Inherited thrombophilia in children with venous thromboembolism and the familial risk of thromboembolism: an observational study

Validation of a predictive model for identifying an increased risk for recurrence in adolescents and young adults with a first provoked thromboembolism

BACKGROUND

To develop and validate a predictive model to determinate patients at increased risk to suffer from recurrence following a first provoked deep vein thrombosis (VTE).

METHODS

Predictive variables, i.e. male sex [1 point], inherited thrombophilia (IT) status (none [0 points], single [1 point], combined variants [2 points]), blood group non-0, and age at first VTE onset were included into a risk assessment model, which was derived in 511 patients and then validated in 509 independent subjects.

RESULTS

VTE recurrence risk score (maximum 4 points, range 0-3) was below two for patients scored as low-risk (LRS) and ≥2 for patients at high-risk (HRS). Within a median time of 3 years after withdrawal of anticoagulation (AC) recurrence rate in LRG (derivation) was 11.8% versus 26.0% in HRS (p < 0.001). In the validation cohort within 2.2 years the recurrence rate was 9.8% in LRS versus 30.1% in HRS (p < 0.001). In multivariable analysis adjusted for age at first VTE and blood group the recurrent risk in HRS was significantly increased compared with the LRS (derivation: hazard/95% confidence interval: 3.7/1.75-7.91; validation: 4.7/2.24-9.81; combined 5.2/1.92-13.9). Model specificity (sensitivity) was 79.0% (52.0%) in the derivation cohort compared with 78.0% (43.0%) in the validation group. In conclusion, in the prediction model presented here the risk of VTE recurrence was associated with male gender and combined ITs. Based on the negative predictive value calculated the model may identify patients with a first provoked VTE not being at risk for recurrence.

Thrombophilia screening revisited: an issue of personalized medicine

Clinical thrombophilia is the consequence of multiple gene and/or environment interactions. Thrombophilia screening requires a targeted patient with specific indication, in which a finding would have implications. Carrying out a thrombophilia examination in the physician's practice is often a cause of uncertainty and concern. The concerns begin in choosing the right patient to be examined, are associated with the time of investigation, with the choice of analysis, the test-material and with the correct interpretation of the results. Difficulties, which can influence the results, can occur with both organization and blood sampling. As common for any analysis, pre-analytical, analytical and post-analytical factors should be considered, as well as the possibility of false positive or false negative results. Finally, recommendation of correct therapeutic and prophylactic measures for the patient and his relatives is an additional focus. In this article we want to provide-on the basis of the evidence and personal experience-the theory of thrombophilia-investigation, the indications for testing, as well as practical recommendations for treatment options.

Hemostasis Laboratory Diagnostics: Characteristics, Communication Issues, and Current Challenges Resulting from Centralization of Laboratory Medicine

Laboratory diagnostics of patients with bleeding and thrombotic disorders can be a delicate task, which requires special skills and expertise. In this article, characteristic features of hemostasis testing are reviewed, including staged protocols and synoptic assessment of the patient history, clinical symptoms, and laboratory findings. Despite major progress in the diagnostic and therapeutic management, centralized testing of hemostasis can be associated with substantial challenges, resulting from the current dissociation between the clinical and laboratory world. To address some of these challenges, possible solutions are discussed, including adaptation of an established working paradigm.

Two Novel Variants in the Protein S Gene PROS1 Are Associated with Protein S Deficiency and Thrombophilia

Protein S (PS) is an important anticoagulant. Its main function is to act as a non-enzymatical cofactor of activated protein C. PS deficiency is defined as low plasma levels of PS and/or loss of function associated with variable risk of venous thromboembolism (VTE). We report 2 novel variants in the PS gene (PROS1) which are associated with PS deficiency and severe thrombophilic diathesis in 2 patients. Patient 1 suffered from 3 VTE events, including a spontaneous VTE at the age of 19. Patient 2 suffered from 2 provoked VTE events. In both patients decreased plasma levels of PS antigen as well as decreased PS activity were found. Gene sequencing results showed a heterozygous deletion of 8 base pairs (c.938_945delTAAAATTT, p.Leu313Serfs13*) in exon 9 of the PROS1 gene in patient 1 and a missense variant (c.1613C>T, p.Ser538Phe) in patient 2. Due to the clinically proven history of recurrent VTE events in both patients, genetic testing of first-degree relatives is discussed.

