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A variant in prothrombin (clotting factor II), a G to A transition at nucleotide position 20210, has recently been shown to be associated with the prothrombin plasma levels and the risk of both venous and arterial thrombosis. The purpose of this study was to investigate the prevalence of carriership of this mutation in various populations. We combined data from 11 centres in nine countries, where tests for this mutation had been performed in groups representing the general population. We calculated an overall prevalence estimate, by a precision-weighted method, and, since the distribution of the prevalences did not appear homogeneous, by an unweighted average of the prevalences. We examined differences in the prevalences by geographical location and ethnic background as a possible explanation for the heterogeneity. Among a total of 5527 individuals who had been tested, 111 heterozygous carriers of the 20210A mutation were found. The prevalence estimates varied from 0.7 to 4.0 between the centres. The overall prevalence estimate was 2.0 percent (CI95 1.4-2.6%). The variation around the summary estimate appeared more than was expected by chance alone, and this heterogeneity could be explained by geographic differences. In southern Europe, the prevalence was 3.0 percent (CI95 2.3 to 3.7%), nearly twice as high as the prevalence in northern Europe (1.7%, CI95 1.3 to 2.2%). The prothrombin variant appeared very rare in individuals from Asian and African descent. The 20210A prothrombin variant is a common abnormality, with a prevalence of carriership between one and four percent. It is more common in southern than in northern Europe. Since this distribution within Europe is very different to that of another prothrombotic mutation (factor V Leiden or factor V R506Q), founder effects are the most likely explanation for the geographical distribution of both mutations.

The presence of lupus anticoagulant (LAC) is strongly correlated with a history of thrombosis in patients with SLE. LAC activity can be caused by anti-prothrombin (FII)- and/or anti-beta2glycoprotein I (beta2GPI)-antibodies. In the present study, the contribution of anti-FII-antibodies to LAC activity was measured in 28 LAC positive plasmas. Plasmas were incubated with prothrombin or BSA, immobilized on CNBr-activated Sepharose, to absorb all anti-FII-antibodies. In 4 out of the 28 plasmas LAC activity was completely dependent on anti-FII-antibodies. In 7 out of the 28 plasmas, anti-FII-antibodies did not contribute to LAC activity. These anti-FII-antibodies can be regarded as non-functional antibodies. In the majority (17/28) of the samples, LAC activity within a single plasma was caused by a combination of antibodies with different specificities. Both dRVVT and KCT showed comparable sensitivity for the detection of functional anti-FII-antibodies. In conclusion, in most samples LAC activity is not caused by anti-FII-antibodies alone but by a combination of different types of antibodies. The presence of LAC activity and anti-FII-antibodies in one plasma does not automatically implicate that these antibodies are responsible for the LAC activity.

Conflicting results of an association between the human platelet antigen 1b (HPA-1b or PlA2) allele and the risk of myocardial infarction and coronary artery disease have been reported. To assess the reason for this discrepancy, we determined the HPA-1 genotype in 298 men who had undergone coronary angiography, including 124 individuals with myocardial infarction, 83 individuals with coronary artery disease but no history of myocardial infarction, and 91 control patients. Among patients with acute or recent onset myocardial infarction (< 1 year), the prevalence of HPA-1b was higher than among patients with coronary artery disease but without myocardial infarction (33 percent vs. 14 percent, p = 0.016). In patients under 60 years of age this difference was even more pronounced (45 percent vs. 15 percent, p = 0.003). Unlike conventional risk factors HPA-1b does not represent a risk factor for coronary artery disease itself but appears to be associated with increased platelet thrombogenicity.

