Hemostatic plug formation in normal and von Willebrand pigs: the effect of the administration of cryoprecipitate and a monoclonal antibody to Willebrand factor

Hemostatic plug (HP) formation was investigated in the ear bleeding time incision in normal and von Willebrand pigs. HP volume was calculated by integrating the areas of serial sections. In normal pigs (n = 11), platelets immediately formed a layer on the surface of the cut channel. Platelet aggregates formed at the ends of transected vessels and gradually enlarged. Finally, all transected vessels were occluded by HP and bleeding stopped. In contrast, large HPs were formed in the incision in von Willebrand's disease (vWD) pigs (n = 4); these HPs did not cover the ends of the transected vessels, which continued to bleed, allowing the formation of large hemostatically ineffective platelet aggregates in the incision. Canals traversed these HPs, and bleeding from the open vessels may have continued through them. After infusion of cryoprecipitate into a vWD pig, the bleeding time shortened, and the morphological findings of the HPs were similar to those of normal pigs. In normal pigs (n = 3) infused with an anti- Willebrand factor monoclonal antibody, which prolonged the bleeding time, a large HP formed in the incision, similar to that observed in the vWD pig. The volume of the normal and vWD HPs increased with time. These in vivo findings suggest that Willebrand factor is involved in the localization of the HP to the damaged vessel and may also play a role in platelet-platelet interaction. A computerized morphometric technique was used for measuring the volume of the hemostatic plugs and the distance of sequential points on the perimeter of the HP from the center of selected bleeding vessels.     

Studies of thromboxane B2, platelet factor 4, and fibrinopeptide A in bleeding-time blood of patients deficient in von Willebrand factor, platelet glycoproteins Ib and IIb-IIIa, and storage granules

The blood volumes and concentrations of thromboxane B2 (TxB2), platelet factor 4 (PF4), and fibrinopeptide A (FPA) were measured every 30 seconds in bleeding-time blood in normal subjects and in patients with idiopathic thrombocytopenic purpura (ITP), delta and alpha delta storage pool deficiency (SPD), Bernard-Soulier Syndrome (BSS), thrombasthenia (TSA), and von Willebrand's disease (vWD). Data were fitted to second-order (TxB2, PF4, and FPA) or third-order (volumes) polynomials. Average values for various parameters over fixed-time intervals were determined by numerical methods. The bleeding time was greater than 15 minutes in all patient groups and the initial bleeding, as reflected by the initial slope of the fitted blood volume curves, was increased in ITP, BSS, and SPD (delta-SPD in particular), but not in vWD and TSA. The increased values for both the initial slope and the volume of blood collected after 2 minutes in SPD suggest that vascular tone may be modulated, in part, by dense granule substances such as adenosine triphosphate (ATP) or serotonin. In TSA, uniquely, both platelet (TxB2 and PF4) and coagulation (FPA) values were increased in early bleeding samples (initial slope). In vitro studies of TxB2 production, together with previous flow studies of fibrin formation, also suggest enhanced activation and coagulant properties of thrombasthenic platelets. In other patients, reduced values of all substances at later times may reflect impaired platelet-fibrin plug formation in the high-shear regions at the ends of transected blood vessels. However, the initial slopes of the fitted curves for both TxB2 and PF4 were normal in vWD, suggesting that the early appearance of these substances may typically be from platelets that are adherent to collagen within the lower shear environment of the wound surface. The finding that FPA values were not decreased initially in any patient group, including ITP, but were decreased at later times (except for TSA), suggests that early fibrin formation occurs independently of platelets in the low-shear environment of the wound surface, whereas at later times fibrin is formed in a platelet-dependent manner in the high- shear regions at the ends of transected vessels.     

