Inherited Platelet Dysfunction Research Articles

Use of a Von Willebrand Factor/Coagulation Factor VIII Complex for Treatment of Refractory Inherited Platelet Disorders

Inherited platelet disorders are recognized as an important cause of mild to severe bleeding in both children and adults. Patients with platelet disorders may present with mucocutaneous bleeding, gastrointestinal bleeding, menorrhagia, postsurgical, and/or excessive bleeding from traumatic injury. Delta storage pool deficiencies (delta-SPD) are among the most frequent platelet disorders, characterized by dysfunctional dense platelet granules. Bernard Soulier syndrome (BSS) is an autosomal recessive platelet disorder caused by mutations in various polypeptides in the GpIb/IX/V complex, which is the principal receptor for von Willebrand factor (VWF). Treatment of platelet disorders is mainly supportive. Normal hemostasis requires VWF and factor VIII (FVIII) to support platelet adhesion and aggregation at sites of vascular injury. von Willebrand factor is a large multimeric glycoprotein present in human plasma as a series of polymers called multimers. Molecular weights for multimers ranges from 500 kDa for the dimer to over 10,000 kDa for the high molecular weight multimers (HMWM) forming the largest known protein present in human plasma. Each multimeric subunit of VWF has binding sites for the receptor GpIb on nonactivated platelets and the receptor GpIIb/IIIa to facilitate platelet adhesion and platelet aggregation, respectively, making the VWF HMWM important for normal platelet function. Desmopressin (DDAVP), which is known to stimulate the release of VWF and FVIII, is commonly used for treatment of platelet disorders. Potentiation of platelet aggregation at high shear rate may be one mechanism by which DDAVP shortens the prolonged bleeding time of patients with congenital platelet defects. For severe bleeding, platelet transfusion may be required, but patients may develop isoantibodies, rendering this therapy ineffective. For this reason, it may be prudent to reserve platelet transfusion in this patient population for emergent situations, such as trauma. Other patients and/or clinical situations may require recombinant active factor VII (rFVIIa), but this therapy is very costly and not always effective and/or available. Antifibrinolytics may also be used but are not always effective. In four (4) patients with platelet disorders (delta-SPD [n=3]; BSS [n=1]), common supportive therapies were not effective, tolerable, and/or available. It was postulated that off-label infusions of a cost-effective von Willebrand factor/coagulation factor VIII (VWF/FVIII) complex (Wilate, Octapharma SA) might be of benefit in these refractory patients (Table 1). The mechanism of action of DDAVP treatment efficacy relies on the release of existing, stored, functional VWF. In refractory patients with suboptimal VWF functionality, it was reasoned that infusion of exogenous, functional VWF and FVIII could potentially encourage platelet adhesion and aggregation. All refractory patients studied were treated successfully with the VWF/FVIII complex with positive clinical outcomes. As mentioned, the adhesive activity of VWF depends on the size of its multimers, and HMWM are the most effective in supporting interaction with collagen and platelet receptors and in facilitating wound healing under conditions of shear stress in the human vascular system. The VWF/FVIII complex utilized in these patients is known to have minimal amounts of the plasma metalloproteinase ADAMTS13. The HMWM of VWF are, under normal conditions, cleaved by ADAMTS13 to smaller, less adhesive multimers. During the manufacturing process, if the ADAMTS13 is not filtered out of the product almost entirely, the VWF in the vial may become highly proteolyzed. Therefore, a reduction or lack of HMWM resulting from inclusion of ADAMTS13 in the manufactured product is believed to reduce product functionality. Multimeric analysis of the VWF/FVIII complex has shown that it exhibits a physiological triplet structure which resembles normal plasma. In addition, the product has a high safety profile and tolerability as protein impurities are eliminated in the manufacturing process. In summary, the use of a VWF/FVIII complex in four (4) patients with inherited platelet disorders, who were refractory to conventional treatments, provided beneficial, cost-effective clinical outcomes with resolution of bleeding. Disclosures Federizo: Octapharma: Consultancy, Honoraria, Other: Publication support, Speakers Bureau; Sanofi: Consultancy, Honoraria, Research Funding, Speakers Bureau; American Thrombosis and Hemostasis Netowrk: Research Funding; Aptevo: Consultancy, Speakers Bureau; National Hemophilia Foundation: Consultancy, Honoraria. OffLabel Disclosure: von Willebrand/FVIII concentrate is currently approved for the treatment of Hemophilia A and von Willebrand. This abstract will review the off-label use of this medication in the treatment of inherited platelet dysfunction.