Role of prothrombin 19911 A>G polymorphism, blood group and male gender in patients with venous thromboembolism: Results of a German cohort study

The role of the A>G polymorphism at position 19911 in the prothrombin gene (factor [F] 2 at rs3136516) as a risk factor for venous thromboembolism [VTE] is still unclear. To evaluate the presence of the F2 polymorphism in VTE patients compared to healthy blood donors and to adjust the results for common inherited thrombophilias [IT], age at onset and blood group [BG], and to calculate the risk of VTE recurrence. We investigated 1012 Caucasian patients with a diagnosis of VTE for the presence of the F2 rs3136516 polymorphism and compared these with 902 healthy blood donors. Odds ratios [OR] together with their 95% confidence intervals were calculated adjusted for F5 at rs6025, F2 at rs1799963, blood group, age and gender. In addition, we evaluated the risk of recurrent VTE during patient follow-up calculating hazard ratios [HR] together with their 95% CI. Compared with the AA wildtype, the F2 GG and AG genotypes (rs3136516) were associated with VTE (OR 1.48 and 1.45). The OR in F5 carriers compared to controls was 5.68 and 2.38 in patients with F2 (rs1799963). BG "non-O" was significantly more often diagnosed in patients compared to BG "O" (OR 2.74). VTE recurrence more often occurred in males (HR 2.3) and in carriers with combined thrombophilia (HR 2.11). Noteworthy, the rs3136516 polymorphism alone was not associated significantly with recurrence. In Caucasian patients with VTE the F2 GG/GA genotypes (rs3136516) were moderate risk factors for VTE. Recurrence was associated with male gender and combined thrombophilia.

Association of SERPINC1 Gene Polymorphism (rs2227589) With Pulmonary Embolism Risk in a Chinese Population

Background and Aims: Genetic variants in the gene SERPINC1 have been shown to be associated with antithrombin deficiency, which subsequently contributes to the susceptibility to venous thrombosis. However, several other studies have shown conflicting results regarding the association of SERPINC1 gene polymorphisms (rs2227589) with the risk of thrombosis. Hence, in the present study, we conducted a case-control study to further evaluate the association between the variant rs2227589 with antithrombin deficiency in pulmonary embolism (PTE). A pooled systematic analysis was also conducted to evaluate the risk of rs2227589 in venous thromboembolism (VTE) among multiple populations. Methods: This case-control study involved 101 patients and 199 healthy controls. The allele frequency of SERPINC1 variant rs2227589 was analyzed by Sequenom assay. Antithrombin anticoagulant activity was detected using an automatic coagulation analyzer. In addition, a pooled systematic analysis on 10 cohorts consisting of 5,518 patients with VTE and 8,935 controls was performed. Results: In total, 27 (26.7%) PTE subjects were diagnosed as having antithrombin deficiency. Our results showed that antithrombin plasma activity was slightly lower in T allele carriers than that in C allele carriers. However, there was no significant correlation between rs2227589 genotype and antithrombin anticoagulant activity. The recessive model showed that rs2227589 was significantly associated (p = 0.026) with an increased risk {odds ratio [OR]: 2.31, 95% confidence interval [CI] (1.09-4.89)} of Chinese PTE. The pooled systematic analysis of all case-control study and meta-analysis showed that rs2227589 polymorphism was associated with an increased risk of VTE in the additive model [OR: 1.09, 95% CI (1.01-1.18), P = 0.029] and dominant model [OR: 1.10, 95% CI (1.01-1.20), P = 0.034]. Conclusions: Our study demonstrated that variant rs2227589 is associated with an increased risk of PTE in a Chinese population but no correlation with antithrombin anticoagulant activity. However, pooled systematic analysis of multiple populations showed a significant association between rs2227589 and the risk of VTE in the additive and dominant genetic model.

