一例2N型遗传性血管性血友病家系的表型诊断和基因型分析

目的：探讨1个遗传性血管性血友病（von Willebrand disease,vWD）2N型家系的表型诊断和基因型分析结果,明确患者的发病机制。方法：对该家系的先证者和家系成员进行出血时间、活化部分凝血活酶时间、瑞斯托霉素诱导的血小板聚集（ristocetin induced platelet aggregation,RIPA）试验、血管性血友病因子（von Willebrand factor,vWF）瑞斯托霉素辅因子、vWF抗原、vWF活性测定、vWF胶原结合试验、凝血因子Ⅷ（coagulation factor Ⅷ,FⅧ）活性、vWF与FⅧ结合试验检测,并作出表型诊断。提取先证者的外周血基因组DNA,用PCR法扩增VWF基因和F8基因的所有外显子及侧翼序列,通过直接测序分析VWF基因和F8基因变异。结果：vWD家系先证者的活化部分凝血活酶时间和出血时间明显延长,血浆瑞RIPA试验、vWF瑞斯托霉素辅因子、vWF抗原、vWF活性和vWF胶原结合试验检测结果均正常,FⅧ活性下降,vWF与FⅧ的结合能力降低。对先证者进行基因测序,发现其VWF基因19号外显子存在c.2446C>T（p.Arg816Trp）错义突变,其儿子在该位点为杂合突变,而先证者及家系成员的F8基因未发现突变。结论：c.2446C>T（p.Arg816Trp）错义突变是导致该家系先证者发生2N型遗传性vWD的原因。     

3型血管性血友病的基因突变与临床研究

目的：研究３型血管性血友病（ｖＷＤ）的分子病理机制。方法：应用聚合酶链反应（ＰＣＲ）结合变性梯度凝胶电泳（ＤＧＧＥ）筛选了３型ｖＷＤ患者ｖｏｎＷｉｌｅｂｒａｎｄ因子（ｖＷＦ）基因编码区的基因突变，对ＰＣＲ－ＤＧＧＥ行为发生改变的片段直接进行ＤＮＡ序列分析。结果：检测到１例基因突变，在ｖＷＦ基因外显子３第２１２号核苷酸，发生了Ｃ→Ａ的替换，使Ｓｅｒ７１突变为终止密码子。该突变创造了ＸｂａⅠ酶切位点，消除了原有的ＴａｑⅠ位点。结论：ＰＣＲ－ＤＧＧＥ和酶切分析均证实，患者为该突变的纯合子，其父母则均为该突变的携带者。     

Point mutation in a leucine-rich repeat of platelet glycoprotein Ib alpha resulting in the Bernard-Soulier syndrome.

Leucine-rich repeats are a conserved structural motif, of yet undefined significance, found in a group of proteins from different species. Among these are the four components of the human platelet glycoprotein Ib-IX-V complex, a membrane receptor that performs an essential role in the thrombogenic function of platelets by interacting with the adhesive protein, von Willebrand factor. We have found that a single amino acid substitution (Ala156-->Val) within one of the six leucine-rich repeats in the alpha-subunit of glycoprotein Ib results in a variant form of the congenital bleeding disorder, Bernard-Soulier syndrome, characterized by giant dysfunctional platelets. Genetic studies of the propositus and his family members were complemented by immunological and functional analysis of expressed recombinant GP Ib alpha fragments to demonstrate that the observed mutation is the cause of defective von Willebrand factor binding. These studies define the molecular basis of the Bernard-Soulier syndrome within this family and demonstrate that structural integrity of a leucine-rich repeat is necessary for normal function of the glycoprotein Ib-IX-V receptor complex and, possibly, for normal platelet morphology.     

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.     

Type 2M von Willebrand disease variant characterized by abnormal von willebrand factor multimerization

