Platelets from Calreticulin mutated essential thrombocythemia patients are less reactive than JAK2 V617F mutated platelets

Both JAK2V617F and calreticulin (CALR) mutated essential thrombocythemia (ET) patients have different clinical characteristics, with lower thrombosis risk in patients with CALR mutations. To elucidate the mechanism for this lower risk we studied platelet function in ET patients with either JAK2V617F or a CALR mutation. Platelet activation state was similar in ET and healthy controls at baseline using P-selectin and PAC1 flow cytometry analysis. However, CALR mutated platelets were significantly less activated following ADP stimulation, compared to control or JAK2 mutated platelets (P < .001). In live-cell imaging of platelet attachment to immobilized fibrinogen by Interference Reflection Microscopy (IRM), the number of attached CALR mutated platelets was lower compared to control and JAK2 mutated platelets, with lower fractions of platelets achieving the fully spread state (90%, 78% and 54% of adherent cells for control, JAK2 and CALR mutated subjects, respectively). Compared to controls, ET patients, regardless of the mutation type, had increased numbers of immature platelets (IP) and leukocyte platelet aggregates (LPA), as well as plasma sP-selectin. These were all correlated with the platelet count and not to the state of platelet activation. We also found that intracellular free Ca²⁺ was increased in resting ET compared to control platelets. Note, CALR had a more dispersed localization in activated ET platelets compared to healthy controls, and mutated CALR interact physically with TpoR in CALR mutated platelets. We hypothesize that defects in platelet activation and spreading in CALR mutated patients can explain, at least in part, the lower thrombotic tendency in CALR mutated ET patients.

The reduced form of coagulation factor XI is associated with illness severity and coagulopathy in critically-ill septic patients

Coagulation Factor XI (FXI) contributes to the pathobiology of sepsis-associated thrombosis and is a target for new therapeutics. Through cleavage of disulfide bonds, FXI becomes reduced (rFXI), accelerating intrinsic coagulation cascade activation. The role of rFXI in human sepsis has never been studied. We determined levels of total FXI and rFXI in critically-ill septic patients with and without overt disseminated intravascular coagulation (DIC, a dysregulated pro-thrombotic condition). Total FXI and rFXI plasma levels were measured on ICU admission in prospectively enrolled septic patients (n = 32) from three academic medical centers and matched, healthy controls (n = 15). In septic patients, hematologic and physiologic parameters and pathological thrombosis (presence or absence of overt DIC) were determined. rFXI was higher in septic patients than controls (p < 0.05). In septic patients, rFXI was significantly associated with platelet count (r = 0.3511, p < 0.05) and APACHE II score (r = - 0.359, p < 0.05), indices of illness severity. rFXI was lower in patients with overt DIC (p = 0.088), suggesting a consumptive coagulopathy. In contrast, while total FXI levels were reduced in sepsis, they failed to correlate with illness severity, thrombosis, or hematologic parameters. We establish, for the first time, that rFXI is increased in patients with sepsis and correlates with illness severity (APACHE II score and platelet count) and pathological coagulopathy (overt DIC). Total FXI levels, in contrast, are decreased in sepsis but fail to associate with any indices. These findings suggest that rFXI has unique activity in human sepsis.

Low Concentrations of Recombinant Factor VIIa May Improve the Impaired Thrombin Generation of Glanzmann Thrombasthenia Patients

Introduction Glanzmann thrombasthenia (GT) is a rare bleeding disorder. The disease is caused by the lack or dysfunction of platelet membrane glycoprotein IIb/IIIa (integrin αIIbβ3) which is essential for platelet aggregation. Bleeding episodes are usually managed by platelet transfusions. Recombinant activated factor VII (rFVIIa) is a common adjunct or alternative treatment option.

Objective This article evaluates GT patients' response to increasing concentrations of rFVIIa using an ex vivo thrombin generation assay to elaborate the knowledge in which rFVIIa treats a platelet dysfunction for bleeding episodes and preoperative management.

Materials and Methods Twenty-four GT patients in a non-bleeding state were enrolled into the study. Thrombin generation was measured in platelet-rich plasma (PRP) in the presence of 0.7 to 7.0 µg/mL rFVIIa. Clinical data of rFVIIa used to treat GT patients' bleeding episodes was collected, and patients' follow-up course was documented.

Results Thrombin generation was significantly decreased in GT patients compared with controls. An individual response to rFVIIa spiking was noted in GT patients' PRP. In the majority of patients, a significant improvement in thrombin generation was already demonstrated with low concentrations (0.7 µg/mL) of rFVIIa.

Conclusion Thrombin generation is improved in the majority of GT patients following ex vivo spiking with rFVIIa. The magnitude of this improvement is individual and was noted at low concentrations of rFVIIa. There is a need for a prospective clinical trial to find the optimal doses or rFVIIa for treatment of GT patients.

Factor XIII Deficiency due to a Leu660Pro Mutation in the Factor XIII Subunit-a Gene in Three Unrelated Palestinian Arab Families

In this report we describe the molecular basis of FXIII a-subunit deficiency in three unrelated Palestinian Arab families. In three patients representing each family two substitutions were identified in exon 14 on both alleles: C to G change resulting in a Gln651Glu substitution (a previously described polymorphism) and a T to C transition causing Leu660Pro substitution. The latter is a new mutation which creates a restriction site for FnuDII enzyme. Restriction analysis performed in members of the three families clearly distinguished between severely affected patients, obligate carriers and unaffected subjects. A population survey failed to detect the mutation among 250 Jewish individuals but did detect two heterozygotes among 300 Arabs suggesting a 0.0033 frequency for the Pro660 allele in this population. In two out of the three families the Pro660 allele was linked to allele 5 of the 5’ short tandem repeat polymorphism within the FXIII a-subunit gene suggesting that the mutation might have occurred at least twice. cDNA obtained from mRNA isolated from patients’ platelets and monocytes appeared similar in size to that of normal control indicating that the Leu660Pro mutation does not affect mRNA synthesis. Computer modeling based on cristallographic studies of the a-subunit of factor XIII predicted that the mutant protein is expected to misfold into a structure which is either unstable or susceptible to degradation.

Purpura Fulminans Induced by Disseminated Intravascular Coagulation following Infection in 2 Unrelated Children with Double Heterozygosity for Factor V Leiden and Protein S Deficiency

Purpura fulminans is associated with homozygous protein C and homozygous protein S deficiency or may follow bacterial or viral infections. We present 2 children from 2 unrelated Arab families with purpura fulminans who were double heterozygotes for factor V Leiden inherited from their fathers and protein S deficiency inherited from their mothers. No previous thrombotic events have occured in either patient or their respective family members. In one patient sepsis accompanied by disseminated intravascular coagulation appeared to be the trigger of purpura fulminans. In the other patient varicella infection preceded purpura fulminans and was also associated with disseminated intravascular coagulation. This report emphasizes the need for evaluation of hereditary defects in the inhibitory mechanisms of blood coagulation in patients with purpura fulminans at any age.

