Hereditary Macrothrombocytopenia Research Articles

неЩасливий випадок як поштовх до діагностики хвороби у 16-річного хлопця, пов’язаної з MYH9. Сюжет із практики гематолога

MYH9-related disease (MYH9-RD) is an autosomal dominant hereditary thrombocytopenia caused by mutations in the MYH9 gene with characteristic laboratory features - the presence of giant platelets and basophilic cytoplasmic inclusions in neutrophils (similar to Dele bodies). Patients with MYH9-RD are at high risk for deafness, cataracts, and renal dysfunction, most often occurring in adulthood. Platelet counts in patients with MYH9-RD range from severe thrombocytopenia to near-normal values, although they are usually stable. Propensity for hemorrhagic Complications correlate with platelet count and are usually absent or limited to minor bleeding in patients with mild thrombocytopenia, but may lead to spontaneous and potentially life-threatening bleeding with persistent platelet counts <50×109/l. Purpose - to describe a clinical case of a disease caused by a heterozygous mutation in the MYH9 gene with an emphasis on the importance of genetic tests for the final verification of the disease. Clinical case. Features of diagnosis caused by a heterozygous mutation in the MYH9 gene in a 16-year-old boy are described. Throughout the child's life, the manifestations of the hemorrhagic syndrome were moderate (periodically a small number of bruises on the skin, to which the parents did not pay much attention, bleeding from the gums when brushing the teeth), the child’s blood tests were performed occasionally without determining the number of platelets. The boy suffered a displaced radius fracture as a result of the injury. The orthopedic traumatologist performed an operation of limited reposition of bone fragments followed by implantation of a needle for proper bone fusion without complications. During a general blood test, thrombocytopenia was detected, which prompted the child to be consulted by a hematologist. During the examination at the Western Ukrainian Specialized Pediatric Medical Center, Lviv, it was noted in the hardware count of the hemogram that the number of platelets was 22.0-30.0×109/l, the microscopic count of platelets was 147.0-156.0×109/l, the entire population of platelets was represented by macroforms with mean platelet volume 14.9 fl. We found good aggregation of platelets with ristocytin, and reduced aggregation with epinephrine, arachidonic acid, and adenosine. Verification of the final diagnosis of MYH9-RD caused by a heterozygous mutation in the MYH9 gene occurred by genome sequencing. Therefore, the application of the genome sequencing technique can contribute to the early diagnosis of hereditary macrothrombocytopenia caused by a heterozygous mutation in the MYH9 gene. The research was carried out in accordance with the principles of the Helsinki Declaration. The informed consent of the patient was obtained for conducting the studies. No conflict of interests was declared by the authors.

Study of Bernard-Soulier Syndrome Megakaryocytes and Platelets Using Patient-Derived Induced Pluripotent Stem Cells.

Bernard-Soulier syndrome (BSS) is a hereditary macrothrombocytopenia caused by defects in the glycoprotein (GP) Ib-IX-V complex. The mechanism of giant platelet formation remains undefined. Currently, megakaryocytes (MKs) can be generated from induced pluripotent stem cells (iPSCs) to study platelet production under pharmacological or genetic manipulations. Here, we generated iPSC lines from two BSS patients with mutations in different genes (GP1BA and GP1BB: termed BSS-A and BSS-B, respectively). The iPSC-derived MKs and platelets were examined under electron microscopy and stained by immunofluorescence to observe proplatelet formation and measure platelet diameters which were defined by circumferential tubulin. BSS-iPSCs produced abnormal proplatelets with thick shafts and tips. In addition, compared with the normal iPSCs, the diameters were larger in platelets derived from BSS-A and BSS-B with the means ± standard deviations of 4.34 ± 0.043 and 3.88 ± 0.045 µm, respectively (wild-type iPSCs 2.61 ± 0.025 µm, p < 0.001). Electron microscopy revealed giant platelets with the abnormal demarcation membrane system. Correction of BSS-A and BSS-B-iPSCs using lentiviral vectors containing respective GP1BA and GP1BB genes improved proplatelet structures and platelet ultrastructures as well as reduced platelets sizes. In conclusion, the iPSC model can be used to explore molecular mechanisms and potential therapy for BSS.

