Thromboembolic events in patients with severe inherited fibrinogen deficiency.

Inherited afibrinogenemia and hypofibrinogenemia are rare bleeding disorders characterized by markedly reduced levels of fibrinogen in blood. Thrombotic complications in these disorders have been rarely described. We performed a multicenter retrospective study and reviewed the occurrence of thrombotic complications among patients with inherited fibrinogen deficiency. Cases were identified during a review of medical records of all patients with inherited fibrinogen deficiency followed at three different university hospitals in Israel. Nine patients were included in this study: five were afibrinogenemic and four hypofibrinogenemic. There were seven thrombotic events, mostly venous, that occurred in four out of nine patients (44 %). All thrombotic events occurred in afibrinogenemic patients. Mean age at the time of thrombosis was 45 (range 28-61) years. Thrombophilic evaluation performed was negative in all cases. At the time of thrombosis in five out of seven (71.4 %) events, fibrinogen replacement therapy was concurrently given. Therapeutic approach was different among patients ranging from supportive therapy alone, antiplatelet agents and anticoagulant therapy with the concurrent administration of fibrinogen replacement therapy. This study discloses a high rate of thrombosis in patients with afibrinogenemia. Events were both venous and arterial and may be recurrent. Management is highly problematic due to the precarious balance between bleeding and thrombotic risk in these patients. Fibrinogen replacement therapy should be cautiously used in these patients as most thrombotic events followed the administration of fibrinogen replacement therapy. Larger cohorts are warranted to better characterize the best management strategy in these paradoxical events.

The impact of thrombin generation and rotation thromboelastometry on assessment of severity of factor XI deficiency.

The phenotype of bleeding in patients with severe FXI deficiency is unpredictable and unlike other bleeding disorders, it is not directly correlated with levels of FXI. In this study we analyzed whether the global coagulation assays can serve as a clinical tool in predicting bleeding tendency in patients with severe FXI deficiency undergoing surgery, taking into account the large inter-individual variability of FXI levels and genotypes. Thrombin generation (TG) was measured in 39 platelet-poor plasma with or without tissue factor (TF) and in the presence or absence of corn trypsin inhibitor (CTI). Rotation thromboelastometry (ROTEM) was performed with fresh whole blood of 26 patients applying NATEM and INTEM tests. TG induced by recalcification can distinguish between bleeding and non-bleeding patients with severe FXI deficiency particularly among those with FXI activity of 2-20IU/dl. The addition of TF or TF and CTI to the TG assay masked the ability to differentiate between XI activity, genotype as well as bleeding and non-bleeding patients. ROTEM assays failed to distinguish bleeding from non-bleeding patients but could do so between different FXI activity levels and genotypes. In conclusion, in the current study we found a sensitive tool to distinguish between bleeding and non-bleeding patients. In order to recommend TG as a predictive tool for treatment tailoring, a larger patient group is required.

Severe factor X deficiency in three unrelated Palestinian patients is caused by homozygosity for the mutation c302delG-correlation with thrombin generation and thromboelastometry.

Factor X (FX) is one of the vitamin K-dependent serine proteases, which forms the prothrombinase complex converting prothrombin into thrombin. To search for mutations in F10 gene giving rise to severe FX deficiency and to study the contribution of thrombin generation and thromboelastometry as a tool for evaluation of hemostasis. Mutations in the F10 gene were sought by direct sequencing of all the eight exons and intron/exon boundaries. Thrombin generation and thromboelastometry were performed. Three unrelated Palestinian patients had undetectable FX level (<1 U/dl). All patients were found to be homozygous for c302delG, a new frameshift mutation in the F10 gene causing a stop codon at amino acid 73. The mutant allele was not detected among 152 Palestinians analyzed. Thrombin generation was examined in one of the patients 4 days after fresh frozen plasma was applied, when his FX level was 2 U/dl. Minute thrombin generation was observed, as compared to normal thrombin generation in heterozygotes for the mutation and a healthy control. Thromboelastometry revealed prolonged lag phase when patient's platelet-poor plasma and platelet-rich plasma were tested, with a slightly decreased initial clot formation rate, as compared to carriers' and control sample. Genetic analysis disclosed a unique mutation causing a severe phenotype. Thrombin generation assay may serve as a quick tool for confirming severe deficiency until the specific mutation is identified. Thrombin generation can also serve for monitoring and optimizing treatment. The correlation of thromboelastometry assay and severe FX deficiency is less striking.