Detection of the Glanzmann's Thrombasthenia Mutations in Arab and Iraqi-Jewish Patients by Polymerase Chain Reaction and Restriction Analysis of Blood or Urine Samples

Severe Glanzmann's thrombasthenia is relatively frequent in Iraqi-Jews and Arabs residing in Israel. We have recently described the mutations responsible for the disease in Iraqi-Jews – an 11 base pair deletion in exon 12 of the glycoprotein IIIa gene, and in Arabs – a 13 base pair deletion at the AG acceptor splice site of exon 4 on the glycoprotein IIb gene. In this communication we show that the Iraqi-Jewish mutation can be identified directly by polymerase chain reaction and gel electrophoresis. With specially designed oligonucleotide primers encompassing the mutation site, an 80 base pair segment amplified in healthy controls was clearly distinguished from the 69 base pair segment produced in patients. Patients from 11 unrelated Iraqi-Jewish families had the same mutation. The Arab mutation was identified by first amplifying a DNA segment consisting of 312 base pairs in controls and of 299 base pairs in patients, and then digestion by a restriction enzyme Stu-1, which recognizes a site that is absent in the mutant gene. In controls the 312 bp segment was digested into 235 and 77 bp fragments, while in patients there was no change in the size of the amplified 299 bp segment. The mutation was found in patients from 3 out of 5 unrelated Arab families. Both Iraqi-Jewish and Arab mutations were detectable in DNA extracted from blood and urine samples. The described simple methods of identifying the mutations should be useful for detection of the numerous potential carriers among the affected kindreds and for prenatal diagnosis using DNA extracted from chorionic villi samples.

The Relative Frequency of Hereditary Thrombotic Disorders Among 107 Patients with Thrombophilia in Israel

Since most patients with thrombophilia in Israel are referred for diagnosis to our center, it was possible to estimate the relative frequency of the hereditary disorders leading to thrombophilia. 107 unrelated patients were evaluated over 4 years. Diagnoses were established in 23 patients (21.5%) while in 84 (78.5%) no abnormality was detected. Antithrombin III deficiency was found in 8 patients (7.5%), dominant protein C deficiency in 6 (5.6%), recessive homozygous protein C deficiency in 1, protein S deficiency in 3 (2.8%) and dysfibrinogenemia in 1. Four additional patients (3.7%) had a lupus anticoagulant. The frequency of deep vein thrombosis and pulmonary embolism was similar in patients with and without a definite diagnosis. Thrombosis of visceral or cerebral vessels and a positive family history were more frequent among patients in whom a definite diagnosis was made. In both groups there was a substantial lag between the time of presentation of the first thrombotic episode and the time of evaluation. Since the number of referred patients with thrombophilia has gradually increased over the period of the study, it is at present impossible to establish the prevalence of the various hereditary disorders leading to thrombophilia in the population.

Patterns of Incorporation of 75Se-Methionine into Fibrinogen and Other Plasma Proteins in Rabbits Stimulated by Different Test Conditions

Rabbits were injected with 75Se-Methionine (75SeM) 4-8 hr after being subjected to a variety of experimental conditions: injection of ACTH, growth hormone, glucagon, adrenalin, endotoxin, turpentine, hydrocortisone and laparotomy. All of these experimental conditions except injection of glucagon were associated with increased incorporation of 75SeM into fibrinogen. Three patterns of incorporation of 75SeM into plasma proteins were recognized: 1. the pituitary pattern, which was observed in animals injected with ACTH, growth hormone or endotoxin, and which was characterized by increased incorporation of 75SeM only into fibrinogen and by a delayed incorporation of 75SeM into α2 and β1 globulins; 2. the tissue injury pattern, which was characterized by a markedly increased incorporation of 75SeM into fibrinogen and no alteration in incorporation of 75SeM into α2 or β1 globulins; and 3. the pharmacologic corticosteroid pattern, which was characterized by a moderately increased incorporation of 75SeM into fibrinogen and a strikingly increased incorporation of 75SeM into α2 and β1 globulins.

A Glanzmann’s Thrombasthenia Cluster Among Iraqi Jews in Israel

A country-wide survey of Glanzmann’s thrombasthenia in Israel identified 44 patients. The patients belong to 23 unrelated families, 17 of whom are of Iraqi Jewish origin. The frequency of thrombasthenia among Iraqi Jews in Israel (total population 270,000) is 1:7714 and thus the calculated frequency of the carrier state is 2.3%.

Cyclosporine Therapy for Acquired Factor VIII Inhibitor in a Patient with Systemic Lupus Erythematosus

The case of a 27-year-old woman with systemic lupus erythematosus and development of an autoantibody against factor VIII during an exacerbation of her underlying disorder is described. Attempts to eliminate the antibody with high dose gammaglobulin and repeated courses of cyclophosphamide failed, whereafter she received cyclosporine in increasing doses. When therapeutic serum levels of cyclosporine were achieved (150-350 ng/ml) the inhibitor rapidly decreased and disappeared with a concomitant normalization of the factor VIII levels. Treatment with cyclosporine was subsequently reduced and discontinued after one year, and at present no inhibitor is detectable. In view of the successful results with cyclosporine treatment in 4 of 6 previous cases and in all 3 previous cases with autoimmune disorders, this regimen should be evaluated in a systematic manner as a potential first line drug in patients with acquired hemophilia and an underlying autoimmune disorder.

Characterization of Three Mutations Causing von Willebrand Disease Type IIA in Five Unrelated Families

Von Willebrand disease (vWD) type IIA is characterized by decreased ristocetin-induced platelet aggregation, and by the absence from plasma of high molecular weight multimers of von Willebrand factor (vWF). Most mutations causing vWD type IIA are clustered within the A2 domain of the mature vWF subunit that is encoded by exon 28. Using the polymerase chain reaction (PCR), the entire exon 28 from patients with vWD type IIA and normal controls was amplified and sequenced. Three missense mutations were detected that result in the amino acid substitutions Arg(834)→Trp, Gly(742)→Glu, and Ser(743)→Leu. The first mutation occurred independently in three unrelated families; each of the latter mutations was found in one family. By restriction endonuclease analysis and allele-specific oligonucleotide (ASO) hybridization the mutations were confirmed in affected family members and excluded in unaffected members and 50 normal controls. The apparently high frequency of identical independent mutations among patients with vWD type IIA suggests that a precise diagnosis may be possible in a majority of patients using relatively simple recombinant DNA screening assays.

Clinical and Genetic Aspects of Glanzmann’s Thrombasthenia in Israel

Twenty two patients (12 males and 10 females) from all over Israel fulfilled the ‘Criteria for establishing the diagnosis of Glanzmann’s thrombasthenia. All have been observed to have a severe bleeding tendency since infancy or early childhood. In 8 out of 10 adult patients (7 females and 3 males) the bleeding manifestations have persisted over the years. In 2 adult patients major surgery was performed under platelet transfusions which appeared to prevent excessive bleeding. Pedigree analysis was possible for 21 patients who belong to 13 unrelated kindreds. Twelve kindreds are Jewish and one is Arab. Eleven of the 12 Jewish kindreds belong to the Iraqi Jewish community. Analysis of 16 sibships disclosed a corrected segregation ratio of 0.2, which is compatible with an autosomal recessive mode of inheritance. No bleeding manifestation whatsoever were observed in 30 obligatory carriers of thrombasthenia, and the haemostatic functions tested in 12 of them were entirely normal.