The clinical characteristics and molecular pathogenesis of a variant Glanzmann's thrombasthenia-like pedigree

目的报告一个遗传性血小板功能障碍家系并探索其分子发病机制。方法收集该家系临床资料，采用二代高通量测序法进行遗传性血液病和血小板功能相关近600种基因突变筛查。采用RT-PCR及一代测序法检测先证者及其父母RASGRP2基因部分转录本序列。结果该遗传性血小板功能障碍家系临床表现符合变异型血小板无力症，表现为反复皮肤黏膜严重出血，先证者血小板对多种不同浓度的生理性诱聚剂反应低下甚至缺如。先证者未检出整合素αⅡbβ3基因突变，而存在RASGRP2 IVS3-1C>G纯合突变，其父母均为该位点杂合突变。先证者在扩增区检测出2种转录本，功能型RASGRP2蛋白对应的正常转录本未检出，其父母同时存在正常转录本及异常转录本，但以正常转录本为主。结论RASGRP2基因IVS3-1C>G纯合突变是导致该家系先证者发生血小板功能障碍性出血的原因。RASGRP2基因IVS3-1C>G突变导致RASGRP2异常剪接，发挥激活Rap1的RASGRP2蛋白缺失，进而导致血小板功能障碍。本研究为国内首次报道RASGRP2基因异常导致血小板功能障碍性出血，也是国际上首次报道该突变类型。

Molecular phenotype and bleeding risks of an inherited platelet disorder in a family with a RUNX1 frameshift mutation.

Inherited defects in RUNX1 are important causes of platelet function disorders. Our goals were to evaluate RUNX1-related platelet disorders among individuals evaluated for uncharacterized, inherited platelet function disorders and test a proof of concept that bleeding risks could be quantitatively estimated for typical families with an inherited platelet function disorder. Index cases with an uncharacterized inherited platelet function disorder were subjected to exome sequencing with confirmation of RUNX1 mutations by Sanger sequencing. Laboratory findings were obtained from medical records and persistence of platelet non-muscle myosin heavy chain IIB (MYH10), a biomarker of RUNX1 defects, was assessed by Western blotting. Bleeding histories were assessed using standardized assessment tools. Bleeding risks were estimated as odds ratios (OR) using questionnaire data for affected individuals compared to controls. Among 12 index cases who had their exomes sequenced, one individual from a family with eight study participants had a c.583dup in RUNX1 that segregated with the disease and was predicted to cause a frameshift and RUNX1 haploinsufficiency. Unlike unaffected family members (n = 2), affected family members (n = 6) had increased bleeding scores and abnormal platelet aggregation and dense granule release responses to agonists but only some had thrombocytopenia and/or dense granule deficiency. This family's mutation was associated with persistence of MYH10 in platelets and increased risks (OR 11-440) for wound healing problems and mild bleeding symptoms, including bleeding interfering with lifestyle in women. Inherited platelet dysfunction due to a RUNX1 haploinsufficiency mutation significantly increases bleeding risks.

