Activated protein C resistance: from phenotype to genotype and clinical practice

Genomic characterisation of the overlap of endometriosis with 76 comorbidities identifies pleiotropic and causal mechanisms underlying disease risk

Comorbid conditions can be driven by underlying pleiotropic and causal mechanisms that can provide insights into shared molecular and biological processes contributing to disease risk. Endometriosis is a chronic condition affecting one in nine women of reproductive age and poses many challenges including lengthy diagnostic delays and limited treatment efficacy owing to poor understanding of disease aetiology. To shed light on the underlying biological mechanisms and to identify potential risk factors, we examine the epidemiological and genomic relationship between endometriosis and its comorbidities. In the UK Biobank 292 ICD10 codes were epidemiologically correlated with endometriosis diagnosis, including gynaecological, immune, infection, pain, psychiatric, cancer, gastrointestinal, urinary, bone and cardiovascular traits. A subset of the identified comorbidities (n = 76) underwent follow-up genetic analysis. Whilst Mendelian randomisation suggested causality was not responsible for most comorbid relationships, 22 traits were genetically correlated with endometriosis, including pain, gynaecological and gastrointestinal traits, suggestive of a shared genetic background. Pleiotropic genetic variants and genes were identified using gene-based and colocalisation analysis. Shared genetic risk factors and potential target genes suggest a diverse collection of biological systems are involved in these comorbid relationships including coagulation factors, development of the female reproductive tract and cell proliferation. These findings highlight the diversity of traits with epidemiological and genomic overlap with endometriosis and implicate a key role for pleiotropy in the comorbid relationships.

The clinical and functional relevance of microparticles induced by activated protein C treatment in sepsis

INTRODUCTION

Activated protein C (APC) induces release of microparticles (MP) from primary physiological cells, which are found in patients undergoing treatment with recombinant human APC (rhAPC) for severe sepsis. We hypothesised that APC on these circulating MPs activate endothelial protease-activated receptor 1 (PAR1) to induce anti-apoptotic and anti-inflammatory properties that can improve patient outcome.

METHODS

This was an experimental study on clinical samples in an intensive care setting, and included patients with severe sepsis who fulfilled criteria for treatment with rhAPC. The number of CD13+ MPs from the patients were analysed to determine their origin. They were also quantified for endothelial protein C receptor (EPCR) and APC expression. Clinical relevance of these MPs were ascertained by comparing survival between the group receiving rhAPC (n = 25) and a control group of untreated patients (n = 25). MPs were also incubated with endothelial cells to analyse apoptotic gene expression, cytoprotection and anti-inflammatory effects.

RESULTS

rhAPC treatment induced a significant increase in circulating MP-associated EPCR by flow cytometry (P < 0.05) and by quantitative ELISA (P < 0.005). APC expression also showed significant increases (P < 0.05). Numerically, CD13+ MPs were higher in rhAPC-treated survivors versus non-survivors. However, the number of non-survivors was low and this was not significantly different. APC on MPs was demonstrated to induce anti-apoptotic and endothelial barrier effects through the activation of endothelial PAR1.

CONCLUSIONS

rhAPC treatment in patients with sepsis significantly increases circulating EPCR + MPs. These MPs were noted to express APC, which has specific anti-apoptotic and anti-inflammatory effects, with a non-significant correlative trend towards survival. This suggests that MPs could disseminate APC function and activate endothelial PAR1 at distal vascular sites.

Mutations C677T and A1298C of the 5,10-methylenetetrahydrofolate reductase gene and fasting plasma homocysteine levels are not associated with the increased risk of venous thromboembolic disease

Mild hyperhomocysteinemia is associated with homozygosity for the thermolabile variant of 5,10-methylenetetrahydrofolate reductase (MTHFR) and could increase the risk of venous thromboembolic disease (VTD). Recently, the second A1298C mutation of the MTHFR gene was described. The present study aimed to analyze both mutations of the MTHFR gene and plasma homocysteine levels in subjects with VTD. The study groups comprised 146 patients with VTD and 100 healthy subjects. There were no statistical differences in carrier frequency and allelic frequency for both A1298C and C677T mutations, nor were there any differences encountered between subjects with VTD and controls in either plasma homocysteine levels or according to C677T or A1298C genotypes of MTHFR. In our VTD patients and controls, neither MTHFR 677CT/1298CC nor MTHFR 677TT/1298CC combined genotypes were observed; double heterozygotes (A1298C/C677T) were represented only in 11% of VTD patients, and in 15% of the controls. In conclusion, the polymorphisms C677T and A1298C of MTHFR and fasting plasma homocysteine levels do not seem to be significant risk factors for venous thromboembolic disease.