Superficial venous thrombotic (SVT) events are a feature of thrombophilic abnormalities, particularly those involving the protein C pathway. We have determined the incidence of SVT associated with pregnancy and the early postpartum period in a retrospective study involving 72000 deliveries. Fourty-nine cases occurring in 47 individuals were recorded, with an overall incidence of 0.68/1000 deliveries (95% CI 0.48-0.88). None had a previous history of deep vein thrombosis or pulmonary embolism. Most events occurred in the early postpartum period (0.54/1000 deliveries). Twenty-four/fourty-seven were screened for established thrombophilic abnormalities, with only 1 abnormality detected (FV(Leiden) heterozygote). Thrombophilia may play a minor role in the aetiology of SVT associated with pregnancy, although a larger study is required to confirm this.

Reduced fibrinolytic capacity due to increased plasminogen activator inhibitor-1 (PAI-1) activity in plasma is a common finding in patients with coronary heart disease or venous thromboembolism, although its clinical significance is debated. Recently, a dimorphism in the PAI-1 promoter (4G-5G) has been reported and homozygosity for the 4G allele is associated with increased transcription and higher PAI-1 levels. Homozygous 4G genotype has been suggested to be a risk factor for myocardial infarction. In the present study, the 4G-5G dimorphism was determined in 349 individuals from 21 thrombophilic families with hereditary protein S deficiency and in 140 unrelated healthy controls. Among the 143 protein S deficient individuals, there was no relationship between deep or superficial venous thrombosis and the PAI-1 dimorphism. However, 26% (12/46) of individuals having protein S deficiency combined with homozygosity for the 4G allele had suffered pulmonary embolism as compared to 7% (7/97) of protein S deficient individuals carrying at least one 5G allele (p = 0.0019). In protein S deficient individuals, arterial thrombosis was found to be associated with smoking and 4G homozygosity. No association was found between the PAI-1 dimorphism and arterial or venous thromboembolism in family members without protein S deficiency. In conclusion, the PAI-1 genotype affects the phenotypic expression of thrombophilia in protein S deficient individuals.

Severe hyperhomocysteinemia in its most frequent form, is caused by a homozygous enzymatic deficiency of cystathionine beta-synthase (CBS). A major complication in CBS deficiency is deep venous thrombosis or pulmonary embolism. A recent report by Mandel et al (N Engl J Med 334:763, 1996) postulated factor V Leiden (FVL) to be an absolute prerequisite for the development of thromboembolism in patients with severe hyperhomocysteinemia. We studied 24 patients with homocystinuria caused by homozygous CBS deficiency from 18 unrelated kindreds for FVL and for the 677C-->T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene and investigated their possible interaction in the risk of venous thrombosis. Thrombotic complications were diagnosed in six patients, of whom only one was a carrier of FVL. On the contrary, thermolabile MTHFR caused by the 677C-->T mutation, was frequently observed among homocystinuria patients, especially among those with thromboembolic complications: three of six homocystinuria patients who had suffered from a thromboembolic event had thermolabile MTHFR. These data indicate that FVL is not an absolute prerequisite and probably not even a major determinant of venous thrombosis in homocystinuria, but, interestingly, thermolabile MTHFR may constitute a significant risk factor for thromboembolic complications in this inborn error of methionine metabolism.

To evaluate the significance of common thrombophilic genotypes in subjects with idiopathic antiphospholipid antibodies (aPL) we determined the methylenetetrahydrofolate reductase C677-->T (MTHFR) and factor V A506-->G (FV Leiden) polymorphisms in 49 subjects with idiopathic aPL (57% of whom suffered spontaneous vein thrombosis), in 70 subjects with a history of spontaneous vein thrombosis and in 193 healthy subjects. The prevalence of MTHFR C677-->T+/+ (homozygotes) was 25%, 18% and 17% respectively amongst aPL thrombotics, non aPL thrombotics and controls and that of MTHFR C677-->T+/- (heterozygotes) was 53%, 59% and 53% respectively in the same groups. The prevalence of FV Leiden was higher in aPL thrombotics (14%) and in non aPL thrombotics (18%) than in controls (4%) (p < or = 0.05). APL thrombotics with MTHFR C677-->T+/+ had a lower mean age at first thrombotic event (22 +/- 6 years) than aPL thrombotics with MTHFR C677-->T+/- and non mutated considered together (38 +/- 14 years, p = 0.0004) and than non aPL thrombotics with MTHFR C677-->T+/+ (38 +/- 14 years, p = 0.003). FV Leiden may contribute to the hypercoagulability of a small, albeit significant proportion of thrombotic aPL subjects, whereas the association between MTHFR C677-->T+/+ and aPL may have an impact on age at first occlusive event and suggests a possible pathogenetic interaction.