Flow Cytometry With Inflorescence-An Accessible Method in the Study of Qualitative and Quantitative Modifications of Blood Platelets in Immune Thrombocytopenic Purpura

The immune thrombocytopenic purpura (ITP) is a polymorphic and hematologic pathology, in terms of both clinical manifestations and etiopathogenic mechanisms, which bring on this disease. Establishing the type of thrombocytopenia, which can either be primary or secondary, peripheral or central, is essential for a further proper therapeutic conduct. The current means of diagnosis include a large variety of hematologic, immunologic and biochemical explorations, from the traditional ones to the latest methods, either genetical or molecular. The purpose of this paper is to emphasize the importance of a classical method of diagnosis, used in the primary triage of patients suffering from thrombocytopenia, highly valuable in the diagnosis process: the analysis of the mean platelet volume (MPV) and of the platelet distribution width (PDW), parameters revealed by the CBC (complete blood count). Evaluating the size of the platelets is a useful tool in the differential diagnosis between immune thrombocytopenic purpura and hereditary macrothrombocytopenia. The platelet distribution width and the mean platelet volume are read simultaneously, in order to differentiate the immune peripheral thrombocytopenia from the central one. The classical, viable and accessible method facilitates the measurement of MPV and PDW with the automatic analyzer, which functions according to the principle of flow cytometry with inflorescence, by using a LASER semiconductor and hydrodynamic focusing.

Evaluation of the immature platelet fraction contribute to the differential diagnosis of hereditary, immune and other acquired thrombocytopenias

The differential diagnosis of immune (ITP) and hereditary macrothrombocytopenia (HM) is key to patient management. The immature platelet fraction (IPF) represents the subset of circulating platelets with higher RNA content, and has been shown to distinguish hypo- from hyperproliferative thrombocytopenias. Here we evaluated the diagnostic accuracy of IPF in the differential diagnosis between HM and other thrombocytopenias in a population of patients with post-chemotherapy thrombocytopenia (n = 56), bone marrow failure (n = 22), ITP (n = 105) and HM (n = 27). TPO levels were also measured in HM and ITP matched for platelet counts. Platelet counts were similar in all patient groups. Higher IPF values were observed in both ITP (12.3%; 2.4–65.6%) and HM (29.8%; 4.6–65.9%) compared to hypoproliferative thrombocytopenias. IPF values were also higher in HM compared to ITP, yielding a diagnostic accuracy of 0.80 (95%CI 0.70–0.90; P < 0.0001) to distinguish these two conditions. Intra- and inter-assays reproducibility of IPF in HM patients revealed that this is a stable parameter. In conclusion, IPF is increased in HM compared to both ITP and other thrombocytopenias and contributes to the differentiation between ITP and HM. Further studies are warranted to understand the biological rationale of these findings and to its incorporation in diagnostic algorithms of HM.

R1933X mutation in the MYH9 gene in May-Hegglin anomaly mimicking idiopathic thrombocytopenic purpura

May-Hegglin anomaly (MHA) is a rare autosomal dominant disorder characterized by the triad of thrombocytopenia, giant platelets, and inclusion bodies in leukocytes. Recent evidence links MHA to mutations in the MYH9 gene. MHA has not been reported in Taiwan before. We report a 25-year-old Taiwanese man who presented with prolonged bleeding after dental extraction. Examination of peripheral blood smear revealed thrombocytopenia (platelet = 35,000/μL), giant platelets, and Döhle-like cytoplasmic inclusions in neutrophils. A strong family history of thrombocytopenia favored hereditary macrothrombocytopenia over idiopathic thrombocytopenic purpura (ITP). Electron microscopy revealed a spindle shape and parallel order of filaments in the inclusions, consistent with the diagnosis of MHA. We performed mutational analysis using polymerase chain reaction followed by direct sequence of the MYH9 gene for the patient, his maternal uncle and cousin, and all showed the same heterozygous R1933X mutation in exon 40. MHA should be considered when a young patient has thrombocytopenia, frequently misdiagnosed as ITP. Morphological examination of peripheral blood smear, family history tracing and genetic studies are required to make an accurate diagnosis and avoid unnecessary and even harmful therapies such as corticosteroids and splenectomy.

