Intrinsic Platelet Defect Research Articles

The spleen

The spleen

Platelet disorders: an overview.

Thrombocytes or platelets are anucleated cells derived from megakaryocytes by process of megakaryopoiesis, with maturation time of 4-5 days. They are small and discoid in shape with size ranging from 2 to 4 μm. The platelet concentration in blood varies between 150, 000 and 400, 000 cells/μl of blood. They are involved in both hemostasis and wound healing. Hence, any abnormalities in platelets can lead to various bleeding disorders. Platelet disorders include thrombocythemia and thrombocytosis, thrombocytopenia and platelet dysfunction. Thrombocythemia and thrombocytosis are associated with increased platelet count because of overproduction of platelets. Thrombocytopenia includes decreased platelet count because of failed platelet production, increased sequestration of platelets in spleen, dilution of platelets and combination of these mechanisms. Platelet dysfunction can be because of intrinsic platelet defect or an extrinsic factor that alters the normal platelet function and can be hereditary or acquired. The following review provides a comprehensive overview of the above platelet disorders.

Pregnancy-Induced Thrombocytopenia in Pseudo-Von Willebrand Disease

Abstract 4658Platelet-type von Willebrand disease, or pseudo-VWD, is a rare congenital platelet disorder due to a mutation in the glycoprotein 1b alpha receptor. This results in increased binding of normal VWF to platelets, leading to platelet aggregation and intermittent thrombocytopenia. Although the mechanism is similar to type IIb VWD, this gain of function mutation affects the platelet, rather than plasma VWF.We report a patient with pseudo-VWD who developed progressive thrombocytopenia during pregnancy. She was initially seen at 10 weeks gestation, when the platelet count was 143 × 109 /L (figure 1). As the pregnancy progressed, the platelet count decreased, accompanied by an inverse rise in VWF antigen and activity, factor VIII activity, and an increase in high molecular weight (HMW) multimers (figure 2). The VWF activity to antigen ratio remained abnormal at all times. At the time of delivery, the platelet count reached a nadir of 36 × 109/L. Post-partum, the platelet count normalized to 185 × 109/L with a concomitant fall in VWF antigen and activity levels. VWF multimer analysis after delivery showed an absence of high molecular weight multimers. [Display omitted] FIGURE 2Weeks GestationPlatelet count (×109 /L)VWF antigenVWF activityFactor VIIIPlatelet aggregationVWF multimers1014381%35%88%↑ ristocetin 0.6normal3654144%57%205%not donenormal+15 post-partum18555%19%49%not doneHMW multimers absentThe likely etiology of the progressive decrease in the platelet count is secondary to the physiologically stimulated rise in VWF levels during pregnancy. With rising VWF levels, the abnormal platelet GP1b alpha receptor binds VWF, resulting in platelet-VWF aggregates with subsequent clearance. Transfusion of normal platelets would be the only way to correct the abnormality. Our patient, a Jehovah's Witness, would not accept platelet transfusion if it became necessary. She underwent an uncomplicated cesarean section for obstetric indications.Our patient's family was the subject of the landmark article initially describing this condition (Weiss HJ, Meyer D, Rabinowitz R, et al. Pseudo- von Willebrand's disease: An intrinsic platelet defect with aggregation by unmodified human factor VIII/von Willebrand factor and enhanced adsorption of its high-molecular-weight multimers. N Engl J Med 1982; 306:326-333). This patient is the 2-year old who was not tested when the family was initially evaluated. To our knowledge, this is the first reported case of pregnancy-associated thrombocytopenia in a patient with pseudo-VWD. Disclosures:No relevant conflicts of interest to declare.