Twenty-nine clinically well-characterized, symptomatic index patients, 15 with protein C and 14 with protein S deficiency, in whom the genetic defect had been identified, were investigated for the presence of factor V Leiden. In six of 15 (40%) propositi with protein C and four of 14 (29%) with protein S deficiency, factor V Leiden was present. The age at first thrombosis was significantly lower (P < 0.001) in the ten propositi with a combined genetic defect (mean age 18.4 +/- 6.6 years) than in those with a single defect (mean age 32.6 +/- 10.4 years). Spontaneous occurrence, recurrence and site of thrombosis were similar in propositi with the single and the combined defect. Family studies led to the identification of a combined defect in 18 individuals from 11 families (11 propositi and 29 relatives), seven subjects had no abnormality, and in 15 a single defect was found. In individuals with a combined defect, thrombosis-free survival time was significantly shorter than in individuals with a single defect, even after exclusion of index patients. None of the seven individuals without genetic abnormality had experienced thrombosis. Our findings indicate a higher risk for development of thrombosis in individuals with a combined defect compared with those with a single defect.

Several studies have demonstrated a higher risk of thrombosis in carriers of anticoagulant deficiencies than in non-deficient individuals from families with thrombophilia. The prevalences in Spain were established in a multicenter study (the EMET study) and all the deficient individuals were invited to recruit all available family members to be screened for the same deficiency in order to establish the risk of thrombosis in deficient individuals. Five-hundred-and-eighty-three individuals from 114 families with natural anticoagulant deficiencies were analysed. Propositi and relatives with a history of thrombosis were asked about the localization and the age at the first episode and whether or not it was spontaneous. Three families with antithrombin deficiency, 35 with protein C, 60 with protein S, four with plasminogen, four with heparin cofactor II, seven with combined deficiencies and one family with dysfibrinogenemia were included in the analysis. The risk of thrombosis was increased for individuals deficient in antithrombin (adjusted odds ratio 21.23; 95% confidence interval 5.71-78.94), protein C (adjusted odds ratio 12.62; 95% confidence interval 4.75-33.51), protein S type I (adjusted odds ratio 19.95; 95% confidence interval 7.40-53.82), protein S type III (adjusted odds ratio 8.11; 95% confidence interval 2.66-21.99) or in protein C plus protein S (adjusted odds ratio 8.99; 95% confidence interval 2.79-28.93), but not for those deficient in plasminogen or heparin cofactor II. The thrombosis-free survival was shortened for deficient individuals in antithrombin (median 30 years), protein C (median 46 years), protein S type-I (median 48 years), protein S type III (median 61 years) and combined protein C and S (median 40 years). In conclusion, individuals carrying anticoagulant deficiencies have an increased risk of thrombosis, especially those with antithrombin, protein C or type I protein S deficiencies.

IgA anticardiolipin (IgA aCL) and IgA anti beta2-glycoprotein-I (IgA anti beta2GP1) antibodies are common in SLE and have been associated in some studies with thromboses and thrombocytopenia. Experimental work suggests that IgA aCL are as prothrombotic as the IgG-IgM isotypes. However, in SLE there appears to be less concordance between IgA aCL and IgA anti beta2GP1 as compared with the concordance between IgG and IgM isotypes, suggesting significant differences in their origins and specificities. For example, there may be a greater mucosal contribution to production of IgA antibeta2GP1 than IgA aCL. Infections may have a greater role in the presence of IgA aCL than IgA antibeta2GP1 antibodies.

