The factor V gene A4070G mutation and the risk of venous thrombosis

The A4070G polymorphism in exon 13 of the factor V (FV) gene, which replaces His by Arg at position 1299 of the B domain, was recently shown to influence circulating FV levels and to contribute to the activated protein C (APC) resistance phenotype. We examined the impact of this polymorphism in a population of unselected patients with venous thromboembolic disease (VTE). The prevalence of the G4070 (R2) allele was determined in 205 patients and 394 healthy subjects of similar age and sex distribution. Thirty-seven patients (18%) were heterozygous for the R2 allele and 1 (0.5%) was homozygous. Forty-four controls (11.2%) were heterozygous for the R2 allele and 1 (0.2%) was homozygous. Thus, the allelic frequency was significantly higher in the patients with VTE than in the healthy controls, with respective values of 9.5% and 5.8%. The odds ratio was 1.8 (95% CI: 1.1-2.8, p = 0.02), pointing to an increased risk of VTE in carriers of the R2 allele. After excluding subjects with putative or confirmed gene defects (mainly the FV R506Q mutation), the R2 allele was still a risk factor for VTE in the remaining patients, with an odds ratio of 2.0 (95% CI: 1.2-3.5, p = 0.01), demonstrating that this polymorphism is itself a risk factor. This study also confirms that the R2 allele influences APC resistance (APCR) in the absence of the FV R506Q mutation.

The factor II G20210A and factor V G1691A gene transitions and coronary heart disease

BACKGROUND

G to A transitions at nucleotide position 20210 of the factor II (Fll) gene and at 1691 of the factor V (FV) gene have been shown to be associated with an increased risk of venous thrombosis. Since it is still unclear whether both gene variations are also related to an increased risk of coronary heart disease (CHD), we studied the relation of both gene variations to coronary artery disease (CAD) and myocardial infarction (MI) in a sample of 2210 male individuals whose coronary anatomy were defined by coronary angiography.

RESULTS

In the total sample, the FII G20210A gene variation was not associated with the presence or the extent of CAD, the latter defined either by the degree of vessel disease or by a CHD score according to Gensini. However, individuals with unfavourable lipid profiles showed pronounced differences in CHD scores between GA heterozygotes and GG homozygotes: this observation applied in particular to younger patients (<62 years; mean age of total sample) who simultaneously had low apoAI/apoB ratios (< 1.19, mean value) and high Lp(a) plasma levels (>28 mg/dl; mean value). In addition, in subjects without acetylsalicylic acid treatment GA heterozygotes had clearly higher CHD scores than AA genotypes. Further restriction to smokers, to subjects with high fibrinogen plasma levels (>3.47 g/l; mean value) or to patients with high glucose concentrations (>112 mg/dl; mean value) tended to increase the difference in CHD score between FII G20210A genotypes. An association of the FII G20210A gene variation with non-fatal MI was not observed. In the total sample and in high and low risk subpopulations, an association of the FV G1691A gene variation was not detected neither with presence and extent of CAD or with nonfatal MI.

CONCLUSION

The importance of the factor II G20210A gene variation for CHD may be restricted to individuals with major cardiovascular risk factors. In addition, the present study did not strengthen the hypothesis of the factor V G 1691 A transition as a risk factor of coronary heart disease neither in the total sample nor in subgroups of individuals who were at high or low risk of CHD.

Thrombophilia as a multigenic disease

BACKGROUND AND OBJECTIVE

Venous thrombosis is a common disease annually affecting 1 in 1000 individuals. The multifactorial nature of the disease is illustrated by the frequent identification of one or more predisposing genetic and/or environmental risk factors in thrombosis patients. Most of the genetic defects known today affect the function of the natural anticoagulant pathways and in particular the protein C system. This presentation focuses on the importance of the genetic factors in the pathogenesis of inherited thrombophilia with particular emphasis on those defects which affect the protein C system.

INFORMATION SOURCES

Published results in articles covered by the Medline database have been integrated with our original studies in the field of thrombophilia.

