Evaluation of a highly specific functional test for the detection of factor V Leiden

Thrombophilia Screening: Not So Straightforward

Although inherited thrombophilias are lifelong risk factors for a first thrombotic episode, progression to thrombosis is multifactorial and not all individuals with inherited thrombophilia develop thrombosis in their lifetimes. Consequently, indiscriminate screening in patients with idiopathic thrombosis is not recommended, since presence of a thrombophilia does not necessarily predict recurrence or influence management, and testing should be selective. It follows that a decision to undertake laboratory detection of thrombophilia should be aligned with a concerted effort to identify any significant abnormalities, because it will inform patient management. Deficiencies of antithrombin and protein C are rare and usually determined using phenotypic assays assessing biological activities, whereas protein S deficiency (also rare) is commonly detected with antigenic assays for the free form of protein S since available activity assays are considered to lack specificity. In each case, no single phenotypic assay is capable of detecting every deficiency, because the various mutations express different molecular characteristics, rendering thrombophilia screening repertoires employing one assay per potential deficiency, of limited effectiveness. Activated protein C resistance (APCR) is more common than discrete deficiencies of antithrombin, protein C, and protein S and also often detected initially with phenotypic assays; however, some centres perform only genetic analysis for factor V Leiden, as this is responsible for most cases of hereditary APCR, accepting that acquired APCR and rare F5 mutations conferring APCR will go undetected if only factor V Leiden is evaluated. All phenotypic assays have interferences and limitations, which must be factored into decisions about if, and when, to test, and be given consideration in the laboratory during assay performance and interpretation. This review looks in detail at performance and limitations of routine phenotypic thrombophilia assays.

Activated protein C resistance impact on Syrian candidates for in vitro fertilisation and the benefit of anticoagulation therapy: a retrospective cohort study

Activated protein C resistance (APCR) is a common thrombophilia, caused mainly by a mutation. The impact of APCR on the efficacy of In Vitro Fertilization (IVF) are still unclear, and no solid recommendations for its management were published. To investigate the effect of APCR on IVF outcomes and assess the efficacy of our management protocol, we retrospectively scanned the medical records of women who were tested with APCR assay in 2019 at our fertility centre. The 66 women (12%) positive for APCR had lower odds of reaching clinical pregnancies after IVF 0.18 [95% CI: 0.07-0.47] and fewer live births. The administration of low-molecular-weight heparin and aspirin associated with more implantation in treated compared to untreated APCR-positive women with an odds ratio of 43.2 [7.51-248.6]. In conclusion, APCR negatively affects the number of clinical pregnancies after IVF, but anticoagulation therapy can mitigate this effect and significantly increase clinical pregnancies.Impact StatementWhat is already known on this subject? The evidence about the impact of APCR on IVF outcomes is still inconclusive. According to the Canadian guideline, routine screening for thrombophilia in patients with recurrent pregnancy loss is not recommended. No clear recommendations regarding the management of APCR in the planning for IVF are yet available.What do the results of this study add? APCR significantly increases implantation failure among infertile women who conduct IVF. Management of APCR using LMWH and aspirin was effective in mitigating this effect and increasing successful implantation.What are the implications of these findings for clinical practice and/or further research? Our findings can support the recommendation to include APCR assay in the routine tests for infertile women conducting IVF, and suggest the combination between LMWH and aspirin as an effective therapy to increase successful implantation in APCR positive candidates. However, more controlled clinical trials are still needed to confirm our results.

Snake Venoms in Diagnostic Hemostasis and Thrombosis

Snake venoms have evolved primarily to immobilize and kill prey, and consequently, they contain some of the most potent natural toxins. Part of that armory is a range of hemotoxic components that affect every area of hemostasis, which we have harnessed to great effect in the study and diagnosis of hemostatic disorders. The most widely used are those that affect coagulation, such as thrombin-like enzymes unaffected by heparin and direct thrombin inhibitors, which can help confirm or dispute their presence in plasma. The liquid gold of coagulation activators is Russell's viper venom, since it contains activators of factor X and factor V. It is used in a range of clotting-based assays, such as assessment of factor X and factor V deficiencies, protein C and protein S deficiencies, activated protein C resistance, and probably the most important test for lupus anticoagulants, the dilute Russell's viper venom time. Activators of prothrombin, such as oscutarin C from Coastal Taipan venom and ecarin from saw-scaled viper venom, are employed in prothrombin activity assays and lupus anticoagulant detection, and ecarin has a valuable role in quantitative assays of direct thrombin inhibitors. Snake venoms affecting primary hemostasis include botrocetin from the jararaca, which can be used to assay von Willebrand factor activity, and convulxin from the cascavel, which can be used to detect deficiency of the platelet collagen receptor, glycoprotein VI. This article takes the reader to every area of the diagnostic hemostasis laboratory to appreciate the myriad applications of snake venoms available in diagnostic practice.