The presence of the 20210A allele of the prothrombin (PT) gene has recently been shown to be a risk factor for venous thromboembolism. This is probably mediated through increased plasma prothrombin levels. The aim of this study was to compare the prevalence of the prothrombin 20210A allele in control subjects and in subjects with recognised thrombophilia and to establish whether the additional inheritance of the PT 20210A allele is associated with an increased risk of venous thromboembolism. 101 subjects with a history of venous thromboembolism and diagnosed as having either factor V Leiden (R506Q) or heritable deficiencies of protein C, protein S or antithrombin were studied. The prevalence of the PT 20210A allele in this group was compared with the results obtained for 150 control subjects. In addition, the relationships were examined between genetic status and the number of documented thromboembolic episodes, and between plasma prothrombin levels and possession of the PT 20210A allele. 8 (7.9%) of the 101 patients were also heterozygous for the PT 20210A allele. This compares with 0.7% in the control subjects (p = 0.005). After exclusion of patients on warfarin, the mean plasma prothrombin of 113 subjects without 20210A was 1.09 U/ml, as compared with 1.32 U/ml in 8 with the allele (p = 0.0002). Among the 101 patients with either factor V Leiden, protein S deficiency, protein C deficiency or antithrombin deficiency, the age adjusted mean (SD) number of venous thromboembolic episodes at diagnosis was 3.7 (1.5) in those with the PT 20210A allele, as compared with 1.9 (1.1) in those without (p = 0.0001). We have demonstrated that the prevalence of the PT 20210A allele is significantly greater in subjects with venous thrombosis and characterised heritable thrombophilia than in normal control subjects and that the additional inheritance of PT 20210A is associated with an increased risk of venous thromboembolism. We have also confirmed that plasma prothrombin levels are significantly greater in subjects possessing the PT 20210A compared with those who do not.

The hypothesized relationships between plasminogen activator inhibitor (PAI-1) genotypes, PAI-1 levels, and their potential regulation by hypertriglyceridemic (HTG) very low density lipoprotein (VLDL) and lipoprotein(a) [Lp(a)] was examined in a PAI-1 genotyped human umbilical vein endothelial cell (HUVEC) culture model system. Individual human umbilical veins were used to obtain cultured ECs and were genotyped for PAI-1 by using the HindIII restriction fragment length polymorphism (RFLP) as a marker for genetic variation. Digested genomic DNA, examined by Southern blot analysis and probed with an [alpha-32P]dCTP-labeled 2.2-kb PAI-1 cDNA, yielded three RFLPs designated 1/1 (22-kb band only), 1/2 (22-plus 18-kb bands), and 2/2 (18-kb band only). Individual PAI-1 genotyped HUVEC cultures were incubated in the absence or presence of HTG-VLDL (0 to 50 micrograms/mL) or Lp(a) (0 to 50 micrograms/mL) at 37 degrees C for various times (4 to 24 hours), followed by analyses of PAI-1 antigen (by ELISA) and mRNA (by ribonuclease protection assay) levels, EC surface-localized plasmin generation assays, and nuclear run-on transcription assays. Secreted PAI-1 antigen levels were increased approximately 2- to 3-fold by HTG-VLDL and approximately 1.6 to 2-fold by Lp(a); mRNA levels were increased approximately 3- to 4.5-fold by HTG-VLDL and approximately 2.5- to 3.2-fold by Lp(a) compared with medium-incubated controls, primarily in the 2/2 PAI-1 genotype HUVEC cultures. Increases in PAI-1 mRNA induced by HTG-VLDL or Lp(a) could be abolished by coincubation with actinomycin D (2 x 10(-6) mol/mL) or puromycin (1 microgram/mL). In addition, nuclear transcription run-on assays typically demonstrated that HTG-VLDL increased PAI-1 gene transcription rates by approximately 5- to 6-fold and approximately 4- to 5-fold, respectively, primarily in the 2/2 PAI-1 genotype HUVEC cultures compared with 1/1 PAI-1 genotype HUVEC cultures or medium-incubated controls. The positive control interleukin-1 increased both 2/2 and 1/1 PAI-1 mRNA levels by approximately 5- to 6-fold. Increased PAI-1 antigen and mRNA expression were associated with a concomitant 50% to 60% decrease in plasmin generation. These combined results demonstrate the genotype-specific regulation of PAI-1 expression by HTG-VLDL and Lp(a) and further indicate that these risk factor-associated components regulate PAI-1 gene expression at the transcriptional level in cultured HUVECs. Results from these studies further suggest that individuals with this responsive 2/2 PAI-1 genotype may reflect the additional inherent potential for later HTG-VLDL- or Lp(a)-induced fibrinolytic dysfunction, resulting in the early initiation of thrombosis, atherogenesis, and coronary artery disease.

