Factor XII deficiency: a thrombophilic risk factor for retinal vein occlusion

[Cardiovascular risk factors, haemostasis and antithrombotic treatment in retinal vessel occlusion]

Venous and arterial retinal vascular occlusions are age-related disorders, generally associated with classical cardiovascular risk factors, rather than an isolated ocular disease. As affected patients often also have an increased general risk for other vascular diseases, such as ischemic stroke, an interdisciplinary clarification of cardiovascular risk factors and systemic comorbidities is essential for all patients. Extended hemostaseological investigations may be recommended in those patients who do not match the typical risk profile. Patients at a young age by the time of manifestation, without conventional risk factors as well as patients with an increased risk of developing antiphospholipid syndrome may require a selective clinical investigation including testing for thrombophilic risk factors. Recent studies have clearly demonstrated an association between coagulation and lipid metabolism disorders and the development of both retinal vein and artery occlusions in specific subgroups of patients. Therapeutic approaches to treat retinal vascular occlusions or reduce the long-term risk of recurrences with anticoagulant or antiplatelet drugs have not gained widespread acceptance. However, intravenous thrombolysis may be a valuable treatment option for central retinal artery occlusions within a short time to treatment therapeutic window. For defined disorders of the coagulation system, the administration of antithrombotic drugs to reduce the general vascular risk can be a reasonable approach. This article provides an overview of cardiovascular risk factors, the general vascular risk and the current state of knowledge on ophthalmologically relevant disorders of coagulation and lipid metabolism in patients with venous and arterial retinal vascular occlusions.

Platelet and Thrombophilia-Related Risk Factors of Retinal Vein Occlusion

Retinal vein occlusion (RVO) is a heterogenous disorder in which the formation of a thrombus results in the retinal venous system narrowing and obstructing venous return from the retinal circulation. The pathogenesis of RVO remains uncertain, but it is believed to be multifactorial and to depend on both local and systemic factors, which can be divided into vascular, platelet, and hypercoagulable factors. The vascular factors include dyslipidaemia, high blood pressure, and diabetes mellitus. Regarding the platelet factors, platelet function, mean platelet volume (MPV), platelet distribution width (PDW), and platelet large cell ratio (PLCR) play key roles in the diagnosis of retinal vein occlusion and should be monitored. Nevertheless, the role of a hypercoagulable state in retinal vein occlusion remains unclear and requires further studies. Therefore, the following article will present the risk factors of RVO associated with coagulation disorders, as well as the acquired and genetic risk factors of thrombophilia. According to Virchow’s triad, all factors mentioned above lead to thrombus formation, which causes pathophysiological changes inside venous vessels in the fundus of the eye, which in turn results in the vessel occlusion. Therefore, a diagnosis of retinal vein occlusion should be based on both eye examination and general examination, including laboratory tests.

Case Report: An Adult Patient With Deficiency of Adenosine Deaminase 2 Resembled Unilateral Frosted Branch Angiitis

Purpose: Deficiency of adenosine deaminase 2 (DADA2) is a rare autosomal recessive systemic autoinflammatory disorder. We describe a rare case of an adult patient with DADA2 who presented with unilateral frosted branch angiitis (FBA) combined with branch retinal vein occlusion and panuveitis.

Method: This paper is a clinical case report.

Results: A 31-year-old male patient complained of blurred vision in his right eye for 2 days. His fundus examination showed FBA combined with branch retinal vein occlusion and panuveitis. He had a medical history of intermittent and recurrent fever, skin rash and aphthous ulcer for 5 years, and lacunar infarction for 1 month. Laboratory examinations showed hypogammaglobulinemia and mild prolonged activated partial thromboplastin time (APTT). Brain magnetic resonance imaging (MRI) revealed old lacunar infarction in the right basal ganglia and the lateral ventricle and fresh lacunar infarction in the right pons, respectively. The perivascular sheathing of FBA and macular edema were resolved after steroid administration and treatment of intravitreal anti-VEGF injection. During the period of follow-up, the patient subsequently suffered from recurrence of strokes, abnormality of coagulation function, sudden hearing loss of the left ear, and diplopia. His gene sequencing results demonstrated several deletion mutations in ADA2, and the diagnosis of DADA2 was eventually confirmed.

