gsalpha expression, and multiple genotype-phenotype relationships. Phenotypes resulting from genetic and epigenetic abnormalities of the GNAS region include Albrights hereditary osteodystrophy, pseudohypoparathyroidism types Ia (PHPIa) and Ib (PHPIb), and pseudopseudohypoparathyroidism (PPHP). OBJECTIVE The aim was to study the complex GNAS pathology by a functional test as an alternative to the generally used but labor-intensive erythrocyte complementation assay. DESIGN AND PATIENTS We report the first platelet-based diagnostic test for Gsalpha hypofunction, supported by clinical, biochemical, and molecular data for six patients with PHPIa or PPHP and nine patients with PHPIb. The platelet test is based on the inhibition of platelet aggregation by cAMP, produced after Gsalpha stimulation. RESULTS Platelets are easily accessible, and platelet aggregation responses were found to reflect Gsalpha signaling defects in patients, in concordance with the patients phenotype and genotype. Gsalpha hypofunction in PHPIa and PPHP patients with GNAS mutations was clearly detected by this method. Mildly decreased or normal Gsalpha function was detected in patients with PHPIb with either an overall or exon 1A-only epigenetic defect, respectively. Platelet Gsalpha expression was reduced in both PHPIb patient groups, whereas XLalphas was up-regulated only in PHPIb patients with the broad epigenetic defect. CONCLUSION The platelet-based test is a novel tool for establishing the diagnosis of Gsalpha defects, which may otherwise be quite challenging.

Clinical practice: immune thrombocytopenia in paediatrics

Immune thrombocytopenia (ITP) is a disease affecting both children and adults. It is defined as acquired isolated thrombocytopenia caused by the autoimmune production of anti-platelet antibodies. Childhood ITP most frequently occurs in young children who have been previously well, although a viral respiratory tract infection often precedes thrombocytopenia. A benign and self-limiting course is common, but major bleeding complications such as intracranial haemorrhage may occur. Yet one cannot predict which child will have a prolonged course of thrombocytopenia and who will develop an intracranial haemorrhage. In children without atypical characteristics, only minimal diagnostic investigations are needed, and most paediatric ITP patients do not need platelet-enhancing therapy even though various treatment options are available. A “watch and wait” strategy should be considered in paediatric patients with mild disease. Steroids, intravenous immunoglobulin G or anti-D immunoglobulin are the current first-line therapeutic measures for children at risk for severe bleeding. When life-threatening bleeding occurs, a combination of therapies is needed. In this review, we summarise the current knowledge on primary ITP in children and adolescents.

Human platelet pathology related to defects in the G-protein signaling cascade

Summary.  Platelets are highly responsive to signals from their environment. The sensing and processing of some of these stimuli are mediated by G‐protein signal transduction cascades. It is well established that proteins involved in signal transduction may be targets for naturally occurring mutations resulting in human diseases. The best‐studied molecules in platelets in relation to disease are the G‐protein coupled receptors being the most platelet‐specific. Many of the other signal transduction genes are often not only present in platelets but also in other tissues. Therefore, the clinical phenotype of signaling defects in platelets, apart from the membrane receptor defects, is seldom isolated to a hemostatic phenotype. Moreover, as platelets are easily accessible cells, and one of the best‐studied models regarding signaling, platelets are easily applicable to investigate defects in ubiquitously expressed genes. Apart from a discussion on classical thrombopathies, this review will also deal with the less commonly known relation between platelet signaling defects and disorders with a broader clinical phenotype.

What’s new in using platelet research? To unravel thrombopathies and other human disorders

This review on platelet research focuses on defects of adhesion, cytoskeletal organisation, signal transduction and secretion. Platelet defects can be studied by different laboratory platelet functional assays and morphological studies. Easy bruising or a suspected platelet-based bleeding disorder is of course the most obvious reason to test the platelet function in a patient. However, nowadays platelet research also contributes to our understanding of human pathology in other disciplines such as neurology, nephrology, endocrinology and metabolic diseases. Apart from a discussion on classical thrombopathies, this review will also deal with the less commonly known relation between platelet research and disorders with a broader clinical phenotype. Classical thrombopathies involve disorders of platelet adhesion such as Glanzmann thrombastenia and Bernard-Soulier syndrome, defective G protein signalling diseases with impaired phospholipase C activation, and abnormal platelet granule secretion disorders such as gray platelet disorder and delta-storage pool disease. Other clinical symptoms besides a bleeding tendency have been described in MYH9-related disorders and Duchenne muscular dystrophy due to adhesion defects, and also in disorders of impaired Gs signalling, in Hermansky Pudlack disease and Chediak Higashi disease with abnormal secretion. Finally, platelet research can also be used to unravel novel mechanisms involved in many neurological disorders such as depression and autism with only a subclinical platelet defect.

