Recessively inherited coagulation disorders

The obstetric and gynaecological management of women with inherited bleeding disorders - review with guidelines produced by a taskforce of UK Haemophilia Centre Doctors' Organization

The gynaecological and obstetric management of women with inherited coagulation disorders requires close collaboration between obstetrician/gynaecologists and haematologists. Ideally these women should be managed in a joint disciplinary clinic where expertise and facilities are available to provide comprehensive assessment of the bleeding disorder and a combined plan of management. The haematologist should arrange and interpret laboratory tests and make provision for appropriate replacement therapy. These guidelines have been provided for healthcare professionals for information and guidance and it is also intended that they are readily available for women with bleeding disorders.

Cryptic splice site usage in exon 7 of the human fibrinogen Bbeta-chain gene is regulated by a naturally silent SF2/ASF binding site within this exon

In this work we report the identification of a strong SF2/ASF binding site within exon 7 of the human fibrinogen Bbeta-chain gene (FGB). Its disruption in the wild-type context has no effect on exon recognition. However, when the mutation IVS7 + 1G>T--initially described in a patient suffering from congenital afibrinogenemia--is present, this SF2/ASF binding site is critical for cryptic 5'ss (splice site) definition. These findings, besides confirming and extending previous results regarding the effect of SF2/ASF on cryptic splice site activation, identify for the first time an enhancer sequence in the FGB gene specific for cryptic splice site usage. Taken together, they suggest the existence of a splicing-regulatory network that is normally silent in the FGB natural splicing environment but which can nonetheless influence splicing decisions when local contexts allow. On a more general note, our conclusions have implications for the evolution of alternative splicing processes and for the development of methods to control aberrant splicing in the context of disease-causing mutations.

Insights into abnormal hemostasis in the Quebec platelet disorder from analyses of clot lysis

BACKGROUND

The Quebec platelet disorder (QPD) is inherited and characterized by delayed-onset bleeding following hemostatic challenge. Other characteristics include increased expression and storage of active urokinase-type plasminogen activator (u-PA) in platelets in the setting of normal to increased u-PA in plasma. There is also consumption of platelet plasminogen activator inhibitor-1 and increased generation of plasmin in platelets accompanied by proteolysis of stored alpha-granule proteins, including Factor V.

AIMS AND METHODS

Although fibrinolysis has been proposed to contribute to QPD bleeding, the effects of QPD blood and platelets on clot lysis have not been evaluated. We used thromboelastography (TEG), biochemical evaluations of whole blood clot lysis, assessments of clot ultrastructure, and perfusion of blood over preformed fibrin to gain insights into the disturbed hemostasis in the QPD.

RESULTS

Thromboelastography was not sensitive to the increased u-PA in QPD blood. However, there was abnormal plasmin generation in QPD whole blood clots, generated at low shear, with biochemical evidence of increased fibrinolysis. The incorporation of QPD platelets into a forming clot led to progressive disruption of fibrin and platelet aggregates unless drugs were added to inhibit plasmin. In whole blood perfusion studies, QPD platelets showed normal adherence to fibrin, but their adhesion was followed by accelerated fibrinolysis.

CONCLUSIONS

The QPD is associated with "gain-of-function" abnormalities that increase the lysis of forming or preformed clots. These findings suggest accelerated fibrinolysis is an important contributor to QPD bleeding.

Bruising and bleeding in infants and children - a practical approach

Bruising and bleeding are commonly seen in children and are usually associated with minor injury and trauma. However, in two groups of children the bruising may be more significant than expected: those with an underlying haemostatic abnormality, such as an inherited bleeding disorder, or those who have been subjected to non-accidental injury (NAI). Diagnosing inherited bleeding disorders in children is fraught with difficulty, from venous access to interpretation of results; the possibility of NAI should be borne in mind, even in those children with proven significant bleeding disorders when the severity of the injury and the history are non-compatible. We describe the investigation of the haemostatic system in children with bruising and/or bleeding with emphasis on the key haemostatic disorders that need to be excluded.