A highly sensitive thrombin generation assay for assessment of recombinant activated factor VII therapy in haemophilia patients with an inhibitor.

Bypass agents are the common treatment for haemophilia patients who develop inhibitory antibodies. Laboratory assessment of the efficacy of bypassing agent therapy is a challenge. In the present work we modified the conditions triggering thrombin generation (TG) assay in order to find the most sensitive assay for detection of rFVIIa and its analogue NN1731 in haemophilic plasma. TG was measured in samples of normal plasma, plasma of haemophilia patient with inhibitors, as well as haemophilia induced plasma. Recalcification-induced TG was compared to tissue factor (TF) -induced TG in the presence and absence of rFVIIa and NN1731. Recalcification-induced TG (without TF) in haemophilic plasma yielded baseline flat curves, with increased TG as a consequence of spiking the plasma rFVIIa. Using our system, we observed both dose-dependence and time-dependence of rFVIIa effect on TG. Elevated concentrations of TF mask the difference between rFVIIa-treated and non-treated haemophilic plasma. NN1731 yielded normalisation of recalcification-induced TG curves (without TF) which may reflect high potency. In conclusion, we suggest that triggering TG by recalcification-only may be the most sensitive assay for determining the impact of bypassing agents in haemophilic plasma, and may serve as a caution surrogate safety marker in future studies.

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.

[Laboratory evaluation of lupus anticoagulant in Israel].

Lupus anticoagulants (LAC) are antibodies which are detected by a prolongation of phospholipid-dependent coagulation assays, and are associated with thrombotic events and pregnancy complications in patients with the antiphospholipid syndrome. The antiphospholipid syndrome is defined by arterial or venous thrombosis and/or pregnancy morbidity and by laboratory diagnosis of antiphospholipid antibodies. The laboratory diagnosis is based on LAC and/or anticardiolipin and/or anti-beta2-glycoprotein I antibodies present in plasma, on two or more occasions at least 12 weeks apart. ALthough the presence of LAC correlates best with thrombosis, the Laboratory testing of LAC is not well standardized. In this article, the Laboratory evaluation of LAC will be explained, including the different tests that are recommended by the Israeli Sub-committee of Thrombosis and Hemostasis Laboratories, the possibility to evaluate LAC in patients treated with antithrombotic therapy, and how to report and interpret the results.

Risk factors for failure of heparin thromboprophylaxis in patients with acute traumatic spinal cord injury.

UNLABELLED: Venous thromboembolism (VTE) is a well-recognized complication of Acute Traumatic Spinal Cord Injury (ATSCI). Despite prophylaxis by heparins, VTE occurs in a substantial number of ATSCI patients without an obvious explanation. In this matched case-control study we examined whether thrombophilia and other risk factors are associated with failure of thromboprophylaxis. Cases and controls receiving heparin thromboprophylaxis were selected from consecutively admitted ATSCI patients. Patients who developed a new, objectively confirmed, symptomatic VTE despite prophylaxis at hospital were matched by gender, age, level and mechanism of ATSCI with 2-3 controls without VTE. Patients were interviewed about VTE risk factors and tested for factor V Leiden (FVL), prothrombin G20210A (PT), methylenetetrahydrofolate reductase C677T homozygosity (MTHFR), lupus anticoagulant, homocysteine (Hcy) and plasma factor VIII (FVIII) levels. Twenty-two patients with new VTE episodes and 64 controls were ascertained. The total number of gene alterations for MTHFR, FVL and PT or elevated levels of Hcy or FVIII was significantly more common in patients compared to controls (82% vs. 48%, p=0.006). Multiple logistic regression proved the PT mutation, a positive family history of thrombosis and elevated levels of either FVIII or Hcy to be predictors of thrombosis. CONCLUSION: A positive family history of VTE, carriership of the prothrombin mutation and elevated FVIII or Hcy levels were significantly associated with failure to prevent VTE by heparin therapy following ATSCI. Testing for thrombophilia in patients with ATSCI and possibly a more intense thromboprophylactic regimen seem desirable but need to be verified by a prospective study.

Thrombin generation assay as a possible tool for assessment of reduced activity of clotting factors induced by antiphospholipid antibodies and in-vitro evaluation of treatment options.