Prospective Evaluation of ISTH-BAT As a Predictor of Bleeding Disorder in Adolescent Girls with Heavy Menstrual Bleeding

Background. Heavy menstrual bleeding (HMB) is a frequent complaint in adolescence and is often multifactorial. Of the possible causes, anovulation is likely to be the most common reason but there is mounting evidence that bleeding disorders (BDs) are often an unidentified cause of HMB. Wide ranges of reported prevalence, difficulty in discerning normal from excessive menstrual bleeding and the semi-empiric use of hormonal therapy makes identifying BDs in adolescents challenging. Bleeding assessment tools (BATs) have been developed- primarily in the adults - to improve diagnostic accuracy, predict bleeding phenotype and describe symptoms. The International Society of Haemostasis and Thrombosis (ISTH) BAT was specifically designed to quantify bleeding symptoms that are pediatric specific. An ISTH-BAT score of > 3 for children is considered abnormal. The ISTH BAT has not yet been specifically tested in adolescents presenting with HMB. The objective of this study was to examine the diagnostic utility of ISTH-BAT bleeding score (BS) of > 3 as a predictor of BDs in adolescents with HMB. Methods. We prospectively analyzed clinical data on 70 adolescents without a known BD, referred for HMB, to the Adolescent, Gynecology and multidisciplinary Young Women's Blood Disorders Clinics at University of Texas Southwestern Medical Center from July 2014 to June 2016. This cohort is part of an ongoing prospective study investigating the incidence of BDs in adolescents with HMB (planned n=200). All subjects underwent a standardized comprehensive diagnostic approach, including the ISTH BAT to quantify bleeding symptoms accurately. The ISTH-BAT was applied by two trained investigators and any discrepancy in scores was settled by discussion. As per National Heart, Lung, and Blood Institute guidelines, VWF:Ag and/or VWF:RCo<30 IU/dL were labeled "definite von Willebrand disease (VWD)" while 30-50 IU/dL were labeled as "low VWF levels" which were grouped together to represent vWD. Receiver operating characteristics (ROC) of ISTH-BAT were determined to assess its value for predicting BD in our cohort. Results. The mean age of study participants was 14.4+1.8 years (range: 11-18 years). Twenty-eight out of 70 patients (40%) were found to have a BD; 8 met criteria for VWD, 12 had low VWF levels, 2 were hemophilia A carriers, 5 were diagnosed with inherited platelet dysfunction and 1 had inherited thrombocytopenia. The mean BS was higher in subjects with VWD (N=20) as compared to those without a BD (N=42) (4.5 +1.6, vs. 3.6+ 1.0, p= 0.02). At least one other bleeding symptom was present in 8 (40%) of the 20 girls with vWD. The most commonly reported bleeding symptoms were epistaxis (35%), oral (15%), cutaneous (10%) and post-surgical (5%). There was no difference in patterns of menstrual bleeding (anovulatory vs. ovulatory) between girls with and without a BD (55% ovulatory vs. 41% ovulatory, p-=0.28). ROC analysis of the ISTH-BAT bleeding scores showed that at a BS of > 3, the sensitivity of the ISTH BAT was 100% but specificity was only marginal at 2.4% with an accuracy of 41%, whereas at a BS of > 5, sensitivity, specificity and accuracy were 30%, 88.10% and 69%, respectively. ROC analysis showed area under the curve of 0.66 (CI: 0.52-0.80) indicating poor discrimination for the ISTH-BAT score in determining BD in girls with HMB. Conclusion. Our study is the first attempt to prospectively examine the applicability of using ISTH-BAT score as a screening tool to exclude the presence of BD in adolescent girls presenting with HMB. In this study cohort, ISTH-BAT bleeding score of > 3 demonstrated poor diagnostic accuracy in ruling out vWD. A score of > 5 had high specificity which can decrease false positive diagnosis and repetitive testing. Future data from the ongoing study will help understand how a combination of BATs and a laboratory testing algorithm can unravel hemostatic defects in adolescents with HMB. Disclosures Jain: Bayer: Membership on an entity's Board of Directors or advisory committees; Biogen: Speakers Bureau; Novo Nordisk: Honoraria. Sarode:CSL Behring: Consultancy, Honoraria. Journeycake:CSL: Consultancy; Biogen: Consultancy; Baxalta/Shire: Consultancy. Zia:NHLBI K23: Research Funding.