Platelet adhesion defect in type I Gaucher Disease is associated with a risk of mucosal bleeding

Patients with type I Gaucher Disease (GD) may have a clinically significant bleeding tendency that is disproportionate to their platelet count. We hypothesized that impaired platelet adhesion might contribute to bleeding tendency. Adult patients with type I GD with platelet counts ≥130×10(9) /l and haematocrit ≥30% (n=48), obligatory carriers (n=52), and healthy controls (n=19) were studied. Platelet adhesion, using the IMPACT-R (Cone and Plate(let) Analyser), and platelet aggregation were determined. Type I GD patients had significantly lower platelet adhesion [surface coverage %, median (interquartile range)] 4·6 (3·2-7·5), compared to controls, 8·7 (7·6-10·3), or carriers, 8·1 (6·5-9·4; P=0·001). Platelet adhesion was not affected by the use of disease-specific enzyme replacement therapy but was improved in patients after splenectomy, 7·2 (5·8-9·3). Mixing tests showed that the reduced adhesion was an intrinsic platelet defect. Mucosal bleeding was reported in 17 (35·4%) patients and was associated with abnormal adhesion [P=0·037, with an Odds Ratio (95% confidence interval) of 5·73 (1·1-29·6)]. Five patients (22%) had reduced platelet aggregation, all of whom had reduced platelet adhesion. Platelet aggregation defect was not associated with mucosal bleeding. In conclusion, platelet adhesion defect is a major thrombocytopathy in type I GD patients and can explain part of the increased tendency to bleeding.

A Numerical Analysis Model Allows Quantification of Lifespan-Dependent and Random Kinetic Processes Contributing to the Thrombocytopenia of Murine WAS.

AbstractAbstract 3684In vivo platelet consumption is thought to be due to two kinetically distinct types of process: random processes, such as hemostasis and/or immune-mediated clearance, and lifespan-dependent apoptosis. The Mills Dornhorst equation, which has been used to model platelet consumption, has several theoretical and practical drawbacks: 1) It assumes apoptosis is instantaneous, an assumption at odds with the lack of linearity that in vivo platelet consumption data shows at late points in the population lifespan; 2) It does not allow an explicit solution for the random consumption rate constant; and 3) It cannot be applied to in vivo platelet consumption data generated with allogeneic platelets. While a recent alternative model (Dowling et al., Blood. 2010 Jun 7. [Epub ahead of print]) offers a solution to the first of these problems, it does not address the others – and its application to platelet consumption data requires the estimation of a large number of kinetic modeling parameters (seven). Here we use a simpler numerical analysis model to quantify random and lifespan-dependent platelet consumption processes in normal and thrombocytopenic (WASP(-)) mice. Increased platelet turnover is thought to contribute the thrombocytopenia of WAS.Numerical analysis is a well established algorithm-based alternative to the use of analytic models such as the Dornhorst equation. Our model applies three parameter values (a random consumption rate constant, a “nominal lifespan”, and a random apoptosis rate constant) to a matrix comprising a series of platelet cohorts (in columns) which are sequentially produced and fractionally consumed in a series of time intervals (rows). Cohorts are consumed at a random (exponential) rate until they reach their nominal lifespan, after which they are consumed at a rate equal to the sum of the first rate and a random apoptosis rate. The summed cohort values achieved after equilibration of production and consumption comprise the population platelet count. Continued platelet consumption (after production is halted) then serves to model in vivo platelet consumption data, a process which takes into account consumption rate-dependent variation in the starting population's age distribution.A least squares fitting procedure is used to find parameter values which best fit observed platelet consumption data obtained with fluorescently tagged WT platelets in WT recipients, and WASP(-) platelets in WASP(-) recipients. Comparison of the resultant absolute random platelet consumption rate to known thresholds for thrombocytpenia-induced hemorrhage allows estimation of the effects of platelet preparation and labeling on the observed consumption rate (the “preparation lesion”). Inferred platelet lifespan distributions are in turn used to model the consumption of WT platelets in WASP(-) recipients, and of WASP(-) platelets in WT recipients. This type of comparison is not feasible with the MIlls-Dornhorst model.Our findings suggest that rapid random in vivo consumption due to an intrinsic (“cis”) platelet defect contributes significantly to the thrombocytopenia of murine WAS. Platelet production is increased in WASP(-) mice, but not as much as would be expected from the increased number of megakaryocytes in bone marrow and spleen. This result supports the idea that thrombopoiesis per megakaryocyte is inhibited by WASP deficiency. No significant “trans” effect of host WASP deficiency on the consumption rate of transfused WT platelets is seen, the differing appearances of raw platelet consumption data notwithstanding. However, the method also allows quantification of a significant “cis/trans” contribution of host WASP deficiency to the rapid consumption of WASP(-) platelets. The mechanism for the cis/trans effect is unknown.Application of this numerical analysis method to clinical platelet consumption data for thrombocytopenias of unknown etiology should allow quantification of the separate contributions of impaired platelet production and accelerated platelet consumption in such cases. Disclosures:No relevant conflicts of interest to declare.