Factor X deficiency presenting as a pseudotumor

The authors report their experience in successfully treating a 15-week-old child who became comatose following a spontaneous intracerebral hemorrhage. It was initially believed that a tumor in the right frontal lobe caused the hemorrhage. Coagulation studies revealed abnormal results on presentation, and the problem was only partially corrected after an infusion of fresh frozen plasma. The child underwent an emergency craniotomy in which the hematoma was evacuated, and a biopsy specimen was obtained from a firm mass at the base of the hematoma cavity. Postoperatively, the child recovered completely, and an analysis of detailed coagulation studies revealed that the child had a factor X deficiency. Histological analysis of the biopsy specimen revealed normal brain tissue with hemorrhagic infiltration. Subsequently, the child achieved normal developmental milestones. A diagnosis of congenital bleeding disorder should be considered in children with spontaneous intracerebral hemorrhage, even in those with no prior episode of extracerebral spontaneous hemorrhage.

Inherited defects of coagulation factor V: the hemorrhagic side

Coagulation factor V (FV) is the protein cofactor required in vivo for the rapid generation of thrombin catalyzed by the prothrombinase complex. It also represents a central regulator in the early phases of blood clot formation, as it contributes to the anticoagulant pathway by participating in the downregulation of factor VIII activity. Conversion of precursor FV to either a procoagulant or anticoagulant cofactor depends on the local concentration of procoagulant and anticoagulant enzymes, so that FV may be regarded as a daring tight-rope walker gently balancing opposite forces. Given this dual role, genetic defects in the FV gene may result in opposite phenotypes (hemorrhagic or thrombotic). Besides a concise description on the structural, procoagulant and anticoagulant properties of FV, this review will focus on bleeding disorders associated with altered levels of this molecule. Particular attention will be paid to the mutational spectrum of type I FV deficiency, which is characterized by a remarkable genetic heterogeneity and by an uneven distribution of mutations throughout the FV gene.

Role of hepatocyte nuclear factor 4alpha in control of blood coagulation factor gene expression

Hepatocyte nuclear factor 4alpha (HNF4alpha) plays an important role in the maintenance of many liver-specific functions. Liver-specific HNF4alpha-null mice were used to determine whether hepatic HNF4alpha regulates blood coagulation in vivo. These mice exhibited reduced expression of hepatic coagulation factors V, IX, XI, XII, and XIIIB and a prolonged activated partial thromboplastin time but not prothrombin time. Promoter analysis of the mouse FXII and FXIIIB genes was performed to determine whether HNF4alpha directly regulates the genes encoding these coagulation factors. Sequence analysis revealed the presence of one and two HNF4alpha binding sites in the mouse FXII and FXIIIB genes, respectively. Using transient transfection and electrophoretic mobility shift analyses with the mouse FXII and FXIIIB promoters, it was established that the high levels of promoter activity were dependent on HNF4alpha binding sites and the expression of HNF4alpha. In conclusion, HNF4alpha has a critical role in blood coagulation homeostasis by directing transcription of the FXII and XIIIB genes.

Hemostasis and menstruation: appropriate investigation for underlying disorders of hemostasis in women with excessive menstrual bleeding

The evaluation of excessive menstrual bleeding carries a relatively high yield of discovering an underlying disorder of hemostasis in females. This review highlights important components in a structured history and outlines primary and secondary hematologic testing that should be considered in the evaluation of excessive menstrual bleeding.

Requirements for research investigations to clarify the relationships and management of menstrual abnormalities in women with hemostatic disorders

This article highlights a comprehensive range of research investigations which are required to clarify the relationships between the symptom of excessively heavy menstrual bleeding and different disorders of systemic hemostasis and their management. The need for these investigations was stimulated by an international workshop involving hematologists and gynecologists with expertise and interests in these fields. The field was reviewed by a group of experts who systematically considered nomenclature, definitions, investigations, and management and identified areas of uncertainty, controversy, or absence of information. This article is an extension of those preliminary research discussions. Recommendations are made for a range of important research studies to define the nomenclature, definitions, mechanisms, clinical investigations and management of heavy menstrual bleeding in women with disorders of systemic hemostasis.