Bleeding is a rare manifestation of antiphospholipid syndrome, unless associated with reduced clotting factors or severe thrombocytopenia. Accurate assessment of the autoantibodies in plasma is very important since the autoantibodies can lead to bleeding or thrombosis. The objective of the present study was to define the inhibitors causing reduced clotting activity in a patient with antiphospholipids antibodies and to assess the potential of thrombin generation assay to assist in establishment of optimal treatment in case of major bleeding. Levels of clotting factors as well as inhibitors to factors II, V, VII, VIII, IX, X and XI were defined. For detection of inhibitors to prothrombin crossed immunoelectrophoresis was used. IgG was purified by commercial protein A column. Thrombin generation was measured using a fluorometric assay in platelet-poor and platelet-rich plasma. Inhibitors toward the activity of factors V, VII, VIII, IX, X and XI were defined and also an inhibitor to prothrombin antigen. No thrombin generation was induced in the patient's plasma by recalcification even in the presence of recombinant factor VIIa or factor VIII inhibitor bypassing activity. In contrast, addition of platelets from either donor or patient or synthetic phospholipids normalized the thrombin generation. The thrombin generation model showed that the addition of platelets and no recombinant factor VIIa or factor VIII inhibitor bypassing activity would correct thrombin generation in vitro. On this basis, platelet concentrates were administered to a patient with bleeding caused by lupus anticoagulant and low clotting factors activity.

Induction of an inhibitor antibody to factor XI in a patient with severe inherited factor XI deficiency by Rh immune globulin.

In this paper, we report an inhibitor antibody to factor XI (FXI) in a woman with severe inherited FXI deficiency, induced by FXI present in an Rh immune globulin preparation. The patient is homozygous for the Glu117Stop mutation, associated with a FXI level of less than 1 U/dL. Unlike all previously described patients with severe FXI deficiency and an inhibitor, the patient had never been exposed to blood products. Following 3 injections of Rh immune globulin during pregnancy, she developed an inhibitor to FXI (8 Bethesda units) that was shown to bind specifically to FXI and inhibit factor IX cleavage by purified FXIa. The administered Rh immune globulin and 2 other similar products were shown to contain FXI. Clinicians should be aware of the potential for immunization of severely FXI-deficient patients by FXI present in Rh immune globulin preparations.

Characterization of seven novel mutations causing factor XI deficiency.

BACKGROUND AND OBJECTIVES: Factor XI (FXI) deficiency is a rare autosomal recessive disorder, the main manifestation of which is injury-related bleeding. The disorder is rare in most populations, but common among Jews in whom two mutations, E117X and F283L, account for 98% of cases. Other mutations, C38R and C128X, are prevalent in French Basques and Britons, respectively. Additional sporadic mutations have been described in most parts of the world. The objective of this study was to identify the mutations in 15 unrelated FXI-deficient patients and characterize missense mutations by expression in baby hamster kidney (BHK) cells. DESIGN AND METHODS: Clinical and laboratory information and DNA samples were obtained from the patients and mutations were identified by sequencing. Missense mutations were expressed in BHK cells and their effect on FXI secretion and dimerization was assessed using enzyme-linked immunosorbent assay and immunoblotting. RESULTS: Of 16 mutations detected, seven are novel including two deletions, one splice site and four missense mutations. Expression of the four novel missense mutations (C58Y, Y427C, C527Y and V20A) in cells revealed no secretion of FXI-C58Y, Y427C and C527Y and secretion of only 22% of normal in the medium for FXI-V20A. Secretion of FXI from BHK cells harboring a previously reported E297K substitution cells was also impaired (4.5% of wild-type). Homodimerization was normal for all five mutants. INTERPRETATION AND CONCLUSIONS: Defective homodimerization of FXI was previously recognized as a major mechanism for defective secretion of FXI from producing cells. In this study, five FXI missense mutations (four novel) were associated with impaired secretion albeit normal dimerization, underscoring the existence of other mechanisms for defective secretion.

Age estimates of ancestral mutations causing factor VII deficiency and Dubin-Johnson syndrome in Iranian and Moroccan Jews are consistent with ancient Jewish migrations.