Role for platelet von Willebrand factor in supporting platelet-vessel wall interactions in von Willebrand disease

Twelve infusions of plasma concentrates of von Willebrand factor (vWF) were given to four patients with severe (type III) von Willebrand disease (vWD). Their prolonged bleeding times were either completely or partially corrected after five infusions and had not changed after the remaining seven. In contrast, the low platelet coverage of the subendothelial surface of rabbit aorta perfused with normal washed platelets and red cells resuspended in preinfusion patient plasma was completely or partially corrected in ten instances by replacing preinfusion plasma with postinfusion plasma and remained unchanged in two. Postinfusion improvement in surface coverage was greater than that in bleeding time, suggesting that vWF from normal platelets is needed to support optimal platelet-vessel wall interactions in vWD. This possibility was further explored through other perfusion experiments. The subendothelial surface covered by platelets from an untreated patient with type III vWD (containing no measurable vWF) or from a type IIA vWD patient (containing dysfunctional vWF) resuspended in normal plasma was much smaller than that covered by normal platelets resuspended in normal plasma. These results establish that platelet vWF is important in supporting platelet-vessel wall interactions in vWD and also provide experimental support in favour of the therapeutic transfusion of normal platelets in addition to vWF concentrates to correct the bleeding time in vWD patients.     

A probable double heterozygous type II von Willebrand's disease with increased ristocetin induced platelet aggregation.

We have identified a patient with von Willebrand's disease (vWD) resembling type IIB vWD, with increased ristocetin induced platelet aggregation (RIPA), the absence of the large multimers of von Willebrand factor (vWF) in plasma, and the presence of the large multimers in platelets in whom a family study indicated a probable double heterozygous inheritance pattern. The propositus was a 12-year-old boy with frequent epistaxis and bruising. Abnormal hemostatic findings included a prolonged bleeding time (BT), decreased levels of factor VIII coagulant activity (VIIIC), von Willebrand factor antigen (vWF:Ag), ristocetin cofactor (RCof), and an increased RIPA. In the presence of ristocetin, binding of the patient's plasma vWF to normal platelets was increased but binding of normal vWF to his platelets was normal. SDS-agarose gel (1.5%) electrophoresis revealed that plasma vWF lacked the large multimers, and 3.0% gel electrophoresis revealed that the multimers had a 5-band pattern similar to normal. The above findings were consistent with type IIB vWD, but 1-deamino[8-D-arginine]-vasopressin (DDAVP) infusion resulted in a shortened BT and the transient appearance of large multimers without a decrease in the platelet count. Family studies revealed that his mother has mild bleeding symptoms, decreased VIIIC, vWF:Ag, and RCof levels and normal to slightly reduced RIPA with a multimer pattern consistent with type I vWD. In contrast, the father, sister, and paternal grandfather were asymptomatic, with a slightly decreased VIIIC level but a normal BT and vWF:Ag and RCof levels. Their RIPA and vWF binding to normal platelets were increased, but unlike the propositus their plasma contained large multimers. We concluded that the propositus is a type IIB-like variant differing from previously reported IIB variants in two ways: 1) his response to DDAVP and 2) a possible double heterozygous mode of inheritance rather than the usual dominant route.     

Hemostatic effect of platelet von Willebrand factor.

In type III von Willebrand disease (vWD) patients, the bleeding time was only partially corrected or not modified after cryoprecipitate infusion, although the levels and the multimeric structure of plasma von Willebrand factor (vWF) were normal. However, the adhesion of normal platelets on the vessel wall subendothelium in the presence of postinfusion patient plasma improved more significantly than the bleeding time. These results suggest a role of the vWF released from normal platelets which is absent in type III vWD platelets. In 5 patients transfusion of normal platelet concentrates performed 1 h after cryoprecipitate infusion without modification of the bleeding time (> 30 min) normalized this parameter, and platelet adhesion to the subendothelium elicited a marked improvement. These last results confirm the suggestion that platelet vWF plays an important 'in vivo' role in the hemostatic process, particularly in patients suffering from severe vWD.     