STATE OF THE ART AND PERSPECTIVES

The risk of venous thrombosis is increased when the hemostatic balance between pro- and anti-coagulant forces is shifted in favor of coagulation. When this is caused by an inherited defect, the resulting hypercoagulable state is a lifelong risk factor for thrombosis. Resistance to activated protein C (APC resistance) is the most common inherited hypercoagulable state found to be associated with venous thrombosis. It is caused by a single point mutation in the factor V (FV) gene, which predicts the substitution of Arg506 with a Gln. Arg506 is one of three APC-cleavage sites and the mutation results in the loss of this APC-cleavage site. The mutation is only found in Caucasians but the prevalence of the mutant FV allele (FV:Q506) varies between countries. It is found to be highly prevalent (up to 15%) in Scandinavian populations, in areas with high incidence of thrombosis. FV:Q506 is associated with a 5-10-fold increased risk of thrombosis and is found in 20-60% of Caucasian patients with thrombosis. The second most common inherited risk factor for thrombosis is a point mutation (G20210A) in the 3' untranslated region of the prothrombin gene. This mutation is present in approximately 2% of healthy individuals and in 6-7% of thrombosis patients, suggesting it to be a mild risk factor of thrombosis. Other less common genetic risk factors for thrombosis are the deficiencies of natural anticoagulant proteins such as antithrombin, protein C or protein S. Such defects are present in less than 1% of healthy individuals and together they account for 5-10% of genetic defects found in patients with venous thrombosis. Owing to the high prevalence of inherited APC resistance (FV:Q506) and of the G20210A mutation in the prothrombin gene, combinations of genetic defects are relatively common in the general population. As each genetic defect is an independent risk factor for thrombosis, individuals with multiple defects have a highly increased risk of thrombosis. As a consequence, multiple defects are often found in patients with thrombosis.

Careful selection of sample dilution and factor-V-deficient plasma makes the modified activated protein C resistance test highly specific for the factor V Leiden mutation

The aim of this study was to evaluate critically the recently modified activated-partial-thromboplastin-time (APTT)-based activated protein C (APC)-resistance tests, which are more specific for the factor V Leiden mutation than the first generation APC-resistance tests. The only modification to these tests is the predilution of the plasma sample in factor-V-deficient plasma. The intended effect of this predilution is to bring the concentrations of all clotting factors, except factor V, to the same normal levels. This, in principle, makes the tests also suitable for assaying the plasma of patients treated with oral anticoagulants and heparin, or of patients with a lupus anticoagulant. However, not every factor-V-deficient plasma is suitable for this application. Because the factor V:factor VIII ratio is important in establishing the APC ratio, the factor-V-deficient plasma should contain a sufficiently high factor VIII concentration. We also found that the optimal dilution to obtain the same APC ratios for patients, whether or not treated with coumarins or heparin, is not the same for each test or factor-V-deficient plasma. We compared two modified APTT-based APC-resistance tests (one developed in our laboratory and one commercial) with respect to their ability to discriminate between carriers and non-carriers of the factor V Leiden mutation. Both modified tests gave complete separation of carriers and non-carriers of the factor V Leiden mutation whether or not they are treated with anticoagulants. This makes these tests very suitable for routine screening.

Symptoms of inherited factor V deficiency in 35 Iranian patients

The type of bleeding symptom has been evaluated in 35 Iranian patients with an inherited deficiency of factor V, with plasma levels between 1% and 10%. The most frequent symptoms included epistaxis and excessive bleeding after surgery. Haemarthroses and muscle haematomas were less common, even in severely deficient patients. More severe symptoms such as gastrointestinal and central nervous system bleeding were rare. The severity of bleeding symptoms was only partially related to the degree of factor V deficiency in plasma. On the whole, human factor V deficiency is characterized by a moderately severe bleeding phenotype.