The Immature Platelet Fraction Is Sensitive to the Platelet Size and a Useful Parameter for Screening for Macrothrombocytopenia

Abstract 1097The immature platelet fraction (IPF) is a useful parameter indicating thrombopoietic activity to differentiate the causes of thrombocytopenia. We previously reported that the percentage of IPF (%IPF) is negatively correlated to the platelet count among ITP patients, and not among myelodysplastic syndrome (MDS) patients. We also noticed that some MDS patients exhibited extremely high %IPF values, which were dissociated from the percentages of reticulated platelets (%RP) measured by flow cytometry. Such discrepancies were also observed in hereditary macrothrombocytopenias, which are sometimes difficult to be distinguished from ITP, because ITP also exhibits increased number of reticulated platelets in a slightly larger size. Once misdiagnosed, a hereditary macrothrombocytopenia patient might be subjected to an invasive treatment such as splenectomy. In order to avoid such mistreatments, a clear marker to differentiate macrothrombocytopenia is desperately needed. In this study, we investigated the IPF values of 16 individuals from 12 families with various hereditary macrothrombocytopenia in order to clarify whether the IPF could be a useful marker to distinguish macrothrombocytopenia from ITP, and examined the IPF during EDTA aggregation and cold-storage to elucidate how platelet size may affect the IPF value.The IPF values were about 5 times higher in MYH9 disorders (%IPF 48.0 ± 1.8) and about 1.5 times higher in other macrothrombocytopenias (%IPF 17.0 ± 2.2) than immune thrombocytopenic patients with similar platelet counts (%IPF 9.3 ± 0.4). These results suggested that the platelet size can affect the IPF value. However it still remains the possibility that some factors specific to these macrothrombocytopenias other than the platelet size might make an influence on the IPF, because the characteristic of large platelets in hereditary macrothrombocytopenia has not been fully understood, and no one knows whether large platelets are functionally identical to normal platelets except for the size. In order to exclude the possibility, we next examined the changes of IPF values during EDTA aggregation and cold-storage. The IPF was significantly increased during storage in a time dependent manner along with forming platelet clumps. The IPF was strongly influenced by a few tiny platelet aggregates rather than other platelet indices, such as mean platelet volume (MPV), platelet-large cell ratio (P-LCR) and platelet distribution width (PDW).In conclusion, the IPF is susceptible to the platelet size, and could be a useful parameter for screening of macrothrombocytopenia from ITP. Disclosures:No relevant conflicts of interest to declare.

Intriguing outcome of JAK2V617F mutation seen in a patient with MYH9-related hereditary macrothrombocytopenia

Intriguing outcome of JAK2V617F mutation seen in a patient with MYH9-related hereditary macrothrombocytopenia -

Chronic isolated macrothrombocytopenia with autosomal dominant transmission: a morphological and qualitative platelet disorder.

We studied 47 subjects belonging to 13 unrelated families with a history of mild haemorrhagic diathesis and chronic thrombocytopenia. 36 patients presented some degree of thrombocytopenia: 7/36 (19%) had slight thrombocytopenia (100-150 x 10(9)/L); 26/36 (72%) had mild thrombocytopenia (50-100 x 10(9)/L) and 3/36 (8%) had severe thrombocytopenia (< 50 x 10(9)/L). No correlation was observed between platelet count and the degree of haemorrhagic diathesis, which was mild in the majority of patients. Transmission was autosomal dominant. Platelet anisocytosis, increased percentage of large platelets and absence of leukocyte inclusions were observed in 26/30 (87%) of the examined blood smears. The ultrastructural appearance of platelets was normal. Megakaryocytes appeared normal in number in 10/10 patients, but showed asynchronous nuclear-cytoplasm maturation and mainly nonlobulated nuclei. Platelet aggregation was studied in 26 patients and either increased or decreased curves were variably observed in response to different aggregating agents. Platelet-associated IgG (PAIgG) was increased in 18/31 (58%) patients, while serum autoantibodies against platelet glycoproteins Ib/IX or IIb/IIIa were demonstrable in only 1 case. An increased expression of platelet surface glycoproteins Ib and IIb/IIIa, as studied by murine monoclonal antibodies binding in 17 cases, was observed. Platelet survival performed by 111Inoxine-labelled autologous platelets was normal in the 3 studied patients. Congenital macrothrombocytopenia confirms to be a distinct clinical disorder for which the name of "chronic isolated hereditary macrothrombocytopenia" is proposed.