Function of von Willebrand factor after crossed bone marrow transplantation between normal and von Willebrand disease pigs: effect on arterial thrombosis in chimeras.

von Willebrand factor (vWF) is essential for the induction of occlusive thrombosis in stenosed and injured pig arteries and for normal hemostasis. To separate the relative contribution of plasma and platelet vWF to arterial thrombosis, we produced chimeric normal and von Willebrand disease pigs by crossed bone marrow transplantation; von Willebrand disease (vWD) pigs were engrafted with normal pig bone marrow and normal pigs were engrafted with vWD bone marrow. Thrombosis developed in the chimeric normal pigs that showed normal levels of plasma vWF and an absence of platelet vWF; but no thrombosis occurred in the chimeric vWD pigs that demonstrated normal platelet vWF and an absence of plasma vWF. The ear bleeding times of the chimeric pigs were partially corrected by endogenous plasma vWF but not by platelet vWF. Our animal model demonstrated that vWF in the plasma compartment is essential for the development of arterial thrombosis and that it also contributes to the maintenance of bleeding time and hemostasis.     

von Willebrand's disease characterized by increased ristocetin sensitivity and the presence of all von Willebrand factor multimers in plasma

In eight members of one family, platelets in platelet-rich plasma aggregated at much lower ristocetin concentrations than normal. Ivy bleeding time was variously prolonged, and von Willebrand factor antigen (vWF:Ag), ristocetin cofactor activity, and factor VIII coagulant activity were decreased. Most of the affected members had had slight to rather severe bleeding symptoms. Platelet-type von Willebrand's disease (vWD) could be ruled out. All multimers of vWF:Ag were found in plasma as well as platelets. Administration of 1-desamino-8-D-arginine vasopressin (DDAVP) to the propositus did not cause thrombocytopenia, and platelet-poor plasma obtained immediately after did not aggregate normal platelets. The molecular defect in this family, inherited as an autosomal dominant, resembles the one in type IIB because of the response to ristocetin but differs from IIB because all vWF:Ag multimers are present in plasma and the response to DDAVP is atypical. We conclude that this family has a new subtype of vWD and propose that structural as well as functional criteria should be used for a proper classification of vWD.     

Absence of tubular structures and immunolabeling for von Willebrand factor in the platelet alpha-granules from porcine von Willebrand disease [published erratum appears in Blood 1987 Feb;69(2):707]

The electron microscopic localization of von Willebrand factor (vWF) was studied in platelets from normal and von Willebrand disease (vWD) pigs. In normal pig platelets, immunolabeling for vWF was far more intense and extensive than in human platelets and was either localized at one pole of the alpha-granule or all along its periphery or long axis. As in human platelets, this immunolabeling coincided with the presence of tubules about 200 nm in diameter. These structures were more numerous than in human platelets, with up to 30 tubules per alpha- granule. They were easily identified either in transverse sections, usually grouped in a less electron-dense part of the matrix at one pole of the alpha-granule, or in longitudinal sections parallel to the long axis of the elongated granules, or coiled around the alpha-granule core. They closely resemble those structures found in Weibel-Palade bodies. In platelets from pigs with severe vWD, these structures were absent, as was the immunolabeling for vWF; however, cytoplasmic microtubules were normally present in these platelets. Thus, the granule-associated tubules can be distinguished from the microtubules, which are larger in diameter (250 nm), are present in both normal and vWD platelets, and do not stain for vWF. These results strongly suggest that the tubular structures present in the alpha-granules of normal porcine platelets correspond to the vWF molecule itself.     