Variability in factor V:C assays in UK National External Quality Assessment Scheme surveys: there is a need for an international standard

Severe familial factor V:C deficiency is a rare, recessively inherited coagulation disorder but there is little information in respect of the accuracy and reliability of factor V:C assays that are required for diagnosis and treatment monitoring. We present here the results of three External Quality Assessment exercises in respect of factor V:C assays undertaken by 192--225 participating laboratories performed over a 2-year period. Consistent significant differences were observed between results obtained using different reference plasmas and different thromboplastins. The relationship between results obtained with different reference plasmas was not constant and varied between the surveys. In-house studies confirmed the observation derived from the External Quality Assessment surveys that the choice of commercial reference plasma significantly affects the results of factor V:C assays. These results clearly indicate the necessity for an international standard for factor V:C.

von Willebrand disease and other disorders of hemostasis in the patient with menorrhagia

Separately, von Willebrand disease and menorrhagia are two relatively common conditions; in combination they occur at a prevalence of approximately 11-16%. Such patients exhibit a reduced quality of life and can incur a relatively high rate of gynecologic interventions; for example dilatation and curettage, endometrial ablation and hysterectomy. Initial evaluation involves a focused history for the following bleeding symptoms: menorrhagia since menarche, easy bruising of greater than 5 cm 1-2 times/month, frequent gum bleeding when flossing or brushing teeth or epistaxis 1-2 times/month. In addition, for those who have already undergone invasive interventions with the subsequent risk for hemorrhage, inquiry should be made regarding excessive bleeding with childbirth, dental tooth extraction and/or surgery. Step-wise testing includes a complete blood cell count and an assessment of the prothrombin time, activated partial thromboplastin time, iron profile, serum creatinine and thyroid-stimulating hormone level, followed by Factor VIII level, von Willebrand factor antigen and ristocetin cofactor, followed by consideration of platelet aggregation studies. Additional hemostatic studies may include obtaining a Factor XI level and euglobulin clot lysis time. Intuitively, failure to diagnose an underlying hemostatic disorder may lead to continued menorrhagia and diminished quality of life, as well as unnecessary surgical interventions that may in turn be fraught with an increased risk of bleeding. The management of von Willebrand disease-related menorrhagia involves consideration of the patient's age, childbearing status and preference. In the adolescent, surgical intervention is not an option, whereas an older patient beyond her childbearing years may choose a hysterectomy as a definitive treatment in lieu of continued medical therapy with intranasal/subcutaneous 1-deamino-8-D-arginine vasopressin (DDAVP), oral antifibrinolytic agents or oral contraceptive. The sexually active patient may initially choose a trial of oral contraceptive or the levonorgestrel intrauterine device, Mirena((R)). Pending ongoing comparative trials in von Willebrand disease-related menorrhagia of intranasal DDAVP, tranexamic acid and the levonorgestrel intrauterine device, specific recommendations cannot be made at present regarding the superiority of one intervention compared with another. It should also be noted that the dose and schedule of intranasal DDAVP, tranexamic acid and epsilon-amino caproic acid have not been well established and warrant further study in combination and at various doses and schedules.

Molecular genetics of hereditary prothrombin deficiency in Indian patients: identification of a novel Ala362 --> Thr (Prothrombin Vellore 1) mutation

Prothrombin deficiency is a rare (1:200 000) autosomal recessive disorder caused by diverse mutations in prothrombin gene. We have studied the molecular basis of this disorder in four unrelated Indian patients. The diagnosis was based on prolonged prothrombin (PT) and activated partial thromboplastin times and low factor II coagulant activity (FII: C) measured using a PT based assay. FII: C levels ranged between 4.7% and 17.5%. Mutations were identified in all the four patients. Five different causative mutations including four (80%) missense and an in-frame deletion (20%) were identified. One of them was a novel, Ala362 --> Thr amino acid change affecting 'B' chain of -thrombin. This mutation was present in a compound heterozygous state with a previously reported Arg-1 --> Gln missense change affecting pro-peptide cleavage site. Ala362 --> Thr occurred at a codon, evolutionarily conserved in all the 24 different prothrombins or its related serine proteases studied. Molecular modeling of this mutation was found to cause a conformational change around the region involving a catalytic triad residue His363 and a cysteine residue at codon 364. The FII: C level in this patient was 17.5%. Three other previously reported mutations were also detected in the homozygous state: Arg271 --> Cys in Kringle-2 region, a Glu309 --> Lys in "A" chain of -thrombin and an in-frame deletion of 3 bp (AAG) leading to Del Lys301/302 in "A" chain of -thrombin. This is the first report of the molecular basis of prothrombin deficiency in Indian patients and we suggest the eponym 'Prothrombin Vellore 1' for Ala362 --> Thr mutation.