We describe a von Willebrand disease (VWD) variant characterized by low plasma and platelet von Willebrand factor (VWF), impaired ristocetin-induced VWF binding to platelet glycoprotein Ib (GPIb), and abnormal VWF multimer pattern not associated with the absence of large forms. A C-to-T transition at nucleotide 4120 in exon 28 of the VWF gene was found; this mutation introduces a cysteine at the codon for Arg 611 of mature VWF. In addition to the decreased factor VIII (FVIII) and VWF levels, ristocetin-induced platelet aggregation (RIPA) was almost absent, and VWF ristocetin cofactor activity (VWF:RCo) was significantly more decreased than VWF antigen. The patients (mother and son) also showed a defect in VWF collagen-binding activity. Plasma VWF multimers were decreased, with no limit in the size of large forms, and the normal discontinuous multimer organization was replaced by a diffuse smear, especially detectable in the large forms. This picture was emphasized by 1-deamino-8-D -arginine vasopressin (DDAVP) infusion, so that the abnormal VWF multimers appeared to have a molecular weight higher than those present in, or released by, human umbilical vein endothelial cells. DDAVP also increased FVIII and VWF levels but did not normalize the GPIb-dependent VWF functions expressed as RIPA and VWF:RCo. We include this variant in type 2M VWD, focusing on the abnormality in GPIb-dependent VWF function. We advance that this defect depends on the mutation in the GPIb binding domain of VWF rather than the abnormal VWF multimer pattern.     

A novel mutation in the glutaryl‐CoA dehydrogenase gene (GCDH) in an Iranian patient affected with Glutaric acidemia type 1

Our findings revealed the mutation c.536T>C (p. Leu179Pro) in GCDH gene although has not been reported so far, but the in‐silico analysis and clinical symptoms of the patient indicated that the mutation is pathogenic full stop. Also, it can be diagnosed and prevented in families affected by the disease.     

Laboratory diagnosis of von Willebrand disease

Von Willebrand disease is the most-common inherited bleeding disorder, including both quantitative (types 1 and 3) and qualitative (type 2) defects of von Willebrand factor. Among patients with suspected von Willebrand disease, the laboratory diagnosis requires three levels of testing: screening tests, specific assays for von Willebrand factor to establish the diagnosis, and discriminating tests to allow accurate characterization of the numerous types and subtypes of the disease. Because of their poor sensitivity, normal screening tests do not exclude the diagnosis. In most cases, specific measurements of von Willebrand factor antigen, von Willebrand factor ristocetin cofactor activity, and factor VIII levels in plasma allow differentiation of quantitative (proportionately decreased levels) and qualitative (discrepant levels) deficiencies of von Willebrand factor. Among the latter, a decreased von Willebrand factor ristocetin cofactor activity/von Willebrand factor antigen ratio is in favor of the three subtypes (2A, 2M, and 2B) defined by an abnormal interaction between von Willebrand factor and platelet glycoprotein Ib, whereas a decreased factor VIII/von Willebrand factor antigen ratio suggests subtype 2N, defined by a defective binding of von Willebrand factor to factor VIII. Several discriminating tests are available to definitively characterize each subtype. Moreover, for all variants, the link between phenotype and genotype is established using DNA analysis. In all cases, the precise characterization of type and subtype of von Willebrand disease remains essential for the choice of optimal therapeutic monitoring of each patient. Presented at the Joint Meeting of the World Health Organization and the International Society for Thrombosis and Hemostasis “Impact, Prevention and Control of von Willebrand’s disease” London, October 12–14, 1998     

Detection of novel mutations in the gyrA gene of Staphylococcus aureus by nonradioisotopic single-strand conformation polymorphism analysis and direct DNA sequencing.

A total of 36 clinical isolates of Staphylococcus aureus (29 fluoroquinolone-resistant strains and 7 fluoroquinolone-susceptible strains) were studied for the presence of point mutations in the gyrA gene by nonradioisotopic single-strand conformation polymorphism (Non-RI SSCP) analysis with silver stain. Direct DNA sequencing analysis of the PCR-amplified DNA fragments confirmed the results obtained by Non-RI SSCP analysis and revealed that fluoroquinolone resistance is closely associated with six types of mutations in the gyrA gene, of which three types of mutations were newly identified: (i) Ser-84-->Leu and Glu-88-->Gly, (ii) Ser-84-->Leu and Glu-88-->Lys, and (iii) Glu-88-->Gly. Furthermore, the novel ATT-->ATC mutation at codon 86 (silent mutation) was seen in only one fluoroquinolone-susceptible strain. All seven mutational types were separated from the wild type in a single electrophoretic step within 3 h after PCR amplification. Thus, we conclude that this new technique is a rapid, simple, and useful screening method for the genotyping of gyrA mutations associated with fluoroquinolone resistance.     