Type IIB von Willebrand's disease associated with a complex thrombocytopenic thrombocytopathy

A familial bleeding disorder characterized by an association of Type IIB von Willebrand's disease (vWD) with a complex thrombocytopenic thrombocytopathy is described in two patients from the same generation. Findings typical of type IIB vWD included enhanced ristocetin-induced binding of patient von Willebrand factor (vWF) to platelets of patients and normal individuals in association with the absence of larger multimers from plasma. Abnormalities in platelet function included deficient platelet aggregation to ADP, collagen, epinephrine, and arachidonic acid; and defective release of 14C-serotonin, vWF, and platelet factor 4 (PF4) in response to thrombin, collagen, or ADP. Platelet factor 4 and platelet vWF were decreased when measured per mg of total platelet protein. In addition, the binding of normal vWF to patient platelets stimulated with thrombin was decreased. Platelet size was increased with a very heterogeneous distribution width. Electron microscopic evaluation showed giant platelets with dense and alpha bodies present. The platelet count was borderline or slightly decreased in the resting state and declined to frankly thrombocytopenic levels at the time of acute bleeding episodes; this state was associated with the presence of platelet aggregates in blood smears.     

Heterogeneous phenotypes of platelet and plasma von Willebrand factor in obligatory heterozygotes for severe von Willebrand disease

To characterize the heterogeneity of severe (type III) von Willebrand disease (vWD), plasma and platelet von Willebrand factor antigen (vWF:Ag) and ristocetin cofactor activity (Ricof) were measured in 28 obligatory heterozygotes (ie, parents or children of probands from 15 different kindreds with severe vWD). On the average, heterozygotes had low levels of vWF in both platelets and plasma. There was, however, considerable heterogeneity, with four distinct patterns. Eleven heterozygotes had concordant reduction of vWF:Ag and Ricof in both plasma and platelets; five had low levels of vWF:Ag and Ricof in plasma contrasting with normal levels in platelets; eight had a peculiar pattern, the reverse of the above (ie, low levels in platelets and normal levels in plasma); and in one, both vWF measurements were normal in plasma and platelets. These patterns were genetically determined: they were consistent in four couples of consanguineous heterozygotes and in two couples carrying the same gene deletion. Only the remaining three heterozygotes had no clearly identifiable pattern. Other findings of this study were that although most of the heterozygotes had normal bleeding times, the 7 of 28 who had prolonged bleeding times had concordantly low levels of vWF measurements in both plasma and platelets. In conclusion, this large series of obligatory heterozygotes provides evidence for phenotypic and genotypic heterogeneity of severe vWD.     

A new mutation, Ala1500-->Glu, responsible for type 2A von Willebrand disease

Two patients (from the same family) with a bleeding disorder were diagnosed with type 2A von Willebrand disease (vWD). The 28th exon of the von Willebrand factor (vWF) gene was obtained by polymerase chain reaction and then screened by denaturing gradient gel electrophoresis. The fragments displaying abnormal melting behavior were directly sequenced. A heterozygous C-->A substitution changing alanine 1500 to glutamic acid at position 4750 in the A2 domain of vWF was found. The structure of recombinant A1500E vWF within transfected COS-7 cells and the secretion of high-molecular-weight (HMW) multimers were similar to wild-type vWF. HMW forms of vWF multimers were absent in plasma but present in platelets. The mutation described here corresponds to the group II type 2A vWD characterized by normal secretion of all vWF multimers.     

Abnormal proteolytic degradation of von Willebrand factor after desmopressin infusion in a new subtype of von Willebrand disease (ID)

We describe two members of a single family, father and son, with mild factor XII deficiency associated to von Willebrand disease (vWD) with aberrant structure in whom distinct multimeric abnormalities and an abnormal proteolytic processing of von Willebrand factor (vWF) after desmopressin (DDAVP) administration were present. They had a mild bleeding history, low levels of vWF-related activities, and a prolonged bleeding time. Low-resolution agarose gel electrophoresis showed a vWF with all size multimers in plasma and platelets. Higher-resolution agarose gels demonstrated that the main band was present, but the relative proportion of the satellite bands was markedly reduced. The smallest oligomer was not increased. After the infusion of DDAVP to the father, a transient increase in the relative proportion of the satellite bands was seen, as described in normal individuals. No difference in the structure of vWF was observed when blood was collected with proteinase inhibitors. The analysis of native subunits of vWF and their proteolytic derived fragments, after DDAVP administration, showed a temporary augmentation of the 176 kDa fragment, as seen in normal subjects, as well as an increase of the 189 kDa fragment. This finding had not been reported previously either in normal individuals or in patients with vWD.     

