Genetic linkage of two intragenic restriction fragment length polymorphisms with von Willebrand''s disease type IIA. Evidence for a defect in the von Willebrand factor gene.

Restriction fragment length polymorphisms (RFLPs), using the enzymes Bgl II and Xba I in conjunction with human von Willebrand factor (vWF) cDNA probes, have been described previously. In the present study we demonstrate the localization of both genetic markers within the vWF gene. The RFLPs were used to study the segregation of alleles associated with von Willebrand's disease (vWD) type IIA in a comprehensive, affected family. Individuals of this family were tested for their bleeding time and their plasma was analyzed for vWF antigen concentration and vWF ristocetin-cofactor activity. Based on these data, the affected members were diagnosed as vWD type-IIA patients; this conclusion was confirmed by the analysis of the multimeric vWF pattern of some of the patients. It was demonstrated that both RFLPs are completely linked with the vWD type-IIA trait. From this finding, we conclude that the defect that causes the vWD type IIA is most likely due to a mutation in the vWF gene and not to a mutation in a gene involved in posttranslational processing of the vWF protein.     

vWD2N型诊断试验的新探索

目的血管性血友病(von Willebrand disease,vWD)分3型,各型具有不同的病理生理机制、临床特点、治疗方法,为了更好的治疗,需要明确其分型。vWF:FⅧ结合试验(vWF:FⅧ)可作为vWD2N型的确诊实验之一。方法对20例vWD患者进行改良的vWF:FⅧ结合试验,及各种vWD分型实验,对结合试验诊断为vWD2N型患者的血管性血友病因子(von Willebrand Factor,vWF)所有外显子及其侧翼序列进行基因序列分析,以此评价改良的结合实验对vWD2N型诊断的准确性。结果对20例vWD患者进行改良的vWF:FⅧ结合试验结果为FⅧ结合正常者10例,FⅧ结合减少者8例,FⅧ结合缺失者2例。对FⅧ结合缺失2例患者进行的vWF 52个外显子基因及其侧翼序列进行检测,分别发现基因突变E15 72648-72653insCCGTG杂合、E25 106026C>T(T1122M)杂合,故这两例患者可确诊为vWD2N型。结论本文中所建立的改良的vWF:FⅧ结合试验可以较好的确诊vWD2N型。     

血管性血友病四种指标实验检测意义的比较

目的探讨血管性血友病4种检测实验诊断方法的临床应用价值。方法使用vWF抗原水平检测(vWFAg)、vWF胶原结合分析实验(vWFCBA)、瑞斯托霉素辅因子活性测定(vWFRcof)、瑞斯托霉素诱导的血小板聚集试验(RIPA)4种方法同时对正常献血员、vWD患者及其他出血性疾病患者进行检测,比较其检测方法的优越性。结果4种检测血管性血友病的实验其结果在vWD患者组与正常献血员组和其他出血性疾病组比较P<001,差异均有统计学意义;正常献血员组与其他出血性疾病组比较P>005,差异无统计学意义。1型vWD患者组中4种检测方法相关性比较显示,vWFCBA与vWF∶Ag相关性最好(r=09610),其次为vWF∶Rcof与RIPA(r=09164),而vWF∶Ag与RIPA相关性最差(r=08132)。vWF∶CBA的变异系数(39%)最小,vWF∶Ag(41%)次之,而vWF∶Rcof和RIPA较高(分别为155%和173%)。4种检测方法与诊断的总符合率分别为vWF∶Ag857%,vWF∶Rcof762%,RIPA809%,vWF∶CBA952%。结论vWF∶CBA操作简便、重复性较好,在常规vWD的诊断分型中可替代vWF∶Rcof和RIPA。     

Acquired von Willebrand disease

Acquired von Willebrand disease (AvWD) is a relatively rare acquired bleeding disorder that usually occurs in elderly patients, in whom its recognition may be delayed. Patients usually present predominantly with mucocutaneous bleeding, with no previous history of bleeding abnormalities and no clinically meaningful family history. Various underlying diseases have been associated with AvWD, most commonly hematoproliferative disorders, including monoclonal gammopathies, lymphoproliferative disorders, and myeloproliferative disorders. The pathogenesis of AvWD remains incompletely understood but includes autoantibodies directed against the von Willebrand factor (vWF), leading to a more rapid clearance from the circulation or interference with its function, adsorption of vWF by tumor cells, and nonimmunologic mechanisms of destruction. Laboratory evaluation usually reveals a pattern of prolonged bleeding time and decreased levels of vWF antigen, ristocetin cofactor activity, and factor VIII coagulant activity consistent with a diagnosis of vWD. Acquired vWD is distinguished from the congenital form by age at presentation, absence of a personal and family history of bleeding disorders, and, often, presence of a hematoproliferative or autoimmune disorder. The severity of the bleeding varies considerably among patients. Therapeutic options include desmopressin and certain factor VIII concentrates that also contain vWF. Successful treatment of the associated illness can reverse the clinical and laboratory manifestations. Intravenous immunoglobulins have also shown some efficacy in the management of AvWD, especially cases associated with monoclonal gammopathies. Awareness of AvWD is essential for diagnosis and appropriate management.     