Dominant inheritance of a novel integrin 3 mutation associated with a hereditary macrothrombocytopenia and platelet dysfunction in two Italian families

Defects of integrin alpha(IIb)beta(3) are typical of Glanzmann's thrombasthenia, an inherited autosomal recessive bleeding disorder characterized by the failure of platelets to aggregate in response to all physiological agonists, but with no abnormalities in the number or size of platelets. Although large heterogeneity has been described for Glanzmann's thrombasthenia, no family has so far been described as having an autosomal dominant form of this disease. We describe two Italian families with moderate thrombocytopenia with large platelets, defective platelet function and moderate/severe mucocutaneous bleeding, transmitted as an autosomal dominant trait and associated with a novel integrin beta(3)-gene (ITGB3) mutation. The characteristics of our families are moderate macrothrombocytopenia and defective platelet function associated with a mild reduction of surface alpha(Ib) beta(3), impaired platelet aggregation to physiological agonists but not to ristocetin, normal clot retraction, reduced fibrinogen binding and expression of activated alpha(IIb)beta(3) upon stimulation, normal platelet adhesion to immobilized fibrinogen but reduced platelet spreading and tyrosine phosphorylation, indicating defective alpha(IIb)beta(3)-mediated outside-in signaling. Molecular analysis revealed a novel mutation of ITGB3 that determines an in-frame deletion producing the loss of amino acids 647-686 of the betaTD ectodomain of integrin beta(3). Haplotype analysis indicated that the two families inherited the mutation from a common ancestral chromosome. This novel autosomal dominant macrothrombocytopenia associated with platelet dysfunction raises interesting questions about the role of integrin beta(3), and its betaTD domain, in platelet formation and function.

Peripartum Management of Women with Suspected Hereditary Thrombocytopenia.

Introduction: Hereditary macrothrombocytopenic disorders are rare syndromes characterized by mild to moderate thrombocytopenia, large platelets, and a variable bleeding phenotype. In general, the diagnosis must be made clinically and management is empiric. Because of the autosomally inherited nature of these disorders, peripartum management must take into account the risk of bleeding for both mother and baby, during the pregnancy and at delivery. Study Purpose: To describe the peripartum management and bleeding complications in pregnant women with suspected inherited macrothrombocytopenic disorders and their children. Study Design: We performed a retrospective review of all mothers referred to our tertiary care hospital from 2004 to 2007 for evaluation of macrothrombocytopenia in pregnancy where hereditary thrombocytopenia was suspected. The diagnosis was confirmed if at least 2 of the following clinical features were present: life-long thrombocytopenia; family history of thrombocytopenia that spanned at least 2 generations; and the lack of a platelet count response to IVIG or corticosteroids. Data relating to bleeding and therapies used to treat or to prevent bleeding before or during delivery for mother and child were extracted from medical charts. Blood films were reviewed with experts in morphology, and diagnostic testing was performed when possible. Results: A total of 5 mothers and 8 babies were included. The median platelet count of mothers at delivery was 54 x 109/L (range 15–83 x 109/L) and the median MPV was 9.8 fL (range 7.4–11.3 fL). Of the 8 babies, 4 were thrombocytopenic with a median platelet count at birth of 50 x 109/L (range 9–93 x 109/L) and a median MPV of 9.4 fL (range 8.9–9.6fL). One mother and her baby had neutrophilic Dohle body inclusions, and none had skeletal, neurologic or renal abnormalities. Three mothers were previously treated with IVIG, including one who also received prednisone, with no platelet count response. During pregnancy, fetal blood sampling for platelet count measurements was not done. None of the mothers had epidural anesthesia, all delivered vaginally and 7 of 8 labours were induced. Two mothers received prophylactic tranexamic acid at the time of active labour and 1 received DDAVP. Prophylactic platelet transfusions were not given. One mother had bleeding associated with spontaneous rupture of membranes, and one had a post partum hemorrhage associated with uterine atony and vaginal laceration. The latter was repaired surgically and treated with platelet transfusions and DDAVP. None of the babies bled, but 1 was given a platelet transfusion because of severe thrombocytopenia at birth (platelet count = 9 x 109/L) with persistent platelet clumping. Conclusions: The frequency of pregnancy-related bleeding in mothers with hereditary macrothrombocytopenia was low in this cohort even in the absence of prophylaxis. There is a need for improved diagnosis and risk stratification of mothers with hereditary macrothrombocytopenia. A multicentre prospective study would assist in determining optimal peripartum management.