Conclusions: FBA represents a very rare ocular feature of DADA2 and may in some cases be the presenting manifestation. Therefore, ophthalmologists need to be aware of this rare autoinflammatory disease.

Retinal hemorrhage and bleeding disorders in children: A review

BACKGROUND

Retinal hemorrhages (RH) are a common manifestation of abusive head trauma (AHT) resulting from acceleration-deceleration injury with or without blunt impact. Evaluation of a child with RH requires careful consideration of these differential diagnoses. The extent to which coagulopathy alone can cause RH would be useful to understand as coagulopathy may accompany AHT.

OBJECTIVE

In this systematic review, we sought to identify whether coagulopathies have been reported with RH similar to those of AHT.

METHODS

We performed a literature search for ocular manifestations of bleeding disorders in children less than 18 years old. We included clotting factor deficiencies, vitamin K deficiency, platelet function abnormalities, thrombocytopenia, disseminated intravascular coagulation (DIC), and trauma induced coagulopathy (TIC). We included only pediatric reports of intraocular bleeding or documented eye examinations that indicated no hemorrhages. We then re-examined cases for ocular and systemic findings that could potentially mimic abuse.

RESULTS

Our initial search yielded 816 results. Sixty-one articles met our inclusion criteria. Of these, there were 32 children within the AHT age range (less than 5 years old) who had RH and concomitant coagulopathy. Only 5 cases might potentially be confused for abuse. Of these, no classic characteristics of RH from abuse such as retinoschisis or retinal folds were found. Systemic features were inconsistent with AHT.

CONCLUSIONS

The presence of coagulopathy alone does not rule out the possibility that the child has been abused. Coagulopathy alone has not been reported as an etiology of RH that are consistent with AHT, especially when other findings are present.

Antibody inhibition of contact factor XII reduces platelet deposition in a model of extracorporeal membrane oxygenator perfusion in nonhuman primates

BACKGROUND

The contact factor XII (FXII) activates upon contact with a variety of charged surfaces. Activated FXII (FXIIa) activates factor XI, which activates factor IX, resulting in thrombin generation, platelet activation, and fibrin formation. In both in vitro and in vivo rabbit models, components of medical devices, including extracorporeal oxygenators, are known to incite fibrin formation in a FXII-dependent manner. Since FXII has no known role in hemostasis and its inhibition is therefore likely a safe antithrombotic approach, we investigated whether FXII inhibition also reduces accumulation of platelets in extracorporeal oxygenators.

OBJECTIVES

We aimed to determine the effect of FXII inhibition on platelet deposition in perfused extracorporeal membrane oxygenators in nonhuman primates.

METHODS

A potent FXII neutralizing monoclonal antibody, 5C12, was administered intravenously to block contact activation in baboons. Extracorporeal membrane oxygenators were temporarily deployed into chronic arteriovenous access shunts. Radiolabeled platelet deposition in oxygenators was quantified in real time using gamma camera imaging. Biochemical assays were performed to characterize the method of action of 5C12.

RESULTS

The anti-FXII monoclonal antibody 5C12 recognized both the alpha and beta forms of human and baboon FXII by binding to the protease-containing domain, and inhibited FXIIa activity. Administration of 5C12 to baboons reduced platelet deposition and fibrin formation in the extracorporeal membrane oxygenators, in both the presence and absence of systemic low-dose unfractionated heparin. The antiplatelet dose of 5C12 did not cause measurable increases in template bleeding times in baboons.

CONCLUSIONS

FXII represents a possible therapeutic and safe target for reducing platelet deposition and fibrin formation during medical interventions including extracorporeal membrane oxygenation.

Elevated lipoprotein (a) levels are an independent risk factor for retinal vein occlusion

PURPOSE

To investigate the prevalence of lipoprotein (a) [Lp(a)] and other thrombophilic disorders among retinal vein occlusion (RVO) patients with regard to age and various risk factors.