Von Willebrand Factor Multimer Patterns in Pregnancy-Induced Hypertension

Microangiopathy and disseminated platelet aggregation have been reported in thrombotic thrombocytopenic purpura (TIP) and pregnancy-induced hypertension (PIH). Since unusually large von Willebrand factor (vWF) multimers have been implicated in the evolvement of TTP, we analyzed factor VIII/vWF parameters in patients with PIH. Mean vWF: Ag level was significantly higher in 27 patients with PIH as compared to 20 matched healthy pregnant women (358 ± 160 u/dl vs. 274 ± 125 u/dl, p < 0.05). Moreover, plasma vWF: Ag levels and the ratio of vWF: Ag to factor VIII were found to be linearly correlated to the severity of PIH. In contrast, no significant differences in mean levels of factor VIII and ristocetin cofactor were observed between these groups. Crossed immunoelectrophoresis of vWF revealed a higher incidence of a pre-peak and an increased migration index in the PIH group as compared to the control group (60% vs. 44% and 1.27 ± 0.26 vs. 1.19 ± 0.18, p < 0.01 respectively). Analysis of plasma vWF multimer patterns by 1.4% agarose electrophoresis in 0.1% SDS revealed excessive amounts of large, medium and small size multimers in the PIH patients. Conceivably, the quantitative changes in vWF multimers reflect endothelial injury and may play a role in the microangiopathy observed in PIH.

Effect of Corticosteroids upon Fibrinogen Metabolism in Rabbits

The effect of pharmacologic doses of adrenal corticosteroids upon plasma fibrinogen level, incorporation of 75Se-Methionine (75SeM) into fibrinogen, and disappearance of plasma 125I-fibrinogen was evaluated in rabbits. Single 25 mg doses of hydrocortisone or cortisone transiently increased both 75SeM incorporation into fibrinogen and plasma fibrinogen levels, but 1 to 5 mg doses of hydrocortisone had no significant effect upon plasma fibrinogen levels. Repeated daily injections of 25 mg of hydrocortisone did not increase plasma fibrinogen levels progressively. Two doses of 25 mg of hydrocortisone, given 24 hr apart, failed to alter the rate of disappearance of plasma 125I-fibrinogen radioactivity, i.e., plasma fibrinogen catabolism. Intramuscular injection of 2.5 ml of propylene glycol solvent caused a prolonged rise in plasma fibrinogen level, whereas injection of 25 mg of corticosterone dissolved in propylene glycol resulted in an attenuated and transient rise in plasma fibrinogen level. Apparently, the presence or absence of a coexistent inflammatory stimulus determines the overall effect of large pharmacologic doses of corticosteroids upon fibrinogen metabolism in the rabbit. In the presence of inflammation, corticosteroids decrease synthesis with a resultant fall in plasma fibrinogen level; in the absence of inflammation, corticosteroids may increase synthesis transiently with a resultant slight increase in plasma fibrinogen level.

Severe Hereditary Deficiency of Factor VII during Pregnancy

In normal pregnant women factor VII level is increased. This may also be observed in women with hereditary partial factor VII deficiency.

In a 38 year old woman with severe hereditary factor VII deficiency no change of the factor level was observed during pregnancy. The patient underwent two uneventful caesarian sections because of placenta praevia and transverse lie of the fetus.

During the second caesarian section factor VII level was simultaneously determined in blood obtained from the antecubital and uterine veins and from the umbilical vein and artery. Factor VII levels in the umbilical vessels were similar and exceeded the levels observed in the mother’s vessels. In 3 control patients similar examinations were performed during caesarian sections but reversed ratios of factor VII levels were observed. These data seem to prove that factor VII does not cross the placenta.

In the family study 2 siblings were found to have severe factor VII deficiency whereas several other members had either normal or partial deficient levels. The results obtained support again the assumption that factor VII deficiency is inherited by an autosomal gene that in the homozygous state is manifested by severe factor VII deficiency and in the heterozygous state by mild deficiency or normal factor VII levels.

Disseminated Intravascular Coagulation in Experimental Heatstroke

Heatstroke was induced experimentally in dogs, in order to clarify the mechanism of haemorrhage in that disorder.

Controls were provided both by dogs subjected to maximal effort at normal ambient temperatures and by dogs exposed to high enviromental temperature without exercise.

It was found that above a critical temperature (43.3° C), dogs show a typical clinical and laboratory picture of heatstroke, similar to that occurring in human beings.

Quick value and platelets dropped markedly, as did most of the clotting factors including factor V, II, VII and X.

Factor VIII was sometimes raised, but also fell terminally. Significant fibrinolysis and shortened half life of labelled fibrinogen were further strong indications of general defibrination.

The post-mortem presence of thrombi, provided confirmatory evidence of diffuse intravascular clotting (consumption coagulopathy).

Responses of Platelets to Strains of Streptococcus sanguis: Findings in Healthy Subjects, Bernard-Soulier, Glanzmann’s, and Collagen-Unresponsive Patients

The ability of endocarditis and dental strains of Streptococcus sanguis to induce platelet aggregation in plasma (PRP) from normal subjects were examined and compared to responses of PRP with known platelet membrane glycoprotein (GP) and response defects.

S. sanguis strains differed in their ability to induce normal PRPs to aggregate. Strains that induced PRP aggregation in more than 60% of donors were significantly faster agonists (mean lag times to onset of aggregation less than 6 min) than those strains inducing response in PRPs of fewer than 60% of donors.

Platelets from patients with Bernard-Soulier syndrome aggregated in response to strains of S. sanguis. In contrast, platelets from patients with Glanzmann’s thrombasthenia and from a patient with a specific defect in response to collagen were unresponsive to S. sanguis. These observations show that GPIb and V are not essential, but GPIIb-IIIa and GPIa are important in the platelet response mechanism to S. sanguis. Indeed, the data suggests that the platelet interaction mechanisms of S. sanguis and collagen may be similar.

Possible Role of Fibrinogen in the Aggregation of White Blood Cells

In order to verify whether leukocyte aggregation correlated with aggregation of other cellular elements during inflammation, we examined the state of leukocyte adhesiveness/aggregation (LAA) in the peripheral blood and red cell aggregation. Correlation was found to be significant as was the correlation between LA A and fibrinogen, and with the fibrin/fibrinogen degradation products concentration during various inflammatory states. In vitro leukocyte aggregation was decreased when the cells were suspended in autologous heat defibrinogenated plasma as compared to cells suspended in autologous native plasma. Heat aggregated fibrinogen but not native fibrinogen caused leukocyte aggregation in vitro. Finally, Arvin defibrinogenation in rabbits reduced the state of LAA in endotoxinemic rabbits. Integrating all this information, we assume that fibrinogen participates not only in the aggregation phenomena of red cells and platelets, but also in those of leukocytes.

The Role of Factor XI in Thrombin Generation Induced by Low Concentrations of Tissue Factor

Thrombin generation has been studied in the plasma of severely factor XI deficient patients under conditions in which contact activation did not play a role. In platelet-rich as well as platelet-poor plasma, thrombin generation was dependent upon the presence of factor XI at tissue factor concentrations of between 1 and 20 pg/ml i.e. ~ 0.01 to 0.20% of the concentration normally present in the thromboplastin time determination. The requirement for factor XI is low; significant thrombin generation was seen at 1% factor XI; at 10%, thrombin formation was nearly normalised. A suspension of normal platelets in severely factor XI deficient plasma did not increase thrombin generation. This implies that there is no significant factor XI activity carried by normal platelets, although the presence of factor XI and factor XI inhibitors in platelets cannot be ruled out.