Perioperative management of MYH9 hereditary macrothrombocytopenia (Fechtner syndrome)

Hereditary thrombocytopenias characterized by mutations in the gene for non-muscle myosin heavy chain IIA (NMMHC-IIA) are known as MYH9-related hereditary macrothrombocytopenia, and include the May-Hegglin anomaly, Sebastian platelet syndrome, Fechtner syndrome, and Epstein syndrome. Despite the presence of thrombocytopenia, these patients often have only mild or non-bleeding phenotypes. A major risk for these patients can be inappropriate treatment with long-term corticosteroids or splenectomy for misdiagnosed chronic autoimmune thrombocytopenia, as well as inadequate peri- and postoperative management. Using the case of a 44-yr-old male with Fechtner syndrome (macrothrombocytopenia, leukocyte inclusions, sensorineural deafness, glomerulonephritis) who underwent neurosurgery for an intracerebral arteriovenous malformation, we describe current methods to diagnose hereditary MYH9-related macrothombocytopenia by analysis of the blood smear, immunofluorescence staining of the NMMHC-IIA in leucocytes, and by MYH9-gene sequencing. Clusters of NMMHC-IIA in granulocytes and a R1165C mutation in the MYH9-gene in two macrothrombocytopenic family members confirmed the diagnosis of a MYH9-related disease. The patient had no bleeding diathesis by history or physical examination. Thus no perioperative prohemostatic pharmacologic therapies or transfusions were given, with only minimal bleeding observed. Postoperative antithrombotic thromboprophylaxis was not given because of anticipated enhanced risk for bleeding. However, the patient developed symptomatic pulmonary embolism on postoperative day 6, which was successfully managed with 8 months of anticoagulation. MYH9-related hereditary macrothrombocytopenia does not necessarily protect against postoperative venous thromboembolism, and affected patients who do not evince bleeding diathesis should be considered for routine postoperative pharmacologic thromboprophylaxis.

Genotype–phenotype correlation in MYH9‐related thrombocytopenia

Mutation of the non-muscle myosin heavy chain type II-A results in MYH9-related hereditary macrothrombocytopenia (HMTC), including four autosomal dominant platelet disorders: May-Hegglin anomaly (MHA), Sebastian (SBS), Fechtner (FS) and Epstein (EPS) syndrome. Denaturing high-performance liquid chromatography (DHPLC) was optimised for rapid screening of the seven exons harbouring all but one of the previously reported mutations of MYH9. Individuals from 13 families with phenotypes suggestive of MYH9-related HMTC were screened for mutations by DHPLC followed by direct sequencing of samples with aberrant column retention time. Mutations were identified in all 13 families. Six distinct missense heterozygous mutations were found in 10 families, including six families with MHA or SBS (E1841K, D1424N), three families with FS (R702H, R1165C, and D1424Y), and one family with EPS (S96L). A truncating mutation (R1933X) was found in three MHA families. A review of all published mutations suggests that mutation in the C-terminal coiled coil region or truncation of the tailpiece is associated with haematological-only phenotype, while mutation of the head ATPase domain frequently is associated with nephropathy and/or hearing loss. Mutations of other regions have intermediate expression of non-haematological characteristics. Further study is required to confirm these associations and understand the molecular basis for this genotype-phenotype relationship.