Liver histology of an afibrinogenemic patient with the Bbeta-L353R mutation showing no evidence of hepatic endoplasmic reticulum storage disease (ERSD); comparative study in COS-1 cells of the intracellular processing of the Bbeta-L353R fibrinogen vs. the ERSD-associated gamma-G284R mutant

BACKGROUND

Type I fibrinogen deficiencies (hypofibrinogenemia and afibrinogenemia) are rare congenital disorders characterized by low or unmeasurable plasma fibrinogen antigen levels. Their genetic bases are represented by mutations within the three fibrinogen genes. Among the 11 reported missense mutations, a few have been characterized by expression studies and found to have an impaired fibrinogen assembly and/or secretion. Histopathological analyses were previously reported in two hypofibrinogenemic cases with discernible hepatic disease, revealing that both underlying mutations (gamma-Gly284Arg and gamma-Arg375Trp) were associated with hepatic fibrinogen endoplasmic reticulum storage disease (ERSD).

OBJECTIVE

The objective of this study was to investigate the liver histology in an afibrinogenemic patient, homozygous for the Bbeta-Leu353Arg mutation, and to study the intracellular processing of the mutant protein.

PATIENTS AND METHODS

Liver histology was evaluated by light microscopy, electron microscopy and immunocytochemistry. Intracellular processing of mutant fibrinogen was analyzed by pulse-chase labeling and immunoprecipitation experiments. Messenger RNA levels were determined by real-time reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

The histopathological characterization of the liver showed no signs of fibrinogen accumulation, a difference from the previously reported findings in two hypofibrinogenemic kindreds with ERSD. To evaluate whether the Bbeta-Leu353Arg mutation and the ERSD-associated gamma-Gly284Arg mutation affected intracellular fibrinogen trafficking differently, both mutant proteins were expressed in COS-1 cells. Bbeta-Leu353Arg led to a more severe secretion defect, but no differences that could explain phenotype-genotype correlation were found in the intracellular processing. Endoglycosidase-H analysis demonstrated a secretion block before translocation to the Golgi medial stacks. Real-time RT-PCR studies showed normal levels of the Bbeta mRNA in the patient's liver.

CONCLUSIONS

The results confirm that Bbeta-Leu353Arg is associated with impaired fibrinogen secretion, but not with hepatic ERSD.

Blood coagulation and its regulation by anticoagulant pathways: genetic pathogenesis of bleeding and thrombotic diseases

Blood coagulation and its regulation by anticoagulant pathways: genetic pathogenesis Platelet-mediated primary haemostasis and blood coagulation have evolved as important defence mechanisms against bleeding. The formation of the platelet plug provides the initial occlusion of the vascular lesion. This is temporally co-ordinated with the activation of the coagulation system, which occurs in response to the rupture of endothelium and the exposure of blood to the extravascular tissue. The reactions of blood coagulation are carefully controlled by several anticoagulant mechanisms and under normal conditions they prevail over the procoagulant forces. Genetic or acquired disturbances of the natural balance between the pro- and anticoagulant systems may result in bleeding or thrombotic diseases.

Diagnosis and Management of Mild Bleeding Disorders

Mild bleeding disorders are a common reason for a referral to a hematologist and these conditions can be challenging to evaluate. Recent research has highlighted that some bleeding symptoms are quite common in the general population and that there is clinical variability in symptom expression among individuals with defined bleeding problems. Moreover, bleeding risks for many bleeding disorders are unknown. This article reviews symptoms and problems that can be considered suspicious of a mild form of bleeding disorder and the diagnostic investigations useful to evaluate these problems. A stepwise approach is presented for the diagnostic evaluation, to allow detection of common and rare coagulation and fibrinolytic defects, and adequate assessments of potential von Willebrand factor and platelet problems. Some common problems in the diagnosis and management of mild bleeding problems are reviewed, including the common failure to establish a diagnosis with testing. An approach is proposed for translation of knowledge to patients who are challenged by mild bleeding problems.