Use of ISTH bleeding assessment tool to predict inherited platelet dysfunction in resource constrained settings

Background: The International Society of Thrombosis & Hemostasis (ISTH) bleeding assessment tool (ISTH-BAT) is used to record bleeding symptoms in patients with possible bleeding disorders.Aim: To investigate the utility of the ISTH-BAT in predicting platelet dysfunction in individuals with suspected inherited platelet function disorders.Method: Individuals with clinical evidence of bleeding and suspected inherited platelet function disorder and healthy volunteers were included in the study. The ISTH-BAT questionnaire was applied prior to light transmission aggregometry (LTA).Results: A total of 261 participants were included (100 healthy volunteers, and 161 with suspected inherited platelet function disorders). The ISTH-BAT score in participants with suspected inherited platelet function disorders (median 2; interquartile range [IQR] 5–1) was significantly higher than in healthy volunteers (median 0; IQR 2–0). There was also a significant difference between participants with suspected inherited platelet function disorders with a platelet defect detected by LTA (median 4; IQR 8–3) and those with normal platelet function (median 2; IQR 3–1) (p < 0.001). The ISTH-BAT score was associated with a demonstrable platelet defect on platelet function testing (area under the receiver operating characteristic curve = 0.8 [95% confidence interval 0.72–0.87, p = < 0.001] and odds ratio 3.25 [95% confidence interval 2.13–4.37, p = < 0.001]).Conclusion: The ISTH-BAT is a useful tool for documenting bleeding symptoms and the score obtained is also predictive of the presence of a platelet defect on LTA in patients with suspected inherited platelet dysfunction.

Hematopoietic transcription factor mutations and inherited platelet dysfunction.

The molecular and genetic mechanisms in most patients with inherited platelet dysfunction are unknown. There is increasing evidence that mutations in hematopoietic transcription factors are major players in the pathogenesis of defective megakaryopoiesis and platelet dysfunction in patients with inherited platelet disorders. These hematopoietic transcription factors include RUNX1, FLI1, GATA-1, and GFI1B. Mutations involving these transcription factors affect diverse aspects of platelet production and function at the genetic and molecular levels, culminating in clinical manifestations of thrombocytopenia and platelet dysfunction. This review focuses on these hematopoietic transcription factors in the pathobiology of inherited platelet dysfunction.

Use of Desmopressin in Children With Inherited Platelet Dysfunctions Undergoing Adenotonsillar Procedures

Introduction and goalsAdenotonsillar surgery represents a major haemostatic challenge in paediatric patients with mild inherited platelet dysfunction. While there are recommendations for perioperative haemostatic management, there are no reports of the outcomes with the different recommendations in these children when undergoing adenotonsillectomy. Our objective was to evaluate the management of perioperative bleeding with desmopressin in children with mild platelet dysfunctions who underwent adenotonsillar surgery in our hospital. MethodsWe performed a retrospective study aimed at determining the perioperative bleeding and complication rate in children with mild inherited platelet dysfunction in whom desmopressin was used while undergoing adenotonsillar procedures. ResultsBetween 2004 and 2010, 27 children with mild inherited platelet dysfunction underwent adenotonsillar procedures in our hospital and were treated with desmopressin. One patient developed perioperative bleeding (3.7%) and there was 1 child (3.7%) who presented transitory hypotension as a side effect of desmopressin. ConclusionsThe use of desmopressin allowed adequate perioperative bleeding prophylaxis management in children with mild inherited platelet dysfunction who underwent adenotonsillar procedures without presenting severe complications.