Acquired von Willebrand syndrome – report of 10 cases and review of the literature

Acquired von Willebrand syndrome (AvWS) is a rare bleeding disorder with clinical and laboratory features closely resembling hereditary von Willebrand disease (vWD), arising in previously haemostatically normal individuals. We present a retrospective review of 10 cases with AvWS diagnosed over 17 years. The severity of the bleeding tendency varied from mild to severe forms. Multimers electrophoresis showed that 8/10 patients had a normal pattern similar to type 1 vWD, 1/10 had a type 2A vWD pattern (with absence of high and intermediate molecular weight multimers) and 1/10 had a type 3 vWD pattern. An inhibitor screen was performed in 6/10 patients and autoantibodies against von Willebrand factor were found in only two cases. The underlying cause/associated conditions were identified in 8/10 patients. Treatment of the bleeding diathesis was successfully achieved with desmopressin or clotting factor concentrates. Resolution of underlying hypothyroidism (in two cases) and multiple myeloma (in one case) led to normalization of the coagulation parameters. The report on this cohort of 10 patients with AvWS illustrates the complexity of AvWS and its multifactorial aetiology. A brief review of the recent literature on AvWS is also presented, with emphasis on the current opinions in pathogenesis and treatment. Acquired von Willebrand syndrome (AvWS) is an acquired bleeding disorder, characterized by a phenotype similar to the inherited von Willebrand disease (vWD), with a prolonged bleeding time and low plasma levels of factor VIII - von Willebrand factor (vWF) measurements. It occurs in patients with no family history of vWD, who present with recent onset of bleeding symptoms. AvWS appears to be associated mainly with lymphoproliferative disorders, immunological conditions and neoplasia. AvWS is a rare condition and it is difficult to conduct prospective studies, therefore it is important to document the experience with such cases. The aim of this paper is first, to report 10 cases of AvWS identified at our Haemophilia Centre during the past 17 years. Second, to present a brief review of the recent literature on AvWS - outlining the salient features, associated disorders, mechanisms of acquisition and the available options of treatment.     

DDAVP shortens the prolonged bleeding times of patients with severe von Willebrand disease treated with cryoprecipitate. Evidence for a mechanism of action independent of released von Willebrand factor

After infusion of cryoprecipitate, the very prolonged bleeding time of patients with severe von Willebrand disease (vWD) is shortened but not always normalized in spite of normalization of plasma von Willebrand factor (vWF) levels. Therefore treatments that further improve primary hemostasis in severe vWD patients are needed. Since DDAVP shortens the bleeding time in a variety of bleeding disorders, we investigated in a double-blind, placebo-controlled crossover study the effects of the intravenous (IV) infusion of DDAVP (0.3 microgram/kg) on the bleeding times of 10 patients with severe vWD treated with cryoprecipitate. Their very prolonged bleeding times (greater than 30 minutes), partially corrected by the infusion of cryoprecipitate (14 +/- 2 minutes, mean +/- SEM), were further shortened by the administration of DDAVP (9 +/- 2 minutes, P less than .01) but not of saline (15 +/- 3 minutes, ns). Plasma vWF levels, raised from unmeasurable to normal values by cryoprecipitate, were not changed after DDAVP or saline. The defective deposition of platelets from eight patients onto human umbilical artery subendothelium was increased but not normalized by cryoprecipitate and was not significantly affected by DDAVP or saline. Therefore the infusion of DDAVP after cryoprecipitate may be of clinical benefit for management of bleeding episodes in severe vWD patients. Since severe vWD patients do not have releasable tissue stores of vWF, DDAVP must shorten their prolonged bleeding times independently of released vWF.     