METHODS

We retrospectively reviewed the medical records of 100 patients with central, hemicentral or branch RVO who had undergone routine thrombophilia screening. Data were compared with 100 controls. Both cohorts were divided into three subgroups (≤45 years, >45-≤60 years or >60 years), depending on the patients' age at the time of the RVO or a previous thromboembolic event.

RESULTS

Elevated Lp(a) plasma levels were significantly more prevalent among RVO patients than among controls (p < 0.0001; OR: 4.8). Moreover, we determined age ≤60 years by the time of the first thromboembolic event as a strong predictor of elevated Lp(a) (p = 0.0002). The coincidence of elevated Lp(a) with other coagulation disorders further increased the OR for RVO to 9.3 (95% CI 2.1-41.8). Multivariate analysis revealed the presence of cardiovascular risk factors (OR: 3.1, p = 0.0004), elevated lipoprotein (a) levels (OR: 5.2, p = 0.0001) and increased factor VIII activity (OR: 5.9, p = 0.001) as independent risk factors for the development of RVO among patients.

CONCLUSION

Our results indicate that elevated plasma levels of Lp(a) are associated with the development of RVO. Selective screening of young patients and subjects with a personal or family history of thromboembolism may be helpful in identifying RVO patients with elevated Lp(a).

Platelet activation by ADP is increased in selected patients with anterior ischemic optic neuropathy or retinal vein occlusion

To investigate whether adenosine diphosphate (ADP)-induced platelet hyperaggregability is associated with nonarteritic anterior ischemic optic neuropathy (NAION) or retinal vein occlusion (RVO). We retrospectively reviewed thrombophilia screening data of patients with NAION or RVO without a history of arterial hypertension, diabetes mellitus, hyperlipidemia, obesity, and cigarette abuse. Patients with a positive family history for thromboembolism were not excluded. Platelet aggregation (area under the curve, AUC) after induction of 0.5, 1.0, and 2.0 µmol of ADP was estimated in 25 NAION and RVO patients and compared with 25 healthy controls. We observed significantly greater platelet aggregation post 0.5 (P = 0.002) and 1.0 (P = 0.008) µmol of ADP among NAION and RVO patients compared with healthy controls. Platelet hyperaggregability was significantly more prevalent in patients than in controls (56% vs. 8%; P = 0.0006). Our results suggest that in NAION and RVO patients without a history of arterial hypertension, diabetes mellitus, hyperlipidemia, obesity, and cigarette abuse, platelets are significantly hyperreactive after induction of very low concentrations of ADP when compared with healthy individuals. This hyperreactivity is particularly evident in patients with a family history of thromboembolism.

Selective Thrombophilia Screening in Young Patients with Retinal Artery Occlusion

Purpose: To investigate the prevalence of various thrombophilic disorders among young patients with retinal artery occlusion (RAO). Procedures: We retrospectively reviewed thrombophilia screening data of young patients ≤60 years of age with RAO and healthy controls matched for gender and age. Results: Thrombophilia screening data of 25 young patients and 62 healthy controls were analyzed. Mean patient age by the time of the RAO was 43.3 ± 10.8 years. Overall, thrombophilic defects were found to be present in 17 patients (68%) compared with 11 of 62 controls (17.7%; p < 0.0001). Multivariate logistic regression analysis confirmed a statistically significant association between the development of RAO and increased levels of lipoprotein(a) (odds ratio: 9.48; p = 0.001) and factor VIII (odds ratio: 6.41; p = 0.024). There was a strong association between the presence of thrombophilic disorders and a personal or family history of thromboembolism (p = 0.01). Conclusions: Our results indicate that screening for thrombophilic disorders among selected young patients with RAO yields positive results in a high percentage of cases.

[Changes in hemostasis-related parameters of blood and lacrimal fluid in patients with retinal vein occlusion]

High prevalence of retinal vein occlusion in young people as well as treatment complexity and inadequate control of hemostatic parameters of blood and lacrimal fluid determine the significance of relevant research in patients with retinal vascular pathology. The data thus obtained may be useful for disease prognosis, severity evaluation and therapy control. This review is aimed to study hemostasis-related parameters of blood and lacrimal fluid in such patients.