We studied 172 Greek patients (72 men aged 44.0 +/- 16.7 years and 100 women aged 46.5 +/- 14.1 years) with an unexplained thrombophilic tendency. One hundred and four apparently healthy persons (63 men aged 34.2 +/- 10.0 years and 41 women aged 37.1 +/- 13.3 years) were included as a control group. We performed the activated protein C resistance (APC-r) test using a clotting test (Chromogenix kit), detection of factor V Leiden using polymerase chain reaction (PCR)-restriction fragment length polymorphisms and measurement of thrombin-antithrombin complexes (TAT) and prothrombin fragment 1 + 2 (F1 + 2) levels with an immunoenzymatic assay. The normal range for the APC-r test (> 2.12) was determined from the controls. The factor V Leiden mutation was found in 31.9% of all the patients tested, in 28.1% of the unrelated patients with documented thrombophilic tendency of unknown origin and in 4.8% of the healthy controls. The APC-r test had a sensitivity of 0.42 and a specificity of 0.91 for the detection of factor V Leiden. Furthermore, we found no significant difference in levels of TAT and F1 + 2 between patients with and without the mutation and there was no correlation between aPC-r values and levels of TAT and F1 + 2.

This case-control study examined the prevalence of a prothrombin gene mutation in the 3'-untranslated region (UTR) first reported by Poort et al in Dutch subjects with a history of venous thrombosis and in matched control subjects without a history of thrombosis. We tested the hypothesis that the presence of the 3'UTR prothrombin mutation would convey a higher risk of venous or arterial thrombosis and therefore would be found in a higher-than-normal percentage of subjects with a history of thrombosis. Our study included 100 subjects: 50 with a history of thrombosis (21 with venous thrombosis and 29 with arterial thrombosis, who had been recruited from an anticoagulation clinic) and 50 control subjects without a history of thrombosis. DNA from these subjects was analyzed by polymerase chain reaction and agarose gel electrophoresis. We found a statistically significant increase in the prevalence of the 3'UTR mutation in subjects with a history of venous thrombosis compared with subjects without thrombosis. The prevalence of the 3'UTR prothrombin mutation was 19% (4/21;3 heterozygous and 1 homozygous) in subjects with a history of venous thrombosis, 0% (0/29) in subjects with a history of arterial thrombosis, and 2% (1/50) in control subjects (P < .0245, by Fisher's exact test for comparison of subjects with versus those without a history of venous thrombosis). The G-->A mutation at nucleotide 20,210 in the 3'UTR was confirmed by direct DNA sequencing. The similar increased prevalence of the 3'UTR mutation in subjects with venous thrombosis in our population and in the Dutch population studied by Poort et al suggests that this mutation is an important risk factor for venous thrombosis in the general white population.

