Clinical significance of factor V Leiden and prothrombin G20210A-mutations in cerebral venous thrombosis – comparison with arterial ischemic stroke

Abbreviations

1 Introduction

Acute cerebral ischemia arising from arterial occlusion is the most common cause of stroke. A variety of risk factors favor the development of cerebral ischemia. These include cardiovascular diseases such as absolute arrhythmia, cardiogenic embolism, arterial hypertension or metabolic disorders such as diabetes, hyperlipidemia, hyperuricaemia or obesity. Other risk factors include nicotine abuse and estrogen-containing hormonal therapies [16]. Furthermore, the cerebrovascular risk is significantly influenced by increased age and genetic factors. In some cases haemostasis disorders associated with hypercoagulability play an etiological role [3, 21].

Cerebral venous thrombosis, particularly affecting the dural sinus, is a less common form of cerebral circulatory disorders. It mainly occurs in younger patients with a high proportion of females [4, 21]. Etiologically, local and systemic bacterial infections are a common source. Non-infectious causes include hormonal conditions such as pregnancy or the use of contraceptives, paraneoplastic factors, inflammation, or mechanical and traumatic factors [16, 20]. Finally, disorders of hemostasis associated with an increase of blood coagulation particularly arising from thrombophilia are of special significance in the pathogenesis of cerebral venous thrombosis [1, 26].

Thus, alterations of hemostasis play a distinct role both in arterial and venous occlusions of the cerebrum, in spite of some diversities in anatomy and function of the cerebral vascular system. On the other hand, little is known about its similarities and differences, although such insights might play an important role in assessing the individual risk and for adequately deciding anticoagulant therapy [8]. For this reason, a comparative study was conducted evaluating the influence of thrombophilia on cerebral vein thrombosis and on arterial cerebral ischemia on the other hand. The more common factor V-type-Leiden- and prothrombin-20210-mutations, which were regarded as highly representative markers, were analyzed in this study.

2 Patients, materials and methods

The study was performed according to the ethical guidelines of Clinical Hemorheology and Microcirculation [2]. Adult patients referred to our out-patient department for thrombophilia testing who had suffered one or more events of cerebral sinus vein thrombosis (CVT) were enrolled in this study. CVT had to be confirmed by computed brain tomography, digital subtraction angiography or magnetic resonance imaging. Patients suffering from arterial ischemic stroke (AIS) were included as comparison group. AIS had to be ascertained by either computed brain tomography or magnetic resonance imaging. On the basis of a case-control study with matched pairs each CVT-patient was consecutively assigned to an AIS-patient of same sex and equivalent age (range: +/–10%) at the first event of cerebral vascular disorder. An age- and gender-matched cohort of regional healthy blood donors was taken as controls. Laboratory analysis of factor V (Leiden) G1691A- and prothrombin G20210A-mutations was done by using a multiplex allele-specific polymerase chain reaction assay (Thrombo Type plus, HAIN LifeScience, Nehren (Germany)). Statistical analysis was performed by using Chi-square-testing and Fisher’s exact test. Values of p < 0.05 were regarded as significant.

3 Results

This case-control study includes 101 patients (77 females, 24 males) suffering from cerebral sinus vein thrombosis (CVT) aged 18 to 76 years (mean: 38.78 years). They were compared with age- and gender-matched patients suffering from arterial ischemic stroke (AIS) aged 20 to 74 years (mean 40.74 years). Demographic data of patients and controls are presented in Table 1. Females were 3.2-fold more frequent than males. The number of patients aged less than 40 years was 1.6-fold higher than of those aged 40 years and higher (61 versus 40).

Factor V Leiden-mutations were found in 17/101 (16.8%) cases of cerebral sinus vein thrombosis (OR: 3.89, 95% CI: 1.27–12.63) and in 18/101 (17.8%) cases of arterial ischemic stroke (OR: 4.16, 95% CI: 1.38–13.46) occurring more frequently (p = 0.01152) than in controls at a rate of 5/101 (4.95%). Prothrombin-mutations occurred more frequently (p = 0.00521, OR: 5.70, CI 95% :1.48–25.69) in cerebral sinus vein thrombosis at a rate of 15/102 (14.9%) versus 3/101 (2.97%) in controls. This does not comply with arterial ischemic stroke showing a rate of 5/101 (4.95%) of prothrombin-mutations in comparison with controls. Factor V Leiden-mutations were not different in cerebral sinus venous thrombosis versus arterial ischemic stroke (s. Table 1).

In contrast, prothrombin-mutations were significantly more frequent in cerebral sinus venous thrombosis at a rate of 15/101 (14.9%) than in arterial ischemic stroke with a rate of 5/101 (4.95%) (OR 3.35, 95% CI: 1.07 to 11.05). Furthermore, 3 cases with combined heterozygosity of factor V Leiden-mutation and prothrombin-mutation have been identified in cerebral sinus venous thrombosis, but not in arterial ischemic stroke or controls.

Summarizing all factor V- and prothrombin-mutations in both groups the prevalence was higher in CVT at a rate of 29/101 (28.71%) compared to a rate of 23/101 (22.77%) in AIS. However, the difference was not significant (Table 2). All of the above mutations were exclusively heterozygous.