LIN28B overexpression defines a novel fetal-like subgroup of juvenile myelomonocytic leukemia

Juvenile myelomonocytic leukemia (JMML) is a rare and aggressive stem cell disease of early childhood. RAS activation constitutes the core component of oncogenic signaling. In addition, leukemic blasts in one-fourth of JMML patients present with monosomy 7, and more than half of patients show elevated age-adjusted fetal hemoglobin (HbF) levels. Hematopoietic stem cell transplantation is the current standard of care and results in an event-free survival rate of 50% to 60%, indicating that novel molecular-driven therapeutic options are urgently needed. Using gene expression profiling in a series of 82 patient samples, we aimed at understanding the molecular biology behind JMML and identified a previously unrecognized molecular subgroup characterized by high LIN28B expression. LIN28B overexpression was significantly correlated with higher HbF levels, whereas patients with monosomy 7 seldom showed enhanced LIN28B expression. This finding gives a biological explanation of why patients with monosomy 7 are rarely diagnosed with high age-adjusted HbF levels. In addition, this new fetal-like JMML subgroup presented with reduced levels of most members of the let-7 microRNA family and showed characteristic overexpression of genes involved in fetal hematopoiesis and stem cell self-renewal. Lastly, high LIN28B expression was associated with poor clinical outcome in our JMML patient series but was not independent from other prognostic factors such as age and age-adjusted HbF levels. In conclusion, we identified elevated LIN28B expression as a hallmark of a novel fetal-like subgroup in JMML.

Regulator of G-protein signaling 18 controls megakaryopoiesis and the cilia-mediated vertebrate mechanosensory system

RGS18 was originally identified as a R4 subfamily member of regulators of G‐protein signaling (RGS) with specific expression in hematopoietic progenitors, myeloerythroid cells, and megakaryocytes, though its physiological role in hematopoiesis remained unknown. Here, we show that lentiviral RGS18 overexpression during differentiation of mouse Sca1+ hematopoietic stem cells induced a 50% increase of megakaryocyte proliferation. RGS18 depletion in zebrafish results in thrombocytopenia, as 66 to 88% of the embryos lack thrombocytes after injection of an ATG or splice‐blocking morpholino, respectively. These embryos have no defects in early hematopoiesis, erythropoiesis, or leukocyte number and migration. In addition, all RGS18 depleted embryos have curly tails and an almost absent response to acoustic stimuli. In situ hybridization in zebrafish, Xenopus, and mouse embryos shows RGS18 expression in thrombocytes and/or hematological tissues but also in brain and otic vesicles. RGS18 interferes with development of cilia in hair cells of the inner ear and neuromast cells. On the basis of literature evidence that RGS‐R4 members interact with the G‐protein‐modulated Wnt/calcium pathway, Wnt5b‐but not Wnt5a‐depleted embryos phenocopy all RGS18 knockdown effects. In summary, our study is the first to show that RGS18 regulates megakaryopoiesis but also reveals its unexpected role in ciliogenesis, at least in lower vertebrates, via interference with Wnt signaling.—Louwette, S., Labarque, V., Wittevrongel, C., Thys, C., Metz, J., Gijsbers, R., Debyser, Z., Arnout, J., Van Geet, C., Freson, K. Regulator of G‐protein signaling 18 controls megakaryopoiesis and the cilia‐mediated vertebrate mechanosensory system. FASEB J. 26, 2125‐2136 (2012). www.fasebj.org

An Estimation of the Incidence and Demographic Picture of the Major Hemoglobinopathies in Belgium (From a Confidential Inquiry)

An estimation of the incidence and demographic picture of the major hemoglobinopathies in Belgium has been approached through a confidential inquiry sent to 228 pediatric and adult hematological departments. Forty-two percent of responses showed that 417 patients are known in Belgium: 83% with sickle cell disease, 13% with β-thalassemia (β-thal) major, 2% with β-thal intermedia, and 1% with Hb H disease. Twenty-five percent of the sickle cell disease patients and 54% of those suffering from a β-thal major were older than 20 years. Three hospitals ensure the follow-up of 70% of the patients and are situated in Brussels, Belgium; a follow-up of less than 20 patients was reported at 21 centers. These results confirm that sickle cell disease is the major hemoglobinopathy in Belgium; it concerns mostly pediatricians but adult hematologists are also confronted with these pathologies. Therefore, it is necessary to implement integrated programs of prevention and treatment.

Obsessive-compulsive behavior as presenting symptom of primary antiphospholipid syndrome

Objective This study aimed to improve understanding and treatment of psychiatric symptoms in antiphospholipid syndrome (APS) and to present an approach to the medical management of patients presenting with obsessive-compulsive disorder (OCD) with suspected neurovascular pathology. Method A 15-year-old boy presented with severe OCD of recent onset. An infarct of the caudate nucleus was identified as the initial presentation of primary APS. This case report includes a selective literature review of the neuropsychiatric correlates of APS. Results The patient had OCD for 3 months with increasing symptoms resulting in admission for psychiatric reasons. After referral to the emergency department 3 weeks later, an infarct of the caudate nucleus was documented using magnetic resonance images of the brain, and APS was diagnosed based on additional laboratory findings. Anticoagulant treatment (enoxaparin and phenprocoumon) in this patient was effective in reducing obsessive-compulsive symptom severity. Conclusion OCD may present as a neuropsychiatric manifestation of APS. The present observations are consistent with a thrombotic mechanism for neurologic or psychiatric symptoms in APS. In general, routine medical workup for childhood OCD is not indicated, but a comprehensive psychiatric, medical, and family history taking and physical examination are essential, particularly if OCD is of recent onset. The role of anticoagulant therapy in neuropsychiatric manifestations of APS without the presence of a cerebral infarct requires further research.

LIN28B is over-expressed in specific subtypes of pediatric leukemia and regulates lncRNA H19

LIN28B is an RNA-binding protein with an oncofetal expression pattern. High LIN28B expression is crucial during human embryogenesis and is down-regulated in most tissues after birth.[1][1] However, reactivation during oncogenesis is common in a plethora of adult cancers, including leukemia, and was