Analgésie péridurale obstétricale chez une patiente présentant une macrothrombocytopénie familiale

Epidural analgesia is often considered as risk of epidural haematoma in a patient with thrombocytopenia. In this observation, uncomplicated epidural analgesia was performed in a pregnant woman with hereditary macrothrombocytopenia. She received continuous epidural labour analgesia for a vaginal delivery with a platelet count at 63 × 10 9/l but platelets with high mean platelet volume (20 fL) and normal function. No neurological sequelae or excessive bleeding occurred.

The E1841K Mutation in MYH-9 of a Patient with May-Hegglin Anomaly Inhibits the Disassembly of Non-Muscle Myosin IIA (MYH-9) Responsible for the Phenotype of the Disease.

It has been demonstrated that MYH-9 (non-muscle myosin IIA) is responsible for the hereditary macrothrombocytopenia, such as May-Hegglin Anomaly (MHA), Fechtner syndrome (FS) and Sebastian syndrome (SS). We identified the E1841K mutation of MYH-9 gene of a patient with May-Hegglin Anomaly. Immunofluorescent staining of her peripheral blood smear samples revealed that non-muscle myosin IIA and actin filaments were co-localized at the Döhle-like inclusion bodies of neutrophils. To investigate the mechanism by which the E1841K mutation causes the phenotype of MHA, we first expressed GFP-tagged wild type and E1841K mutant MYH-9 cDNA in NIH3T3 cells. The mutant was able to form filaments and some inclusion bodies such as Döhle-like bodies, although it seemed to make no influences on the shape of the fibroblasts. Next we expressed the GFP-tagged wild and E1841K mutant MYH-9 in HEL cells and induced differentiation with TPA. HEL cells expressing the E1841K mutant failed in full differentiation. They could not produce the proplatelet-like projections as the cells overexpressing wild type of MYH-9 did. These results demonstrate that overexpression of this mutant can induce some phenotype similar to MHA. To clarify what molecular characteristics of the mutant myosin can cause the MHA phenotype, we expressed the recombinant wild and mutant proteins of non-muscle myosin IIA using Baculo-virus system. The mutant myosin failed to dissolve even in high ionic strength, suggesting this mutant can assemble in cytoplasm even under the condition, in which wild type myosin changes the conformation and exchanges dynamically assembly to disassembly. Next we induced myosin filaments in HEL cells by over-expressing the mutant of myosin light chain (DD mutant), which mimics the double-phosphorylated form. The DD mutant of myosin light chain also inhibited the proplatelet-like projections. Moreover silencing of MYH-9 gene with siRNA could have no inhibitory effects on the differentiation of HEL cells, producing rather more proplatelet-like projections than the control. These results indicated that filament formation of myosin is not critical for proplatelet-like projections, but disassembly of myosin is rather essential. Collectively, the E1841K mutant inhibits the disassembly of myosin to prevent the proplatelet-like formation of HEL cells, and the assembled myosin forms the Döhle-like inclusion bodies probably with actin filaments.

A Unique Immunofluorescence Method Promotes Accurate Diagnosis in MYH9 Disorders: A Case Report.

The identification of a mutation in the MYH9 gene in hereditary macrothrombocytopenia has established a distinct entity proposed as "MYH9 disorders," which previously have often been misdiagnosed as chronic immune thrombocytopenic purpura. The authors describe clinical and laboratory characterization of a family with the disorder demonstrating giant platelets, thrombocytopenia, and leukocyte inclusion bodies. The authors emphasize the efficacy of a unique immunofluorescence method for the nonmuscle myosin heavy chain A in the diagnosis, because it is more sensitive than May-Grünwald-Giemsa staining and more practical than electron microscopy or direct sequencing. MYH9 disorders may be much more common than previously realized if accurately diagnosed.