Intracranial Hemorrhage in a Patient with Osteogenesis Imperfecta Due to Inherited and Acquired Platelet Dysfunction.

A 42 year-old man with Osteogenesis Imperfecta (OI) had three episodes of spontaneous Subdural Hematoma (SH) after binge drinking. There is no remote history of abnormal bleeding or easy bruising despite multiple fractures. Medications included Aspirin (ASA). The first and second SH occurred within the preceding year and were treated conservatively. The third SH occurred while on ASA and drinking more than 500cc liquor/day. The Platelet Function Assay (PFA-100) was significantly abnormal (see table). After platelet transfusions the SH was surgically evacuated without complications. An MRA of the head showed no vascular abnormality. CBC, serum chemistries, PT, PTT, factor VIII and von Willebrand factor were normal. The patient stopped taking ASA, but continued to drink. The PFA-100, although abnormal, had improved. After a month-long alcohol abstinence his PFA-100 normalized. He has been without SH ever since. However the platelet aggregation study still shows a lack of second wave response to ADP.EVENTASAETOHCollagen/EpiCollagen/ADPPlatelet CountSH3(+)(+)>300112266Plt transfusionn/an/a12251347Follow up(−)(+)219108231Follow up(−)(−)11780276Reference Range118–162 Seconds59–103 Seconds140–370Discussion: Both OI and ETOH are known factors of causing intrinsic platelet defect. The Framingham Offspring Study showed that alcohol consumption is inversely associated with both platelet activation and aggregation, particularly in men. ETOH is capable of inhibiting collagen induced platelet aggregation, secretion, arachidonate mobilization, and TXA2 formation. Also it has been suggested that intracellular Ca2+ homeostasis and aggregation in platelets are impaired by ethanol through the generation of H2O2 and oxidation of sulphydryl groups. OI causes vascular fragility and intrinsic platelet defect. In one study the most frequent abnormalities were increased capillary fragility (35%), decreased platelet retention (33%) and reduced factor VIII R:Ag (23%). Reduced ristocetin cofactor, deficient platelet aggregation induced by collagen and prolonged bleeding time were less common findings. The combination of vascular, platelet related and plasmatic defects may reflect that OI is a heterogeneous group of disorders with common clinical expression.Conclusion: Patients with OI are at risk for intracranial bleeding due to vascular fragility and intrinsic platelet defect. Our patient had a normal PFA-100, off ASA and ETOH. The platelet aggregation study -a more sensitive test- was able to detect a platelet secretion defect in our patient. The abnormal platelet aggregation study was likely due to his OI, which never caused abnormal bleeding by itself. The additional affect of ASA and ETOH on his platelets led to recurrent episodes of SH. Many OI patients are on NSAID/ASA due to chronic bone pain. Special attention should be paid to alcohol abuse in this group of patients. Normal platelet counts and coagulation tests may not be sufficient to evaluate the risk of bleeding. We suggest performing a PFA-100 or a platelet aggregation study, when platelet dysfunction is suspected.

Characterization of the cDNA Encoding αIIb and β3 in Normal Horses and Two Horses with Glanzmann Thrombasthenia

Glanzmann thrombasthenia (GT) is an inherited, intrinsic platelet defect characterized by a quantitative or qualitative change in the platelet glycoprotein complex IIb-IIIa (integrin alpha(IIb)beta3). The subunits are encoded by separate genes and both subunits must be expressed for a stable complex to form on the platelet surface; therefore, a defect in either gene can result in GT.

Von Willebrand Disease in Children with Glycogen Storage Disease Type Ia.