遗传性血管性血友病7例实验诊断和分子发病机制研究

目的:建立系统的血管性血友病(vWD)实验诊断和研究的方法,对7个遗传性vWD家系进行系列的实验诊断和分子发病机制研究。方法:自行建立瑞斯托霉素诱导的血小板凝集试验(RIPA)、血管性血友病因子(vWF)瑞斯托霉素辅因子(vWF:RCo)、vWF抗原(vWF:Ag)、vWF胶原结合试验(vWF:CB)和多聚体分析方法,对vWD患者及家系成员进行测定。采用PCR产物测序以鉴定vWF基因缺陷。采用定点突变、剪接位点分析、序列复杂性分析和核基质结合区评分等生物信息学方法,研究基因突变对蛋白功能的影响。结果:明确诊断vWD患者1型1例,2A型2例,2B型1例,2M型1例及3型2例,其中1型、2M型和2B型vWD为国内首次报道。鉴定到10个基因突变,其中6个为国际上首次发现。体外表达实验显示,R1374S突变引起细胞分泌下降;R1308C突变导致蛋白功能降低;C2327S突变影响多聚体形成。结论:本研究建立的方法和推荐的组合实验适合于绝大多数vWD患者的诊断和分型需要。R1374S、R1308C和C2327S突变分别导致患者出现1型、2B型和2A型vWD表型。插入、缺失和无义突变诱发无义介导的mRNA衰变(NMD),导致vWF合成减少,是本研究中3型患者的发病机制。     

Rapid formation of large molecular weight alpha-polymers in cross-linked fibrin induced by high factor XIII concentrations. Role of platelet factor XIII.

Among all patients with von Willebrand disease (vWD), alloantibodies to von Willebrand factor (vWF) have been described only in severe vWD (type III). The relationship between the development of alloantibodies and the nature of the genetic lesion in vWD is not known. In hemophilia B, large deletions within the factor IX gene appear to correlate with the occurrence of alloantibodies, whereas in hemophilia A no such correlation is apparent. We have studied 19 patients with severe recessive vWD (type III) and 19 with autosomal dominant vWD (type I) by Southern blotting with probes encompassing the full 9 kilobases (kb) of the vWF cDNA. Two apparently unrelated patients were shown to have large deletions within the vWF gene. Both patients had severe vWD (type III) and were the only patients among those studied that had inhibitory alloantibodies to vWF. The extent of deletion was similar in both patients, corresponding to at least the 3'-7.4 kb of the vWF cDNA. The deletion in each patient was estimated to exceed 110 kb. In addition, the localization of the vWF gene to chromosome 12 was confirmed, and a homologous sequence on chromosome 22 was identified.     

A practical approach to genetic testing for von Willebrand disease

von Willebrand disease (vWD) is the most commonly diagnosed congenital bleeding disorder. The laboratory diagnosis of type 2 variants and type 3 vWD is reasonably well defined, and characterization of the von Willebrand factor (vWF) gene has facilitated definition of their molecular basis. However, for type 1 vWD, the laboratory diagnosis poses a diagnostic dilemma, and knowledge of its molecular basis is evolving. Characterization of the vWF gene and refinement of genetic techniques have led to an evolving repertoire of genetic tests. Genetic testing is costly, and thus judicious use will be increasingly important for appropriate genetic-counseling of patients with vWD and their family members. This article provides a practical approach to utilization of genetic testing in vWD.     