Risk Factors Associated with Postpartum Ovarian Vein Thrombosis

Thrombosis of the ovarian vein is a remarkable process occuring within a few days of labor in 1:500-1:2000 women. Its presentation is characterized by fever, abdominal pain and occasionally by a palpable abdominal mass that in earlier years sometimes lead to explorative laparotomy. With the advent of modern imaging techniques the diagnosis can be made relatively easily. The pathogenesis has been attributed to an infectious process expanding from the uterus to the right ovarian vein and stasis. A predisposition towards thrombosis has not been so far explored. In this study we retrospectively analysed the clinical features, diagnosis and treatment of 22 patients with objective documentation of post partum ovarian vein thrombosis (POVT) and assessed potential risk factors. In 11 of the 22 patients (50%) inherited prothrombotic risk factors were detected as follows: 4 were heterozygous for factor V G1691 A, 2 had protein S deficiency, one had protein S deficiency and was heterozygous for factor V G1691A, and 4 were homozygous for MTHFR C677T. Eight of the 11 patients who bore a prothrombotic predisposition underwent cesarean section. Taken together, the data suggest that POVT may result from the combined effect of an infection, cesarean section and a prothrombotic tendency.

Mutations in the αIIb and β3 Genes that Cause Glanzmann Thrombasthenia Can Be Distinguished by a Simple Procedure Using Transformed B-Lymphocytes

Glanzmann thrombasthenia (GT) is caused by a defect in either glycoprotein (GP) IIb (αIIb) or GPIIIa (β3) genes and therefore screening of both genes is required for mutation identification. The β subunit of the GPIIb/IIIa complex (β3) forms a complex with another α subunit (αv) yielding the αvβ3 vitronectin receptor (VnR). GT patients with mutations in the GPIIIa gene that cause diminished synthesis of GPIIIa are deficient in both GPIIb\IIIa and VnR, whereas patients with mutations in the GPIIb gene are deficient in GPIIb\IIIa, yet express normal or increased VnR in their platelets. The presence or absence of VnR in platelet membranes of GT patients has therefore been used for distinguishing between mutations in the GPIIb gene and mutations in the GPIIIa gene. However, the method of assessing VnR in platelets is cumbersome and use of fresh platelets is indispensible. In the present work we devised a procedure for detection of the VnR in B-lymphocytes transformed by Epstein-Bar virus (EBV). The transformed lymphocytes transcribed GPIIIa mRNA but not GPIIb mRNA and expressed VnR on their surface. Using flow cytometry analysis or immuno-precipitation and western blotting VnR was found in B-lymphocytes of GT patients bearing a well characterized mutation in the GPIIb gene. In contrast, in B-lymphocytes of GT patients bearing 2 different mutations in the GPIIIa gene no VnR was detectable. Thus, for determining which gene is mutated in a GT patient, EBV-transformed B-lymphocytes are useful and can as well be used for analyses of GPIIIa mRNA and genomic DNA. Ten ml of blood are sufficient for the procedure.

Disulfide bond disruption by a β3-Cys549Arg mutation in six Jordanian families with Glanzmann thrombasthenia causes diminished production of constitutively active αIIbβ3

αIIbβ3 integrin mediates platelet aggregation following its activation. Its absence or dysfunction causes Glanzmann thrombasthenia (GT), an inherited bleeding disorder that is rare worldwide but relatively frequent in several populations with high rates of consanguinity, including Arabs in Israel and Jordan. Cysteine residues in the β3 epidermal growth factor (EGF) domains are involved in αIIbβ3 formation and activation. In this study we present a novel Cys549Arg mutation in β3 identified in six Jordanian families, which in the homozygous state is manifested by severe GT. The mutation is located in EGF-3 of β3 predicting disruption of a conserved disulfide bond between Cys549 and Cys558. Haplotype analysis disclosed a common founder whose age estimate was 120–150 years. Flow cytometry revealed 1–14% of normal αIIbβ3 expression at the patients' platelet surface. The Cys549Arg or artificial Cys549Ser mutations were introduced into a β3 expression vector. Co-transfection of baby hamster kidney cells with normal or mutant β3 along with normal αIIb demonstrated reduced surface expression of αIIbβ3 by both mutants. The mutants were constitutively active as demonstrated by 20-fold increased binding of the ligand-mimetic antibody PAC-1. Immunoblotting and immunoprecipitation experiments showed reduced β3 and αIIbβ3 expression and a higher than normal ratio of pro-αIIb to mature αIIb. Immunofluorescence experiments showed that β3 and αIIbβ3 were mostly retained in the endoplasmic reticulum. In conclusion, the novel ancestral mutation found in a cluster of Jordanian GT patients disrupts a conserved Cys549-Cys558 bond which results in reduced production of constitutively active αIIbβ3.

ADAMTS-13 regulates platelet adhesion under flow

ADAMTS-13 cleaves large and ultra-large vonWillebrand factor multimers normally secreted by endothelial cells. Severe deficiency of this enzyme leads to thrombotic thrombocytopenic purpura (TTP). We applied the Impact-R system [Cone and plate(let) Analyzer, CPA] to determine optimal conditions for ADAMTS-13 function, to assess it’s activity in TTP patients and to distinguish inheritedTTP (inTTP) from acquiredTTP (acTTP). The role of ADAMTS-13 in platelet adhesion under different conditions was investigated applying recombinant forms of VWF and ADAMTS-13. rVWF was first treated by rADAMTS-13 either in solution or when immobilized on the surface of the well, under static or flow conditions, in the presence or absence of BaCl2. The resulting cleavedVWF fragments were then immobilized and served to assess type 3 von Willebrand disease whole blood platelet adhesion under flow. Maximal effect of the rADAMTS-13 (decrease of platelet adhesion in the absence compared to the presence of BaCl2), was observed when the rVWF was pre-immobilized and the cleavage step took place under flow (85%). Mixing plasma ofTTP patients with normal blood (1:3) yielded a 1.6 to 2-fold increase of platelet adhesion under flow compared to mixing normal plasma with normal blood, at shear rate range of 1,800–2,500s−1. Maximal increase of platelet adhesion was observed under 2,050s−1. Under these conditions, the extent of adhesion was similarly higher in patients with inTTP and acTTP versus control [surface coverage (SC) 14.5 ± 2.8% and 14.6 ± 2.5% vs. 7.4 ± 1.7%, respectively]. ADAMTS-13 activity measured by collagen-binding test was similarly low (4.2 ± 3.8% and 3.5 ± 2.4% vs. 72.2 ± 8.0%, respectively). An inverse correlation between SC and ADAMTS-13 activity was observed in a patient with inTTP assayed eight times during plasma infusion treatment. Addition of BaCl2 to the mixture of TTP plasma and normal whole blood yieldeda decrease in platelet adhesion in inTTP (by 51%) but not in acTTP. The lack of reduction of platelet adhesion in acTTP could presumably be due to the presence of ADAMTS-13 inhibitor in these patients. These results suggest that VWF immobilization and high shear flow yielded optimal conditions for ADAMTS-13 activity, and that introduction of BaCl2 in the Impact-R (CPA) test may be useful for differentiation between inherited and acquired TTP.