Glycogen storage disease, Type Ia (GSD-Ia) is an autosomal recessive disease, characterized by hepatomegaly, hypoglycemia, hyperuricemia, and bleeding diathesis. Easy bruising and epistaxis are common and are associated with a prolonged bleeding time as a result of impaired platelet aggregation and adhesion. Two of four of our GSD-Ia patients were evaluated because of bleeding diathesis and both were diagnosed as von Willebrand's disease (vWd) with normal platelet count, prothrombin time and activated partial thromboplastin time.Case 1: Six year old boy diagnosed as GSD-Ia when he was 3 month of age and bleeding diathesis was first recognized 5th year of his life. His bleeding time was prolonged (15 minutes). Measurement of serum factor VIII-related antigen (vWf-Ag) revealed a decrease (% 31) and ristocetin cofactor activity was abnormal (% 37).Case 2: Nine year old girl diagnosed as GSD-Ia when he was 6 month of age and bleeding diathesis was first recognized 4th year of his life. His bleeding time was prolonged (3.5 minutes). Measurement of serum factor VIII-related antigen (vWf-Ag) revealed a decrease (% 17) and ristocetin cofactor activity was abnormal (% 5.7).Frequent diagnosis of vWd among our GSD-Ia patients might suggest alterations in membrane glycoprotein synthesis. There is no definitive explanation addresses how these alterations actually cause defective platelet aggregation. Although, the presence of association between these two separate diseases might be coincidental, in literature, diagnosis of vWd among GSD-Ia patients had been reported in only one paper. We conclude that GSD-Ia patients may have a metabolically acquired form of vWd as well as an acquired intrinsic platelet defect. Further molecular studies may be necessary to clarify the etiopathogenesis of this association.

Markers of endothelial and in vivo platelet activation in patients with essential thrombocythemia and polycythemia vera.

We investigated endothelial and in vivo platelet activation in a cohort of 52 patients with essential thrombocythemia (ET) and polycythemia vera (PV) before and after cytoreductive treatment, 22 healthy controls, and 17 patients with acute cerebrovascular ischemia (ACVI) and normal platelet counts. We measured platelet expression of CD62P and CD63 antigens and levels of soluble vascular cell adhesion molecule 1 (sVCAM-1). We found increased in vivo platelet activation in all patients with ET and PV, both before and after cytoreductive treatment, compared with controls. In patients with arterial thrombosis, platelet expression of CD62P, and in patients with erythromelalgia, expression of both markers was higher compared with expression in patients without thrombotic complications. In patients with ET and PV before and after treatment, sVCAM-1 expression was increased compared with expression in controls but also compared with expression in patients with ACVI and normal platelet counts. In patients with arterial thrombosis and erythromelalgia, in vivo platelet activation correlated with the level of sVCAM-1. Our findings indicated that in vivo platelet activation reflects intrinsic platelet defects in patients with ET and PV, persists after cytoreductive treatment, and results in endothelial damage, probably through release of angiogenic factors and/or activation of white blood cells.

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 …

Platelet function in cirrhosis and the role of humoral factors.

Haemorrhagic complications are common in patients with cirrhosis of the liver and contribute to the morbidity and mortality seen in this condition. Several pathological processes are involved in these complications, including a delay and overall reduction in platelet aggregation. To determine whether impaired aggregation in cirrhosis is the result of an intrinsic abnormality in platelet function or is induced by a factor present in the blood of cirrhotic patients. Liver unit patients in a teaching hospital. Blood was taken from 11 patients with cirrhosis (Child's B or C) and 11 healthy controls. Crossover experiments were carried out, suspending platelet pellets from patients in platelet-poor plasma from controls, and vice versa. Aggregation of both samples and also of platelet-rich plasma from patients and controls was measured. Aggregation after 1 min was impaired significantly in patient, compared with control, platelets following incubation in either patient (P = 0.0012), or control (P = 0.0242), plasma. Correspondingly, maximum aggregation of patient platelets was also reduced significantly (P = 0.0036) after incubation in patient plasma. Aggregation after 1 min, and maximum aggregation, of control platelets was increased significantly (P = 0.034 and 0.013, respectively) following incubation in patient plasma. Furthermore, there was a trend (non-significant) towards reduced aggregation of patient platelets incubated in control plasma. These results confirm both an intrinsic platelet defect causing impaired aggregation and a circulating factor in the plasma of patients with cirrhosis which may compensate for this functional defect.