Factor VII (FVII) deficiency and Dubin-Johnson syndrome (DJS) are rare autosomal recessive disorders caused by mutations in F7 and MRP2 genes, respectively. Both disorders are relatively frequent among Iranian and Moroccan Jews. FVII deficiency in both populations is caused by a founder A244V mutation in the F7 gene and DJS is caused by two founder mutations, I1173F and R1150H in the MRP2 gene that are specific for Iranian and Moroccan Jewish patients, respectively. We estimated the age of FVII A244V and MRP2 I1173F by analysis of microsatellite markers flanking F7 and MRP2 genes, respectively, in 13 Iranian Jewish homozygotes for the I1173F mutation and 21 Iranian and Moroccan Jewish homozygotes for the A244V mutation. Dating of the mutations was estimated by the DMLE+2.0 program employing observed linkage disequilibria of multiple genetic markers. The estimated age of the I1173F mutation was approximately 1500 years, and the age of the A244V mutation was approximately 2600 years. These estimates suggest that I1173F causing DJS in Iranian Jews occurred after the separation of Iranian Jews from Moroccan Jews 2000-2600 years ago, while A244V causing FVII deficiency in Iranian and Moroccan Jews occurred prior to the divergence of these two populations.

Prothrombin 20210G>A is an ancestral prothrombotic mutation that occurred in whites approximately 24,000 years ago.

Prothrombin 20210G>A and factor V Leiden are common prothrombotic mutations in whites for which founder effects have been established. In this study, we analyzed the frequencies of 5 single nucleotide polymorphisms (SNPs) and 9 microsatellites flanking the prothrombin gene (F2) in 88 homozygotes for 20210A and 66 homozygotes for 20210G. For estimating the age of the prothrombin 20210G>A mutation, we used the DMLE+2.0 program, which analyzed linkage disequilibria between the mutation and the multiple markers that had been assessed. This analysis yielded an age estimate of 23,720 years (95% credible set, 19,080-31,340 years). A similar analysis by the DMLE+2.0 program was performed on 5 SNPs from previously studied homozygotes for factor V Leiden and controls that yielded an age estimate of 21,340 years (95% credible set, 16,880-29,480 years). The occurrence of the 2 mutations in whites toward the end of the last glaciation and their presently wide distribution in whites suggest selective evolutionary advantages for which some evidence was reported (diminished blood loss) or is controversial (protection against infections).

Inhibitors to Factor XI in patients with severe Factor XI deficiency.

Factor XI (FXI) deficiency is a rare bleeding disorder that may arise from any of a number of missense, nonsense, splice site, insertion, and deletion mutations within the FXI gene. Severely affected patients are at considerable risk of developing inhibitors to FXI and, although spontaneous bleeding is uncommon in such patients, bleeding after surgery or trauma can be severe. As treatment with fresh frozen plasma (FFP) or FXI concentrates is ineffective in patients with inhibitors, other therapies must be sought. Traditionally, such patients have been treated with various agents and methods, including plasma exchange, cyclophosphamide, intravenous immunoglobulin, and prothrombin complex concentrates. However, emerging data indicate that recombinant activated factor VII (rFVIIa; NovoSeven, Novo Nordisk, Bagsvaerd, Denmark) may also be effective in FXI deficiency with inhibitors. Further work is required to determine the optimal dosing schedules of the agent in this indication.

Of four mutations in the factor VII gene in Tunisian patients, one novel mutation (Ser339Phe) in three unrelated families abrogates factor X activation.

Hereditary factor VII (FVII) deficiency is a rare bleeding disorder. Dysfunctional FVII variants characterized by normal or reduced levels of FVII antigen and discordantly low FVII activity have been described. In this study, seven unrelated Tunisian patients with FVII deficiency were examined. Molecular analysis revealed that three probands harbored a novel Ser339Phe mutation, one proband was inferred to have a novel splice site mutation in intron 2, c.226-2 A>G and three probands had two previously described mutations, Arg304Gln and Cys310Phe. Expression of Ser339Phe in baby hamster kidney cells yielded secretion of FVII antigen at a concentration of 225+/-50 ng/ml, compared with 181+/-47 ng/ml in cells transfected with wild-type FVII but with no demonstrable FVII activity. FVII Ser339Phe bound to tissue factor similarly to the binding of commercial recombinant activated FVII or recombinant wild-type FVII and was normally activated by activated factor X. The major defect of FVII Ser339Phe was its inability to activate factor X in the presence of tissue factor. Modeling predicted that the substitution of Ser339 by Phe abrogated substrate docking.

A novel ancestral splicing mutation in the multidrug resistance protein 2 gene causes Dubin-Johnson syndrome in Ashkenazi Jewish patients.