Management of antithrombin deficiency: an update for clinicians

Introduction. Antithrombin is a serpin that inhibits multiple procoagulant serine proteases and acts as an endogenous anticoagulant. Thus, congenital antithrombin deficiency constitutes a major thrombophilic state, the most severe so far. Areas covered. In the present work, we globally review the biology, genetics, diagnosis, and management of congenital antithrombin deficiency, and also discuss puzzling questions and future perspectives regarding this severe inherited thrombophilia. Expert opinion. Although this disorder exerts high clinical heterogeneity, many carriers will need careful and long-term anticoagulation and/or thromboprophylaxis, especially in high-risk situations, such as surgery and pregnancy. Notably, antithrombin concentrates constitute a considerable arsenal for both treatment and prevention of acute venous thrombosis in subjects with antithrombin deficiency. Current evidences are based almost exclusively on retrospective case series, so an integrated functional, biochemical and molecular characterization will be of clinical relevance and guide hematologists' personalized decisions.

Diagnostic challenge of the newborn patients with heritable protein C deficiency

ABSTARCT

OBJECTIVE: The diagnosis of neonatal-onset protein C (PC) deficiency is challenging. This study aimed to establish the neonatal screening of heritable PC deficiency in Japan.

STUDY DESIGN

We determined the changes in plasma activity levels of PC and protein S (PS) in healthy neonates, and studied newborn patients with PROC mutation in the Japanese registry.

RESULT

Physiological PC and PS levels increased with wide range. The PC/PS-activity ratios converged after birth. The PC/PS-activity ratios of 19 patients with biallelic mutations, but not, 9 with monoallelic mutation, were lower than those of 13 without mutation. The logistic regression analyses established a formula including two significant variables of PC activity (cut-off < 10%, odds ratio = 30.0) and PC/PS-activity ratio (cut-off < 0.35, odds ratio = 22.7), with 93% sensitivity and 44% specificity for determining patients with mutation(s).

CONCLUSION

The PC/PS-activity ratio is an effective parameter for the genetic screening of neonatal-onset PC-deficiency in Japanese population.

Thrombophilia testing in children: What and when should be tested?

Venous thrombosis (VTE) in children is gaining increased awareness and apart from underlying medical conditions, recently reported systematic reviews on pediatric VTE (70% provoked) have shown significant associations between thrombosis and presence of inherited thrombophilic risk factors (IT), such as protein C-, protein S- and antithrombin deficiency, mutations of factor 5 (F5: rs6025) and factor 2 (F2: rs1799963), even more pronounced when combined IT were involved. Although we have learned more about the pathophysiology of VTE with the increased discovery of IT evidence is still lacking as to whether IT influence the clinical outcome in pediatric VTE. It still remains controversial as to whether children with VTE or offspring from thrombosis-prone families benefit from IT screening. Thus, IT testing in children should be individualized. If the decision "pro screening" is discussed as an appropriate option in adolescents with unprovoked VTE and in children with a positive family history for VTE screening should be performed in a specialized coagulation unit for acquired or inherited and prothrombotic defects based on the individual population background. Apart from the laboratory assessment for the presence/absence of lupus anticoagulants and antiphospholipid antibodies screening should be performed beyond the acute VTE onset and after withdrawal of anticoagulant medication possibly influencing laboratory results.