Wilson's disease with concomitant beta thalassaemia and factor V deficiency

A case of late presentation of Wilson's disease in a female with a thalassaemic trait is reported in whom diagnosis of Factor V deficiency was made. Despite ignoring the disease for years the patient had compensated cirrhosis. She had a dramatic family history of Wilson's disease affecting at least two brothers and two sisters. Moreover, her haematologic problems were not clinically revealed until diagnosis had been made on the basis of suspicions arising from laboratory results. The therapy of choice for hepatolenticular degeneration was not feasible due to the patient's refusal. Zinc salts were, therefore, administered. To our knowledge the association of such rare genetic disorders has not been reported.

Different risks of thrombosis in four coagulation defects associated with inherited thrombophilia: a study of 150 families

Deficiency of the naturally occurring anticoagulant proteins, such as antithrombin, protein C and protein S, and activated protein C resistance due to the factor V Leiden gene mutation is associated with inherited thrombophilia. So far, no direct comparison of the thrombotic risk associated with these genetic defects is available. In this study, we wish to compare the lifetime probability of developing thrombosis, the type of thrombotic symptoms, and the role of circumstantial triggering factors in 723 first- and second-degree relatives of 150 index patients with different thrombophilic defects. We found higher risks for thrombosis for subjects with antithrombin (risk ratio 8.1, 95% confidence interval [CI], 3.4 to 19.6), protein C (7.3, 95% CI, 2.9 to 18.4) or protein S deficiency (8.5, 95% CI, 3. 5 to 20.8), and factor V Leiden (2.2, 95% CI, 1.1 to 4.7) than for individuals with normal coagulation. The risk of thrombosis for subjects with factor V Leiden was lower than that for those with all three other coagulation defects (0.3, 95% CI, 0.1 to 1.6), even when arterial and superficial vein thromboses were excluded and the analysis was restricted to deep vein thrombosis (0.3, 95% CI, 0.2 to 0.5). No association between coagulation defects and arterial thrombosis was found. The most frequent venous thrombotic manifestation was deep vein thrombosis with or without pulmonary embolism (90% in antithrombin, 88% in protein C, 100% in protein S deficiency, and 57% in factor V Leiden), but a relatively mild manifestation such as superficial vein thrombosis was common in factor V Leiden (43%). There was a predisposing factor at the time of venous thromboembolism in approximately 50% of cases for each of the four defects. In conclusion, factor V Leiden is associated with a relatively small risk of thrombosis, lower than that for antithrombin, protein C, or protein S deficiency. In addition, individuals with factor V Leiden develop less severe thrombotic manifestations, such as superficial vein thrombosis.

Inherited prothrombotic states and ischaemic stroke in childhood

OBJECTIVE

To investigate the prevalence of currently recognised inherited prothrombotic states in a population of children with arterial stroke.

METHODS

Children with arterial stroke presenting to a tertiary level paediatric neurology centre between 1990 and 1996 were investigated for inherited prothrombotic states.

RESULTS

Sixty seven children with arterial stroke were investigated. Abnormalities were initially identified in 16 patients; however, only eight children (12%) had an inherited prothrombotic state. This was type 1 protein S deficiency in one patient, the factor V Leiden mutation in six, and activated protein C resistance (without the factor V Leiden mutation) in one. The prevalence of the factor V Leiden mutation was not significantly higher in children with arterial stroke (12%) than in a control population of children without thrombosis attending the same institution (5.2%; Fisher's exact test, p=0.19; difference in prevalence between patients and controls (95% confidence interval)=6.8% (-2.78% to 16.8%)).

CONCLUSIONS

Currently recognised inherited prothrombotic tendencies were rarely associated with stroke in this group of children, although larger numbers of patients would be needed to confirm this. Age appropriate normal values should be used when interpreting the results of a prothrombotic screen. Prothrombotic abnormalities seen acutely are as often transient as inherited. Longitudinal assessment and family studies are required before low concentrations of an anticoagulant protein found acutely can be attributed to an inherited abnormality.