Prevalence and risk factors of retinal vein occlusion: the Gutenberg Health Study

OBJECTIVE

To determine the age- and sex-specific prevalence and determinants of retinal vein occlusions (RVOs) in a large population-based German cohort.

METHODS

The investigation included 15,010 participants (aged 35-74 years) from the Gutenberg Health Study. We determined the prevalence of RVO (central retinal vein occlusion [CRVO] and branch retinal vein occlusion [BRVO]) for the local population by assessing fundus photographs of 12 954 (86.3%; 49.8% women and 50.2% men) participants. Further, we analyzed the associations of RVO with cardiovascular, anthropometric, and ophthalmic parameters.

RESULTS

The weighted prevalences of RVO, CRVO, and BRVO were 0.40%, 0.08%, and 0.32%, respectively. Men were 1.7 times more frequently affected by RVO than were women. Prevalence of RVO was 0.2% in participants aged 35-44 and 45-54 years, respectively, 0.48% in those aged 55-64 years, and 0.92% in those aged 65-74 years. Of persons with RVO, 91.5% had one or more cardiovascular risk factor or disease vs. 75.9% of persons without RVO. BRVO was associated with arterial hypertension (odds ratio 2.69, 95% confidence interval 1.27-5.70) and atrial fibrillation (3.37, 1.24-9.12) and CRVO with higher age (7.02, 1.63-30.19) and a family history of stroke (4.64, 1.18-18.25). Median visual acuity (base 10 logarithm of minimum angle of resolution) was 0.2 in persons with RVO vs. 0.05 in those without.

CONCLUSION

The prevalence of RVO in this German population was 0.4%, and men were 1.7 times more frequently affected than women. CRVO was associated with higher age and a family history of stroke, and BRVO was associated with arterial hypertension and atrial fibrillation.

Role of Factor XII in hemostasis and thrombosis: clinical implications

The plasma coagulation system reacts quickly to limit blood loss from injury sites but also contributes to vascular thrombosis. In current models of hemostatic balance, normal coagulation and thrombosis represent two sides of the same coin, however, recent data from gene-deleted murine models have challenged this dogma. Deficiency of coagulation Factor XII (Hageman factor), a serine protease that initiates the intrinsic pathway of coagulation, severely impairs arterial thrombus formation but is not associated with excessive bleeding. These findings suggest that fibrin-generating mechanisms that operate during pathologic thrombus formation involve pathways distinct from those that are active during normal hemostasis. As Factor XII selectively contributes to thrombus formation in occlusive disease, but not to normal hemostasis, inhibition of this protease may offer a novel treatment strategy for prevention of arterial thrombosis with minimal or no risk of bleeding.

Retinal venous thrombosis in a young patient with coagulation factor XII deficiency

CASE REPORT

A 35-year-old woman, with no relevant medical history, was referred for sudden vision loss in the left eye. Ophthalmological examination showed best corrected visual acuity of 1.0 in the right eye and 0.3 in left eye, with normal anterior pole and intraocular pressure. Fundus examination of the left eye revealed a venous thrombosis in the superior temporal branch, with dilated and tortuous retinal veins. The patient was referred to the hematology unit for thrombophilia study, and was diagnosed with a coagulation XII or Hageman factor deficiency.

DISCUSSION

The development of retinal vessel occlusions, in patients under 50 years of age, is frequently associated with thrombophilia or hypercoagulability disorders. Factor XII deficiency is a rare condition, and its presence could contribute to a higher risk of thromboembolic events.

Factor XII promotes blood coagulation independent of factor XI in the presence of long-chain polyphosphates

BACKGROUND

Inorganic polyphosphates (polyP), which are secreted by activated platelets (short-chain polyP) and accumulate in some bacteria (long-chain polyP), support the contact activation of factor XII (FXII) and accelerate the activation of FXI.

OBJECTIVES

The aim of the present study was to evaluate the role of FXI in polyP-mediated coagulation activation and experimental thrombus formation.