Role of protein S deficiency in children with venous thromboembolism

Venous thromboembolism [TE] is a multifactorial disease, and protein S deficiency [PSD] constitutes a major risk factor. In the present study the prevalence of PSD and the clinical presentation at TE onset in a cohort of children is reported. In 367 unselected paediatric patients with TE (age 0.1–18 years) recruited between July 1996 and December 2013, a comprehensive thrombophilia screening was performed along with recording of anamnestic data. Thirty of 367 paediatric patients (8.2 %) derived from 27 families had PSD. Mean age at first TE onset was 14.5 years (range 0.1 to 18). Thrombotic locations were cerebral veins (n=8), calf vein TE (n=3) deep veins (DVT) of the leg (n=12), DVT & pulmonary embolism (n=5) and intra-cardiac veins (n=1) or purpura fulminans (n=1). PSD co-occurred with the factor 5 mutation at rs6025 or the homozygous factor 2 susceptibility variant at rs1799963 in one case each. The Heerlen polymorphism detected in five children presented with milder PSD. In 18 patients (60 %) a concomitant risk factor for TE was identified. A second TE event within primarily healthy siblings occurred in three of 27 PSD families (11.0 %). In this cohort of children with symptomatic TE, the prevalence of PSD adjusted for family status was 7.4 %. Given its clinical implication for patients and family members, thrombophilia testing should be performed and the benefit of medical or educational interventions should be evaluated in this high-risk population.

The clinical presentation and genotype of protein C deficiency with double mutations of the protein C gene

BACKGROUND

Severe protein C (PC) deficiency is a rare heritable thrombophilia leading to thromboembolic events during the neonatal period. It remains unclear how individuals with complete PC gene (PROC) defects develop or escape neonatal stroke or purpura fulminans (PF).

PROCEDURE

We studied the onset of disease and the genotype of 22 PC-deficient patients with double mutations in PROC based on our cohort (n = 12) and the previous reports (n = 10) in Japan.

RESULTS

Twenty-two patients in 20 unrelated families had 4 homozygous and 18 compound heterozygous mutations. Sixteen newborns presented with PF (n = 11, 69%), intracranial thromboembolism and hemorrhage (n = 13, 81%), or both (n = 8, 50%), with most showing a plasma PC activity of <10%. Six others first developed overt thromboembolism when they were over 15 years of age, showing a median PC activity of 31% (range: 19-52%). Fifteen of the 22 patients (68%) had the five major mutations (G423VfsX82, V339M, R211W, M406I, and F181V) or two others (E68K and K193del) that have been reported in Japan. Three of the six late-onset cases, but none of the 16 neonatal cases, had the K193del mutation, which has been reported to be the most common variant of Chinese thrombophilia. A novel mutation of A309V was determined in a family of two patients with late onset.

CONCLUSIONS

The genotype of double-PROC mutants might show less diversity than heterozygous mutants in terms of the timing of the onset of thrombophilia (newborn onset or late onset).

Whole Exome Sequencing Reveals Severe Thrombophilia in Acute Unprovoked Idiopathic Fatal Pulmonary Embolism

BACKGROUND

Acute unprovoked idiopathic fatal pulmonary embolism (IFPE) causes sudden death without an identifiable thrombogenic risk. We aimed to investigate the underlying genomic risks of IFPE through whole exome sequencing (WES).

METHODS

We reviewed 14years of consecutive out-of-hospital fatal pulmonary embolism records (n=1478) from the ethnically diverse population of New York City. We selected 68 qualifying IFPE cases for WES. We compared the WES data of IFPE cases to those of 9332 controls to determine if there is an excess of rare damaging variants in the genome using ethnicity-matched controls in collapsing analyses.

FINDINGS

We found nine of the 68 decedents (13·2%) who died of IFPE had at least one pathogenic or likely pathogenic variant in one of the three anti-coagulant genes: SERPINC1 (Antithrombin III), PROC, and PROS1. The odds ratio of developing IFPE as a variant carrier for SERPINC1 is 144·2 (95% CI, 26·3-779·4; P=1·7×10-7), for PROC is 85·6 (95% CI, 13·0-448·9; P=2.0×10-5), and for PROS1 is 56·4 (95% CI, 5·3-351·1; P=0·001). The average age-at-death of anti-coagulant gene variant carriers is significantly younger than that of non-carriers (28·56years versus 38·02years; P=0·01).

INTERPRETATION

This study showed the important role of severe thrombophilia due to natural anti-coagulant deficiency in IFPE. Evaluating severe thrombophilia in out-of-hospital fatal PE beyond IFPE is warranted.