一个重症vWD家系临床与基因分析

目的：研究重症血管性血友病（ｖＷＤ）患者家系成员临床表型特征，并分析血管性血友病因子（ｖＷＦ）基因缺陷的传递规律。方法：应用ｖＷＦ多聚体分析和ＥＬＩＳＡ法检测重症ｖＷＤ患者父母家系四代２６位成员临床表型。在此基础上针对ｖＷＦ基因内多个ＲＦＬＰ和ＶＮＴＲ位点，对所有家系成员进行缺陷基因遗传分析。结果：患者血浆ｖＷＦ∶Ａｇ＜２％，检测不到多聚体条带。基因分析表明两条ｖＷＦ等位基因分别来自父方和母方家系，且均有缺陷。部分家系成员携有一条缺陷基因，ｖＷＦ水平正常或有轻度下降，多聚体图谱正常。结论：①先证者可能为复合杂合子型的３型ｖＷＤ患者，携带者的缺陷基因可被正常基因弥补。②应用ｖＷＦ基因多种多态性标志行ＤＮＡ分析对重症ｖＷＤ家系遗传咨询有实用意义。     

Subunit composition of plasma von Willebrand factor. Cleavage is present in normal individuals, increased in IIA and IIB von Willebrand disease, but minimal in variants with aberrant structure of individual oligomers (types IIC, IID, and IIE).

We have evaluated the subunit composition of plasma von Willebrand factor (vWF) and found evidence that cleavage is present in normal individuals, increased in IIA and IIB von Willebrand disease (vWD), but decreased or absent in variants with aberrant structure of individual oligomers. vWF was rapidly purified from plasma on an analytical scale by monoclonal antibody immunoaffinity chromatography in the presence of protease inhibitors. After reduction and electrophoresis in 5% polyacrylamide gels containing sodium dodecyl sulfate, fragments of 189, 176, and 140 kD, as well as the predominant 225-kD subunit, were identified in plasma vWF from 25 normal individuals. The vWF polypeptides were detected by immunoblotting with a mixture of 55 anti-vWF monoclonal antibodies followed by 125I-rabbit anti-mouse antibody and autoradiography. In five individuals with type IIA and five individuals with type IIB vWD, the proportions of 176 and 140-kD fragments were increased relative to the intact 225-kD subunit, as determined by excising each band and quantitating incorporated radioactivity. In contrast, these fragments were either not detectable or were present in only trace amounts in variants with abnormal structure of individual oligomers (types IIC and IID, and a new variant, type IIE vWD). The results reported here provide evidence that absence of large vWF multimers in these two groups of variants results from different mechanisms. In addition, they demonstrate that partial cleavage of the plasma vWF subunit is a normal event.     

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.     

von Willebrand factor and animal models: contributions to gene therapy, thrombotic thrombocytopenic purpura, and coronary artery thrombosis

Use of animal models of von Willebrand factor (vWF) deficiency, both inherited and induced, continues to advance the knowledge of vWF-related diseases. Three examples are reviewed in this article--von Willebrand's disease (vWD), thrombotic thrombocytopenic purpura, and coronary artery thrombosis. The success of gene transfer by liver and bone marrow transplantation in porcine vWD and canine hemophilia A, with a change in phenotype that establishes improved hemostasis, portends imminent testing of gene therapy in these models. With use of recombinant technology, the phenotype of hemophilia B fibroblasts has been transformed to normal, as evidenced by secretion of the normal hemostatically active protein. This result is a prelude to implantation in hemophilic animals. Thrombotic thrombocytopenic purpura is characterized by qualitative and quantitative alterations in vWF. A new animal model induced by the venom factor botrocetin, a cofactor of vWF, closely mimics the human syndrome. A proposed pathophysiologic mechanism for thrombotic thrombocytopenic purpura is outlined. The third contribution is recognition that occlusive coronary thrombosis is a vWF-dependent condition. Without vWF, as in porcine vWD or normal pigs treated with a monoclonal anti-vWF antibody, occlusive thrombi do not develop, even with luminal stenosis. The thrombogenicity of coronary atheromas, including those with fissures of the fibrous cap, is also vWF-dependent.     

Epitope mapping of the von Willebrand factor subunit distinguishes fragments present in normal and type IIA von Willebrand disease from those generated by plasmin.

A small but consistent proportion of the von Willebrand factor (vWF) in normal plasma is composed of 189, 176, and 140 kD fragments cleaved from the 225 kD subunit. A monoclonal antibody map of vWF, based on the reactivity of individual antibodies with cyanogen bromide and tryptic fragments of known carboxy and/or amino termini, showed that in normal and IIA von Willebrand disease (vWD) plasmas the 140 kD fragment was derived from the amino-terminal region, whereas the 176 kD fragment was derived from the carboxy-terminal region of the subunit. In type IIA vWD, however, the fragments comprised a greater proportion of circulating vWF. In contrast, plasmin cleaved a 176 kD fragment from the amino terminus and a 145 kD fragment from the carboxy terminus of the subunit. Species similar to these plasmin-cleaved fragments were demonstrated in plasmas from four patients treated with fibrinolytic agents, but not in IIA vWD.     

