Inherited thrombocytopenias are rare, heterogenous and probably under-diagnosed because often classified as autoimmune thrombocytopenia. About 20 genes were described responsible for these thrombocytopenias. Precise diagnosis is necessary because the prognosis is different and some of them can evolve into hemopathies. First of all, it is important to gather a body of evidence to orientate towards an inherited cause: presence of the thrombocytopenia since childhood and of other family cases is a strong argument. Secondly, it is difficult to target the genetic investigations that settle the precise diagnosis. Genetic variants responsible for inherited thrombocytopenias affect different stage during megakaryocytopoiesis and cause thrombocytopenias with distinct characteristics. Presence of extra hematological features, platelets' size measurement and evaluation of bone marrow megakaryocyte morphology when it is possible allow a primary orientation. We propose a diagnostic approach considering extra-hematological features, mode of inheritance, morphology, molecular and functional platelets' studies and bone marrow megakaryocyte morphology in order to better target genetic study. Nevertheless, despite this approach, some inherited thrombocytopenias remain still unexplained and could benefit from new methods of new generation sequencing in the future. (C) 2015 Societe nationale francaise de medecine interne (SNFMI). Published by Elsevier Masson SAS. All rights reserved.

Les thrombopénies constitutionnelles sont des entités rares et hétérogènes mais certainement sous-diagnostiquées car souvent étiquetées thrombopénies auto-immunes. Une vingtaine de gènes ont été décrits comme responsables de ces thrombopénies. Leur diagnostic précis est nécessaire car elles n’ont pas toutes le même pronostic, certaines pouvant notamment se compliquer d’hémopathies. Dans un premier temps, il est important de réunir un faisceau d’arguments orientant vers l’origine constitutionnelle : l’existence dès l’enfance de la thrombopénie et d’autres cas dans la famille constitue un argument fort. La deuxième difficulté est d’orienter l’étude génétique permettant de poser un diagnostic précis. Les variants à l’origine de ces thrombopénies agissent à des phases distinctes de la mégacaryocytopoïèse et entraînent des thrombopénies aux caractéristiques différentes. L’existence de signes extra-hématologiques, l’évaluation précise de la taille plaquettaire ainsi qu’une étude cytologique des mégacaryocytes médullaires quand elle est possible peuvent permettre une première orientation. Nous proposons une démarche diagnostique prenant en considération la présence de signes extra-hématologiques, le mode de transmission, des études plaquettaires à la fois cytologiques, fonctionnelles et moléculaires et l’aspect des mégacaryocytes médullaires afin d’orienter au mieux l’étude génétique. En dépit de cette démarche, un certain nombre de thrombopénies constitutionnelles demeurent encore inexpliquées et devraient bénéficier dans les années à venir des progrès des techniques de séquençage de nouvelle génération.

Reactive thrombocytosis (secondary thrombocytosis) is frequent and typically moderate. We report a case of extreme thrombocytosis and leukocytosis secondary to all iron deficiency anemia. A 21-year-old woman is admitted in emergency department for acute headache. Biological assessment reveals a severe microcytic anaemia (5.4 g/dL) with thrombocytosis (2500 giga/L) and leukocytosis (35 giga/L) leading to multiple diagnosis hypotheses. Finally, biological evaluation concludes to a diagnosis of iron deficiency anaemia related to insufficient oral intake and menorrhagia. Reactive hyperleukocytosis and thrombocytosis rapidly resolved with iron supplementation. This case is a reminder that iron deficiency-related thrombocytosis can sometimes be severe. However. the associated reactive leukocytosis is quite exceptional. (C) 2008 Elsevier Masson SAS. Tons droits reserves.

A major determinant in platelet production is the megakaryocyte (MK) size that is regulated both by ploidization and the increase in cytoplasmic volume at the end of maturation. Here we investigated the involvement of the mammalian target of rapamycin (mTOR) pathway in the regulation of megakaryopoiesis. We show that phosphorylation of mTOR, p70S6K1, and 4E-BP1 was diminished in thrombopoietin-cultured human MKs after rapamycin treatment. Rapamycin induced an inhibition in the G1/S transition and a decrease in the mean MK ploidy via a diminution of p21 and cyclin D3 occurring at a transcriptional level. Both cycling (2N/4N) and polyploid (8N/16N) MKs were reduced in size, with a size reduction slightly more pronounced in mature polyploid MKs than in immature ones. Rapamycin also induced a delay in the expression of MK markers and prevented the generation of proplatelet MKs. Additional experiments performed in vitro with MKs from mutant mice showed that the decrease in mean ploidy level and the delay in MK differentiation in the presence of rapamycin were less pronounced in CdknIa (p21)-/- MKs than in CdknIa (p21)+/+ MKs. These findings indicate that the mTOR pathway plays an important role during megakaryopoiesis by regulating ploidy, cell size, and maturation, in part by regulating p21 and cyclin D3.

The cyclin-dependent kinase inhibitor p21(Waf-1/Cip-1) is expressed at high level during megakaryocyte differentiation, but its precise function remains unknown. In this study, it is confirmed that p21 was expressed at a high level in hypoploid (2N and 4N) and polyploid (at least 8N) human megakaryocytes derived from CD34(+) cells. A high expression of p27(Kip1), p16, cyclin E, and cyclin D3 was also found in both populations associated with a hypophosphorylated form of retinoblastoma protein, suggesting that the majority of hypoploid and polyploid megakaryocytes are G(1)-arrested cells. As human megakaryocytes grown in vitro present a defect in their polyploidization, the study switched to the murine model. The modal ploidy of megakaryocytes derived from lineage-negative cells was 32N, and an elevated expression of p21 was found in high-ploidy megakaryocytes. In addition, p21 and p27 were coexpressed in the majority of mature polyploid megakaryocytes. The p21 was detected by immunofluorescence in megakaryocytes derived from p53(-/-) mice, demonstrating a p53-independent regulation during megakaryocyte differentiation. Megakaryocytopoiesis of p21(-/-) mice was subsequently studied. No marked abnormality in the ploidy of primary or cultured megakaryocytes was detected. Overexpression of p21 in p21(-/-) or normal murine megakaryocytes and in human megakaryocytes showed in all these cases a marked inhibition in megakaryocyte polyploidization. In conclusion, while a reciprocal relation is observed between p21 levels in megakaryocytes and the cycling state of the cells, p21 is not essential for the determination of the ploidy profile in normal megakaryocytes in vivo. However, high levels of its expression in cultured megakaryocytes arrest the endomitotic cell cycle.