Corrigendum: The new Italian registry of infantile thrombosis (RITI): a reflection on its journey, challenges and pitfalls.

[This corrects the article DOI: 10.3389/fped.2023.1094246.].

Venous Thromboembolism in Children: The Rivaroxaban Experience.

The incidence of venous thromboembolism (VTE) in the pediatric population has increased more than 10-fold in the last 20 years, as a consequence of the advancement of resuscitation and surgical techniques and the global increase in life expectancy of children suffering from chronic pathologies. Monitoring anticoagulant therapy to achieve outcomes within the target range in childhood VTE, parenteral administration of medications, and frequent blood tests in children are often cumbersome. Availability of safe and effective oral agents with pediatric data to support use would be of clear benefit. A physiologically based pharmacokinetic model was developed to estimate the appropriate dosing schedule for rivaroxaban in children. This incorporated growth/maturation and variability in anthropometrics (e.g., body height, weight, and body mass index), anatomy (e.g., organ weight), physiology (e.g., blood flow rates), metabolism and excretion. Rivaroxaban use in pediatric population underwent a complete investigational program, consisting mainly of one phase I pharmacokinetics/pharmacodynamics trial, three phase II trials, one phase III trial. The phase III trial enrolled 500 patients from birth to <18 years and documented the efficacy and safety of rivaroxaban regimens at dose equivalent to the adult 20 mg dose for the prevention of fatal or symptomatic nonfatal recurrent VTE and major bleeding versus heparin or vitamin K antagonists. Results were similar to those in rivaroxaban studies in adults. The efficacy and safety of rivaroxaban in children reported in the EINSTEIN JUNIOR trial provide further support to previous trials in adults (EINSTEIN Program), which demonstrate a favorable profile for the use of rivaroxaban for the management of VTE in challenging patient populations. Other clinical evidence contributing to the use of rivaroxaban among different risk groups in pediatric VTE population confirms the consistency with principal trial. Our review aims to describe the rationale for using rivaroxaban oral suspension in clinical practice and to summarize its multiple indications in each vascular bed (e.g., cerebral venous thrombosis, symptomatic or asymptomatic central venous catheter-associated thrombosis), etiology, and patients setting.

The new Italian registry of infantile thrombosis (RITI): A reflection on its journey, challenges and pitfalls.

Introduction: Thrombotic events in neonates and children represent a rare although severe occurrence in view of the associated risk of mortality and sequelae. Quality evidence is limited in this field, and registry studies provide an essential base for research. The aim of this paper is to present the new Italian Registry of Infantile Thrombosis (RITI), set it into the scene of international thrombosis and stroke registries, and provide some insight on the challenges associated with registry management. Methods: We present the detailed structure and content of the new RITI registry, a brief overview of its main data, and a reflection on its features, pitfalls and the main challenges related to its management. Results: The RITI, initially started in 2007 and officially re-launched in 2017 after structural modifications, is a non-interventional retrospective and prospective registry study collecting data on neonatal and pediatric patients (0-18 years) who experienced a systemic or cerebral thrombotic event in Italy. The RITI is managed by a multidisciplinary team with expertise in pediatric thrombosis, and participation is open to all Italian physicians, on a voluntary basis. The overall aim of the registry is to acquire new evidence to better characterize the population of children with thrombotic events and improve their management and outcome. 48 Italian pediatric and intensive care units are actively involved in the RITI, including 85 medical doctors from 16 Italian regions. A total of 1,001 neonates and children affected by cerebral or systemic thrombosis have been enrolled. Discussion: The RITI is one of the largest available European registries of neonatal and pediatric thrombosis. National registries like the RITI represent a model for the study of rare conditions based on multidisciplinary and multicenter collaboration, aimed at overcoming the limitations due to small populations of patients, and creating a network of experts for patient referral and continuous education. Moreover, registry studies have a pivotal role in the research on pediatric thrombosis, due to the limited feasibility of high-quality studies. In our experience, the main critical stages, pitfalls and challenges in registry management include adequate registry designing, diffusion, data completeness and quality control.