Combined factors V and VIII deficiency--the solution

Combined deficiency of coagulation factor V and factor VIII is an autosomal recessive disorder which has been observed in a number of populations around the world. However, this disease appears to be most common in the Mediterranean basin, particularly in Jews of Sephardic and Middle Eastern origin living in Israel. We have taken a positional cloning approach toward identifying the gene responsible for this disorder. We initially studied 14 affected individuals from nine unrelated Jewish families using a panel of polymorphic genetic markers spaced throughout the human genome. The combined factors V and VIII deficiency gene was mapped to a locus on the long arm of chromosome 18 with a maximal LOD score of 13.22. A detailed genetic analysis identified two distinct haplotypes among these families, suggesting two independent founders or, alternatively, a single ancient founder with a more recent split of these subpopulations. Further work to identify and characterize the gene responsible for combined factors V and VIII deficiency should provide important insights into the biosynthesis of these homologous proteins.

Mutations in the ER-Golgi intermediate compartment protein ERGIC-53 cause combined deficiency of coagulation factors V and VIII

Combined deficiency of factors V and VIII is an autosomal recessive bleeding disorder resulting from alterations in an unknown gene on chromosome 18q, distinct from the factor V and factor VIII genes. ERGIC-53, a component of the ER-Golgi intermediate compartment, was mapped to a YAC and BAC contig containing the critical region for the combined factors V and VIII deficiency gene. DNA sequence analysis identified two different mutations, accounting for all affected individuals in nine families studied. Immunofluorescence and Western analysis of immortalized lymphocytes from patients homozygous for either of the two mutations demonstrate complete lack of expression of the mutated gene in these cells. These findings suggest that ERGIC-53 may function as a molecular chaperone for the transport from ER to Golgi of a specific subset of secreted proteins, including coagulation factors V and VIII.

Severe coagulation factor V deficiency caused by a 4 bp deletion in the factor V gene

Factor V (FV) deficiency (parahaemophilia) is an autosomal recessive bleeding disorder with an incidence of 1:10(6). We have studied a young girl with very mild bleeding symptoms and undetectable levels of plasma factor V antigen and activity (<0.3% and <1.6% of normal, respectively). Both parents showed plasma levels of factor V activity of about 50% of normal. Sequence analysis of the 5'- and 3'-untranslated, coding and adjacent regions of the factor V gene revealed the presence of a 4 bp deletion in exon 13. Subsequent screening of members of the family for the mutation showed that both parents were heterozygous for the mutation, that one healthy sister carried only normal alleles, and that the patient was homozygous for the mutated allele. The mutation introduced a frameshift and a novel premature stop codon in codon 1303, and would predict the synthesis of a truncated factor V molecule that lacks part of the B domain and the complete light chain. However, no factor V heavy chain could be detected in the plasma of the patient. Furthermore, factor V activity could not be detected in the patients' platelets. This is the first reported mutation in the factor V gene that predicts a type I quantitative factor V deficiency. Surprisingly, the patient, who is homozygous for the mutation, so far has only a very mild bleeding tendency.

Pseudo-homozygous activated protein C resistance due to coinheritance of heterozygous factor V Leiden mutation and type I factor V deficiency. Variable expression when analyzed by different activated protein C resistance functional assays

The laboratory diagnosis of activated protein C (APC) resistance is based on a weak anticoagulant response to APC using a chronometric procedure confirmed in almost all cases by molecular diagnosis of the FV Leiden mutation. A recently-developed Xa-based assay (Accelerimat, Biomerieux) was compared with two different activated partial thromboplastin time (APTT)-based procedures (Coatest APC resistance and Modified Coatest, Chromogenix) in 115 patients with a personal or familial history of thrombotic disease, or both, being studied for the FV Leiden mutation. Our results confirmed the improvement in specificity for the FV Leiden mutation when the APTT-based assay was performed after dilution of samples in FV-deficient plasma (Modified Coatest). However, five patients who were heterozygous for the FV Leiden mutation appeared to be homozygous when tested by both APTT-based assays. These patients, belonging to three different families, had a FV type I deficiency with FV plasma levels between 43 and 64%. In contrast, the Xa-based method was not influenced by the decrease in plasma FV levels. Thus, this procedure is more specific than APTT-based assays to predict the genotype status of the FV Leiden mutation.