The Frequency of Factor V Leiden and Concomitance of Factor V Leiden With Prothrombin G20210A Mutation and Methylene Tetrahydrofolate Reductase C677T Gene Mutation in Healthy Population of Denizli, Aegean Region of Turkey

Factor V Leiden causing activated protein C resistance is the most common inherited form of thrombophilia leading to thrombosis. Its frequency shows great ethnic and geographic variations. The aim of this study was to determine the frequency of FV Leiden and coinheritance of FV Leiden with two other frequent hereditary thrombophilia causes, namely, prothrombin G20210A and methylene-tetrahydrofolate reductase ( MTHFR) C677T mutation in the Aegean region of Turkey. The study population consisted of 1030 (500 men and 530 women) apparently healthy subjects. Functional resistance to activated protein C (APC) was measured by using the test kit STA staclot APC-R ((Diagnostica Stago, Asnieres, France, Cat. No. 00721). In subjects with APC resistance, molecular analyses of FV Leiden and of prothrombin G20210A and MTHFR C677T mutation were performed by using FV-PTH-MTHFR StripA (Vienna Lab, Labordiagnostika GmbH, Austria) kit, which was based on hybridization of polymerase chain reaction (PCR) amplified DNA products with mutation-specific oligonucleotide probes. Functional APC resistance was present in 93 subjects (9%). FV Leiden mutation was found in 87 of 93 subjects with APC resistance by PCR method. The FV Leiden carrier frequency was found to be 8.4% (87/1030). Seventy-six individuals were heterozygous (7.3%), and 11 were homozygous (1.06%). Among the 87 subjects with FV Leiden mutation, 45 subjects had MTHFR C677T gene mutation (7 homozygous, 38 heterozygous) and 4 subjects had heterozygote prothrombin G20210A gene mutation. A combination of FV Leiden and prothrombin G20210A and MTHFR C677T gene mutation was detected in 3 subjects. The results indicate that FV Leiden prevalence is quite high and coexistence of FV Leiden with other hereditary causes of thrombosis such as prothrombin G20210A mutation and MTHFR enzyme defect is not rare in healthy population of Aegean region of Turkey.

Evolving methods for single nucleotide polymorphism detection: Factor V Leiden mutation detection

BACKGROUND

The many techniques used to diagnose the Factor V Leiden (FVL) mutation, the most common hereditary hypercoagulation disorder in Eurasians, and the most frequently requested genetic test reflect the evolving strategies in protein and DNA diagnosis.

METHODS

Here, molecular methods to diagnose the FVL mutation are discussed.

RESULTS

Protein-based detection assays include the conventional functional activated protein C resistance coagulation test and the recently reported antibody-mediated sensor detection; and DNA-based assays include approaches that use electrophoretic fractionation e.g., restriction fragment length polymorphism, denaturing gradient gel electrophoresis, and single-stranded conformational PCR analysis, DNA hybridization (e.g., microarrays), DNA polymerase-based assays, e.g., extension reactions, fluorescence polarization template-directed dye-terminator incorporation, PCR assays (e.g., amplification-refractory mutation system, melting curve analysis using real-time quantitative PCR, and helicase-dependent amplification), DNA sequencing (e.g., direct sequencing, pyrosequencing), cleavase-based Invader assay and ligase-based assays (e.g., oligonucleotide ligation assay and ligase-mediated rolling circle amplification).

CONCLUSION

The method chosen by a laboratory to diagnose FVL not only depends on the available technical expertise and equipment, but also the type, variety, and extent of other genetic disorders being diagnosed.

Normal ranges and genetic variants of antithrombin, protein C and protein S in the general Chinese population. Results of the Chinese Hemostasis Investigation on Natural Anticoagulants Study I Group

BACKGROUND

Inherited deficiency of antithrombin, protein C and protein S, three important, naturally occurring coagulation inhibitors, might play a major role in the occurrence of venous thromboembolism in Chinese. The establishment of age- and gender-related normal ranges of these inhibitors is crucial for an accurate diagnosis of these deficiencies.