Treatment of Refractory/High-Risk Pregnancies With Antiphospholipid Syndrome: A Systematic Review of the Literature.

Different treatment protocols have been employed to manage heparin/low-dose aspirin refractory or high-risk pregnancies in antiphospholipid antibody syndrome (APS) pregnancies. A systematic review of the literature on additional treatments used in refractory and/or high-risk APS pregnancies was conducted. Records from February 2006 to October 2021 were retrieved from PubMed, Web of Science, Cochrane, and the www.clinicaltrials.gov platform. Twenty-one studies met our eligibility criteria. Live birth rate is this study's primary endpoint, while pregnancy complications and adverse events are secondary endpoints. A total of 434 pregnancies, 162 (37.3%) refractory and 272 (62.7%) high-risk/refractory pregnancies, were included. Both IVIG <2 gr/kg/monthly/HCQ/LDS and PEX/IA ± LDS led to 100% viable infants in refractory APS. Furthermore, HCQ 200-400 mg showed a higher live birth rate than HCQ + LDS (88.6% vs. 82.7%). Following treatment protocol with HCQ 200-400 mg and IVIG <2 gr/kg/monthly/HCQ/LDS, pregnancy complications rates of 16.7 and 83.3% were registered, respectively. Pravastatin 20 mg, IA weekly + IVIG 2 gr/monthly, and PEX weekly + IVIg 2 gr/kg/monthly showed higher live birth rates in high-risk APS pregnancies of 100, 100 and 92%, respectively, whereas the lower severe pregnancy complications were reported in pregnancies treated with PEX weekly + IVIg 2 gr/kg/monthly (11.1%). One (0.6%) case of dermatitis during treatment with HCQ was observed. The results of this study showed that HCQ 200-400 mg and PEX weekly + IVIG 2 gr/kg/monthly achieved a higher live birth rate in refractory APS and high-risk/refractory APS, respectively. The results presented provide clinicians with up-to-date knowledge in the management of APS pregnancies according to risk stratification.

Risk Factors of Venous Thromboembolism in Noncritically Ill Patients Hospitalized for Acute COVID-19 Pneumonia Receiving Prophylactic-Dose Anticoagulation.

Background: Therapeutic/intermediate-dose heparin reduces the risk of thromboembolic events but increases the risk of major bleeding in patients hospitalized for acute COVID-19 pneumonia. Objectives: To prospectively assess the incidence of objectively proven venous thromboembolism (VTE) and identify predisposing risk factors in a cohort of hospitalized patients with acute COVID-19 pneumonia undergoing prophylactic-dose heparin. Patients and methods: All consecutive patients admitted for acute COVID-19 pneumonia to the General Internal Medicine Unit of Padova University Hospital, Italy between November 2020 and April 2021, and undergoing prophylactic-dose heparin, were enrolled. Demographic and clinical characteristics and laboratory and radiological findings were recorded on admission. Cases were patients who developed VTE during their hospital stay. Univariable and multivariable logistic regression analyses were used to ascertain the risk factors associated with developing in-hospital VTE. Results: 208 patients (median age: 77 years; M/F 98/110) were included; 37 (18%) developed in-hospital VTE during a median follow-up of 10 days (IQR, 4−18). VTE patients were significantly younger (p = 0.004), more obese (p = 0.002), and had a lower Padua prediction score (p < 0.03) and reduced PaO2/FIO2 ratio (p < 0.03) vs. controls. Radiological findings of bilateral pulmonary infiltrates were significantly more frequent in VTE patients than controls (p = 0.003). Multivariable regression showed that obesity (1.75, 95% CI 1.02−3.36; p = 0.04) and bilateral pulmonary infiltrates on X-rays (2.39, 95% CI 1.22−5.69; p = 0.04) were correlated with increased risk of in-hospital VTE. Conclusions: Obesity and bilateral pulmonary infiltrates on imaging may help clinicians to identify patients admitted to medical wards for acute COVID-19 pneumonia at risk of developing VTE despite prophylactic-dose heparin. Further studies are needed to evaluate whether the administration of therapeutic/intermediate-dose heparin may help prevent VTE episodes without further increasing the bleeding risk.