Variable effects of alpha v suppression on VEGFR-2 expression in endothelial cells of different vascular beds

Integrins αvβ3 and αvβ5 have been long considered as proangiogenic receptors, yet genetic ablation studies demonstrated enhanced angiogenesis in mice lacking αvβ3 and αvβ5 integrins, which was attributed to increased expression of vascular endothelial growth factor receptor-2 (VEGFR-2). In this study, we determined the effect of αvβ3 and αvβ5 suppression in endothelial cells (EC) on vascular endothelial growth factor (VEGF) and VEGFR-2 expression. αv was suppressed by shRNA in HUVEC (venous endothelial cells) and HMVEC (microvascular endothelial cells).VEGFR-2 was significantly upregulated by αv suppression in HUVEC and downregulated in HMVEC at both mRNA and protein levels,as assessed by real-time PCR and flow cytometry,respectively.HMVEC displayed completely abolished Sp1 binding to the VEGFR-2 promoter, and HUVEC exhibited enhanced binding to the –170 E- Box element in the VEGFR-2 promoter, assessed by electrophoretic mobility shift assay. Realtime PCR also revealed opposite effects on the expression of 5 additional important genes involved in angiogenesis in the two cell types.VEGF mRNA expression was enhanced in HUVEC and reduced in HMVEC; however, these alterations were not statistically significant.VEGF-induced proliferation was upregulated in HUVEC and reduced in HMVEC following αv suppression. No tube formation on Matrigel was observed in αv suppressed cells, regardless of their origin.These results indicate that suppression of αv integrins can either augment or inhibit VEGFR-2 levels and VEGF-induced proliferation in EC from different vascular beds. Hence, therapeutic antiangiogenic intervention by siRN-Amediated suppression of αv integrins should take into account variable and potentially hazardous responses in different vascular beds.

Patients with severe factor XI deficiency have a reduced incidence of deep-vein thrombosis

Factor XI (FXI) plays a dual role in haemostasis and thrombosis. It contributes to thrombin generation and promotes inhibition of fibrinolysis. Severe FXI deficiency was shown to confer protection against arterial and venous thrombosis in animal models without compromising haemostasis. We have previously shown that patients with severe FXI deficiency have a low incidence of ischaemic stroke, but display the usual incidence of myocardial infarction. In the present study, we compared the incidence of deep-vein thrombosis (DVT) in 219 unrelated patients with severe FXI deficiency aged 20–94 to the incidence in a large population-based study. No cases of DVT were observed in the FXI-deficient cohort, a result that is significantly lower than the expected number (4.68) computed from the population-based study. The low incidence remains statistically significant when compared to three other population-based studies. These data suggest that severe FXI deficiency provides protection against DVT.

Recombinant activated factor VII and tranexamic acid are haemostatically effective during major surgery in factor XI-deficient patients with inhibitor antibodies

One-third of patients with severe factor XI (FXI) deficiency caused by homozygosity for null alleles develop inhibitor antibodies following exposure to plasma. Haemostasis during surgery is achievable in such patients by recombinant activated factor VII (rFVIIa) at doses used in haemophilia A patients with an inhibitor to FVIII. However, thrombosis has occurred in three of 12 such patients. In this study we discerned whether low-dose rFVIIa would secure haemostasis and cause no thrombosis in patients with severe FXI deficiency and an inhibitor during surgery. In vitro, a very low concentration of rFVIIa (0.24 µg/ml) induced thrombin generation in FXI-deficient plasma quite similarly to 1.9 µg/ml (a concentration that is achieved in patients with haemophilia A and inhibitor after infusion of 80 µg/kg). Based on this finding, a protocol was designed for four patients with severe FXI deficiency and an inhibitor or immunoglobulin A deficiency who underwent five major surgical procedures. This included administration of tranexamic acid from two hours before surgery until seven to 14 days after, and single infusion of low-dose rFVIIa. No excessive bleeding or thrombosis were observed. In conclusion, a single low dose of rFVIIa and tranexamic acid secure normal haemostasis in patients with severe FXI deficiency who can not receive blood products.

Platelet factor XI: intracellular localization and mRNA splicing following platelet activation

BACKGROUND

The structure and function of platelet factor XI (FXI) protein and the presence of F11 mRNA in platelets are controversial. Although platelets are anucleated cells they contain spliceosome components and pre-mRNAs. Three platelet proteins have been demonstrated to be spliced upon platelet activation.

OBJECTIVE

To determine whether FXI is also spliced upon activation and to discern the localization of FXI in platelets.

METHODS

Localization of FXI in platelets was assessed by confocal immunofluorescence staining. ELISA, chromogenic assay and western blot analyses were used to measure antigen levels, activity levels and size of FXI in platelets, respectively. Splicing patterns of F11 mRNA were assessed in three states of platelet activation: activated platelets, resting platelets and αIIbβ3-integrin activated platelets.

RESULTS

Platelet FXI was exhibited in platelet granules. Activated platelets exhibited higher levels of mature F11 mRNA and protein and lower levels of F11 pre-mRNA compared to resting or αIIbβ3-integrin activated platelets.

CONCLUSIONS

We confirmed the presence of FXI in platelets and showed that it is localized in granules but is not restricted to the same α-granule subtype as von-Willebrand factor and p-selectin. Our study also shows that F11 is present in platelets as pre-mRNA and is spliced upon platelet activation.

An allosteric disulfide bond is involved in enhanced activation of factor XI by protein disulfide isomerase

Essentials Reduction of three disulfide bonds in factor (F) XI enhances chromogenic substrate cleavage. We measured FXI activity upon reduction and identified a bond involved in the enhanced activity. Reduction of FXI augments FIX cleavage, probably by faster conversion of FXI to FXIa. The Cys362-Cys482 disulfide bond is responsible for FXI enhanced activation upon its reduction.

SUMMARY

Background Reduction of factor (F) XI by protein disulfide isomerase (PDI) has been shown to enhance the ability of FXI to cleave its chromogenic substrate. Three disulfide bonds in FXI (Cys118-Cys147, Cys362-Cys482, and Cys321-Cys321) are involved in this augmented activation. Objectives To characterize the mechanisms by which PDI enhances FXI activity. Methods FXI activity was measured following PDI reduction. Thiols that were exposed in FXI after PDI reduction were labeled with 3-(N-maleimidopropionyl)-biocytin (MPB) and detected with avidin. The rate of conversion of FXI to activated FXI (FXIa) following thrombin activation was assessed with western blotting. FXI molecules harboring mutations that disrupt the three disulfide bonds (C147S, C321S, and C482S) were expressed in cells. The antigenicity of secreted FXI was measured with ELISA, and its activity was assessed by the use of a chromogenic substrate. The effect of disulfide bond reduction was analyzed by the use of molecular dynamics. Results Reduction of FXI by PDI enhanced cleavage of both its chromogenic substrate, S2366, and its physiologic substrate, FIX, and resulted in opening of the Cys362-Cys482 bond. The rate of conversion of FXI to FXIa was increased following its reduction by PDI. C482S-FXI showed enhanced activity as compared with both wild-type FXI and C321S-FXI. MD showed that disruption of the Cys362-Cys482 bond leads to a broader thrombin-binding site in FXI. Conclusions Reduction of FXI by PDI enhances its ability to cleave FIX, probably by causing faster conversion of FXI to FXIa. The Cys362-Cys482 disulfide bond is involved in enhancing FXI activation following its reduction, possibly by increasing thrombin accessibility to FXI.