Inherited Thrombophilia in Pediatric Venous Thromboembolic Disease: Why and Who to Test

Venous thromboembolic disease in childhood is a multifactorial disease. Risk factors include acquired clinical risk factors such as a central venous catheter and underlying disease and inherited thrombophilia. Inherited thrombophilia is defined as a genetically determined tendency to develop venous thromboembolism. In contrast to adults, acquired clinical risk factors play a larger role than inherited thrombophilia in the development of thrombotic disease in children. The contributing role of inherited thrombophilia is not clear in many pediatric thrombotic events, especially catheter-related thrombosis. Furthermore, identification of inherited thrombophilia will not often influence acute management of the thrombotic event as well as the duration of anticoagulation. In some patients, however, detection of inherited thrombophilia may lead to identification of other family members who can be counseled for their thrombotic risk. This article discusses the potential arguments for testing of inherited thrombophilia, including factor V Leiden mutation, prothrombin mutation, and deficiencies of antithrombin, protein C, or protein S and suggests some patient groups in childhood, which may be tested.

Risk factors for symptomatic venous and arterial thromboembolism in newborns, children and adolescents - What did we learn within the last 20years?

Venous thrombosis (VTE) in children is increasingly diagnosed, as advanced medical care has increased treatment intensity of hospitalized pediatric patients. The aim of this review was to summarize the data available and to discuss the controversial issue of thrombophilia screening in the light of the pediatric data available. Follow-up data for VTE recurrence in children suggest a recurrence rate between 3% (neonates) and 21% in individuals with unprovoked VTE. Apart from underlying medical conditions, recently reported systematic reviews on pediatric VTE (70% provoked) have shown significant associations between thrombosis and presence of protein C-, protein S- and antithrombin deficiency, factor 5 (F5: rs6025), factor 2 (F2: rs1799963), even more pronounced when combined inherited thrombophilias [IT] were involved. The F2 mutation, protein C-, protein S-, and antithrombin deficiency did also play a significant role at VTE recurrence. Although we have learned more about the pathophysiology of VTE with the increased discovery of IT evidence is still lacking as to whether IT influence the clinical outcome in pediatric VTE. It still remains controversial as to whether children with VTE or offspring from thrombosis-prone families benefit from IT screening. Thus, IT testing in children should be individualized.

Subtypes of SERPINC1 mutations and the thrombotic phenotype of inherited antithrombin deficient individuals in Chinese Han population

Inherited antithrombin (AT) deficiency is a rare autosomal disease that could increase the risk of venous thromboembolism (VTE) and usually caused by mutations of SERPINC1. Although a number of mutations of SERPINC1 have been reported in Chinese Han population, the impact of different subtypes of these mutations on the thrombotic phenotype is still unknown. Here, we performed a retrospective cohort study including 169 AT patients from 63 families to compare the clinical features between null mutation carriers and missense mutation carriers. We found that patients carrying null mutations have a higher risk of VTE (HR 2.29, 95% CI 1.16-4.69, P=0.02 adjusted for sex and VTE family history) and earlier median onset age of VTE (27 vs. 32years, P=0.045) as well as lower AT activities (47.6±1.0% vs. 59.1±2.3%, P<0.001) than those with missense mutations. We also observed that thrombus location sites showed no difference between null mutation carriers and missense mutation carriers, gene locations of the mutations did not relate with the incidence rate of VTE. This study demonstrated that different types of SERPINC1 mutations may play different roles in the development of VTE and should be considered in the prevention of VTE.

Impact of high risk thrombophilia status on recurrence among children and adults with VTE: An observational multicenter cohort study

BACKGROUND

Antithrombin [AT]-, protein C [PC]- or protein S [PS]-deficiency [D] constitutes a major risk factor for venous thromboembolism [VTE]. Primary study objective was to evaluate if the clinical presentation at first VTE onset differs between children and adults and to compare the individual recurrence risk among patients with respect to age at onset and their thrombophilia status ATD, PCD or PSD.