DESIGN AND METHODS

We designed a prospective cross-sectional study recruiting healthy adults from four university-affiliated hospitals in China. Antithrombin, protein C and protein S were studied by measuring their activity. Gene analysis was performed when natural anticoagulant deficiency was suspected. Polymorphisms of the factor V gene were searched for among subjects who were positive for activated protein C resistance.

RESULTS

In 3493 healthy Chinese adults (1734 men, 1759 women; age 17-83 years), we found higher age-adjusted activities for protein C and protein S in men than in women but no sex difference for antithrombin. In women, mean protein C and protein S activities increased with age. In men, mean protein C levels increased with age up to the age of 49 but decreased after 50 years old; mean protein S levels decreased after 50 years of age. Antithrombin levels remained stable over time in women but decreased significantly after 50 years of age in men. Reference values according to age and sex allowed the identification of 15 genetic variants (protein C:10, antithrombin:3, protein S:2) in subjects with protein activity below the 1(st) percentile.

CONCLUSIONS

This is the largest survey ever conducted in the healthy general Chinese population. These normal ranges provide the essential basis for the diagnosis and treatment of thrombosis in Chinese.

Clinical evaluation of a new functional test for detection of activated protein C resistance (Pefakit® APC-R Factor V Leiden) at two centers in Europe and the USA

A new clotting assay, Pefakit APC-R Factor V Leiden (Pentapharm Ltd., Switzerland), for the detection of an increased resistance of coagulation factor V against degradation by activated protein C, caused mainly by the factor V Leiden mutation, was evaluated in clinical studies at two University Centers in Europe and the US. The performance was compared with the performance of the routinely used predicate device COATEST APC Resistance V (Chromogenix IL, USA). Both tests were run in parallel on a STA-R analyzer (Diagnostica Stago, France). Samples from subjects undergoing routine laboratory thrombophilia screening were examined, 187 at the Institute of Medical and Chemical Laboratory Diagnostics (IMCLD), University of Vienna, Austria, and 236 at the Duke University Medical Center (DUMC), Durham/Raleigh NC, USA. All samples were analyzed for factor V Leiden mutation and prothrombin 20210 G/A mutation using standard PCR methods. The data show that the Pefakit APC-R Factor V Leiden assay discriminates very well between healthy controls and carriers of the factor V Leiden mutation, even in patients with lupus anticoagulant or with deficiency in Protein C or Protein S. Furthermore, this new test is able to discriminate well between heterozygous and homozygous carriers of the factor V Leiden mutation. In both studies the Pefakit assay showed 100% sensitivity and 100% specificity for detection of the factor V Leiden mutation, compared to 93.1% sensitivity and 93.0% specificity for the COATEST APC Resistance V in the IMCLD study and 93.9% sensitivity and 95.6% specificity in the DUMC study. The new test has PCR-like discrimination power which will help to decrease costs by reducing the need for PCR verification of borderline cases.

Practical applications of snake venom toxins in haemostasis

Snake venom toxins affecting haemostasis have facilitated extensively the routine assays of haemostatic parameters in the coagulation laboratory. Snake venom thrombin-like enzymes (SVTLE) are used for fibrinogen/fibrinogen breakdown product assay and for the detection of fibrinogen dysfunction. SVTLE are not inhibited by heparin and can thus can be used for assaying antithrombin III and other haemostatic variables in heparin-containing samples. Snake venoms are a rich source of prothrombin activators and these are utilised in prothrombin assays, for studying dysprothrombinaemias and for preparing meizothrombin and non-enzymic forms of prothrombin. Russell's viper (Daboia russelli) venom (RVV) contains toxins which have been used to assay blood clotting factors V, VII, X, platelet factor 3 and, importantly, lupus anticoagulants (LA). Other prothrombin activators (from the taipan, Australian brown snake and saw-scaled viper) have now been used to assay LA. Protein C and activated protein C resistance can be measured by means of RVV and Protac, a fast acting inhibitor from Southern copperhead snake venom and von Willebrand factor can be studied with botrocetin from Bothrops jararaca venom. The disintegrins, a large family of Arg-Gly-Asp (RGD)-containing snake venom proteins, show potential for studying platelet glycoprotein receptors, notably, GPIIb/IIIa and Ib. Snake venom toxins affecting haemostasis are also used in the therapeutic setting: Ancrod (from the Malayan pit viper, Calloselasma rhodostoma), in particular, has been used as an anticoagulant to achieve 'therapeutic defibrination'. Other snake venom proteins show promise in the treatment of a range of haemostatic disorders.