Uso de desmopresina en niños con disfunción plaquetaria congénita sometidos a adeno y/o amigdalectomía

Introduction and goalsAdenotonsillar surgery represents a major haemostatic challenge in paediatric patients with mild inherited platelet dysfunction. While there are recommendations for perioperative haemostatic management, there are no reports of the outcomes with the different recommendations in these children when undergoing adenotonsillectomy. Our objective was to evaluate the management of perioperative bleeding with desmopressin in children with mild platelet dysfunctions who underwent adenotonsillar surgery in our hospital. MethodsWe performed a retrospective study aimed at determining the perioperative bleeding and complication rate in children with mild inherited platelet dysfunction in whom desmopressin was used while undergoing adenotonsillar procedures. ResultsBetween 2004 and 2010, 27 children with mild inherited platelet dysfunction underwent adenotonsillar procedures in our hospital and were treated with desmopressin. One patient developed perioperative bleeding (3.7%) and there was 1 child (3.7%) who presented transitory hypotension as a side effect of desmopressin. ConclusionsThe use of desmopressin allowed adequate perioperative bleeding prophylaxis management in children with mild inherited platelet dysfunction who underwent adenotonsillar procedures without presenting severe complications.

A Retrospective Evaluation of Children Who Have Suffered a Grade III or IV Intraventricular Hemorrhage and Their Parents for Platelet Dysfunction.

AbstractAbstract 1440This study is intended to evaluate children that have survived a grade III or IV intraventricular head bleed and their parents for a potential autosomal dominant inherited platelet dysfunction due to platelet dense granule deficiency (δ-SPD). Intraventricular hemorrhage (IVH) poses a significant risk in premature neonates less than 32 weeks gestation. Infants suffering from high grade (III-IV) periventricular or intraventicular bleeding have mortality rates approaching 50%. In addition, survivors of high grade IVH may suffer severe brain damage or a multitude of other long term neurological sequelae. Thus, we believe that investigation into the pathogenesis of neonatal IVH is not only crucial for the survival of these infants, but also for their quality of life in the future.Current data suggest that the pathogenesis of IVH in the premature infant is related to a loss of ability to regulate cerebral blood flow. Changes in local blood pressure, which would otherwise be autoregulated, remain unrestrained and result in capillary bleeding. Previous prospective studies from our lab have shown that full term neonates have a transient platelet dysfunction at the time of birth (Blood, 100(11), 691a, 2002), which appears to be related to a platelet dense granule storage pool deficiency (δ-SPD). We have also found that 1 day old, full term neonates have mature platelets similar to adults. Our prospective data suggests that at day 3–5 after birth, premature infants of gestational age 26–33 weeks (n=29) have a δ-SPD similar to that observed in full-term umbilical cord blood platelets suggesting a delay in platelet maturation. Only one preemie included in the study had suffered an IVH (grade I); all preemies who suffered Grade III/IV IVH during our study died before we could obtain blood (Blood 108(11):1113, 2006). Parents evaluated had normal platelet storage pools.Our current and on-going retrospective study of children that have survived a grade III/IV IVH and their parents supports our hypothesis that platelet dysfunction may play a significant role in the etiology of IVH. Survivors were identified from a database and parents sent a letter requesting their participation in the study. For those agreeing to participate, informed consent was obtained for this Institutional Review Board approved project. A vial of peripheral blood was obtained from both the IVH surviving child and their parent(s) to determine the platelet dense granule storage pool using the electron microscopy whole mount technique. Parents completed a vetted bleeding questionnaire for assessment of bleeding history/tendencies. Our preliminary data from 6 families reveals that all children surviving a grade III/IV IVH have a δ-SPD with an average of 2.64 ± 0.14 dense granules per platelet (DG/PL) whereas normal = 4–6 DG/PL. Their mothers also have a tendency for δ-SPD (5/6 δ-SPD and 1 within normal limits) with an overall average of 2.93 ± 0.35 DG/PL. Data collected from the questionnaires substantiate the laboratory results with a history of menorrhagia (determined by an established numerical pictorial method) the most significant correlation in 4/6 mothers. The fathers (4/5) tend to have normal numbers of DG/PL (4.06 ± 0.61; 1 had δ-SPD at 1.72 DG/PL). Interestingly, for the one mother with a normal number of DG/PL, the father had δ-SPD. Thus, all children evaluated to date in this study have δ-SPD and a parent who also has δ-SPD. The implication of these preliminary data suggest that potential identification of platelet dysfunction in women at risk for premature delivery could allow for prophylactic intervention for the premature neonate to reduce the morbidity and mortality related to IVH. As this study is currently ongoing, it is anticipated that additional data will be available for presentation. Disclosures:No relevant conflicts of interest to declare.