Activated protein C resistance (APCR), the most common risk factor for venous thrombosis, is the result of a G to A base substitution at nucleotide 1691 (R506Q) in the factor V gene. Current techniques to detect the factor V Leiden mutation, such as determination of restriction length polymorphisms, do not have the capacity to screen large numbers of samples in a rapid, cost-effective test. The aim of this study was to apply the first nucleotide change (FNC) technology, to the detection of the factor V Leiden mutation. After preliminary amplification of genomic DNA by polymerase chain reaction (PCR), an allele-specific primer was hybridised to the PCR product and extended using fluorescent terminating dideoxynucleotides which were detected by colorimetric assay. Using this ELISA-based assay, the prevalence of the factor V Leiden mutation was determined in an Australian blood donor population (n = 500). A total of 18 heterozygotes were identified (3.6%) and all of these were confirmed with conventional MnlI restriction digest. No homozygotes for the variant allele were detected. We conclude from this study that the frequency of 3.6% is compatible with others published for Caucasian populations. In addition, the FNC technology shows promise as the basis for a rapid, automated DNA based test for factor V Leiden.

In a prospective study, the role of various hemostatic factors known to be associated with thrombotic risk was investigated in 71 patients with peripheral arterial occlusive disease (PAOD, stages II through IV, Fontaine; aged 68 +/- 13 years). Laboratory investigations were done before; 1, 24, and 48 hours after; and 3 and 6 months after percutaneous transluminal angioplasty (PTA). Thirty of 71 (42.3%) patients developed restenosis (> 50% reduction of the lumen diameter) at the site of PTA within 6 months, verified by color-coded duplex sonography. Significantly increased levels of thrombin-antithrombin III complexes (P < .01), prothrombin fragments 1 + 2 (P < .01), and D-dimers (P < .01) were found 1 hour, as well as 24 to 48 hours, after PTA. Fibrinogen (P < .01) and von Willebrand factor (P < .01) were significantly higher 48 hours after PTA. Restenotic patients as a whole had higher plasma fibrinogen (3.46 +/- 1.12 versus 2.95 +/- 0.62 g/L, P < .01) and C-reactive protein (25.4 +/- 46.7 versus 7.9 +/- 6.9 mg/L, P < .05) at baseline, as well as higher fibrinogen (P < .05) and prothrombin fragments 1 + 2 (P < .01) during months 3 to 6 after PTA. There was a nonsignificant tendency for higher values of von Willebrand factor (206 +/- 98% versus 184 +/- 100%, P = .2) at baseline in patients with restenosis, whereas tissue plasminogen activator, plasminogen activator inhibitor, coagulation screening tests, blood cell counts, and serum lipids showed no significant difference between the two groups. The relative risk for developing restenosis within 6 months while having high fibrinogen (> 2.8 g/L) or C-reactive protein at baseline was 2.80 (95% CI: 1.30-6.02, P < .01) and 1.96 (95% CI: 1.07-3.58, P < .05), respectively. Patients with critical limb ischemia (stage III/IV, Fontaine) had significantly higher fibrinogen and von Willebrand factor at repeated points of time, as well as significantly higher C-reactive protein and lower creatinine clearance at entry. In the logistic regression risk factor analysis, baseline plasma fibrinogen, C-reactive protein concentration, and the severity of the arterial disease were significantly predictive of restenosis. Our results indicate that high procoagulant factors and persistent thrombin generation of the hemostatic system might promote restenosis, particularly in patients with extended atherosclerosis. This finding suggests that new treatment strategies should be taken under consideration for patients with PAOD and PTA.