The role of protein disulfide isomerase in the post-ligation phase of β3 integrin-dependent cell adhesion

INTRODUCTION

Protein disulfide isomerase (PDI) catalyzes disulfide bond exchange. It is crucial for integrin-mediated platelet adhesion and aggregation and disulfide bond exchange is necessary for αIIbβ3 and αvβ3 activation. However, the role of disulfide bond exchange and PDI in the post-ligation phase of αIIbβ3 and αvβ3 mediated cell adhesion has yet to be determined.

METHODS

To investigate a possible such role, we expressed wild type (WT) human αIIb and either WT human β3, or β3 harboring single or double cysteine to serine substitutions disrupting Cys473-Cys503 or Cys523-Cys544 bonds, in baby hamster kidney (BHK) cells, leading to expression of both human αIIbβ3 and a chimeric hamster/human αvβ3. Adhesion to fibrinogen-coated wells was studied in the presence or absence of bacitracin, a PDI inhibitor, with and without an αvβ3 blocker.

RESULTS

Flow cytometry showed WT and mutant αIIbβ3 expression in BHK cells and indicated that mutated αIIbβ3 receptors were constitutively active while WT αIIbβ3 was inactive. Both αIIbβ3 and αvβ3 integrins, WT and mutants, mediated adhesion to fibrinogen as shown by reduced but still substantial adhesion following treatment with the αvβ3 blocker. Mutated αIIbβ3 integrins disrupted in the Cys523-Cys544 bond still depended on PDI for adhesion as shown by the inhibitory effect of bacitracin in the presence of the αvβ3 blocker. Mutated integrins disrupted in the Cys473-Cys503 bond showed a similar trend.

CONCLUSIONS

PDI-mediated disulfide bond exchange plays a pivotal role in the post-ligation phase of αIIbβ3-mediated adhesion to fibrinogen, while this step in αvβ3-mediated adhesion is independent of disulfide exchange.

Natural and artificial mutations in αIIb integrin lead to a structural deformation of a calcium-binding site

The platelet integrin αIIbβ3 is widely accepted as a structural and a functional model of the broad integrin protein family. The four calcium-binding sites in the αIIb subunit contribute to biogenesis and stability of the protein. Mansour et al. (J Thromb Haemost 9:192-200, 2011) showed that the natural Asn2Asp mutation causing Glanzmann thrombasthenia, prevented surface expression of αIIbβ3, whereas the artificial Asn2Gln mutation only decreased its level. Molecular dynamics simulations and EDTA chelation assay were used here to explore the mechanism of these structural deformations. We show a considerable expansion of the calcium-binding site 3 in Asn2Asp mutation, whereas the Asn2Gln toggles between normal and expanded conformations. The αIIbβ3 surface expression level correlates to the relative spending time in the expanded conformation. By a comparison to other calcium-binding sites of αIIb and of other α integrins we show that the size of a calcium-binding loop is conserved. EDTA chelation assay shows a sensitivity to calcium removal, which correlates with the reduction in αIIbβ3 surface expression and with the calcium binding site expansion, thus verifying the simulation data. Here we indicate that Asn2 mutation affects a calcium-binding site 3 of αIIb, which structural deformation is proposed to deprive calcium binding and interfere with an integrin intracellular trafficking and its surface expression.

Abnormal plasma clot structure and stability distinguish bleeding risk in patients with severe factor XI deficiency

BACKGROUND

Factor XI (FXI) deficiency is a rare autosomal recessive disorder. Many patients with even very low FXI levels (< 20 IU dL(-1) ) are asymptomatic or exhibit only mild bleeding, whereas others experience severe bleeding, usually following trauma. Neither FXI antigen nor activity predicts the risk of bleeding in FXI-deficient patients.

OBJECTIVES

(i) Characterize the formation, structure and stability of plasma clots from patients with severe FXI deficiency and (ii) determine whether these assays can distinguish asymptomatic patients ('non-bleeders') from those with a history of bleeding ('bleeders').

METHODS

Platelet-poor plasmas were prepared from 16 severe FXI-deficient patients who were divided into bleeders or non-bleeders, based on bleeding associated with at least two tooth extractions without prophylaxis. Clot formation was triggered by recalcification and addition of tissue factor and phospholipids in the absence or presence of tissue plasminogen activator and/or thrombomodulin. Clot formation and fibrinolysis were measured by turbidity and fibrin network structure by laser scanning confocal microscopy.

RESULTS

Non-bleeders and bleeders had similarly low FXI levels, normal prothrombin times, normal levels of fibrinogen, factor VIII, von Willebrand factor and factor XIII, and normal platelet number and function. Compared with non-bleeders, bleeders exhibited lower fibrin network density and lower clot stability in the presence of tissue plasminogen activator. In the presence of thrombomodulin, seven of eight bleeders failed to form a clot, whereas only three of eight non-bleeders did not clot.

CONCLUSIONS

Plasma clot structure and stability assays distinguished non-bleeders from bleeders. These assays may reveal hemostatic mechanisms in FXI-deficient patients and have clinical utility for assessing the risk of bleeding.

Type I mutation in the F11 gene is a third ancestral mutation which causes factor XI deficiency in Ashkenazi Jews

BACKGROUND

Factor XI (FXI) deficiency is one of the most frequent inherited disorders in Ashkenazi Jews (AJ). Two predominant founder mutations termed type II (p.Glu117Stop) and type III (p.Phe283Leu) account for most cases.

OBJECTIVES

To present clinical aspects of a third FXI mutation, type I (c.1716 + 1G>A), which is also prevalent in AJ and to discern a possible founder effect.

METHODS

Bleeding manifestations, FXI levels and origin of members of 13 unrelated families harboring the type I mutation were determined. In addition, eight intragenic and five extragenic polymorphisms were analyzed in patients with a type I mutation, in 16 unrelated type II homozygotes, in 23 unrelated type III homozygotes and in Ashkenazi Jewish controls. Analysis of these polymorphisms enabled haplotype analysis and estimation of the age of the type I mutation.

RESULTS

Four of 16 type I heterozygotes (25%) and 6 of 12 (50%) compound heterozygotes for type I mutation (I/II and I/III), or a type I homozygote had bleeding manifestations. Haplotype analysis disclosed that like type II and type III mutations, the type I is also an ancestral mutation. An age estimate revealed that the type I mutation occurred approximately 600 years ago. The geographic distribution of affected families suggested that there was a distinct origin of the type I mutation in Eastern Europe.

CONCLUSIONS

The rather rare type I mutation in the FXI gene is a third founder mutation in AJ.