Type IIB von Willebrand disease: a paradox explains how von Willebrand factor works

Summary.  Type IIB is a variant form of von Willebrand disease in which a structural abnormality of von Willebrand factor (VWF) causes enhanced binding to the platelet glycoprotein Ib receptor. As a consequence of this functional alteration, there is a decrease in the concentration of the largest VWF multimers in plasma, and the platelet count may be episodically decreased as a consequence of microaggregation. The net result is an apparent paradox, since the presence of a hyperfunctional adhesive molecule in blood causes a bleeding tendency. Here I recall how my colleagues and I managed to understand what goes on in these patients.     

ADAMTS13 and microvascular thrombosis

Interaction between platelet and von Willebrand factor, a circulating adhesive glycoprotein, is essential for hemostasis under the high shear environments of arterioles and capillaries. If unregulated, this interaction may lead to unwarranted platelet thrombosis. ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 motif, number 13), a plasma zinc metalloprotease synthesized primarily in the stellate cells of the liver, cleaves shear stress-activated von Willebrand factor, thereby preventing the occurrence of von Willebrand factor–platelet interaction in the circulation. A profound deficiency of ADAMTS13, due to genetic mutations or autoimmune inhibition, results in intravascular von Willebrand factor platelet aggregation and widespread microvascular thrombosis characteristic of thrombotic thrombocytopenic purpura. Cloning of ADAMTS13 and structure–function analyses of the enzyme are leading to exciting advances in the diagnosis and therapy of this hitherto mysterious disease.     

ADAMTS13 and microvascular thrombosis

Interaction between platelet and von Willebrand factor, a circulating adhesive glycoprotein, is essential for hemostasis under the high shear environments of arterioles and capillaries. If unregulated, this interaction may lead to unwarranted platelet thrombosis. ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 motif, number 13), a plasma zinc metalloprotease synthesized primarily in the stellate cells of the liver, cleaves shear stress-activated von Willebrand factor, thereby preventing the occurrence of von Willebrand factor-platelet interaction in the circulation. A profound deficiency of ADAMTS13, due to genetic mutations or autoimmune inhibition, results in intravascular von Willebrand factor platelet aggregation and widespread microvascular thrombosis characteristic of thrombotic thrombocytopenic purpura. Cloning of ADAMTS13 and structure-function analyses of the enzyme are leading to exciting advances in the diagnosis and therapy of this hitherto mysterious disease.     

Familial hypertrophic cardiomyopathy. Microsatellite haplotyping and identification of a hot spot for mutations in the beta-myosin heavy chain gene.

Familial hypertrophic cardiomyopathy (FHC) is a clinically and genetically heterogeneous disease. The first identified disease gene, located on chromosome 14q11-q12, encodes the beta-myosin heavy chain. We have performed linkage analysis of two French FHC pedigrees, 720 and 730, with two microsatellite markers located in the beta-myosin heavy chain gene (MYO I and MYO II) and with four highly informative markers, recently mapped to chromosome 14q11-q12. Significant linkage was found with MYO I and MYO II in pedigree 720, but results were not conclusive for pedigree 730. Haplotype analysis of the six markers allowed identification of affected individuals and of some unaffected subjects carrying the disease gene. Two novel missense mutations were identified in exon 13 by direct sequencing, 403Arg-->Leu and 403Arg-->Trp in families 720 and 730, respectively. The 403Arg-->Leu mutation was associated with incomplete penetrance, a high incidence of sudden deaths and severe cardiac events, whereas the consequences of the 403Arg-->Trp mutation appeared less severe. Haplotyping of polymorphic markers in close linkage to the beta-myosin heavy chain gene can, thus, provide rapid analysis of non informative pedigrees and rapid detection of carrier status. Our results also indicate that codon 403 of the beta-myosin heavy chain gene is a hot spot for mutations causing FHC.     

A new L1446P mutation is responsible for impaired von Willebrand factor synthesis, structure, and function