METHODS AND RESULTS

Pretreatment of plasma with antibodies that selectively inhibit FXI activation by activated FXII (FXIIa) or FIX) activation by activated FXI (FXIa) were not able to inhibit the procoagulant effect of long or short-chain polyP in plasma. In contrast, the FXIIa inhibitor, corn trypsin inhibitor, blocked the procoagulant effect of long and short polyP in plasma. In a purified system, long polyP significantly enhanced the rate of FXII and prekallikrein activation and the activation of FXI by thrombin but not by FXIIa. In FXI-deficient plasma, long polyP promoted clotting of plasma in an FIX-dependent manner. In a purified system, the activation of FXII and prekallikrein by long polyP promoted FIX activation and prothombin activation. In an ex vivo model of occlusive thrombus formation, inhibition of FXIIa with corn trypsin inhibitor but not of FXI with a neutralizing antibodies abolished the prothrombotic effect of long polyP.

CONCLUSIONS

We propose that long polyP promotes FXII-mediated blood coagulation bypassing FXI. Accordingly, some polyp-containing pathogens may have evolved strategies to exploit polyP-initiated FXII activation for virulence, and selective inhibition of FXII may improve the host response to pathogens.

Comorbidity in patients with branch retinal vein occlusion: case-control study

OBJECTIVES

To evaluate comorbidity before and after the diagnosis of branch retinal vein occlusion to determine whether it is a consequence of arterial thickening and therefore could serve as a diagnostic marker for other comorbidities and to evaluate the risk factors for the development of such occlusion.

DESIGN

Case-control study with prospective follow-up data from Danish national registries.

SETTING

Four secondary referral centres covering about 80% of the Danish population (4.4 million).

PARTICIPANTS

1168 patients with photographically verified branch retinal vein occlusion and 116,800 controls alive and aged ≥ 40 when the occlusion was diagnosed in the corresponding case.

MAIN OUTCOME MEASURES

The risk of comorbidity 10 years and 1 year before the diagnosis of branch retinal vein occlusion and the incident comorbidity in a mean period of seven years after the diagnosis, with odds ratios and incidence rate ratios adjusted for age, sex, and year of diagnosis.

RESULTS

Risk factors present 10 years and 1 year before the diagnosis of branch retinal vein occlusion included peripheral artery disease (odds ratio 1.83, 95% confidence interval 1.14 to 2.95), diabetes (1.74, 1.40 to 2.17) and arterial hypertension (2.16, 1.86 to 2.51). After the diagnosis, patients had an increased risk of developing arterial hypertension (incidence rate ratio 1.37, 95% confidence interval 1.15 to 1.57), diabetes (1.51, 1.17 to 2.04), congestive heart failure (1.41, 1.12 to 1.68), and cerebrovascular disease (1.49, 1.27 to 1.76).

CONCLUSION

Diabetes, hypertension, and peripheral artery disease are associated with an increased risk of developing branch retinal vein occlusion up to a decade later. Branch retinal vein occlusion was associated with an increased risk of subsequently developing hypertension, diabetes, congestive heart failure, and cerebrovascular disease, emphasising the importance of preventive initiatives. These results fit the assumption that branch retinal vein occlusion is a consequence of arterial thickening and that the arteriovenous crossing signs that precede it are hallmarks of arterial disease.

[Thrombophilic and systemic risk factors in patients with retinal vein occlusion]

Over the past years there has been a dramatic increase in the number of identifiable causes of thrombophilia. However, as retinal vein occlusions (RVO) have a strong pathogenic correlation with the presence of hypertension or arteriosclerosis and the average age of affected patients is usually within the sixth or seventh decade of life, thrombophilia screening of RVO patients poses a particularly difficult diagnostic challenge. It is clear that to use medical resources appropriately and improve the level of interdisciplinary patient care in RVO, subgroup analysis is required. Just recently, some studies have demonstrated the significant role of coagulation disorders in specific subgroups of RVO patients and have provided recommendations for clinical practice. These results indicate that thrombophilic risk factors are significantly more prevalent among patients equal or less than 45 years of age at the time of RVO or a previous thromboembolic event, among patients with a remarkable family history of thromboembolism prior to the age of 45 years, or among patients without cardiovascular risk factors. According to these data, thrombophilia screening should be considered in these selected subgroups.