Inherited platelet disorders

Inherited diseases of the megakaryocyte lineage give rise to bleeding when platelets fail to fulfill their hemostatic function upon vessel injury. Platelet defects extend from the absence or malfunctioning of adhesion (GPIb-IX-V, Bernard-Soulier syndrome) or aggregation receptors (integrin αIIbβ3, Glanzmann thrombasthenia) to defects of primary receptors for soluble agonists, secretion from storage organelles, activation pathways and the generation of procoagulant activity. In disorders such as the Chediak-Higashi, Hermansky-Pudlak, Wiskott-Aldrich and Scott syndromes the molecular lesion extends to other cells. In familial thrombocytopenia (FT), platelets are produced in insufficient numbers to assure hemostasis. Some FT affect platelet morphology and give rise to the 'giant platelet' syndromes (e.g. MYH9-related diseases) with changes in megakaryocyte maturation within the bone marrow and premature release of platelets. Diseases of platelet production may also affect other cells and in some cases interfere with development and/or functioning of major organs. Diagnosis of platelet disorders requires platelet function testing, studies often aided by the quantitative analysis of receptors by flow cytometry and fluorescence and electron microscopy. New generation DNA-based procedures including whole exome sequencing offer an exciting new perspective. Transfusion of platelets remains the most common treatment of severe bleeding, management with desmopressin is often used for mild disorders. Substitute therapies are available including rFVIIa and the potential use of thrombopoietin analogues for FT. Stem cell or bone marrow transplantation has been successful for several diseases while gene therapy shows promise in the Wiskott-Aldrich syndrome.

Treatment of inherited platelet disorders

For patients affected by severe inherited platelet dysfunctions, e.g. Glanzmann thrombasthenia (GT) or Bernard-Soulier syndrome (BSS), platelet transfusion is frequently needed for controlling spontaneous bleeding, and is always needed when trauma occurs or surgery is performed. For the mild-to-moderate bleeding entities, e.g. storage pool disease, thrombaxane A2 receptor defect, platelet transfusion is usually unnecessary. Transfusion of platelets should be used selectively and sparingly because of the substantial risk of alloimmunization against HLA antigens and/or platelet glycoproteins (GP) αIIb, β(3), or αIIbβ(3) in GT, and GPI-IX-V in BSS, which may lead to refractoriness to therapy. To reduce the risk, HLA-matched single donors of platelets should be used. If such donors are unavailable, leucocyte-depleted blood components should be used. Therapy other than platelet transfusion includes: (i) Prevention (vaccination against hepatitis B, avoidance of non-steroidal anti-inflammatory drugs, preservation of dental hygiene, correction of iron deficiency and prenatal diagnosis). (ii) Topical measures (compression with gauze soaked with tranexamic acid, fibrin sealants, splints for dental extractions and packing for nose bleeds). (iii) Antifibrinolytic agents that are useful for minor surgery and as adjuncts for other treatment modalities. (iv) Desmopressin that increases plasma levels of von Willebrand factor and factor VIII giving rise to increased platelet adhesiveness and aggregation associated with shortened bleeding time. (v) Recombinant factor VIIa (rFVIIa). GT patients have been treated for bleeding episodes by rFVIIa with partial success. The mechanism by which rFVIIa arrests bleeding is probably related to increased thrombin generation by a tissue factor-independent process, enhanced platelet adhesion and restoration of platelet aggregation. (vi) Female hormones. Excessive bleeding during menarche in patients with GT or BSS can be controlled by high doses of oestrogen followed by high doses of oral oestrogen-progestin. Menorrhagia later in life can be managed by continuous oral contraceptives. Depo-medroxyprogesterone acetate administered every 3 months is an alternative when combined oral contraceptives are contraindicated.

Unique disulfide bonds in epidermal growth factor (EGF) domains of β3 affect structure and function of αIIbβ3 and αvβ3 integrins in different manner

The β3 subunit of αIIbβ3 and αvβ3 integrins contains four epidermal growth factor (EGF)-like domains. Each domain harbors four disulfide bonds of which one is unique for integrins. We previously discerned a regulatory role of the EGF-4 Cys-560-Cys-583 unique bond for αIIbβ3 activation. In this study we further investigated the role of all four integrin unique bonds in both αIIbβ3 and αvβ3. We created β3 mutants harboring serine substitutions of each or both cysteines that disrupt the four unique bonds (Cys-437-Cys-457 in EGF-1, Cys-473-Cys-503 in EGF-2, Cys-523-Cys-544 in EGF-3, and Cys-560-Cys-583 in EGF-4) and transfected them into baby hamster kidney cells together with normal αv or αIIb. Flow cytometry was used to measure surface expression of αIIbβ3 and αvβ3 and their activity state by soluble fibrinogen binding. Most cysteine substitutions caused similarly reduced surface expression of both receptors. Disrupting all four unique disulfide bonds by single cysteine substitutions resulted in variable constitutive activation of αIIbβ3 and αvβ3. In contrast, whereas double C437S/C457S and C473S/C503S mutations yielded constitutively active αIIbβ3 and αvβ3, the C560S/C583S mutation did not, and the C523S/C544S mutation only yielded constitutively active αIIbβ3. Activation of C523S/C544S αvβ3 mutant by activating antibody and dithiothreitol was also impaired. Molecular dynamics of C523S/C544S β3 in αIIbβ3 but not in αvβ3 displayed an altered stable conformation. Our findings indicate that unique disulfide bonds in β3 differently affect the function of αIIbβ3 and αvβ3 and suggest a free sulfhydryl-dependent regulatory role for Cys-560-Cys-583 in both αIIbβ3 and αvβ3 and for Cys-523-Cys-544 only in αvβ3.

A mutation in the β3 cytoplasmic tail causes variant Glanzmann thrombasthenia by abrogating transition of αIIb β3 to an active state

BACKGROUND

The cytoplasmic tails of α(IIb) and β(3) regulate essential α(IIb) β(3) functions. We previously described a variant Glanzmann thrombasthenia mutation in the β(3) cytoplasmic tail, IVS14: -3C>G, which causes a frameshift with an extension of β(3) by 40 residues.

OBJECTIVES

The aim of this study was to characterize the mechanism by which the mutation abrogates transition of α(IIb) β(3) from a resting state to an active state.

METHODS

 We expressed the natural mutation, termed 742ins, and three artificial mutations in baby hamster kidney (BHK) cells along with wild-type (WT) α(IIb) as follows: β(3) -742stop, a truncated mutant to evaluate the effect of deleted residues; β(3) -749stop, a truncated mutant that preserves the NPLY conserved sequence; and β(3) -749ins, in which the aberrant tail begins after the conserved sequence. Flow cytometry was used to determine ligand binding to BHK cells.

RESULTS AND CONCLUSIONS

Surface expression of α(IIb) β(3) of all four mutants was at least 60% of WT expression, but there was almost no binding of soluble fibrinogen following activation with activating antibodies (anti-ligand-induced-binding-site 6 [antiLIBS6] or PT25-2). Activation of the α(IIb) β(3) mutants was only achieved when both PT25-2 and antiLIBS6 were used together or following treatment with dithiothreitol. These data suggest that the ectodomain of the four mutants is tightly locked in a resting conformation but can be forced to become active by strong stimuli. These data and those of others indicate that the middle part of the β(3) tail is important for maintaining α(IIb) β(3) in a resting conformation.

Point mutations regarded as missense mutations cause splicing defects in the factor XI gene

BACKGROUND

Point mutations within exons are frequently defined as missense mutations. In the factor (F)XI gene, three point mutations, c.616C>T in exon 7, c.1060G>A in exon 10 and c.1693G>A in exon 14 were reported as missense mutations P188S, G336R and E547K, respectively, according to their exonic positions. Surprisingly, expression of the three mutations in cells yielded substantially higher FXI antigen levels than was expected from the plasma of patients bearing these mutations.