With 18.03% (10/46) versus 15.0% (16/40) the rate of factor V Leiden mutations in CVT among patients younger than 40 years was almost the same level as in patients aged 40 years and older. The prevalence of patients with corresponding age in AIS was 13.1% (8/61) versus 25.0% (10/40). The differences were not significant.

With 18.03% (11/61) versus 10,0% (4/40) the rate of prothrombin mutations in CVT among patients younger than 40 years was higher (ns) than in patients aged 40 years and older. The prevalence of patients with corresponding age in AIS was 3.28% (2/61) versus 7.5% (3/40). All differences were not significant.

With 20.78% (16/77) versus 4.17% (1/24), factor V Leiden mutations in CVT among females were more common than among males. The prevalence of factor V Leiden among females/males in AIS was 16.88% (13/77) versus 20.83% (5/24). The differences were not significant. With 18.18% (14/77) versus 4.17% (1/24) prothrombin-mutations in CVT among females were more common than among males. The prevalence of prothrombin-mutations among females/males in AIS was 6.49% (5/77) versus 0.00% (0/24). All differences were not significant.

As regards quantitative aspects, the present data already show that hereditary thrombophilia is a serious risk factor for the development of both CVT and AIS. Compared with healthy controls, odds ratios of factor V Leiden and prothrombin mutations were 3.89 and 5.70 in CVT-patients, both on a significant level. The corresponding odds ratios in AIS were 4.16 and 1.7, however, in the latter case (prothrombin-mutation) not significant. The important role of thrombophilia for the development of CVT is already known to some extent, however, data are mainly restricted to comparative studies with healthy controls alone [5, 19]. Our results partially confirm these data.

The particular significance of hereditary thrombophilia for the emergence of AIS, on the other hand, is controversially discussed in the literature, its specific relevance is obviously limited to younger individuals primarily under age 40 [15, 19]. The higher prevalence, as observed in our study-population, is to some extent contradictory to these findings. However, the main purpose of our study was to evaluate comparatively the similarities or differences of thrombophilia between CVT and AIS, and not to analyze typical prevalences in one or in the other form of cerebrovascular disorder. Therefore, since CVT was the leading study-group, choices of AIS-patients on the basis of a matched-pairs design may result in less representative occurrences of AIS with regard to the general population.

In this context, concerning proportions and distribution patterns of parameters as analyzed in our study, considerable differences of thrombophilia could be discovered between both forms of cerebrovascular disorders. Whereas factor Leiden with a rate of 16.8% versus 17.8% among CVT- and AIS-patients was at the same level, prothrombin 20210-mutation was occurring with a rate of 14.9% versus 4.95% and an odds-ratio of 3.35 at a significant higher level among CVT-patients compared to AIS. This underlines the assessment that under specific risk conditions carriers of the prothombin-mutation are severely predisposed to CVT, but not to AIS. The particular risk of prothrombin-mutation in CVT has already been described according to previous reports [12, 24–26]. However, it has not yet been demonstrated that the such a risk in CVT is significantly higher than in AIS. Thus, prothrombin-20210-mutation might play a particular role in the pathogenesis of CVT. A possible explanation for this might be an increased tendency towards fibrin formation, which is associated with a local preference for thrombus formation in the venous system. The mutation at nucleotide 20210 of the prothrombin gene is linked with a regulatory disorder leading to increased protein synthesis [13]. The result is a higher plasma level of prothrombin in the carriers of this gene-variant. Thus, enhanced thrombin-generation arising from elevated prothrombin results in an increased tendency of fibrin-formation and consecutive thrombus generation. There is evidence that neural tissue contains abundant levels of prothrombin which can be released to locally circulating blood by minor perturbances [9, 23]. This strengthen the hypothesis of an anatomic predilection for cerebral venous thrombosis in the presence of prothrombin-mediated procoagulatory activities. Factor V Leiden is an additional mechanism which is capable of enhancing fibrin formation [6]. In association with the PTM it contributes to a self- amplifying effect with highly increased prothrombotic tendency. In this context, 3 patients with combined heterozygosity of FVL and PTM have been identified exclusively in the CVT-group. This further underlines the assessment that fibrin-forming mechanisms support thrombosis generation preferably on the venous side.

We conclude from these data that the prothrombin- 20210-mutation plays a considerable and significant role in the development of cerebral sinus venous thrombosis, but not in arterial ischemic stroke. Factor V Leiden occurring at elevated levels in both groups bears a similarly high risk for CVT and AIS. Furthermore, there is evidence that the combined occurrence of heterozygous prothrombin- and factor V Leiden-mutation which is solely found in CVT-patients strongly favors the emergence of cerebral sinus vein thrombosis, but not of AIS. Therefore, in terms of thrombophilia markers, pathogenesis of arterial and venous occlusions in cerebrovascular disease has to be regarded as different. These findings consequently imply different approaches of anticoagulant therapies in CVT and AIS adequately adjusted to the individual risk.

It should be clear that thrombophilia is not the only mechanism contributing to the occurrence of vascular occlusions. There is a large variety of numerous pathogenic factors involved in thrombosis and embolism including haemodynamic parameters, vascular defects, inflammation, hormons, gender-specific conditions, mechanical and traumatic factors or other circumstances. In this context, disorders of haemostasis or thrombophilia often exert just contributory effects as a cofactor. They should, however, be taken into consideration together with acquired risk factors such as hormonal manipulations, pregnancy, metabolic disorders and others more, in order to adequately assess the individual risk under clinical conditions.