Genetic markers: genes involved in thrombosis

This article summarizes the genetic markers of human venous and arterial thrombotic disorders. For venous thromboembolism, a factor V mutation (Arg 506-->Gln) has the highest risk, followed by protein C, S and antithrombin III gene defects. By contrast, these genetic defects are not associated significantly with arterial atherothrombotic disorders. Instead, a glycoprotein IIIa polymorphism (Pro33 versus Leu 33) has been reported to be associated with myocardial infarction. Fibrinogen Bbeta chain, factor VII, and plasminogen activator inhibitor-1 gene polymorphisms have been reported to influence the plasma levels of these factors and may indirectly be risk factors for arterial thrombotic disorders. Further studies will uncover additional genetic markers for thrombosis.

The locus for combined factor V-factor VIII deficiency (F5F8D) maps to 18q21, between D18S849 and D18S1103

Combined factor V-factor VIII deficiency (F5F8D) is a rare, autosomal recessive coagulation disorder in which the levels of both coagulation factor V and coagulation factor VIII are diminished. In order to map and subsequently clone the gene responsible for this phenotype, DNAs from 19 families (16 from Iran, 2 from Pakistan, and 1 from Algeria) with a total of 32 affected individuals were collected for a genomewide linkage search using genotypes of highly informative DNA polymorphisms. All pedigrees except two contained at least one consanguineous marriage. A maximum LOD score (Zmax) of 14.82 for theta = .02 was generated with marker D18S1129 in 18q21; LOD scores > 9 were obtained for several other markers-D18S849, D18S1103, D18S64, and D18S862. Multipoint analysis resulted in Zmax = 18.91 for the interval between D18S1129 and D18S64. Informative recombinants placed the locus for F5F8D between D18S849 and D18S1103, in an interval of approximately 1 cM. These results are similar to the recently reported linkage of this disease to chromosome 18q in Jewish families (Nichols et al. 1997) and provide evidence that the same gene is responsible for all F5F8D among human populations. The difference in clinical severity of the phenotype in unrelated families, as well as the failure to detect a specific haplotype of DNA polymorphisms in the consanguineous Iranian families, suggests the existence of different molecular defects in the F5F8D gene. There exists an apparently gap-free contig with CEPH YACs linking the two markers on either side of the critical region. Positional cloning efforts are now in progress to clone the F5F8D gene.

Factor V antigen levels in APC resistance, in factor V deficiency and in combined APC resistance and factor V deficiency (pseudohomozygosis for APC resistance)

Factor V antigen levels were measured in 40 patients with factor V deficiency (11 homozygous and 29 heterozygous), in 38 patients with factor V Leiden mutation (16 homozygous and 22 heterozygous) and in three patients with combined heterozygous factor V deficiency and heterozygous factor V Leiden mutation (so-called pseudohomozygosis for APC resistance). Twenty normal subjects of both sexes served as controls. Factor V antigen levels compared well with factor V activity in normal subjects and in all groups of patients. They were normal both in homozygous and heterozygous APC resistance patients. Factor V antigen determination may be useful for the diagnosis of pseudohomozygosis for APC resistance. These patients have a phenotypic picture similar to homozygous APC resistance, but show a factor V antigen level about half the normal value since they are compound heterozygotes for factor V deficiency and APC resistance. In contrast, homozygous patients for APC resistance show normal factor V activity and antigen levels.

Linkage of combined factors V and VIII deficiency to chromosome 18q by homozygosity mapping