METHODS/PATIENTS/RESULTS

In 137 of 688 consecutively enrolled pediatric and adult VTE patients we calculated the absolute risk of VTE recurrence and event-free-survival adjusted for thrombophilia and positive family VTE history. At first VTE children manifested i) with a lower rate of pulmonary embolism, ii) a higher rate of cerebral vascular events or multiple VTEs, and iii) showed a higher proportion of unprovoked VTE compared to adolescents and adults. Adult patients reported more often a positive VTE history compared to younger study participants. The adjusted odds of recurrence in adults was 2.05 compared to children.

CONCLUSION

At disease manifestation children and adults differ with respect to i) thrombotic locations, ii) percentage of unprovoked versus provoked VTE, and iii) different rates of positive VTE family histories. Furthermore, adults showed a two-fold increase risk of VTE recurrence compared to children.

Association of thrombophilia and catheter-associated thrombosis in children: a systematic review and meta-analysis

Essentials It is unclear if thrombophilia increases the risk of catheter-associated thrombosis in children. We conducted a meta-analysis on thrombophilia and pediatric catheter-associated thrombosis. Presence of ≥1 trait confers additional risk of venous thrombosis in children with catheters. Limitations of included studies preclude us from recommending routine thrombophilia testing.

SUMMARY

Background The association between thrombophilia and deep vein thrombosis (DVT) associated with central venous catheter (CVC) use, the most important pediatric risk factor for thrombosis, is unclear in children. Pediatric studies with small sample sizes have reported conflicting results. We sought to evaluate whether, among children with CVCs, thrombophilia increases the risk of CVC-associated DVT (CADVT). Materials and methods We systematically searched MEDLINE, EMBASE, the Web of Science, the Cochrane Central Register for Controlled Trials, PubMed and reference lists for controlled studies published from the inception of the database until September 2015. Included were studies of children aged <21 years with CVCs who were systematically tested for thrombophilic traits that are commonly screened for in clinical practice. Pooled prevalence rates and pooled odds ratios (pORs) of CADVT with thrombophilia were estimated by use of a random effects model. Results We analyzed 16 cohort studies with 1279 children, 277 of whom had CADVT, and with 12 traits tested. There was significant heterogeneity in the included studies. The presence of one or more traits was associated with CADVT (pOR 3.20; 95% confidence interval [CI] 1.56-6.54). Although the prevalence of most traits was < 0.10, children with protein C deficiency, elevated factor VIII levels and the FV Leiden mutation had an increased prevalence of CADVT. The association with thrombophilia seemed to be stronger for symptomatic CADVT (pOR 6.71; 95% CI 1.93-23.37) than for asymptomatic CADVT (pOR 2.14; 95% CI 1.10-4.18). Conclusions On the basis of the low prevalence of specific traits, the relatively weak association with CADVT, and the limitations of the included studies, we cannot recommend routine testing of thrombophilias in children with CADVT.

Issues in the Diagnosis and Management of Hereditary Antithrombin Deficiency

Objective: To review insights gained in the past several years about hereditary antithrombin (AT) deficiency and to outline approaches to the management of patients with AT deficiency in the acute and chronic settings. Data Sources: An extensive literature search of Scopus (January 2008-April 2016) was performed for the terms congenital antithrombin deficiency, inherited antithrombin deficiency, or hereditary antithrombin deficiency. Additional references were identified by reviewing literature citations. Study Selection: All relevant English-language case reports, reviews, clinical studies, meeting abstracts, and book chapters assessing hereditary AT deficiency were included. Data Synthesis: AT deficiency significantly increases the risk of venous thromboembolism (VTE). The risk of VTE is particularly high during pregnancy, the postpartum period, and following major surgery. Effective clinical management includes determination of the appropriate type and duration of antithrombotic therapy (ie, AT replacement for acute situations) while minimizing the risk of bleeding. For persons newly diagnosed with AT deficiency, age, lifestyle, concurrent medical conditions, family history, and personal treatment preferences can be used to individualize patient management. Patients should be informed of the risks associated with hormonal therapy, pregnancy, surgical procedures, and immobility, which further increase the risk of VTE in patients with AT deficiency. Conclusion: AT deficiency poses the highest risk for VTE among the hereditary thrombophilias, often requiring long-term anticoagulation. Undertaking an evaluation for hereditary thrombophilia is controversial; however, a diagnosis of VTE in association with AT deficiency can have management implications. An important treatment option for patients with this disorder in high-risk situations is AT concentrate.