Dubin-Johnson syndrome (DJS) is an inherited disorder characterized by chronic conjugated hyperbilirubinemia due to the absence or dysfunction of the multidrug resistance protein 2 (MRP2). We previously identified two distinct ancestral mutations causing DJS in 22 unrelated Iranian and five unrelated Moroccan Jewish patients, respectively. In this study we identified and characterized the mutation causing DJS in Ashkenazi Jewish patients and assessed a possible founder effect. Sequencing of all 32 exons of the MRP2 gene identified a novel IVS8+4A-->G mutation in three unrelated homozygotes. Haplotype analysis using four intragenic dimorphisms disclosed a founder effect for the mutation. RT-PCR and real time PCR analysis of mRNA from one patient revealed three splice variants all leading to frameshifts and predicting premature termination codons. The main splice variant was a consequence of the use of a cryptic donor splice site inside exon 8. Liver biopsy in one patient revealed complete absence of MRP2 from the canalicular membrane of hepatocytes. In conclusion, our results provide strong evidence that an ancestral IVS8+4A-->G mutation causes DJS in Ashkenazi Jewish patients by abolishing normal splicing of intron 8 leading to aberrantly spliced products that predict truncation of MRP2.

Plasma replacement therapy during labor is not mandatory for women with severe factor XI deficiency.

Severe factor XI deficiency is an injury-related bleeding disorder. The risk of excessive post-partum hemorrhage in affected women has so far been evaluated in a relatively small number of patients and it is uncertain whether prophylactic treatment with fresh frozen plasma or factor XI concentrate is needed during or after vaginal or cesarean delivery. We retrospectively analyzed bleeding manifestations related to vaginal and/or cesarean deliveries in a cohort of 62 women with factor XI activity < 17 U/dl and evaluated whether replacement therapy is essential. Fifty-one women had 139 vaginal deliveries, six women had 13 cesarean deliveries, and five women had seven vaginal as well as five cesarean deliveries. Forty-three of the 62 women (69.4%) never experienced post-partum hemorrhage during 93 deliveries (85 vaginal, eight cesarean). Hemorrhage occurred in 19 women, which in six women accompanied each one of their 17 vaginal deliveries. Post-partum hemorrhage had no relationship with the abnormal genotype that caused factor XI deficiency nor with factor XI level. These observations suggest that the use of fresh frozen plasma or factor XI concentrate during and/or after vaginal delivery is not mandatory in women with severe factor XI deficiency and can be reserved for patients who develop excessive hemorrhage. For women requiring cesarean section it appears that the same policy can be advocated but more observations are needed.

A mutation in LMAN1 (ERGIC-53) causing combined factor V and factor VIII deficiency is prevalent in Jews originating from the island of Djerba in Tunisia.

Combined deficiency of factor V and factor VIII is a rare autosomal recessive bleeding disorder that is caused by mutations in the LMAN1 or MCFD2 genes. These genes encode for proteins that form a complex that takes part in the transport of factor V and factor VIII from the endoplasmic reticulum to Golgi. Two mutations in LMAN1 have been observed in Jews: a guanine (G) insertion in exon 1 among Middle Eastern Jewish families, and a thymidine (T) to cytosine (C) transition in intron 9 at a donor splice site among Tunisian families. For each mutation, haplotype analysis revealed a founder effect. Because all affected Tunisian families belong to an ancient Jewish community in the island of Djerba off the coast of Tunisia, we screened members of this community for the intron 9 T --> C transition. Among 233 apparently unrelated individuals five heterozygotes were detected, predicting an allele frequency of 0.0107 (95% confidence interval, 0.0035-0.0248), while among 259 North African Jews none was found to carry the mutation. The prevalence of the mutation in Djerba Jews is consistent with the observation that all affected Tunisian Jewish families have origins in Djerba and with the finding of a common haplotype for the 9 + 2 T --> C mutation. The G insertion in exon 1 was found in one of 245 Iraqi Jews, predicting an allele frequency of 0.0022 (95% confidence interval, 0.0001-0.0123), but in none of 180 Iranian Jews examined. In view of the relatively low frequency of the mutations in the respective populations it seems reasonable to advocate carrier detection and prenatal diagnosis only in affected families.

High prevalences of vitamin B12 and folic acid deficiency in elderly subjects in Israel.