Overview of Bleeding Disorders in Adolescent Females with Menorrhagia

Women bleed with menses, during childbirth, and after childbirth. Women are more likely to manifest a bleeding disorder as they have more opportunities to experience bleeding challenges in their lifetime. Bleeding disorders such as hemophilia and von Willebrand disease affect 2.5–3 million American women. The most common inherited bleeding disorder in the population is von Willebrand disease with an estimated prevalence of 1–2%. von Willebrand factor (vWF) is required to adhere platelets to exposed subendothelium and protects factor VIII from proteolysis in the circulation. 1 The prevalence of vWF rises in studies involving women with menorrhagia, with estimates ranging as high as 10–20% in white women, and 1–2% among African American women. 2 Other bleeding disorders seen in adolescents with menorrhagia are disorders of inherited platelet dysfunction, clotting factor deficiencies, thrombocytopenia, and disorders of the fibrinolytic pathway. Not only are women more likely to present early in their life with a bleeding disorder, they are also more likely to have other gynecologic manifestations as a result of these disorders. This article presents an overview of the problem and touches upon the different management strategies available.

Decreased Platelet Expression of MYL9 (Myosin Regulatory Light Chain Polypeptide) and Other Genes with Platelets Dysfunction and CBFA2 Mutation: Insights from Platelet Expression Profiling.

We have previously reported (Blood , 87:1368, 1996) a patient with a mild thrombocytopenia, and markedly abnormal aggregation, secretion, phosphorylation of pleckstrin and myosin light chain (MLC), and activation of GPIIb-IIIa complex. We recently showed (Blood 2004, 103: 948–954) in this patient a heterozygous mutation in hematopoietic transcription factor CBFA2 (Core Binding factor A2, also called AML1) and decreased platelet PKC-theta. We postulated that platelet expression profiling would provide insights into the pathophysiological mechanisms and gene expression changes resulting from a CBFA2 mutation. We performed platelet expression profiling in 4 control subjects (6 profiles, 2 individuals profiled twice) and the patient (profiled twice, 10 months apart) using the Affymetrix microarray Human U133A and B GeneChips (total ~44000 probe sets). ~10,000 probe sets (genes and ESTs) are expressed in human platelets. Iterative comparisons of data from each individual platelet profiles had correlation coefficients (r) > 0.85. Using GeneSpring® analytical software we selected genes that showed at least 1 present call in the 8 profiles, and p<0.05 showing a significant difference between the 2 groups. Relative expression values <0.5 and >2 were considered as significant changes. In the patient, 298 probe sets were significantly down regulated and 29 significantly upregulated. We focused on genes showing a > 5-fold decrease (fold change, fc < = 0.20). There was a striking ~75 fold decrease (fc = 0.013; p=0.00022) in myosin regulatory light chain polypeptide (MYL9 gene). Other down-regulated genes included calcium binding protein 5 (CABP5, fc = 0.02; a protein with similarity to calmodulin), Na/K/Ca exchanger member 3 (SLC24A3, fc = 0.11), b3-endonexin (ITGB3BP, fc = 0.01), platelet factor 4 variant 1 (PF4V1, fc = 0.03), chemokine CXCL5 (ENA-78) (fc = 0.20), tropomyosin I (alpha) (TPM1, fc = 0.13) and arachidonate 12-lipoxygenase (ALOX-12, fc = 0.22). The expression array findings were validated by decreased platelet mRNA levels on real time PCR or by immunoblotting (platelet PF4). Several down-regulated genes are directly relevant to the patient's platelet defect. Agonist-stimulated MLC phosphorylation is impaired in patient platelets. The strikingly decreased expression of MYL9 with normal expression of MLC kinase (MLCK, by array and real time PCR) suggests that the blunted myosin phosphorylation arises from decreased MYL9 than due to decreased MLCK. Myosin light chains play a role in diverse processes including in cell contractility, mobility and cytokinesis, and are relevant to impaired platelet function and production. The decreased expression of the Na/K/Ca exchanger and b3-endonexin 3 (both implicated in activation of GPIIb-IIIa) provide mechanisms for the diminished GPIIb-IIIa activation. Chemokine CXCL5 and PF4V1 are expressed in megakaryocytes, and the genes are colocalized to “chemokine cluster” on chromosome 4. 12-lipoxygenase, a major platelet enzyme, regulates arachidonic acid metabolism and production of the 12-hydroxy eicosanoids. This is the first proof of concept that platelet expression profiling can be applied to obtain new insights into the molecular basis of inherited platelet dysfunction. Further studies will provide new information on the genes regulated by CBFA2, and on mechanisms regulating platelet production and activation.