Preclinical evaluation of recombinant von Willebrand factor in a canine model of von Willebrand disease

Dutch Kooiker dogs with hereditary von Willebrand disease (vWD) have undetectable levels of von Willebrand factor (vWF), resulting in spontaneous hemorrhage of mucosal surfaces similar to the clinical picture of vWD in humans. We used this canine model of vWD to study the in vivo effects of a new recombinant von Willebrand factor (rvWF) preparation that contained all species of vWF multimers compared with an rvWF fraction containing only low molecular weight multimers (LMW-rvWF) and with a plasma-derived factor VIII/vWF concentrate (pdvWF). Administration of rvWF in these vWF-deficient dogs resulted in a vWF:Ag half-life of 21.6 hours in one dog and 22.1 hours in a second dog. Administration of pdvWF resulted in a half-life for vWF:Ag of 7.7 hours, and LMW-rvWF, 9 hours. The in vivo recovery of vWF:Ag after administration of rvWF was 59, 64 and 70% in three dogs, respectively; 33% after pdvWF, and 92% after LMW-rvWF. The in vivo recovery of ristocetin cofactor (RCoF) was 78, 110 and 120% for rvWF, and 25% for pdvWF. Both rvWF and pdvWF caused increases in factor VIII. Although no effect was seen on bleeding time at the dosages used, the rate of blood flow from cuticle wounds was reduced after a single bolus administration of rvWF. The rvWF was able to control a severe nose bleed in one dog.     

Hemostasis in patients with severe von Willebrand disease improves after normal platelet transfusion and normalizes with further correction of the plasma defect

BACKGROUND: A defective hemostatic effect of plasma concentrate infusion in patients with severe von Willebrand disease (vWD) has been ascribed to the absence of platelet von Willebrand factor (vWF) STUDY DESIGN AND METHODS: The role of platelet vWF in hemostasis of severe vWD was investigated. A plateletpheresis unit (4-5 × 10(11) platelets) from a normal compatible donor was transfused before any cryoprecipitate infusion to three type 3 vWD patients and to one patient with severe type 1 vWD with low levels of platelet vWF who required replacement therapy for bleeding episodes. Autologous platelets were transfused to one of the patients with type 3 vWD. RESULTS: Partial corrections of bleeding times (14-17 min vs. baseline>30 min) were observed in all patients after the transfusion of normal platelets. During cryoprecipitate infusion, bleeding times were normalized (<6 min), and bleeding episodes stopped when plasma levels of vWF activity ranged from 14 to 18 U per dL. Platelet interactions with the subendothelium increased in parallel with the correction of bleeding times. These results indicate that if approximately 20 percent of the total number of platelets have normal vWF antigen and if plasma vWF levels are at least 14 U per dL, then bleeding times will normalize and mucosal hemorrhages will stop. Transfusion of autologous platelets in one patient with type 3 vWD did not modify bleeding times or platelet adhesion on the subendothelium. CONCLUSION: The hemostatic effect of normal platelets in type 3 vWD seems to be related to the platelet vWF in the transfused platelets.     

一例2A型血管性血友病的基因突变分析

为了对1例2A型血管性血友病（vWD）患者进行基因分析,鉴定导致vWD的基因突变位点,采集患者外周静脉血,应用BT、vWF：Ag、FⅧ：C、瑞斯托霉素诱导血小板聚集（RIPA）和多聚体分析等方法对患者进行表型诊断,PCR法扩增患者vWF基因全部52个外显子,并进行测序。结果表明：该患者BT延长,vWF：Ag、FⅧ：C、RIPA均降低,多聚体分析显示血浆中缺乏大、中分子vWF多聚体。基因分析发现,患者vWF基因28号外显子存在一杂合性错义突变CA738G（L1580V）。结论：患者存在杂合性错义突变（C4738G）,而错义突变影响了vWF多聚体的形成,因而错义突变是患者发病的分子机制。     

2A型血管性血友病vWF基因Ala737→Glu的突变

目的阐明２Ａ型血管性血友病（ｖＷＤ）临床表现型与基因型的相关性。方法研究来自同一家系的２例患者,他们具有初期止血障碍的出血特点,ｖＷＦ∶Ａｇ和ＦⅧ∶ＣＡｇ减少,瑞斯托霉素诱导的血小板聚集明显降低,大、中多聚物分子消失,临床表型符合２Ａ型血管性血友病。用聚合酶链反应方法扩增患者的ｖＷＦ基因的２８号外显子,并用特异性内切酶的方法获得真基因,变性梯度凝胶电泳（ＤＧＧＥ）筛选突变基因,对电泳行为异常的片段进行测序。结果该２Ａ型ｖＷＤ家系ｖＷＦ基因的４３７０～４５９０区域ＤＧＧＥ有明显减慢的条带。ＤＮＡ序列测定,表明在ｖＷＦ基因４４９９位Ｃ→Ａ致ｖＷＦ蛋白Ａ２区域Ａｌａ７３７→Ｇｌｕ。结论该突变有助于研究ｖＷＦ蛋白功能域的精细功能及ｖＷＤ表型与基因型的相关性。     