OBJECTIVES

To test the possibility that the three mutations, albeit their positions within exons, cause splicing defects.

METHODS AND RESULTS

Platelet mRNA analysis of a heterozygous patient revealed that the c.1693A mutation caused aberrant splicing. Platelet mRNA of a second compound heterozygote for c.616T and c.1060A mutations was undetectable suggesting its degradation. Cells transfected with a c.616T minigene favored production of an aberrantly spliced mRNA that skips exon 7. Cells transfected with a mutated minigene spanning exons 8-10 exhibited a significant decrease in the amount of normally spliced mRNA. In silico analysis revealed that the three mutations are located within sequences of exonic splicing enhancers (ESEs) that bind special proteins and are potentially important for correct splicing. Compensatory mutations created near the natural mutations corrected the putative function of ESEs thereby restoring normal splicing of exons 7 and 10.

CONCLUSIONS

The present findings define a new mechanism of mutations in F11 and underscore the need to perform expression studies and mRNA analysis of point mutations before stating that they are missense mutations.

An αIIb mutation in patients with Glanzmann thrombasthenia located in the N-terminus of blade 1 of the β-propeller (Asn2Asp) disrupts a calcium binding site in blade 6

BACKGROUND

Studies of Glanzmann thrombasthenia (GT)-causing mutations has generated invaluable information on the formation and function of integrin αIIbβ(3).

OBJECTIVE

To characterize the mutation in four siblings of an Israeli Arab family affected by GT, and to analyze the relationships between the mutant protein structure and its function using artificial mutations.

METHODS AND RESULTS

Sequencing disclosed a new A97G transversion in the αIIb gene predicting Asn2Asp substitution at blade 1 of the β-propeller. Alignment with other integrin α subunits revealed that Asn2 is highly conserved. No surface expression of αIIbβ(3) was found in patients' platelets and baby hamster kidney (BHK) cells transfected with mutated αIIb and WT β(3). Although the αIIbβ(3) was formed, the mutation impaired its intracellular trafficking. Molecular dynamics simulations and modeling of the αIIbβ(3) crystal indicated that the Asn2Asp mutation disrupts a hydrogen bond between Asn2 and Leu366 of a calcium binding domain in blade 6, thereby impairing calcium binding that is essential for intracellular trafficking of αIIbβ(3). Substitution of Asn2 to uncharged Ala or Gln partially decreased αIIbβ(3) surface expression, while substitution by negatively or positively charged residues completely abolished surface expression. Unlike αIIbβ(3), αVβ(3) harboring the Asn2Asp mutation was surface expressed by transfected BHK cells, which is consistent with the known lower sensitivity of αVβ(3) to calcium chelation compared with αIIbβ(3).

CONCLUSION

The new GT causing mutation highlights the importance of calcium binding domains in the β-propeller for intracellular trafficking of αIIbβ(3). The mechanism by which the mutation exerts its deleterious effect was elucidated by molecular dynamics.

The association of factor V leiden and prothrombin gene mutation and placenta-mediated pregnancy complications: a systematic review and meta-analysis of prospective cohort studies

BACKGROUND

Factor V Leiden (FVL) and prothrombin gene mutation (PGM) are common inherited thrombophilias. Retrospective studies variably suggest a link between maternal FVL/PGM and placenta-mediated pregnancy complications including pregnancy loss, small for gestational age, pre-eclampsia and placental abruption. Prospective cohort studies provide a superior methodologic design but require larger sample sizes to detect important effects. We undertook a systematic review and a meta-analysis of prospective cohort studies to estimate the association of maternal FVL or PGM carrier status and placenta-mediated pregnancy complications.

METHODS AND FINDINGS

A comprehensive search strategy was run in Medline and Embase. Inclusion criteria were: (1) prospective cohort design; (2) clearly defined outcomes including one of the following: pregnancy loss, small for gestational age, pre-eclampsia or placental abruption; (3) maternal FVL or PGM carrier status; (4) sufficient data for calculation of odds ratios (ORs). We identified 322 titles, reviewed 30 articles for inclusion and exclusion criteria, and included ten studies in the meta-analysis. The odds of pregnancy loss in women with FVL (absolute risk 4.2%) was 52% higher (OR = 1.52, 95% confidence interval [CI] 1.06-2.19) as compared with women without FVL (absolute risk 3.2%). There was no significant association between FVL and pre-eclampsia (OR = 1.23, 95% CI 0.89-1.70) or between FVL and SGA (OR = 1.0, 95% CI 0.80-1.25). PGM was not associated with pre-eclampsia (OR = 1.25, 95% CI 0.79-1.99) or SGA (OR 1.25, 95% CI 0.92-1.70).

CONCLUSIONS

Women with FVL appear to be at a small absolute increased risk of late pregnancy loss. Women with FVL and PGM appear not to be at increased risk of pre-eclampsia or birth of SGA infants. Please see later in the article for the Editors' Summary.

[Inherited bleeding disorders common in Jews]

Four inherited disorders of hemostasis have been identified in Jews with a relatively high frequency: Factor XI deficiency, factor VII deficiency, combined factor V and VIII deficiency and GLanzmann thrombasthenia. During the past decades, the bleeding manifestations of these disorders, the diagnosis, the molecular-genetic basis and therapy have been discerned. Furthermore, the prevalence of the respective mutant genes have been delineated in various Jewish Communities. Each one of the disorders can serve as a model enabling better understanding of the pathophysioLogy of the coagulation systems. On the basis of data obtained from the research of Glanzmann thrombasthenia, several widely used drugs have been developed as effective antithrombotic agents.

Cataract extraction without prophylactic treatment in patients with severe factor XI deficiency

PURPOSE

To assess the risks of intraoperative and postoperative bleeding associated with cataract extraction without prophylactic treatment in patients with severe factor XI (FXI) deficiency.

DESIGN

Prospective interventional case series.

METHODS

SETTING

Single institute.

STUDY POPULATION

Consecutive unrelated patients with severe FXI deficiency who underwent cataract extraction under topical anesthesia, with a clear corneal incision, phacoemulsification, and implantation of a foldable posterior chamber intraocular lens (PCIOL) were enrolled. Patients with associated intraocular conditions that could complicate the surgery were excluded.

INTERVENTION

Cataract extraction without prophylactic treatment for the FXI deficiency.

MAIN OUTCOME MEASURES

Assessment of intraoperative and postoperative ocular bleeding and other related complications.

RESULTS

Seven patients ranging in age from 61 to 95 years (median, 79) underwent phacoemulsification and PCIOL implantation in 11 eyes. Five patients (71%) were homozygotes for type II mutation of the FXI gene (activity level of <1 U/dl), 1 patient was a homozygote for type III mutation (activity level of 11 U/dl), and 1 patient was a compound heterozygote for types II and III (activity level of 3 U/dl). Three of the patients (43%), all type II homozygotes, also had an inhibitor antibody to FXI. All 7 patients were followed for at least 1 week after the operation. The surgery was uneventful in all eyes, and neither major nor minor bleeding events were observed in any of the operated eyes during surgery and follow-up.

CONCLUSIONS

Cataract extraction by phacoemulsification in uncomplicated eyes can be performed safely without prophylactic treatment in patients with severe FXI deficiency with or without inhibitor antibodies against FXI.