We report on a new mutation (4337T-->C) in exon 28 of the von Willebrand factor (VWF) gene, resulting in a substitution of L with P at residue 1446 (L1446P) of pre-pro-VWF. The defect is transmitted as a dominant trait and induces a reduced VWF synthesis, an abnormal VWF multimer pattern and a deficient VWF-platelet glycoprotein Ib interaction. The proband had low plasma and platelet VWF antigen levels, a reduced VWF collagen-binding capacity, and a disproportionately low VWF ristocetin cofactor activity, associated with the absence of ristocetin-induced platelet aggregation. Multimer analysis showed that the smaller multimers were slightly low, whereas the larger ones were significantly reduced or absent, with a clear cutoff between the two patterns. Similar hemostatic findings were observed in the proband's sister and nephew. Desmopressin administration restored VWF levels to near normal, but this was not so for VWF ristocetin cofactor activity or ristocetin-induced platelet aggregation. VWF multimers improved after desmopressin, moreover, with the larger forms restored and the smaller ones still relatively more represented. Recombinant P1446 VWF synthesis was reduced at heterozygous level, and its multimer pattern was similar to that observed in plasma VWF. These findings confirm the role of L1446P mutation in determining the von Willebrand disease (VWD) phenotype observed in our patients. Given the lack of large and intermediate VWF multimers, and the fact that the VWF-platelet interaction defect appears to be partially independent of multimer pattern, the VWD associated with L1446P mutation may belong to the type 2A/2M VWD variant.     

Polyphosphate binds to human von Willebrand factor in vivo and modulates its interaction with glycoprotein Ib

Summary. Background: Polyphosphate, a phosphate polymer released by activated platelets, has recently been described as a potent modulator of blood coagulation and fibrinolysis. In blood plasma, polyphosphate binds to and alters the biological functions of factor XII, fibrin(ogen), thrombin and factor VII activating protease. Objectives: The aim of the present study is to investigate whether polyphosphate also binds to von Willebrand factor (VWF) and alters some of its activities. Methods/Results: When studying patients with type 1 von Willebrand disease (VWD) and their healthy relatives, we discovered a significant correlation between von Willebrand factor (VWF) and platelet polyphosphate levels. We have also found polyphosphate in preparations of VWF isolated from normal platelets and plasma. Surface plasmon resonance and electrophoretic mobility assays indicated that polyphosphate interacts with VWF in a dose‐ and time‐dependent manner. Treatment of normal plasma with active exopolyphosphatase decreased the VWF ristocetin cofactor (VWF:RCo) activity, a functional measure of VWF binding to platelet glycoprotein receptor Ib. VWF collagen binding and multimerization were unaltered after polyphosphate depletion. Moreover, addition of polyphosphate increased the deficient VWF:RCo activity presented by plasma from patients with type 1 VWD. Conclusions: Our results reveal that a new role is played by polyphosphate in hemostasis by its interaction with VWF, and suggest that this polymer may be effective in the treatment of some types of VWD.     

von Willebrand factor mutation promotes thrombocytopathy by inhibiting integrin αIIbβ3

von Willebrand disease type 2B (vWD-type 2B) is characterized by gain-of-function mutations in von Willebrand factor (vWF) that enhance its binding to the glycoprotein Ib-IX-V complex on platelets. Patients with vWD-type 2B have a bleeding tendency that is linked to loss of vWF multimers and/or thrombocytopenia. In this study, we uncovered evidence that platelet dysfunction is a third possible mechanism for bleeding tendency. We found that platelet aggregation, secretion, and spreading were diminished due to inhibition of integrin αIIbβ3 in platelets from mice expressing a vWD-type 2B–associated vWF (vWF/p.V1316M), platelets from a patient with the same mutation, and control platelets pretreated with recombinant vWF/p.V1316M. Impaired platelet function coincided with reduced thrombus growth. Further, αIIbβ3 activation and activation of the small GTPase Rap1 were impaired by vWF/p.V1316M following exposure to platelet agonists (thrombin, ADP, or convulxin). Conversely, thrombin- or ADP-induced Ca²⁺ store release, which is required for αIIbβ3 activation, was normal, indicating that vWF/p.V1316M acts downstream of Ca²⁺ release and upstream of Rap1. We found normal Syk phosphorylation and PLCγ2 activation following collagen receptor signaling, further implying that vWF/p.V1316M acts directly on or downstream of Ca²⁺ release. These data indicate that the vWD-type 2B mutation p.V1316M is associated with severe thrombocytopathy, which likely contributes to the bleeding tendency in vWD-type 2B.     

