Characterization of New Candidate Genes in Cases of Human Inherited Thrombocytopenia (CATCH)

Plain-language summary

Circulating blood platelets are small cellular elements that help to control bleeding (a process called hemostasis) and to avoid hemorrhage when blood vessels are injured. Platelets originate from cells in the bone marrow, the megakaryocytes (MKs), following a complex process of morphological transformation and maturation, which finally leads to the production of blood platelets. Multiple genes are implicated in this process. Constitutive thrombocytopenia (CT) are rare hematological diseases characterized by a decreased number of circulating platelets that are often larger than normal, that may lead to more or less severe hemorrhagic events. However, CT can be difficult to diagnose and differentiate from various forms of acquired thrombocytopenia. The ultimate diagnosis for CT is thus based on the molecular diagnosis, obtained by identifying and characterizing the abnormal gene and protein. About 40 genes / proteins have been identified so far as causal in CT, however, in about half of the patients suspected to have CT, genomic analysis does not detect a variant in one of these genes, and etiology of CT thus remains unknown. But insuring the diagnosis of CT is important: it will avoid misdiagnosis and inefficient or deleterious therapeutic interventions, while allowing a proposal of an adapted curative/preventive medical action. At the Resource and Competence Center for Constitutional Hemorrhagic Diseases (CRCMHC) (University Hospital Robert Debré, Paris, France), the investigating team has evidenced in unrelated patients presenting with familial forms of thrombocytopenia and no known molecular diagnosis, variants of genes not yet described as formally implicated in the occurrence of CT. Molecular genetic evidence must be completed by functional studies. Such functional studies are conducted in a research laboratory from the National Institute for Health and Medical Research (Inserm), "Innovative Therapies in Haemostasis (IThEM)" (Faculty of Medical Sciences, University of Paris, Paris, France), and include: * an evaluation of how blood progenitor cells mature into MKs, by comparing cells obtained from patients to those of members free of the disease (the latter taken as normal control subjects); * an evaluation of platelet functionalities, such as ability to form a blood clot similar to what happens during hemostasis, with the aim to detect not only quantitative (number and size) but also any qualitative (functions) defects; * an evaluation of the ultrastructure (the structure of intracellular components) and biochemistry of MKs and platelets, focusing on the molecular pathways the variant protein is implicated in. This clinical trial is aimed to precisely delineate the mechanism of action of newly identified CT genetic variants, and will fulfill the aims of (1) offering the patient(s) a formal molecular diagnosis of CT, (2) ameliorating patients' medical support, both for diagnosis and therapy, (3) providing patients and family members with a pertinent genetic counseling, and (4) expanding the validated panel of genes implicated in CT to be explored in new suspected cases of CT. It will also help in extending the basic knowledge of the process of MK and platelet formation.

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