Treatments for neuro-ophthalmologic conditions

Neuro-ophthalmology covers disorders that fall between the cracks of Neurology and Ophthalmology. Neurologists see patients with neuro-ophthalmic disorders. Recognition of the diagnosis is difficult enough, but treatment can be challenging. This article reviews several common neuro-ophthalmic disorders, outlining their features and treatments, from retinal vascular disorders to eye movements and blepharospasm.

Retinal vein occlusion: evaluation of "classic" and "emerging" risk factors and treatment

Retinal vein occlusion (RVO) is the second most common retinal vein disease and an important cause of blindness and visual morbidity. Systemic risk factors are commonly associated with RVO, while unclear it is the role of the thrombophilic and coagulation disorders. To evaluate "classic" and "emerging" risk factors, and to establish a good treatment for RVO. Fifty patients, 31 males and 19 females, with RVO were selected for our study. RVO patients were divided into two groups: those with central retinal vein occlusion (CRVO) and those with branch retinal vein occlusion (BRVO). All patients were subjected to an anamnestic investigation and were tested for thrombophilia, coagulation disorders and hyperlipidemia. Treatment and prophylaxis were evaluated. We have named "classic" the systemic risk factors associated with RVO and "emerging" those risk factors, haemostasis related, not clearly associated with RVO. RVO occurs more commonly in patients aged over 50. "Emerging" risk factors were more frequent in CRVO, "classic" in BRVO. Hyperhomocysteinemia is the most common "emerging" risk factor related to RVO. 71.4% of tested patients had hypercholesterolemia. Treatment with LMWH would appear to be safe and effective, but the small number of patients considered not allow us a definitive evaluation of its efficacy. Although our study has shown the correlation between RVO and the "emerging" risk factors, more studies are necessary to better know the real role of thrombophilic and coagulation disorders in this disease and to determine a specific protocol for the treatment and prophylaxis of RVO.

Sequence variation and genetic evolution at the human F12 locus: mapping quantitative trait nucleotides that influence FXII plasma levels

The level of Factor XII (FXII) is an important phenotype that exhibits a high genetic component and is associated with thrombotic disease. In a genome-wide linkage scan, we demonstrated that the F12 gene represents a quantitative trait locus (QTL) that influences FXII levels. The current study investigated the genetic architecture of the F12 gene to locate polymorphism(s) responsible for the variation of FXII levels. Re-sequencing of the F12 gene in 40 unrelated individuals (selected from the tails of normal distribution of FXII levels) identified 26 polymorphisms which were genotyped in 398 individuals belonging to 21 families from the GAIT Project. By a measured genotype association analysis, eight of 26 SNPs showed significant P-values less than 10(-5) (after multiple test correction) with FXII levels. In addition, the Bayesian Quantitative Trait Nucleotide method, which infers those polymorphisms most likely to have a direct influence on the trait under study, provided evidence that only rs1801020 variation accounted for the variance attributed to this QTL. Moreover, we have analyzed the evolutionary processes that produced the variation in F12 gene and concluded that is evolutionarily neutral and that the T allele of the rs1801020 appeared approximately 100 000 years ago and spread to most human populations rising to high frequencies by genetic drift. Our study provides a template for future genetic studies of human quantitative traits, as we move beyond QTL localization to the polymorphisms responsible for the variation of important biomedical phenotypes.

Retinal vascular occlusions: an interdisciplinary challenge

INTRODUCTION

Retinal venous and arterial occlusions are common causes of visual loss. Depending on the location and extent, symptoms may vary from very discrete impairments to complete loss of sight.

METHODS

Selective literature review including the authors' own research data with a particular focus on interdisciplinary aspects.