Inherited bleeding disorders in Indian women with menorrhagia.

In order to define the prevalence of haemostatic defects in women presenting with menorrhagia in our region, the coagulation data on women bleeders investigated in the Department of Haematology, AIIMS, were analysed. A total of 337 of the 2200 menorrhagic women investigated were characterized to have an inherited bleeding disorder; 221 of these 337 women presented with menorrhagia alone while 116 also had other associated bleeding manifestations as prolonged bleeding from injury site, ecchymotic patches in the skin, epistaxis, haematomas, haemarthroses and major bleeds like intracerebral bleeding. The tests performed included bleeding time (BT), platelet count, prothrombin time (PT), prothrombin consumption index (PCI), activated partial thromboplastin time (APTT), PF3 release with adenosine diphosphate (ADP) at 0 and 20 min, total PF3 assay and platelet Aggregation studies with collagen, ADP, adrenaline, arachidonic acid and ristocetin. Coagulation factor assays, von Willebrand antigen estimation, ristocetin cofactor assay and electron microscopy were performed wherever necessary. Inherited platelet dysfunction was seen in 283 (83.9%) of the patients. Amongst these, isolated PF3 availability defect was seen in 163 (48.4%) cases. Glanzman's thrombasthenia was seen in 30 (8.9%) patients, Storage pool disease in eight (2.4%) patients, arachidonic acid pathway defect in five (1.5%) patients and Bernard-Soulier Syndrome in six (1.8%) patients. In 71 (21.1%) patients, the platelet function defect could not be classified into any specific subtypes. Inherited defects of coagulation were observed in 54 (16%) of the cases. Amongst these, von Willebrand disease (vWD) was the most frequent being seen in 40 (11.9%) of the cases. Factor XIII deficiency was seen in one (0.3%), factor X deficiency in four (1.2%), factor VII deficiency in one (0.3%) and factor XII deficiency in one (0.3%) of the patients. It is concluded that although hereditary platelet function defects constitute a large majority of women bleeders in India but among the coagulation defects, vWD is the commonest as reported from the caucasian population. It is thus suggested that in women presenting with menorrhagia, screening tests for haemostasis especially for vWD and inherited platelet function defects must be performed.

Congenital disorders of platelet signal transduction.