Interaction of Platelet Membrane Receptors with von Willebrand Factor, Ristocetin, and the Fc Region of Immunoglobulin G

The agglutination of human platelets by ristocetin and von Willebrand factor was inhibited by aggregated immunoglobulin (Ig)G and by Fc fragments of IgG, but not by Fab, F(ab')(2) or pFc fragments of IgG. Because this inhibition occurred with formalin-fixed platelets as well as with normal platelets, a generalized aggregation of fluid membrane components by Fc fragments was not responsible for this inhibition of ristocetin and von Willebrand factor-induced agglutination. Reciprocal inhibition of platelet Fc receptors was produced by prior incubation of platelets with von Willebrand factor and ristocetin. Sucrose density gradient ultracentrifugation studies demonstrated that aggregated IgG did not form fluid-phase complexes with von Willebrand factor and ristocetin. Furthermore, passage of von Willebrand factor and ristocetin through a column of immobilized heat-aggregated IgG did not alter platelet agglutinating activity which indicates that aggregated IgG did not inactivate von Willebrand factor or ristocetin. Thus, it was likely that the IgG-mediated interference with platelet agglutination by ristocetin and von Willebrand factor did not occur in the fluid phase but at the platelet surface. These studies suggest that the platelet membrane Fc receptor may be either a part of, or sterically related to, the membrane glycoprotein I complex that interacts with von Willebrand factor, and that occupation of one of these surface components blocks the availability of the other.     

Identifying type Vicenza von Willebrand disease

Increased clearance of von Willebrand factor (VWF) is one of the main features of type Vicenza von Willebrand disease (VWD), a variant with plasma and platelet VWF level discrepancies and unusually large VWF multimers. Diagnosing type Vicenza VWD may not be easy, due to its heterogeneous phenotype. Here we describe the criteria we adopted to identify type Vicenza in a large group of VWD patients. Emphasizing the contribution of platelet VWF by comparison with plasma values, a first step involved selecting the candidate Vicenza patients on the basis of low or very low plasma VWF and a normal platelet VWF content. After excluding type 2A and 2B VWD patients, who may have normal platelet VWF, 18 candidates were found to meet our selection criteria. Genetic analysis revealed that 15 patients (from 5 unrelated families) were type Vicenza VWD and that all carried both G2220A and G3614A type Vicenza mutations barring one, who only had the G3614A mutation. All patients had a reduced VWF survival, and all but the patient with the G3614A mutation alone had ultralarge VWF multimers. Thus, low-plasma VWF associated with a normal platelet VWF content may be a first useful indicator for identifying type Vicenza VWD patients.     

中国人遗传性高铁血红蛋白血症NADH—细胞色素b5还原酶基因L …

目的：鉴定导致中国人遗传性高铁血红蛋白血症（ＲＣＭ）的ＮＡＤＨ－细胞色素ｂ５还原酶（ｂ５Ｒ）基因突变类型，探讨ＲＣＭ发病的分子基础。方法：逆转录－聚合酶链反应产物直接测序和ｃＤＮＡ克隆测定分析先证者的ｂ５Ｒ编码基因，限制性酶切分析其基因组ＤＮＡ。结果；发现一例ＲＣＭ患者ｂ５Ｒ基因第７２密码子存在新的错义突变（ＣＴＣ→ＣＣＣ）。结论：该突变导致ｂ５Ｒ蛋白第７２位亮氨酸被脯氨酸替换（Ｌ７２Ｐ）是该先证     

Update on the pathophysiology and classification of von Willebrand disease: a report of the Subcommittee on von Willebrand Factor

von Willebrand disease (VWD) is a bleeding disorder caused by inherited defects in the concentration, structure, or function of von Willebrand factor (VWF). VWD is classified into three primary categories. Type 1 includes partial quantitative deficiency, type 2 includes qualitative defects, and type 3 includes virtually complete deficiency of VWF. VWD type 2 is divided into four secondary categories. Type 2A includes variants with decreased platelet adhesion caused by selective deficiency of high-molecular-weight VWF multimers. Type 2B includes variants with increased affinity for platelet glycoprotein Ib. Type 2M includes variants with markedly defective platelet adhesion despite a relatively normal size distribution of VWF multimers. Type 2N includes variants with markedly decreased affinity for factor VIII. These six categories of VWD correlate with important clinical features and therapeutic requirements. Some VWF gene mutations, alone or in combination, have complex effects and give rise to mixed VWD phenotypes. Certain VWD types, especially type 1 and type 2A, encompass several pathophysiologic mechanisms that sometimes can be distinguished by appropriate laboratory studies. The clinical significance of this heterogeneity is under investigation, which may support further subdivision of VWD type 1 or type 2A in the future.