Determination of activated protein C resistance in anticoagulated and lupus positive patients

Clotting-based activated protein C (APC) assays have limitations when testing patients on oral anticoagulant (OA) therapy or with a lupus anticoagulant (LA). Predilution in factor V (FV)-deficient plasma and testing with phospholipid-rich Russell Viper venom (RVV)-based methods have been shown to be the most suitable methods when testing these patient groups, respectively. We evaluated a modified RVV based clotting test (Gradileiden V test; Gradipore, Sydney, Australia) in a large patient cohort and determined its sensitivity to the FV Leiden mutation. We also examined whether normal plasma can be used to dilute plasma from warfarinized patients without compromising sensitivity to the FV Leiden mutation. A total of 1,956 plasmas were studied including congenital protein C (five plasmas), and protein S deficiency (five plasmas), LA (29 plasmas), FV Leiden heterozygote (102 plasmas), and homozygote (five plasmas), warfarin (54 plasmas), standard heparin therapy (37 plasmas) and normal healthy controls (21 plasmas). Molecular analysis was performed on all samples. The effect of FV Leiden concentration on the APC ratio was examined by determining the APC resistance of a homozygous plasma serially diluted in six sources of normal plasma (NP). The relationship was non-linear and dependent on the initial APC ratio of the chosen source of NP. APC resistance was demonstrated in the varying sources of NP in dilutions of 1/4 (25% FV Leiden) to 1/32 (3% FV Leiden). A 1/2 dilution in pooled NP is recommended for patients on OA therapy because the test remains sensitive at levels of 25% FV Leiden and this is the dilution routinely used for other applications in a coagulation laboratory. The effect of a LA on the APC ratio was similarly studied by determining the APC resistance of a homozygous plasma serially diluted in two sources of LA-positive plasma. This relationship was also non-linear and dependent on the initial APC ratio of the LA-positive plasma. APC resistance was demonstrated in dilutions of 1/16 (6% FV Leiden) to 1/64 (1.5% FV Leiden) demonstrating the sensitivity of the test to APC resistance in the presence of a LA. Our results show the modified RVV-based test clearly predicts the presence of factor V Leiden in a large cohort of patients. The method offers advantages when testing patients with a LA and patients receiving warfarin providing a 1/2 predilution step in pooled NP is performed. Pooled NP does not affect the sensitivity of the test to the mutation, is routinely used in coagulation laboratories, and is considerably less expensive than FV-deficient plasma.

The Leiden mutation of coagulation factor V in Hungarian SLE patients

We studied the prevalence and the effect of coagulation factor V Leiden mutation on the occurrence of thrombotic episodes in 120 Hungarian patients having systemic lupus erythematosus (SLE) with or without antiphospholipid antibody. The frequency of the factor V Leiden mutation in Hungarian SLE patients was 13%, which is comparable with those found previously in a healthy Caucasian population. The incidence of venous thrombosis among factor V Leiden carriers has been found to be higher (odds ratio [OR] 1.7) than it is in patients without Leiden mutation (38% vs 29%). In addition, the frequency of venous thrombosis in the heterozygous SLE patients (OR 8.4 [confidence interval (CI) 0.8-83.9] P = 0.06) is dependent on the coexistence of other risk factors, such as antiphospholipid antibody. Moreover, among heterozygous factor V SLE patients, the Leiden mutation could explain the tendency to have significantly higher prevalence of fetal losses (OR 3.9 [CI 1.2-12.0] P = 0.02) and higher prevalence of cerebrovascular lesions, cardiac valvular abnormalities, and Raynaud's syndrome than that found in individuals without factor V Leiden mutation of those having antiphospholipid antibody. Systemic lupus erythematosus patients with combined defects suffer more severely from thrombosis than those with a single risk factor do, suggesting that thrombophilia is a multifactorial disorder in SLE, also. Although, the factor V Leiden mutation does not seem to be a significant risk factor for venous thrombosis in SLE, these data demonstrate that Leiden mutation can be regarded as an additive thrombogenic factor providing higher predisposition to several vasoocclusive disorders in SLE.

The role of inherited thrombophilia in venous thromboembolism associated with pregnancy

Venous thromboembolism is an important cause of maternal morbidity and mortality. The puerperium should be regarded as the period of greatest risk. However, fatalities in early pregnancy emphasise the need to assess thrombotic risk at all stages of pregnancy. In many cases those at increased risk are potentially identifiable on clinical grounds alone such as those with a personal or family history of venous thromboembolism, obesity, or surgery. Identification of women with multiple clinical risks for thrombosis during pregnancy remains the key to reducing the incidence of this condition. In women who present with a personal or family history of proven venous thromboembolism, thrombophilia screening should be performed in early pregnancy, since the results may influence subsequent management during pregnancy. The investigation and management of patients considered at increased risk of venous thrombosis during pregnancy requires close liaison between obstetricians and haematologists familiar with this rapidly expanding and complex field of thrombophilia.