Combined Factors V and VIII deficiency is an autosomal recessive bleeding disorder identified in at least 58 families comprising a number of different ethnic groups. Affected patients present with a moderate bleeding tendency and have Factor V and Factor VIII levels in the range of 5-30% of normal. The highest frequency of the mutant gene is found in Jews of Sephardic and Middle Eastern origin living in Israel with an estimated disease frequency of 1:100,000. We sought to identify the gene responsible for combined Factors V and VIII deficiency using a positional cloning approach. Of 14 affected individuals from 8 unrelated Jewish families, 12 were the offspring of first-cousin marriages. After a genome-wide search using 241 highly polymorphic short tandem repeat (STR) markers, 13 of the 14 affected patients were homozygous for two closely linked 18q markers. Patients and all available family members were genotyped for 11 additional STRs spanning approximately 11 cM on the long arm of chromosome 18. Multipoint linkage analysis yielded a maximal log of the odds (LOD) score of 13.22. Haplotype analysis identified a number of recombinant individuals and established a minimum candidate interval of 2.5 cM for the gene responsible for combined Factors V and VIII deficiency. The product of this locus is likely to operate at a common step in the biosynthetic pathway for these two functionally and structurally homologous coagulation proteins. Identification of this gene should provide new insight into the biology of Factor V and Factor VIII production.

Molecular characterization of a type I quantitative factor V deficiency in a thrombosis patient that is "pseudo homozygous" for activated protein C resistance

Resistance to activated protein C (APC), which is associated with the FV Leiden mutation in the large majority of the cases, is the most common genetic risk factor for thrombosis. Several laboratory tests have been developed to detect the APC-resistance phenotype. The result of the APC-resistance test (APC-sensitivity ratio, APC-SR) usually correlates well with the FV Leiden genotype, but recently some discrepancies have been reported. Some thrombosis patients that are heterozygous for FV Leiden show an APC-SR usually found only in homozygotes for the defect. Some of those patients proved to be compound heterozygotes for the FV Leiden mutation and for a type I quantitative factor V deficiency. We have investigated a thrombosis patient characterized by an APC-SR that would predict homozygosity for FV Leiden. DNA analysis showed that he was heterozygous for the mutation. Sequencing analysis of genomic DNA revealed that the patient also is heterozygous for a G5509-->A substitution in exon 16 of the factor V gene. This mutation interferes with the correct splicing of intron 16 and leads to the presence of a null allele, which corresponds to the "non-FV Leiden" allele. The conjunction of these two defects in the patient apparently leads to the same phenotype as observed in homozygotes for the FV Leiden mutation.

Discrimination between normal wildtype and carriers of coagulation factor V Leiden mutation by the activated protein C resistance test in the presence of factor V deficient plasma

Blood samples from 104 patients with clinically suspected thrombophilia were analyzed for coagulation factor V Leiden mutation (1691, G-->A) by allele-specific polymerase chain reaction. In 86 individuals (82.7%), the mutation was not detectable, whereas 15 patients (14.4%) were heterozygous and three patients (2.9%) were homozygous for factor V Leiden mutation. Plasma samples from these individuals were also tested for functional resistance of coagulation factor V to activated protein C (activated protein C resistance). This test was performed on a Schnitger-Gross coagulometer using an activated partial thromboplastin time-based activated protein C resistance test modified by applying a 1 : 5 dilution with factor V-deficiency plasma. All the individuals negative for factor V Leiden mutation were also negative in the functional activated protein C resistance test. On the other hand, all patients carrying the mutation revealed pathologic results in the activated protein C resistance test. The cutoff value for the activated protein C resistance index (> or = 1.7 = negative) was determined by testing 31 male and female blood donors. One of them was heterozygous for factor V Leiden mutation and had an activated protein C resistance index of 1.4, whereas those without factor V Leiden mutation had an activated protein C resistance index of 1.9 +/- 0.1 (mean +/- SD). Patients with clinically suspected thrombophilia without factor V Leiden mutation had an activated protein C resistance index of 2.1 +/- 0.2 (mean +/- SD), whereas patients heterozygous for the mutation had an index of 1.5 +/- 0.1 (mean +/- SD). Within the group of patients carrying the mutation, the activated protein C resistance test even distinguished between heterozygous and three homozygous (activated protein C resistance 1.0 to 1.2) carriers. The data demonstrate that the activated protein C resistance test in the presence of factor V-deficiency plasma provides a clear-cut discrimination between normal wildtype and carriers of factor V Leiden mutation with a sensitivity and specificity of 100%. Verification of positive activated protein C resistance tests can be performed easily with a simple and reliable polymerase chain reaction protocol for the 1691, G-->A mutation.