RESULTS

Retinal vascular occlusions are not a uniform entity. Rather, they reflect the whole breadth of vascular disease. In arterial occlusion, embolic phenomena and Horton's arteritis should be excluded, in addition to local ophthalmological investigations. In retinal venous occlusion, optimal treatment of arterial hypertension is universally useful, while investigations for thrombophilia are useful in patients under 50 years of age. The results of intravitreal injection of corticosteroids and vascular endothelial growth factor inhibitors appear encouraging in treatment of macular edema secondary to retinal vein occlusion.

DISCUSSION

While local diagnostic and therapeutic measures are performed by ophthalmologists, there is an important role for interdisciplinary cooperation in the investigation and systemic treatment of these events.

Deep venous thrombosis and previous myocardial infarction in mild factor XII deficiency: a risk factor for both venous and arterial thrombosis

Factor XII deficiency is associated with increased risk for both arterial and venous thrombosis. We describe a case of DVT involving superficial femoral and popliteal vein occurred following total hip replacement and despite prophylaxis with low molecular weight heparin in a subject with previous acute myocardial infarction (AMI). Tests of haemostasis documented a slightly prolonged activated partial thromboplastin time (APTT) (45'') due to mild factor XII deficiency (clotting activity 32%). A therapeutic dose of enoxaparin was started, together with warfarin therapy. The patient was advised to continue oral anticoagulation indefinitely. Although cases of both venous and arterial thrombosis in carriers of severe factor XII deficiency have been already reported, to our knowledge this is the first case in the literature occurred in a carrier of partial factor XII deficiency. In conclusion, factor XII deficiency should be suspected if a patient presents with recurrent arterial and/or venous thrombosis and prolonged APTT. If this defect is diagnosed, in the presence of a history of thrombotic events, lifelong anticoagulation could be considered.

Role of thrombophilic gene polymorphisms in branch retinal vein occlusion

OBJECTIVE

Branch retinal vein occlusion (BRVO) is a common cause of severe visual loss. Numerous risk factors, including arterial hypertension, diabetes mellitus, and arteriosclerosis, have been identified. Gene polymorphisms affecting hemostasis may also play a role in the pathogenesis of BRVO. The present study was therefore done to determine the prevalence of genetic polymorphisms in factors implicated in hypercoagulability among patients with BRVO.

DESIGN

Retrospective case-control study.

PARTICIPANTS

The study cohort consisted of 294 patients with BRVO and 294 control subjects, matched for age and gender.

METHODS

Determination of genotypes was done by allele-specific digestion of polymerase chain reaction products, or by 5' exonuclease assay (TaqMan).

MAIN OUTCOME PARAMETERS

Genotypes of factor V R506Q (factor V Leiden), prothrombin 20210G>A, fibrinogen beta -455G> A, factor XII (FXII) 46C>T, and ITGA2 807C>T (platelet glycoprotein Ia [GPIa] 807C>T) and ITGB3 L59P (platelet GPIIIa PlA1/PlA2) polymorphisms.

RESULTS

Genotype distributions of the investigated gene polymorphisms did not differ significantly between patients and control subjects. In contrast, significantly increased prevalences of arterial hypertension and hypercholesterolemia were found among patients with BRVO. In a logistic regression analysis, the presence of arterial hypertension was associated with an odds ratio (OR) of 2.32 (95% confidence interval [CI], 1.62-3.32), whereas hypercholesterolemia yielded an OR of 2.54 (95% CI, 1.74-3.70) for BRVO.

CONCLUSION

Our data indicate that the prevalences of the investigated gene polymorphisms do not differ significantly in patients with BRVO and control subjects. This suggests that these polymorphisms are not major risk factors for BRVO.

Homocysteine, MTHFR C677T gene polymorphism, folic acid and vitamin B 12 in patients with retinal vein occlusion

Background

Many available data have suggested that hyperhomocysteinaemia, an established independent risk factor for thrombosis (arterial and venous), may be associated with an increased risk of retinal vein occlusion (RVO).

Aim of the study

To evaluate homocysteine metabolism in consecutive caucasian patients affected by RVO from Northern Italy.