Role of factor V Leiden mutation in patients with angiographically demonstrated coronary artery disease

The study sought to determine whether coagulation factor V Leiden (FV Leiden) plays a role in the pathogenesis of coronary artery disease and/or myocardial infarction. Association of FV Leiden with venous thromboembolism is well established in the literature, but the role of the mutation in arterial thrombotic events is controversial. Some studies have documented an association between the mutation and myocardial infarction and stroke in juveniles. Few studies have explored its possible contribution to coronary atherosclerosis. We screened FV genotype in 850 predominantly white coronary angiography patients. Coronary artery disease risk factors and history of myocardial infarction were then analyzed by genotype. The FV Leiden mutation occurred in 54 (6.4%) patients. There was one homozygote; a 37-year-old, white male smoker with a history of myocardial infarction. Gene frequencies for white males and females were similar: 0.965 for the normal allele and 0.035 for FV Leiden. Gene frequencies for both genders were in Hardy-Weinberg equilibrium. FV Leiden was not a useful predictor (p=0.23) of the presence of clinically defined atherosclerosis (> or = 50% stenosis) in a logistic regression model adjusting for age, lipoprotein (a), total cholesterol, triglycerides, high density lipoprotein cholesterol, and fibrinogen. In addition, there was no difference in frequency of FV Leiden among those with and without medical histories of myocardial infarction (p=0.51). Allelic frequencies of FV Leiden in this patient group do not differ significantly from those reported for white populations. The FV Leiden mutation in its heterozygous state is not independently associated with coronary artery disease or myocardial infarction.

Evaluation of role of factor V Leiden mutation in fatal pulmonary thromboembolism

Association of a mutation in the coagulation factor V gene (FV Leiden) with deep vein thrombosis and pulmonary thromboembolism has been well documented in the literature, but no study has specifically screened cases of fatal pulmonary thromboembolism for the mutation. This study sought to determine whether FV Leiden plays a role in the pathogenesis of fatal pulmonary thromboembolism. We isolated DNA from archived paraffin-embedded tissues derived from 46 necropsy cases in which pulmonary thromboembolism was listed as the cause of death (n = 27) or was secondarily associated with death (n = 19). FV Leiden genotypes were determined by using polymerase chain reaction and MnlI digestion of amplified products. The Leiden mutation occurred in the heterozygous state in one (2.1%) of the necropsy specimens. The prevalence of the mutation was higher (8.7%) in gender- and ethnic-matched blood donor controls. The FV Leiden mutation is not independently associated with fatal pulmonary thromboembolism in the group of patients analyzed. The results suggest different etiologies for nonfatal, chronic deep vein thrombosis/pulmonary thromboembolism and fatal, acute pulmonary thromboembolism.

Familial thrombophilia: clinical and molecular analysis of Swedish families with inherited resistance to activated protein C or protein S deficiency

This report describes the characterization of Swedish families with inherited resistance to activated protein C (APC resistance) and/or protein S deficiency, two genetic disorders associated with functional impairment of the protein C anticoagulant pathway. The APC resistance phenotype was linked to the factor V gene locus in a kindred with independent inheritance of APC resistance and protein S deficiency. A point mutation changing Arg506 to a Gln (FV:Q506) in the factor V gene was the cause of APC resistance. In studies of 50 families with hereditary APC resistance, the FV:Q506 mutation was identified in 94% (47/50) of the families, and the thrombotic risk was found to be dependent on the factor V genotype. Moreover, 18 families with hereditary deficiency of free protein S were investigated. Type I protein S deficiency (low free and total protein S) and type III deficiency (low free but normal total protein S) coexisted in 78% (14/18) of the families, suggesting the two types to be phenotypic variants of the same genetic disorder. Deficiency of free protein S was caused by equimolar relationship between protein S and beta-chain containing isoforms of C4BP. Though protein S deficiency was a strong risk factor for thrombosis, the FV:Q506 mutation was identified as an additional genetic risk factor in 39% of the families. Thus, familial thrombophilia is a multiple gene disorder. The thrombophilic tendency associated with APC resistance or protein S deficiency was related to increased levels of prothrombin fragment 1 + 2, reflecting increased activation of the common coagulation pathway.