血管性血友病因子的研究进展

血管性血友病因子（von Willebrand factor,vWF）是由血管内皮细胞和骨髓巨核细胞合成的一种多结构域、多功能糖蛋白,在1期和2期止血中发挥重要作用。vWF缺陷将导致血管性血友病（vWD）等出血性疾病,而在静脉栓塞、血栓性血小板减少性紫癜（TTP）、中风等血栓性疾病中,其活性水平可明显增高。血浆vWF水平与多种影响因素有关。随着近年来对vWF的结构、功能以及活性水平调控机制的了解,人们对于出血与血栓性疾病的病理生理,诊断和治疗有了全面的认识。本文将就血浆vWF活性水平调控与上述疾病关系的研究进展作一综述。     

Platelet glycoprotein Ibalpha forms catch bonds with human WT vWF but not with type 2B von Willebrand disease vWF

Arterial blood flow enhances glycoprotein Ibalpha (GPIbalpha) binding to vWF, which initiates platelet adhesion to injured vessels. Mutations in the vWF A1 domain that cause type 2B von Willebrand disease (vWD) reduce the flow requirement for adhesion. Here we show that increasing force on GPIbalpha/vWF bonds first prolonged ("catch") and then shortened ("slip") bond lifetimes. Two type 2B vWD A1 domain mutants, R1306Q and R1450E, converted catch bonds to slip bonds by prolonging bond lifetimes at low forces. Steered molecular dynamics simulations of GPIbalpha dissociating from the A1 domain suggested mechanisms for catch bonds and their conversion by the A1 domain mutations. Catch bonds caused platelets and GPIbalpha-coated microspheres to roll more slowly on WT vWF and WT A1 domains as flow increased from suboptimal levels, explaining flow-enhanced rolling. Longer bond lifetimes at low forces eliminated the flow requirement for rolling on R1306Q and R1450E mutant A1 domains. Flowing platelets agglutinated with microspheres bearing R1306Q or R1450E mutant A1 domains, but not WT A1 domains. Therefore, catch bonds may prevent vWF multimers from agglutinating platelets. A disintegrin and metalloproteinase with a thrombospondin type 1 motif-13 (ADAMTS-13) reduced platelet agglutination with microspheres bearing a tridomain A1A2A3 vWF fragment with the R1450E mutation in a shear-dependent manner. We conclude that in type 2B vWD, prolonged lifetimes of vWF bonds with GPIbalpha on circulating platelets may allow ADAMTS-13 to deplete large vWF multimers, causing bleeding.     

Molecular basis of von Willebrand disease type IIB. Candidate mutations cluster in one disulfide loop between proposed platelet glycoprotein Ib binding sequences.

Many variants of von Willebrand disease (vWD) with qualitatively abnormal von Willebrand factor (vWF) are recognized. In vWD type IIB, the abnormal protein displays enhanced affinity for a platelet vWF receptor, the glycoprotein Ib-IX complex. 14 patients from 7 unrelated families with vWD type IIB were studied to determine the molecular basis for this phenotype. Specific oligonucleotide primers were used to amplify portions of vWF exon 28 encoding a domain that interacts with the platelet glycoprotein Ib-IX complex. Candidate missense mutations were identified for all 14 patients by DNA sequencing, allele specific oligonucleotide hybridization, and restriction endonuclease digestion. These sequence changes occur in an 11 amino acid segment within a single disulfide loop bounded by Cys(509) and Cys(695). All of these sequence changes are C----T transitions within CG dinucleotides. Six patients from two unrelated families were heterozygous for the encoded sequence Arg(543)----Trp. Seven patients from four unrelated families were heterozygous for the encoded sequence Arg(545)----Cys; this sequence change appears to have occurred independently three times, once as a new spontaneous mutation. One patient with apparently sporadic vWD type IIB was heterozygous for the encoded sequence Val(553)----Met, and this appears to be a new mutation. None of these sequence changes was found in 100 normal alleles. These findings suggest that vWD type IIB may be caused by relatively few distinct mutations, that these mutations may cluster within a specific region of one disulfide loop in vWF domain A1, and that this region can modulate the affinity of vWF for the platelet glycoprotein Ib-IX complex.