Patients and Methods

69 consecutive patients from Northern Italy (mean age 64.1 ± 14.6 yy) with recent RVO, were tested for plasma levels of homocysteine (tHcy: fasting and after loading with methionine), cyanocobalamine and folic acid levels (CMIA-Abbot) and looking for MTHFR C677T mutation (Light Cycler-Roche) and compared to 50 volunteers, enrolled as a control group.

Results

Fasting levels of tHcy were significantly higher in patients than in controls: mean value 14.7 ± 7.7 vs 10.2 ± 8 nmol/ml. Post load levels were also significantly higher: mean value 42.7 ± 23.7 vs 30.4 ± 13.3 nmol/ml; Total homocysteine increase was also evaluated (i.e. Δ-tHcy) after methionine load and was also significantly higher in patients compared to control subjects: mean Δ-tHcy 27.8 ± 21.5 vs 21.0 ± 16 nmol/ml (normal value < 25 nmol/ml). Furthermore, patients affected by RVO show low folic acid and/or vitamin B12 levels, although differences with control group did not reach statistical significance. Heterozygous and homozygous MTHFR mutation were respectively in study group 46% and 29% vs control group 56% and 4%.

Conclusion

our data confirm that hyperhomocysteinaemia is a risk factor for RVO, and also that TT genotype of MTHFR C677T is more frequently associated with RVO: if the mutation per se is a risk factor for RVO remains an open question to be confirmed because another study from US did not reveal this aspect.

Hyperomocysteinemia is modifiable risk factor for thrombotic diseases. Therefore, a screening for tHcy plasma levels in patients with recent retinal vein occlusion could allow to identify patients who might benefit from supplementation with vitamins and normalization of homocysteine levels, in fasting and after methionine load.

Folate deficiency-induced hyperhomocysteinemia attenuates, and folic acid supplementation restores, the functional activities of rat coagulation factors XII, X, and II

Hyperhomocysteinemia (HH) constitutes a risk marker for thrombosis, but the pathophysiological mechanisms in thrombus formation are still unresolved. We investigated the influence of HH on single coagulation factor functions and evaluated the platelet GpIIb/IIIa receptor function in HH-induced changes in whole-blood coagulation profiles (WBCP). Three groups of 12 rats were investigated: control rats, folate deficient-HH (FD-HH) rats, and treated rats. Plasma total homocysteine was 7.1 micromol/L in controls, 31.3 micromol/L in FD-HH rats, and 7.6 micromol/L in treated rats. Factor (F) II:C, FX:C, and FXII:C were reduced in FD-HH rats compared with controls and normalized in treated rats (P < 0.05). FVII:C activity did not differ among the groups. Factor VIII:C activity was greater in FD-HH rats than in controls (P < 0.05). Blockage of the platelet GpIIb/IIIa receptor by Integrilin (Schering-Plough A/S) did not abolish the FD-HH-induced increase in whole-blood coagulation velocity, irrespective of the dosage of Integrilin. In conclusion, FD-HH reduced the functional activities of FXII:C, FX:C and FII:C, whereas FVII:C was unchanged and FVIII:C increased. These findings may partially explain the prolonged initiation phase of WBCP in FD-HH rats. The changes in single coagulation factor functions and WBCPs in FD-HH rats were reversed by treatment with folic acid.

Defective thrombus formation in mice lacking coagulation factor XII

Blood coagulation is thought to be initiated by plasma protease factor VIIa in complex with the membrane protein tissue factor. In contrast, coagulation factor XII (FXII)–mediated fibrin formation is not believed to play an important role for coagulation in vivo. We used FXII-deficient mice to study the contributions of FXII to thrombus formation in vivo. Intravital fluorescence microscopy and blood flow measurements in three distinct arterial beds revealed a severe defect in the formation and stabilization of platelet-rich occlusive thrombi. Although FXII-deficient mice do not experience spontaneous or excessive injury-related bleeding, they are protected against collagen- and epinephrine-induced thromboembolism. Infusion of human FXII into FXII-null mice restored injury-induced thrombus formation. These unexpected findings change the long-standing concept that the FXII-induced intrinsic coagulation pathway is not important for clotting in vivo. The results establish FXII as essential for thrombus formation, and identify FXII as a novel target for antithrombotic therapy.