Increased platelet aggregation in patients with decompensated cirrhosis indicates higher risk of further decompensation and death.

BACKGROUND & AIMS: Studies on platelet aggregation in cirrhosis are controversial because interpretation of platelet function is challenged by thrombocytopenia. We conducted a prospective study to investigate whole blood platelet aggregation in cirrhosis and its association with liver-related outcomes. METHODS: Platelet aggregation was assessed by whole blood aggregometry (Multiplate®). To overcome the influence of platelet count and compare cirrhosis with thrombocytopenia vs. controls with normal platelet count, we calculated a ratio between platelet aggregation and platelet count (PLT ratio). Then, we prospectively followed patients with cirrhosis and ascertained predictors of decompensation, transplantation, and death. RESULTS: Two-hundred and three patients with cirrhosis were prospectively recruited (77% decompensated). PLT ratio was significantly higher in cirrhosis than in those with chronic hepatitis and healthy individuals (0.44 vs. 0.25 and 0.26, respectively; p <0.0001). In cirrhosis, the ratio increased with disease severity (Child-Pugh class C>B>A) and was particularly elevated in decompensated patients with severe thrombocytopenia. Among decompensated patients, 65 had further decompensation, underwent transplantation, or died during a 6-month follow-up. On multivariate analysis, PLT ratio (odds ratio 1.87; 95% CI 1.23-2.84; p = 0.003) and MELD score (odds ratio 1.05; 95% CI 1.01-1.08; p = 0.01) were independently associated with outcome. The relative risk of events was 7.5-fold higher in patients with PLT ratio >0.75 vs. patients with PLT ratio <0.25 (95% CI 2.5-21.9; p = 0.003). The increased PLT ratio, its discriminative ability for composite outcome, and the prognostic value of PLT ratio >0.75 were confirmed in an independent cohort of hospitalized patients with decompensated cirrhosis (n = 41). CONCLUSIONS: Patients with cirrhosis, particularly when decompensated, exhibit significantly increased whole blood platelet aggregation. Decompensated patients with a PLT ratio >0.75 have a >80% probability of further decompensation, transplantation, or liver-related death within 6 months. LAY SUMMARY: In patients with cirrhosis, previous studies have suggested that platelets (i.e. circulating blood cells that help form clots to stop bleeding) are dysfunctional. In particular, these studies suggested that platelet aggregation (the process by which platelets adhere to each other to form clots) is reduced. Since platelet aggregation is important for clot formation, it has been hypothesized that alterations of platelet aggregation may be responsible for the increased risk of bleeding observed in patients with cirrhosis. Our study demonstrates: i) that platelet aggregation in patients with cirrhosis is higher than in healthy individuals; ii) that platelet aggregation in patients with decompensated cirrhosis (i.e. those who have already experienced some complications of cirrhosis) is particularly elevated and associated with risk of further complications and death.

Systemic Catheter-Related Venous Thromboembolism in Children: Data From the Italian Registry of Pediatric Thrombosis.