Molecular diagosis of von Willebrand disease

von Willebrand disease (vWD) is one of the most common inherited human bleeding disorders, which is caused by quantitative or qualitative defects of von Willebrand factor (vWF). vWF is a highly multimerized glycoprotein that promotes platelet adhesion and aggregation at a high shear rate, while also acting as a carrier of coagulation factor VIII. vWD has been subdivided into three categories, which reflect their pathophysiology. Type 1 and type 3 vWD reflect partial or complete deficiency of vWF, whereas type 2 vWD reflects qualitative defect of vWF. The ability of vWF to interact with its platelet receptor and factor VIII, and the analysis of the multimeric composition of vWF are essential to identify patients with different vWD subtypes. The prevalence of different vWD subtypes was reported in the literature. In the past years, ninety-one patients with vWD were consulted in our institution. Of all the vWD patients, 56 (61.5%) belong to type 1, 26 (28.6%) type 2 and 9 (9.89%) type 3. The analysis of vWF gene was performed in some type 2 and type 3 vWD by denature gradient gel electrophoresis and sequencing. We have found six cases of point mutations of vWF gene, Ala737-->Glu, Gly 22-->Glu, Met37 Val and Ser71-->stop codon. Substitutions, are first reported in international database. We constructed an expression plasmid pSVA737EvWF containing full length of cDNA of vWF which included the Ala737 Glu substitution by site-direct mutagenesis. The structure of recombinant vWF within transfected COS-7 cells and the secretion of high-molecular-weight (HMW) multimers were similar to wild-type vWF. HMW forms of vWF multimers were absent in plasma but present in platelets. The mutation corresponds to the group II type 2A vWD characterized by normal secretion of all vWF multimers.     

Platelet-type von Willebrand's disease: characterization of a new bleeding disorder

An autosomally transmitted bleeding diathesis sharing some, but not all, features previously described in von Willebrand's disease (vWd) was studied in five patients representing three generations of a single family. Bleeding times in the upper normal range in conjunction with low-normal platelet counts, normal factor VIII coagulant activity and VIII-related antigen, decreased VIII-ristocetin cofactor activity, selective decrease of the higher molecule weight factor VIII/von Willebrand factor (VIII/vWF) multimers, and increased ristocetin- induced platelet agglutination at low ristocetin concentrations were characteristic. Binding of patient VIII/vWF to washed normal platelets was within normal limits, whereas binding of normal VIII/vWF to patient platelets was significantly increased (p less than 0.001 at 0.6 mg/ml ristocetin). This disorder accordingly appears to involve an intrinsic platelet abnormality affecting platelet-VIII/vWF interactions. It is proposed that the concept of vWD be broadened to include patients with this abnormality, which may appropriately be called "Platelet-type von Willebrand's disease."     

Impaired release of tissue plasminogen activator (t-PA) following DDAVP infusion in von Willebrand's disease with low platelet von Willebrand factor content.

Tissue plasminogen activator (t-PA) and von Willebrand factor (vWF) are both released by vascular endothelial cells after the infusion of DDAVP. Such release has not been observed in patients with severe von Willebrand's disease (vWD). In the present work we demonstrate that the degree of simultaneous DDAVP-induced release of t-PA and vWF, in patients with vWD, is strictly related to the platelet vWF content. Twelve patients with type I, and three patients with type III vWD were studied. The type I vWD group included three patients with reduced platelet vWF content (platelet-low) and nine patients with normal levels (platelet-normal). In all patients studied the plasma t-PA levels were within the normal range. No significant change in either t-PA or vWF was observed after DDAVP in the patients with undetectable levels of platelet vWF (type III vWD). A mild increase was found in those patients with type I platelet-low, while in type I platelet-normal vWD the response was similar to that observed in normal subjects. The release of the two molecules appeared, therefore, to be linked to platelet vWF content and the rates of increase in both t-PA and vWF were similar in each group of patients studied. Since platelets are regarded as a tissue compartment of vWF our findings seem to suggest that the presence of vWF and its release from endothelial cells is required for a normal concomitant release of t-PA. In contrast, post-DDAVP release of vWF seems to be independent from that of t-PA since it was normal in a patient with congenital deficiency of t-PA release.     