Thrombin receptor-related hemostatic defect after cardiopulmonary bypass.

Platelet abnormalities have been blamed for the hemostatic defect that develops after cardiopulmonary bypass (CPB), but investigators have not been able to agree upon an intrinsic platelet abnormality responsible for the observed defect. To better define the blood components responsible for this post-operative hemostatic defect, we compared platelet function in whole blood (WB) to that in platelet-rich plasma (PRP) in 33 patients undergoing coronary artery bypass grafting. We measured platelet aggregation in response to various platelet agonists, including thrombin and TRAP-6 (a 6-amino acid peptide that activates the thrombin "tethered ligand" receptor site). In WB there was a lasting, diminished response to TRAP-6, but not to gamma-thrombin, after CPB. Control experiments showed that this diminished response to TRAP-6: (1) was not related to heparin or heparin-protamine complexes, (2) was not the result of hemodilution during CPB, (3) was not related to increased amounts of naturally occurring enzymes (aminopeptidases) that degrade TRAP, and (4) was not able to be reversed by the addition of as much as a 10-fold excess of the usual TRAP-6 aggregating dose to WB preparations. In contrast, no corresponding defect in platelet aggregation could be identified in PRP obtained from patients after CPB. These results show that, in post-operative blood samples, blood components present in WB and not in PRP (eg, red blood cells, activated white cells or platelets bound to white cells) diminish the ability of TRAP peptides to activate the thrombin receptor but do not decrease the ability of gamma-thrombin to induce platelet aggregation. This suggests that for circulating platelets after CPB: (1) interactions of platelets with other blood cell elements are the cause of altered postoperative platelet reactivity rather than any intrinsic CPB-induced platelet defect, (2) drugs, such as aprotinin, that limit activation of white cells and the fibrinolytic system may also have beneficial effects on platelet function after CPB, and (3) alternate mechanisms exist that allow thrombin, but not TRAP-6, to activate platelets normally after CPB (perhaps a second, as yet undefined, thrombin receptor).

Platelet dysfunction contributes to the haemostatic defect in haemorrhagic fever with renal syndrome

To characterize further the nature of haemostatic impairment in haemorrhagic fever with renal syndrome, we assessed platelet function in 9 patients in whom the diagnosis was serologically confirmed. Defective platelet aggregation was demonstrated in every patient. An abnormality of the granule release reaction was demonstrated in all of 7 patients tested. Gel-filtered platelets from a normal subject showed normal aggregation in plasma from a patient with impaired aggregation, which is evidence for an intrinsic platelet defect, and against the presence of a circulating inhibitor in this patient.

Abnormalities of cytoplasmic Ca2+ in platelets from patients with uremia

Uremic patients have a hemorrhagic tendency, often associated with prolonged bleeding times and decreased platelet function in vitro. Whether these defects result from abnormalities in plasma factors affecting platelet activity, platelet surface receptors, intracellular platelet mediators, or other aspects of platelet behavior is unknown. To examine the possibility that the abnormality in platelet function may result from aberrations in Ca2+ homeostasis, blood was obtained from 29 patients with severe uremia. The platelets were washed, loaded with the Ca2+ -sensitive probes indo-1 and aequorin, gel-filtered, and resuspended in either plasma or buffer. Of the 29 patients, seven had template bleeding times prolonged to 11 minutes or more, but platelet aggregation in plasma was not consistently impaired in these patients. However, in aequorin-loaded platelets from the patients with long bleeding times, the highest elevation of cytoplasmic calcium [( Ca2+]i) in response to the Ca2+ ionophore A23187, arachidonate, adenosine diphosphate (ADP), or epinephrine was lower than that seen in platelets from both uremic patients with less prolonged bleeding times and normal volunteers. The reduced [Ca2+]i response was associated with decreased aggregation of gel-filtered platelets suspended in buffer. Suspending washed aequorin-loaded uremic platelets in normal plasma for 20 minutes did not reverse the decreased agonist-induced rise in [Ca2+]i; platelets from a normal donor resuspended in uremic plasma aggregated and produced a normal increase in [Ca2+]i in response to agonists. We conclude that the platelet defect seen in some patients with uremia is associated with a decreased rise in platelet [Ca2+]i after stimulation and that this is a manifestation of an intrinsic platelet defect.