Background: Central venous catheters (CVCs) represent one of the main risk factors for venous thrombotic events (VTEs) in children. Methods: We studied the Italian Registry of Pediatric Thrombosis (RITI) with regard to systemic radiologically confirmed CVC-related VTEs (CVC-VTEs) occurred during 6.5 years in children aged 29 days to 18 years. Results: A total of 78 CVC-VTEs were included, which occurred in 76 patients (40/76, 53% males). CVC-VTEs comprised 67 non-cardiac VTEs (86%) and 11 intracardiac thrombotic events (ICTEs) (14%); the median age at onset was 19 and 17 months, respectively. The most frequent reason for CVC insertion was supportive therapy. The catheters were placed percutaneously in 85% of cases (56/66) and surgically in the remaining 15% (10/66). Peripherally inserted central catheters (PICCs) were used in 47% (31/66) cases, partially implanted catheters in 42% (28/66), non-implantable catheters in 7% (5/66), and totally implanted catheters (Port) in 2% (1/66). CVC-VTEs were symptomatic in 77% of cases (60/78), while in the remaining 23%, they were incidentally detected on the imaging performed for the underlying condition. The median time between CVC insertion and the onset of symptoms was 10 days in non-cardiac VTEs and 39 days in ICTEs. Doppler ultrasound was the diagnostic technique most frequently used. The venous compartment most frequently affected was the veins of the lower extremities (52%, 43/73). Anti-thrombotic treatment was administered in 96% of CVC-VTEs (75/78). About 2.6% (2/76) of patients experienced a second thrombotic event. At discharge, post-thrombotic syndrome was reported in 13.5% (5/37) events with available data, CVC replacement in 10.8% (4/47), and ischemic necrosis with toe finger amputation in 2.7% (1/37). Three patients died due to an underlying condition; no CVC-VTE-related deaths were reported. Conclusions: We have carried out a registry-based study on CVC-VTEs in the children in Italy, providing the data that may help improve the detection and management of this CVC-related complication.

Assessing Clinically Meaningful Hypercoagulability after COVID-19 Vaccination: A Longitudinal Study.

A large number of daily requests to exclude possible prothrombotic risk factors for coronavirus disease 2019 (COVID-19) vaccines were received. Our aim was to longitudinally evaluate coagulation profiles in a series of healthy subjects who received COVID-19 vaccination and assess hypercoagulability thereafter. Volunteers awaiting a first or second dose of either the ChAdOx1 or BNT162b2 vaccine were enrolled. Venous samples were obtained at baseline (before the vaccine) and longitudinally 3 ± 2 days (T1) and 10 ± 2 days after the vaccine (T2). Global coagulation monitoring was assessed via platelet count, whole blood thromboelastometry and impedance aggregometry, plasma thrombin generation, and anti-platelet factor 4 (PF4)/heparin immunoglobulin G antibodies. One hundred and twenty-two subjects were enrolled (61 [50%] ChAdOx1 and 61 BNT162b2). The ChAdOx1 cohort showed a slight but transient increase in thrombin generation (mainly endogenous thrombin potential [ETP] with thrombomodulin and ETP ratio) at T1, which promptly decreased at T2. In addition, the second dose of either vaccine was associated with increased thrombin peak, ETP with thrombomodulin, and ETP ratio. At baseline, 3.2% of the ChAdOx1 cohort and 1.6% BNT162b2 cohort were positive for PF4/heparin antibodies with a stable titer through T1 and T2. No relevant differences were detected in platelet count and aggregation, or thromboelastometry parameters. No thrombotic or hemorrhagic events occurred. We can confirm that no clinically meaningful hypercoagulability occurred after either vaccine, albeit keeping in mind that thrombin generation may increase in the first days after the second dose of either vaccine and after the first dose of the ChAdOx1 vaccine.

Coagulopathy is not predictive of bleeding in patients with acute decompensation of cirrhosis and acute-on-chronic liver failure.

BACKGROUND & AIMS: Understanding factors responsible for the increased bleeding tendency in acute-on-chronic liver failure (ACLF) would improve the management of these complications. We investigated coagulation alterations in ACLF and assessed whether they were predictive of bleeding. METHODS: Cirrhosis patients with ACLF (cases) and acute decompensation (AD, controls) were prospectively recruited and underwent an extensive haemostatic assessment including standard tests, pro and anticoagulant factors, thrombomodulin-modified thrombin generation (TG) and thromboelastometry (ROTEM® ). In study part 1 (case-control), we compared coagulation in ACLF vs AD. In study part 2 (prospective), all patients were followed for bleeding, and predictors of outcome were assessed. RESULTS: Ninety-one patients were included (51 with ACLF, 40 with AD). Infections and ascites/renal dysfunction were the most common precipitating and decompensating events. Platelet count was lower while INR and activated partial thrombin time were longer in ACLF cohort vs AD. Regarding clotting factors, fibrinogen and factor VIII were comparable between groups while protein C and antithrombin were significantly reduced in ACLF. Endogenous thrombin potential by TG was comparable between groups. Clotting formation time and clot stability by ROTEM® were significantly lower in ACLF, indicative of a more hypocoagulable state. No haemostasis alteration could discriminate between patients who had bleeding complications during hospitalization and those who did not. CONCLUSION: We found coagulation changes in ACLF to largely overlap with that of AD and evidence of preserved coagulation capacity in both groups. ROTEM alterations were indicative of a more pronounced hypocoagulable state in ACLF; however, no correlation was found between such alterations and bleeding.