Macrothrombocytopenia and progressive deafness is due to a mutation in MYH9.

In 1992, a family with hereditary macrothrombocytopenia and progressive sensorineural hearing impairment without renal dysfunction was described. Recently, mutations in MYH9, a nonmuscle myosin heavy chain, have been found in several forms of hereditary macrothrombocytopenia. The hereditary macrothrombocytopenia and hearing loss in the previously reported family is due to a mutation in MYH9 gene. Genomic DNA was extracted from the affected proband. Mutation screening of all MYH9 coding exons was carried out using denaturing high-performance liquid chromatography. Abnormal results were followed by direct sequencing of the exon and comparison of the sequence with the normal MYH9 sequence. The results of denaturing high-performance liquid chromatography suggested a potential sequence alteration in exon 30 of MYH9. Direct sequence analysis of this exon in the affected individual identified a G to A single base pair transition at nucleotide 4270 altering codon 1424. This mutations leads to an amino acid change from aspartate (D) to asparagine (N) in the highly conserved coiled-coil domain. A single base pair transition in MYH9, resulting in an amino acid substitution D1424N, is responsible for macrothrombocytopenia and hearing loss in the kindred under study. The presence of hearing impairment and the absence of renal symptoms, as reported in other families with the same mutation MYH9, further highlights the role of genetic background in expression and modification of the affected phenotype.

Indirect study of thrombopoiesis (TPO, reticulated platelets, glycocalicin) in patients with hereditary macrothrombocytopenia.

Chronic isolated hereditary macrothrombocytopenia (CHMT) is a congenital form of macrothrombocytopenia that seems to be due to defective production secondary to a disturbance in megakaryocyte fragmentation. To better understand the pathogenesis of thrombopoiesis in this hereditary thrombocytopenic disorder, we determined the percentage of reticulated platelets (RP), plasma glycocalicin (GC) and thrombopoietin (TPO) levels in 29 patients with CHMT, 23 patients with immune thrombocytopenic purpura (ITP), and 17 patients with thrombocytopenia secondary to decreased bone marrow megakaryocytes (hypoplasia). The % RP was similar in CHMT (2.27 +/- 1.33) and hypoplasia (1.98 +/- 1.35) patients and markedly lower than that in ITP patients (8.80 +/- 7.97; p <0.001), suggesting that the production of new platelets is reduced in CHMT. Plasma GC was within the normal range (0.84 +/- 0.16 microg/mL) both in patients with CHMT (0.63 +/- 0.20 microg/mL) and ITP (0.82 +/- 0.90 microg/mL), while it was significantly decreased in patients with hypoplasia (0.16 +/- 0.04 microg/mL; p < 0.001). When the GC value was normalized for platelet count, the GC index was normal in CHMT patients (2.05 +/- 1.1) and in patients with hypoplasia (0.85 +/- 0.10) while it was significantly increased in ITP patients (10.88 +/- 18.00; p<0.001); thus, patients with CHMT seem to have a normal platelet turnover. TPO was significantly increased in CHMT (195 +/- 72 pg/ml) as compared with normal (80 +/- 53 pg/ml; p < 0.002); however, the mean level was not as high as in ITP patients (345 +/- 167 pg/mL; p < 0.001). This finding suggests that CHMT syndrome is not secondary to a defective production of TPO and that megakaryocyte mass is nearly normal.

Prolonged Bleeding Time With Defective Platelet Filopodia Formation in the Wistar Furth Rat