Abnormalities of Cytoplasmic Ca2+ in Platelets From Patients With Uremia

Uremic patients have a hemorrhagic tendency, often associated with prolonged bleeding times and decreased platelet function in vitro. Whether these defects result from abnormalities in plasma factors affecting platelet activity, platelet surface receptors, intracellular platelet mediators, or other aspects of platelet behavior is unknown. To examine the possibility that the abnormality in platelet function may result from aberrations in Ca2+ homeostasis, blood was obtained from 29 patients with severe uremia. The platelets were washed, loaded with the Ca2+ -sensitive probes indo-1 and aequorin, gel-filtered, and resuspended in either plasma or buffer. Of the 29 patients, seven had template bleeding times prolonged to 11 minutes or more, but platelet aggregation in plasma was not consistently impaired in these patients. However, in aequorin-loaded platelets from the patients with long bleeding times, the highest elevation of cytoplasmic calcium [( Ca2+]i) in response to the Ca2+ ionophore A23187, arachidonate, adenosine diphosphate (ADP), or epinephrine was lower than that seen in platelets from both uremic patients with less prolonged bleeding times and normal volunteers. The reduced [Ca2+]i response was associated with decreased aggregation of gel-filtered platelets suspended in buffer. Suspending washed aequorin-loaded uremic platelets in normal plasma for 20 minutes did not reverse the decreased agonist-induced rise in [Ca2+]i; platelets from a normal donor resuspended in uremic plasma aggregated and produced a normal increase in [Ca2+]i in response to agonists. We conclude that the platelet defect seen in some patients with uremia is associated with a decreased rise in platelet [Ca2+]i after stimulation and that this is a manifestation of an intrinsic platelet defect.

Altered platelet function in cirrhosis of the liver: impairment of inositol lipid and arachidonic acid metabolism in response to agonists.

Hemorrhagic disorders are common in patients with liver cirrhosis and result from several factors including impaired platelet function. We evaluated platelet aggregation and arachidonic acid metabolism in response to standard agonists in platelet-rich plasma from 12 cirrhotic patients with mild impairment of liver function (Child A), 12 patients with severe liver dysfunction (Child B and C) and 12 healthy subjects. Platelet aggregation and thromboxane A2 production were consistently reduced in patients with severe liver impairment. To determine whether the platelet dysfunction is due to an intrinsic platelet defect or a circulating inhibitor, we measured platelet aggregation and thromboxane A2 synthesis on washed platelets in healthy subjects and in Child B and C patients. The aggregating response of washed platelets in response to thrombin, collagen and arachidonic acid was markedly reduced, suggesting an intrinsic platelet defect. The biochemical events underlying platelet aggregation were investigated by prelabeling platelets with [1-14C]arachidonic acid. Thrombin-induced activation of phospholipase C (measured as the release of [1-14C]phosphatidic acid) and phospholipase A2 (measured as the release of [1-14C]arachidonic acid and its metabolites) was greatly impaired in platelets from patients with severe liver impairment. We conclude that in advanced cirrhosis there is a severe reduction in platelet aggregatory response to physiologic agonists due to an intrinsic platelet defect which is related to an impairment of the platelet transmembrane signaling mechanism induced by receptor stimulation.

Immune Thrombocytopenia Treated with High-Dose Intravenous Gamma Globulin and Corticosteroids in Two Patients with Wiskott-Aldrich Syndrome

Wiskott-Aldrich syndrome (WAS) is a primary immunodeficiency disorder characterized by thrombocytopenia, atopic dermatitis, and susceptibility to recurrent infections. The thrombocytopenia, due to an intrinsic platelet defect, is only rarely complicated by immune thrombocytopenia (ITP). We report two patients with WAS in whom ITP complicated their thrombocytopenia. In addition, immune neutropenia accompanied the ITP in one patient. Whereas administration of high-dose intravenous gamma globulin (IGIV) alone did not ameliorate the ITP, corticosteroids did improve the ITP and immune neutropenia. High-dose IGIV appeared to be synergistic with corticosteroids and thus have a steroid-sparing effect.