The risk of arterial thrombosis in carriers of natural coagulation inhibitors: a prospective family cohort study.

BACKGROUND: Whether the carriership of inherited antithrombin (AT), protein C (PC), and protein S (PS) deficiency increases the risk of arterial thromboembolic events (ATE) is controversial. This information has the potential to inform the management of family members of probands with inherited deficiency of natural anticoagulants. PATIENTS/METHODS: We conducted a large prospective family cohort study in 640 subjects (of whom 341 carriers and 299 non-carriers) belonging to 86 families with inherited deficiency of AT, PC, or PS. RESULTS: A total of 4240 and 3810 patient-years were available for carriers and non-carriers, respectively. Risk factors for atherosclerosis were similarly distributed in the two groups. Of the 26 ATE that were recorded, 19 occurred in carriers (5.6%), as compared to 7 in non-carriers (2.3%) [p = 0.07]. After adjusting for confounders, the hazard ratio (HR) for ATE was 4.9 (95% CI 1.5-16.3) in carriers as compared to non-carriers. CONCLUSIONS: Among family members of probands with an inherited deficiency of natural anticoagulants, carriers exhibit a risk of ATE that is almost five times higher than in non-carriers.

Longitudinal Trend of Plasma Concentrations of Extracellular Vesicles in Patients Hospitalized for COVID-19.

Plasma concentrations of extracellular vesicles (EVs) originating from cells involved in COVID-19-associated coagulopathy (CAC), their longitudinal trend and association with clinical outcomes were evaluated. Blood samples of consecutive COVID-19 patients admitted to a medical Unit were longitudinally collected within 48 h of admission, at discharge and 30 days post-discharge. EVs were analyzed using high sensitivity flow cytometry and phospholipid-dependent clotting time (PPL). The following EVs were measured: endothelium-, platelet-, leukocyte-derived, bearing tissue factor (TF)+, angiotensin-converting enzyme (ACE2)+, platelet-derived growth factor receptor-ß (PDGF-ß)+ and SARS-CoV-2-nucleoprotein (NP)+. 91 patients were recruited for baseline EV analysis (mean age 67 ± 14 years, 50.5% male) and 48 underwent the longitudinal evaluation. From baseline to 30-days post-discharge, we observed significantly decreased plasma concentrations of endothelium-derived EVs (E-Selectin+), endothelium-derived bearing TF (E-Selectin+ TF+), endothelium-derived bearing ACE2 (E-Selectin+ACE2+) and leukocyte-EVs bearing TF (CD45+TF+), p < 0.001, p = 0.03, p = 0.001, p = 0.001, respectively. Conversely, platelet-derived (P-Selectin+) and leukocyte-derived EVs (CD45+) increased from baseline to 30-days post-discharge (p = 0.038 and 0.032, respectively). EVs TF+, ACE2+, PDGF-ß+, and SARS-CoV-2-NP+ did not significantly change during the monitoring. PPL increased from baseline to 30-days post-discharge (+ 6.3 s, p = 0.006). P-Selectin + EVs >1,054/µL were associated with thrombosis (p = 0.024), E-Selectin + EVs ≤531/µL with worsening/death (p 0.026) and 30-days P-Selectin+ and CD45 + EVs with persistent symptoms (p < 0.0001). We confirmed increased EVs originating from cells involved in CAC at admission and discharge. EVs derived from activated pericytes and expressing SARS-CoV-2-NP were also detected. 30-days post-discharge, endothelium-EVs decreased, while platelet- and leukocyte-EVs further increased, indicating that cellular activation persists long after the acute phase.