After injury to the blood vessel, platelets adhere to the exposed subendothelium by a process (adhesion) that involves the interaction of a plasma protein, von Willebrand factor (vWF), and a specific protein on the platelet surface, glycoprotein Ib (GPIb; the Figure⇓). Adhesion is followed by recruitment of additional platelets that form clumps, a process called aggregation (cohesion). This involves binding of fibrinogen to specific platelet surface receptors—a complex comprising glycoproteins IIb-IIIa (GPIIb-IIIa). Activated platelets release the contents of their granules (secretion or release reaction), such as ADP and serotonin from dense granules, which subsequently cause recruitment of additional platelets. In addition, platelets play a major role in coagulation mechanisms; several key enzymatic reactions occur on the platelet membrane–lipoprotein surface. A number of physiological agonists interact with specific receptors on the platelet surface to induce responses, including a change in platelet shape from discoid to spherical, aggregation, secretion, and thromboxane A2 (TxA2) production. Other agonists such as prostacyclin inhibit these responses. Ligation of the platelet receptors initiates the production or release of several intracellular messenger molecules, including Ca2+ ions, products of phosphoinositide (PI) hydrolysis by phospholipase C (PLC; diacylglycerol [DG] and inositol 1,4,5-triphosphate [InsP3]), TxA2, and cyclic nucleotides (cAMP; the Figure⇓). These subsequently induce or modulate the various platelet responses of Ca2+ mobilization, protein phosphorylation, aggregation, secretion, and liberation of arachidonic acid. The interaction between the agonist receptors and the key intracellular effector enzymes (eg, PLA2, PLC, adenylyl cyclase) is mediated by a group of GTP-binding proteins that are modulated by GTP. As in most secretory cells, platelet activation results in …

Congenital disorders of platelet function: disorders of signal transduction and secretion.

Congenital defects in platelet function are associated with bleeding manifestations of variable intensity and arise by diverse mechanisms. Defects in platelet-vessel wall interaction (disorders of adhesion) may arise because of qualitative or quantitative abnormalities in plasma von Willebrand factor (von Willebrand disease) or in platelet glycoprotein Ib, the binding site on platelets for von Willebrand factor (Bernard-Soulier syndrome). Disorders characterized by abnormal platelet-platelet interaction (disorders of aggregation) arise because of absence of plasma fibrinogen (congenital afibrinogenemia) or because of qualitative or quantitative abnormalities in platelet glycoprotein IIb-IIIa complex (Glanzmann's thrombasthenia). Patients with abnormalities in platelet secretion and signal transduction are a heterogeneous group characterized by impaired aggregation responses and secretion of granule contents. A small proportion of these patients have deficiency of granule stores (storage pool deficiency [SPD]) or impaired production of thromboxane A2; in most, the mechanisms underlying the platelet dysfunction are unknown. Evidence is accumulating that at least some patients have abnormalities in early signal transduction events. Abnormalities in phospholipase C activation, G-protein activation, and other events (eg, protein phosphorylation) have been documented. Platelets play a major role in blood coagulation, and in Scott syndrome, there is an abnormality in platelet contribution to the mechanisms leading to thrombin generation. In most patients with inherited platelet dysfunction, the underlying mechanisms remain to be delineated. Future studies of these patients should yield valuable new information on normal platelet mechanisms.

Use of DDAVP in inherited and acquired platelet dysfunction

Twenty-one patients with prolonged bleeding times secondary to inherited disorders of platelet function and eight patients with prolonged bleeding times secondary to acquired platelet dysfunction were given 0.3 micrograms per kilogram of DDAVP, 1-deamino-8-D-arginine vasopressin, intravenously. Sixteen of twenty-two DDAVP trials in patients with inherited platelet dysfunction (73%) and seven of the nine DDAVP trials in patients with acquired platelet dysfunction (78%) resulted in normalization or shortening of the prolonged bleeding times by at least 4 min. The bleeding time response did not correlate with changes in the levels of von Willebrand factor (vWf) antigen or ristocetin cofactor activity, nor was it associated with changes in vWf multimeric analysis or in vitro platelet aggregations following the administration of DDAVP. Shortening of the bleeding time with DDAVP was seen in patients with a failure to release/storage pool type defect, thromboxane synthesis type defect, Bernard-Soulier syndrome, Glanzmann's thrombasthenia, the May-Hegglin anomaly, liver disease, nonuremic renal disease, myelofibrosis, and Tangier's disease.