Patients with atrial fibrillation have been reported to exhibit abnormal hemostasis. Since nitric oxide (NO) exerts antithrombotic effects and attenuates platelet function, we evaluated two indicators of plasma NO levels, the plasma levels of nitrite and nitrate (NOx), and the levels of cGMP in platelets. We also examined whether indicators of plasma NO levels were associated with abnormalities in parameters related to platelet function, blood coagulation, and fibrinolysis. We evaluated 45 patients with chronic sustained atrial fibrillation (33 men and 12 women, age range 63 +/- 2 years) compared with 45 sex- and age- (+/- 2 years) matched nonhospitalized subjects with sinus rhythm. There were no significant differences between the two groups in the incidence of risk factors for stroke except for ischemic heart disease or in echocardiographic parameters. Plasma levels of NOx measured using the Greiss reagent (mean [interquartile range]: 15.6 [9.5 to 25.7] versus 24.1 [14.2 to 40.8] mumol/L, n = 45) and the platelet cGMP levels (0.33 [0.16 to 0.67] versus 0.63 [0.31 to 1.29] pmol/10(9) platelets, n = 9) were significantly (P < .05) lower in the patients with atrial fibrillation than in the control subjects. Plasma levels of D-dimer, beta-thromboglobulin, and fibrinogen were significantly (P < .05) higher in the patients with atrial fibrillation. The two groups did not differ as to the plasma levels of tissue plasminogen activator or plasminogen activator inhibitor-1. Our findings suggest that a decrease in plasma NO levels may account for the hemostatic abnormalities observed in patients with atrial fibrillation.

A genetic variation in the 3'-untranslated region of the prothrombin mRNA (20210 G/A) has recently been reported to be associated with elevated plasma prothrombin levels and with an increased incidence of venous thrombosis. We determined the frequency of this mutation, the detection of which was improved by allele-specific amplification of exon 14 and by denaturing gradients (denaturing gradient gel electrophoresis), in cohorts of patients affected by venous thrombosis (n = 132) or by coronary or cerebrovascular diseases (n = 195) and in normal subjects from various populations. An overlapping frequency of the heterozygous genotype (4%) was found in normal subjects from Italy and Cyprus, and no carrier was detected in 40 subjects of Indian or Somali origin. The 20210 GA heterozygous genotype was not increased in frequency in patients with arterial disease. In contrast, the GA genotype was associated (P = .007) with venous thrombosis both in simple heterozygotes (16%) with a family history of thrombosis as well as in double heterozygotes (14%) for other known thrombophilic defects. A synergic interaction between the prothrombin 20210 GA genotype and the factor V Leiden mutation, both potentially affecting the prothrombinase complex, was suggested by the early onset of thrombosis (median age 22 years) in doubly heterozygous patients. The association of the 20210 A allele with higher prothrombin levels was confirmed in the Italian population. However, the prothrombin assay does not allow an efficient preselection of patients for the DNA analysis.

Resistance to activated protein C (APC) is a frequent cause of thrombophilia. Most patients showing APC-resistance have a G to A mutation at codon 506 of the factor V that converts arginine to glutamine. This mutation is present in populations worldwide with frequencies ranging from 0.01 to 0.05. Genotyping of 150 control individuals from the Spanish population showed that 3.33% of them carried the mutation. Several studies have measured resistance to APC (following a classical functional assay) and have determined the factor V genotype in a number of thrombophilic patients, in an attempt to compare the predictive value of both laboratory methods. To assess the incidence of the factor V mutation among Spanish thrombophilic patients, we genotyped 51 of these. The frequency of mutation carriers rose from 3.33% in the controls to 53% in the patients. We found significant differences for the thrombosis-free survival curves and for the age at the first thrombotic event between patients who carried or did not carry the mutation. Analysis of relatives of 16 patients who carried the factor V mutation suggests the existence of additional genes that modulate the effect of the factor V gene in the development of venous thrombosis among carriers of the G to A mutation.

Examining 26 patients with early recurrent venous thrombophilias and ischemic attacks revealed that 6 cases had Va factor resistance to activated C protein. The latter suggests that thrombophilia associated with hereditary C- protein resistance is recorded in the Russian population, among the residents of West Siberia in particular.