Partial F8 gene duplication (factor VIII Padua) associated with high factor VIII levels and familial thrombophilia.

High coagulation factor VIII (FVIII) levels comprise a common risk factor for venous thromboembolism (VTE), but the underlying genetic determinants are largely unknown. We investigated the molecular bases of high FVIII levels in 2 Italian families with severe thrombophilia. The proband of the first family had a history of recurrent VTE before age 50 years, with extremely and persistently elevated FVIII antigen and activity levels (>400%) as the only thrombophilic defects. Genetic analysis revealed a 23.4-kb tandem duplication of the proximal portion of the F8 gene (promoter, exon 1, and a large part of intron 1), which cosegregated with high FVIII levels in the family and was absent in 103 normal controls. Targeted screening of 50 unrelated VTE patients with FVIII levels ≥250% identified a second thrombophilic family with the same F8 rearrangement on the same genetic background, suggesting a founder effect. Carriers of the duplication from both families showed a twofold or greater upregulation of F8 messenger RNA, consistent with the presence of open chromatin signatures and enhancer elements within the duplicated region. Testing of these sequences in a luciferase reporter assay pinpointed a 927-bp region of F8 intron 1 associated with >45-fold increased reporter activity in endothelial cells, potentially mediating the F8 transcriptional enhancement observed in carriers of the duplication. In summary, we report the first thrombophilic defect in the F8 gene (designated FVIII Padua) associated with markedly elevated FVIII levels and severe thrombophilia in 2 Italian families.

Direct Oral Anticoagulants in Patients With Inherited Thrombophilia and Venous Thromboembolism: A Prospective Cohort Study.

Background In this prospective cohort study, we aimed to evaluate the efficacy and safety of direct oral anticoagulants (DOACs) versus heparin/vitamin K antagonists for the treatment of venous thromboembolism (VTE) in patients with inherited thrombophilia. Methods and Results We enrolled consecutive patients with acute VTE and inherited thrombophilia treated with DOACs (cases) or heparin/vitamin K antagonists (controls), matched for age, sex, ethnicity, and thrombophilia type. End points were VTE recurrence and bleeding complications; residual vein thrombosis and post-thrombotic syndrome; VTE recurrence after anticoagulant discontinuation. Two hundred fifty-five cases (age 52.4±17.3 years, Female 44.3%, severe thrombophilia 33.1%) and 322 controls (age 49.7±18.1 years, Female 50.3%, severe thrombophilia 35.1%) were included. The cumulative incidence of VTE recurrence during anticoagulation was 1.09% in cases versus 1.83%, adjusted hazard ratio (HR) 0.67 (95% CI, 0.16-2.77). The cumulative incidence of bleeding was 10.2% in cases versus 4.97%, HR 2.24 (95% CI 1.10-4.58). No major bleedings occurred in cases (versus 3 in controls). No significant differences regarding residual vein thrombosis and post-thrombotic syndrome. After anticoagulant discontinuation, DOACs yielded a significantly lower 2-year VTE recurrence risk versus traditional anticoagulants (HR, 0.61 [95% CI, 0.47-0.82]). Conclusions DOACs and heparin/vitamin K antagonists showed a similar efficacy in treating VTE in patients with thrombophilia. Although major bleeding episodes were recorded solely with heparin/vitamin K antagonists, we noted an overall increased bleeding rate with DOACs. The use of DOACs was associated with a lower 2-year risk of VTE recurrence after anticoagulant discontinuation.

Incidence of VTE in asymptomatic children with deficiencies of antithrombin, protein C, and protein S: a prospective cohort study.