DDAVP infusion in five patients with type Ia glycogen storage disease and associated correction of prolonged bleeding times

Five patients with glycogen storage disease type I (GSD-I) were evaluated for a bleeding diathesis and subsequently were given an infusion of 1-deamino-8-D-arginine vasopressin (DDAVP). Although platelet counts were normal or slightly elevated, the baseline template bleeding times were prolonged in four of the patients. Prothrombin times and activated partial thromboplastin times were normal, while ADP- and epinephrine-induced platelet aggregations were absent in the three patients tested. Ristocetin- and collagen-induced platelet aggregations were abnormal. Laurell and immunoradiometric determinations of the factor VIII-related antigen (vWf antigen) were decreased. Glyoxyl agarose gel electrophoresis of the patients' plasma revealed abnormal multimer patterns in four of the five patients. After the DDAVP infusion the platelet aggregation abnormalities persisted; however, the bleeding time and the von Willebrand antigen and activity corrected. We conclude that GSD-Ia patients may have a metabolically acquired form of von Willebrand's syndrome as well as an acquired intrinsic platelet defect, and that DDAVP may be useful in the management of bleeding in these patients.

DDAVP Infusion in Five Patients With Type Ia Glycogen Storage Disease and Associated Correction of Prolonged Bleeding Times

Five patients with glycogen storage disease type I (GSD-I) were evaluated for a bleeding diathesis and subsequently were given an infusion of 1-deamino-8-D-arginine vasopressin (DDAVP). Although platelet counts were normal or slightly elevated, the baseline template bleeding times were prolonged in four of the patients. Prothrombin times and activated partial thromboplastin times were normal, while ADP- and epinephrine-induced platelet aggregations were absent in the three patients tested. Ristocetin- and collagen-induced platelet aggregations were abnormal. Laurell and immunoradiometric determinations of the factor VIII-related antigen (vWf antigen) were decreased. Glyoxyl agarose gel electrophoresis of the patients' plasma revealed abnormal multimer patterns in four of the five patients. After the DDAVP infusion the platelet aggregation abnormalities persisted; however, the bleeding time and the von Willebrand antigen and activity corrected. We conclude that GSD-Ia patients may have a metabolically acquired form of von Willebrand's syndrome as well as an acquired intrinsic platelet defect, and that DDAVP may be useful in the management of bleeding in these patients.

Von Willebrand factor binds to platelets and induces aggregation in platelet-type but not type IIB von Willebrand disease.

Platelet-type von Willebrand disease (vWD) and pseudo-vWD are two recently described intrinsic platelet defects characterized by enhanced ristocetin-induced agglutination in platelet-rich plasma. A similar finding is also typical of type IIB vWD, where it has been related to a von Willebrand factor (vWF) rather than a platelet abnormality. Platelet aggregation induced by unmodified human vWF in the absence of other stimuli has been reported in pseudo-vWD. In this study we demonstrate that vWF induces aggregation in platelet-type but not type IIB vWD. Aggregation is observed when normal plasma cryoprecipitate or purified vWF are added to platelet-rich plasma. Cryoprecipitate also aggregates washed platelets, although at higher concentrations than required for platelet-rich plasma. Purified vWF, however, induces significant aggregation of washed platelets only when plasma is added. EDTA inhibits vWF-induced aggregation. Its effect can be overcome by calcium but much less effectively by magnesium ions. Unstimulated platelets in platelet-rich plasma from patients with platelet-type but not type IIB vWD bind 125I-vWF in a specific and saturable manner. All different sized multimers of vWF become associated with platelets. Both aggregation and binding exhibit a similar vWF concentration dependence, suggesting that a correlation exists between these two events. Removal of ADP by appropriate consuming systems is without effect upon such binding or upon vWF-induced aggregation. Thrombin-induced 125I-vWF binding to washed platelets is normal in platelet-type as well as type IIB vWD. These results demonstrate that a specific binding site for unmodified human vWF is exposed on unstimulated platelets in platelet-type vWD. The relatively high vWF concentrations required for aggregation and binding may explain the lack of significant in vivo aggregation and thrombocytopenia in these patients. Moreover, these studies provide additional evidence that platelet-type and type IIB vWD are different diseases with distinct pathogeneses.