The prevalences of vitamin B12 and folic acid deficiency in the general Israeli population of elders has not been assessed. We measured plasma cobalamin and folic acid concentrations in 418 subjects from four institutions for the aged, 749 subjects attending 19 geriatric day centres and 104 healthy controls. Methylmalonic acid (MMA) and/or homocysteine concentrations were determined in subjects who had a cobalamin concentration <221 pmol/l or folic acid concentration <11 nmol/l respectively. The prevalences of vitamin B12 deficiency (cobalamin <147 pmol/l and MMA > or =0.24 micromol/l), and folic acid deficiency (folic acid <11 nmol/l and homocysteine of >15 micromol/l) in subjects from day centres were 12.6% and 16.4% respectively, and in subjects from institutions 1.2% and 2.2% respectively (P < 0.001). Multiple logistic regression analysis indicated that the relative risk of living at home versus institutions for the aged was highly significant, with odds ratios (OR) of 6.8 [95% confidence interval (CI) 2.6-18.0] for vitamin B12 deficiency and 6.6 (95% CI 2.9-13.1) for folic acid deficiency. Analysis of data for day centre patients showed that folic acid deficiency was a significant risk factor of vitamin B12 deficiency (adjusted OR 3.68, 95% CI 2.27-5.98), and vitamin B12 deficiency was a significant risk of folic acid deficiency (adjusted OR 3.69, 95% CI 2.27-6.01). These data suggest that malnutrition is a major cause of the highly prevalent deficiencies of vitamin B12 and/or folic acid in elderly Israeli subjects dwelling at home.

Major mutations in calf-1 and calf-2 domains of glycoprotein IIb in patients with Glanzmann thrombasthenia enable GPIIb/IIIa complex formation, but impair its transport from the endoplasmic reticulum to the Golgi apparatus.

The crystal structure of integrin alphavbeta3 comprises 3 regions of contact between alphav and beta3. The main contact on alphav is located in the beta-propeller while calf-1 and calf-2 domains contribute minor interfaces. Whether or not contacts between calf-1 and calf-2 domains of glycoprotein (GP) IIb (alphaIIb) and GPIIIa (beta3) play a role in GPIIb/IIIa complex formation has not been established. In this study we analyzed the effects of 2 naturally occurring mutations in calf-1 and calf-2 domains on GPIIb/IIIa complex formation, its processing, and transport to the cell membrane. The mutations investigated were a deletion-insertion in exon 25 located in calf-2 and an in-frame skipping of exon 20 located in calf-1. Mutated GPIIb cDNAs were cotransfected in baby hamster kidney cells with normal GPIIIa (beta3) cDNA. Analysis by flow cytometry failed to demonstrate detectable amounts of GPIIb or GPIIb/IIIa complex on the surface of cells transfected with each mutation, but immunohistochemical staining revealed their intracellular presence. GPIIb was mainly demonstrable as pro-GPIIb by immunoprecipitation of cell lysates expressing each mutation. Differential immunofluorescence staining of GPIIb and cellular organelles suggested that most altered complexes were located in the endoplasmic reticulum. Homology modeling of normal GPIIb based on the alphavbeta3 crystal structure revealed similar contacts between alphav and beta3 and between alphaIIb and beta3. Introduction of the mutations into the model yielded partial disruption of the normal contacts in the corresponding domains. These data suggest that despite partial disruption of calf-1 or calf-2 domain, GPIIb/IIIa complex is formed but its transport from the endoplasmic reticulum is impaired.

Prevalence, causes, and characterization of factor XI inhibitors in patients with inherited factor XI deficiency.

Factor XI deficiency, an injury-related bleeding disorder, is rare worldwide but common in Jews in whom 2 mutations, Glu117Stop (type II) and Phe283Leu (type III), prevail. Mean factor XI activities in homozygotes for Glu117Stop and for Phe283Leu are 1 and 10 U/dL, respectively. Inhibitors to factor XI in patients with severe factor XI deficiency have been reported in a small number of instances. This study was undertaken to determine the prevalence of acquired inhibitors against factor XI in patients with severe factor XI deficiency, discern whether these inhibitors are related to specific mutations, and characterize their activity. Clinical information was obtained from unrelated patients with severe factor XI deficiency, and blood was analyzed for factor XI activity, inhibitor to factor XI, and causative mutations. Immunoglobulin G purified from patients with an inhibitory activity was tested for binding to factor XI, effects on activation of factor XI by factor XIIa and thrombin, and activation of factor IX by exogenous factor XIa. Of 118 Israeli patients, 7 had an inhibitor; all belonged to a subgroup of 21 homozygotes for Glu117Stop who had a history of plasma replacement therapy. Three additional patients with inhibitors from the United Kingdom and the United States also had this genotype and were exposed to plasma. The inhibitors affected factor XI activation by thrombin or factor XIIa, and activation of factor IX by factor XIa. The results imply that patients with a very low factor XI level are susceptible to development of an inhibitor following plasma replacement.