Although antithrombin, protein C, and protein S defects are well-recognized inherited risk factors for venous thromboembolism (VTE) in adults, whether they predispose children to these vascular disorders as well is undefined. In a prospective cohort study, we assessed the incidence of spontaneous and risk period-related VTE in children who were family members of adults who, after an episode of symptomatic VTE, had then been identified as carriers of these abnormalities. A total of 134 children from 87 families were enrolled. Seventy (51.5%) of these children were carriers of an inherited defect, and the remaining 64 were not; the mean observation period was 4 years (range, 1-16 years) and 3.9 years (range, 1-13), respectively. Sixteen risk periods were experienced by carriers, and 9 by noncarriers. Six VTE occurred in the 70 carriers during 287 observation-years, accounting for an annual incidence of 2.09% patient-years (95% confidence interval, 0.8-4.5), compared with none in the 64 noncarriers during 248 observation-years. Of the 14 children with thrombophilia who experienced a risk period for thrombosis, 4 (28.6%) developed a VTE episode. The overall incidence of risk-related VTE was 25% per risk period (95% confidence interval, 6.8-64). In conclusion, the thrombotic risk in otherwise healthy children with severe inherited thrombophilia does not seem to differ from that reported for adults with the same defects. Screening for thrombophilia in children who belong to families with these defects seems justified to identify those who may benefit from thromboprophylaxis during risk periods for thrombosis.

Peculiar laboratory phenotype/ genotype relationship due to compound inherited protein C defects in a child with severe venous thromboembolism.

A 7-years-old child who developed unprovoked deep vein thrombosis (DVT) and pulmonary embolism (PE) was tested for inherited thrombophilia. Protein C (PC) antigen level (87 %) and PC coagulometric and amidolytic activities (12 % and 11 %, respectively) were consistent with a homozygous PC type IIA phenotype.The patient was carrier of two heterozygous missense mutations causing p.Arg32Cys substitution associated with a type I PC defect ("null allele", from the paternal side) and p.Gly433Ser substitution responsible for a type IIA PC defect (from the maternal side). Thus, the apparently normal PC antigen level in the proband was misleading in the interpretation of phenotype/genotype relationship of this compound PC defect. The child was also carrier of heterozygous prothrombin G20210A variant.Severe venous thromboembolism can occur in otherwise healthy children with complex inherited thrombophilia. Careful laboratory characterization of the phenotype/genotype relationship can be crucial to correctly classify PC defects and for their management with anticoagulants or replacement therapy.

New Prothrombin Mutation (Arg596Trp, Prothrombin Padua 2) Associated With Venous Thromboembolism.

OBJECTIVE: Two different prothrombin variants, p.Arg596Leu and p.Arg596Gln, conferring antithrombin resistance to patients with venous thromboembolism have been recently reported. Here, we describe a novel substitution affecting Arg596 of prothrombin molecule (Arginine596 to Tryptophan or p.Arg596Trp or Arg221aTrp in the chymotrypsinogen numbering system or prothrombin Padua 2) in 2 Italian families with venous thromboembolism. APPROACH AND RESULTS: Prothrombin Padua 2 has been characterized either in plasma of carriers or using Arg596Trp recombinant prothrombin. Routine coagulation tests, thrombin generation, and antithrombin resistance tests were performed, as well as measurement of the levels of thrombin-antithrombin complexes. All carriers were heterozygotes and presented with a mild reduction of the prothrombin activity. Thrombin generation in carriers showed only a markedly prolonged decay. This finding was confirmed in plasma reconstituted with Arg596Trp recombinant prothrombin mimicking a homozygous condition, which showed longer decay and higher endogenous thrombin potential in thrombin generation than wild-type recombinant prothrombin reconstituted plasma. Patient's plasma as well as Arg596Trp recombinant prothrombin showed a clear thrombin resistance to antithrombin inactivation. These findings were supported by the assessment of thrombin-antithrombin complexes formation, which was strongly reduced for Arg596Trp recombinant prothrombin as compared with wild-type recombinant prothrombin. In a series of 400 unrelated consecutive patients with venous thromboembolism, 2 carriers of prothrombin Padua 2 were found (estimated prevalence of 0.5%). CONCLUSIONS: Our study showed that prothrombin Padua 2 induces antithrombin resistance and is associated with an increased risk of venous thromboembolism. Codon 596 (CGG) of prothrombin is a hot spot for mutations, which constitute a new and relatively frequent cause of inherited thrombophilia.