Hereditary macrothrombocytopenia is a hallmark of Wistar Furth (WF) rats. In addition, a platelet/megakaryocyte alpha granule defect, similar to that of patients with gray platelet syndrome, is present. Several observations indicate cytoskeletal abnormalities in WF platelets and megakaryocytes, suggesting the potential for functional defects in hemostatic processes requiring cytoskeletal reorganization, such as platelet adhesion and spreading. However, no bleeding abnormality has been noted. Here, we report a prolonged bleeding time (&gt;30 minutes in 10 of 11 rats tested) with defective clot formation in the WF strain. Prolonged bleeding time can result from defects in platelet adhesion, aggregation, or the release reaction. Because aggregation to collagen and adenosine diphosphate were reported to be normal, we determined whether WF rat platelets are defective in their ability to adhere to substrates. Platelet adherence and spreading was evaluated from 30 seconds to 30 minutes on Formvar-coated, carbon-stabilized grids or poly-L-lysine–coated glass coverslips by transmission electron microscopy or immunofluorescence, respectively, and scanning electron microscopy. We classified the adhered platelets according to their pattern of spreading, ie, rounded, rounded or spreading with short filopodia, spindle-shaped, spreading with long filopodia, spreading with lamellipodia, and fully spread. Adherent normal rat platelets displayed all stages of spreading within 30 seconds to 2 minutes, including many spindle-shaped forms, and forms with multiple, long filopodia. In contrast, adhered WF platelets at these early time points rarely developed long filopodia or were spindle shaped. The majority of adherent WF platelets at these early time points were either round, spread with a few short filopodia, or extensively spread with wide lamellipodial skirts. By 15 to 30 minutes, most platelets in both Wistar and WF samples were fully spread. These data show abnormal WF platelet spreading. The paucity of spindle-shaped forms and forms with long filopodia may reflect an inability of WF platelets to undergo the early stages of spreading, or, alternatively, their more rapid than normal progression through these stages. We hypothesize that this failure to spread normally may relate to prolonged bleeding times in vivo and defective clot formation in WF rats.

Hereditary Macrothrombocytopenia and Pregnancy

Hereditary macrothrombocytopenias (HM) are a group of infrequent disorders characterized by hereditary giant platelets. Little has been published about the course of these diseases during pregnancy and delivery. Forty consecutive thrombocytopenic pregnant women were studied. Platelet count, mean platelet volume and blood smear examination were performed. Platelet antibodies were studied by immunofluorescence. Familial study, bleeding time, ultrastructural platelet examination, a von Willebrand disease screening and aggregation tests were carried out when HM was suspected. Four cases of HM were diagnosed. Giant platelets were observed in all cases, with the typical ultrastructural pattern. Döhle-like cytoplasmic inclusions in granulocytes were observed in one case. Platelet antibodies were detected in only one case. No prophylactic measures to prevent haemorrhage were adopted, and all patients underwent vaginal deliveries. Haemorrhagic events were absent in both mothers and children. The prevalence of HM in pregnant trombocytopenic women is higher than assumed. Prophylactic treatment should be avoided in the absence of a history of haemorrhagic complications and obstetrical risk factors.

Abnormal Subcellular Distribution of Myosin and Talin in Wistar Furth Rat Platelets

The roles of most cytoskeletal proteins in platelet formation and function remain largely undefined. We earlier detected megakaryocyte membrane blebbing and a unique antigenic determinant associated with a missense mutation in the cytoskeletal protein, talin, in an animal model of hereditary macrothrombocytopenia, the Wistar Furth (WF) rat, which led us to examine the distribution of talin and other cytoskeletal proteins in resting normal and WF rat platelets. In contrast to the conclusions of an earlier ultrastructural analysis, our biochemical and ultrastructural immunogold studies indicate a significant membrane-association of talin in both resting normal and WF rat platelets as found earlier for rat megakaryocytes. Talin was associated with plasma membranes, membranes of the surface-connected canalicular system, and with alpha-granule membranes of both normal and WF rat platelets, but as in WF megakaryocytes, talin was absent from the large membrane complexes of WF platelets. An even more striking difference was seen in the distribution of myosin in subcellular fractions of normal and WF rat platelets separated in density gradients, in which the proportion of myosin in the least dense WF rat platelet membrane fraction was one half that in the same normal platelet fraction. This difference was balanced by a fourfold increase in myosin in the most dense WF rat subcellular fraction, which is highly enriched for alpha-granules. These results support our hypothesis that the platelet abnormalities of the WF rat are related to defects in the megakaryocyte-platelet cytoskeleton.