Heat-treated factor VIII/von Willebrand factor concentrate in platelet-type von Willebrand's disease

Cryoprecipitate has proved to correct the hemostatic defects in von Willebrand's disease (vWD) and platelet-type vWD. However, recent studies have revealed that transmission of the AIDS retrovirus (HIV) occurs through exposure to blood products including cryoprecipitate. Treatment with heat-treated factor VIII/von Willebrand factor (vWf) concentrates may have certain advantages over treatment with nonheated products, if these preparations are efficacious in these disorders. We found that a commercially available factor VIII/vWf concentrate, Haemate P, contained the high-molecular-weight multimers of vWf and had a ratio of ristocetin cofactor (RCof) to vWf antigen (vWf:Ag) close to unity. In addition, its capacity to directly induce aggregation of platelet-type vWD platelets in vitro was similar to that for cryoprecipitate. When infused into a patient with platelet-type vWD, Haemate P shortened the prolonged bleeding time and caused spontaneous platelet aggregation in vitro with a mild diminution of platelet count. These results indicate that some of the heat-treated factor VIII/vWf concentrates may provide a safer, yet still effective, treatment for platelet-type vWD.     

Patients with a prolonged bleeding time and normal aggregation tests may have storage pool deficiency: studies on one hundred six patients

One hundred six patients with storage pool deficiency (SPD) were studied with respect to platelet count, bleeding time, total platelet ATP and ADP, platelet serotonin, and in vitro aggregation. The diagnosis of SPD was made on basis of a prolonged bleeding time, a decreased total platelet ADP, and a diminished level of serotonin. Fifty-one patients from 34 unrelated families had congenital SPD, and 55 patients had acquired SPD. Congenital SPD was a common disorder in patients with a lifelong bleeding tendency and a prolonged bleeding time. The frequency in this group of patients was 18%, about one-half the frequency of von Willebrand's disease (vWd). Twenty-three percent of all patients had normal aggregation responses to ADP, epinephrine, and collagen; 33% had aggregation tracings typical for a secretion defect; and 44% had miscellaneous aggregation abnormalities. These findings indicate that SPD is common, heterogeneous, and not necessarily associated with in vitro aggregation abnormalities.     

Investigation of a case of subtype IIC von Willebrand disease: characterization of the variability of this subtype

A variant of von Willebrand disease (vWD) has been identified in a 19-year-old woman with a severe bleeding syndrome. She had a very prolonged bleeding time (over 20 min), 24 U/dl factor VIII coagulant activity (F.VIII:C), 16 U/dl von Willebrand factor antigen (vWF:Ag), no ristocetin cofactor activity, and an anodal mobility of vWF:Ag on crossed immunoelectrophoresis (CIE). vWF:Ag was markedly reduced in her platelet lysate. In plasma and platelets, SDS-agarose electrophoresis consistently demonstrated the absence of large multimers, a relatively increased concentration of the fastest-moving multimer, and gross abnormalities of the internal structure of each vWF multimeric unit. Five members from the maternal side of the family had a double vWF:Ag peak by CIE and a relative increase of the fastest-moving vWF multimer by SDS-agarose electrophoresis; no quantitative or qualitative vWF defects were found in the paternal side of the family. The pattern of the findings in the propositus and her family is similar to those of type IIC vWD. However, there are some unique characteristics suggesting phenotypic variability in this subtype, such as low level of platelet vWF:Ag and the absence of increase of vWF after DDAVP administration.