Impact of high-risk thrombophilia status on recurrence among children with a first non-central-venous-catheter-associated VTE: an observational multicentre cohort study

Deficiency of antithrombin (AT), protein C (PC) or protein S (PS) constitutes a major risk factor for venous thromboembolism (VTE). Individuals at high risk for recurrence who benefit from screening need to be identified. The primary study objective was to determine the individual recurrence risk among children with a first non-central-venous-catheter-associated VTE with respect to their thrombophilia status and to evaluate if the clinical presentation at first VTE onset differs between children with AT, PC or PS deficiency versus no thrombophilia. We calculated the absolute risk of VTE recurrence and event-free-survival adjusted for thrombophilia, age, sex and positive family VTE history in 161 consecutively enrolled paediatric VTE patients. The presence of a deficiency relative to no thrombophilia was evaluated as a potential predictor of recurrence. Predictors for recurrence were AT deficiency (hazard ratio/95% CI: 6·5/2·46-17·2) and female gender (2·6/1·1-6·35). The annual recurrence rates (95% CIs) were 5·4% (2·6-10) in AT-deficient children, 1·3% (0·3-3·8) in patients with PC deficiency, 0·7% (0·08-2·4) in the PS-deficient cohort and 0·9% (0·4-1·8) in patients with no thrombophilia. Positive family VTE history or combined thrombophilias did not predict recurrence. Given the overall annual incidence rate of recurrence of 1·5% we suggest screening for AT deficiency in children with VTE.

Population-specific single-nucleotide polymorphism confers increased risk of venous thromboembolism in African Americans

INTRODUCTION

African Americans have a higher incidence of venous thromboembolism (VTE) than European descent individuals. However, the typical genetic risk factors in populations of European descent are nearly absent in African Americans, and population-specific genetic factors influencing the higher VTE rate are not well characterized.

METHODS

We performed a candidate gene analysis on an exome-sequenced African American family with recurrent VTE and identified a variant in Protein S (PROS1) V510M (rs138925964). We assessed the population impact of PROS1 V510M using a multicenter African American cohort of 306 cases with VTE compared to 370 controls. Additionally, we compared our case cohort to a background population cohort of 2203 African Americans in the NHLBI GO Exome Sequencing Project (ESP).

RESULTS

In the African American family with recurrent VTE, we found prior laboratories for our cases indicating low free Protein S levels, providing functional support for PROS1 V510M as the causative mutation. Additionally, this variant was significantly enriched in the VTE cases of our multicenter case-control study (Fisher's Exact Test, P = 0.0041, OR = 4.62, 95% CI: 1.51-15.20; allele frequencies - cases: 2.45%, controls: 0.54%). Similarly, PROS1 V510M was also enriched in our VTE case cohort compared to African Americans in the ESP cohort (Fisher's Exact Test, P = 0.010, OR = 2.28, 95% CI: 1.26-4.10).

CONCLUSIONS

We found a variant, PROS1 V510M, in an African American family with VTE and clinical laboratory abnormalities in Protein S. Additionally, we found that this variant conferred increased risk of VTE in a case-control study of African Americans. In the ESP cohort, the variant is nearly absent in ESP European descent subjects (n = 3, allele frequency: 0.03%). Additionally, in 1000 Genomes Phase 3 data, the variant only appears in African descent populations. Thus, PROS1 V510M is a population-specific genetic risk factor for VTE in African Americans.

Clinical Data of Neonatal Systemic Thrombosis

OBJECTIVE

To evaluate clinical data and associated risk conditions of noncerebral systemic venous thromboembolism (VT), arterial thromboembolism (AT), and intracardiac thromboembolism (ICT) in neonates.

STUDY DESIGN

Data analysis of first systemic thromboembolism occurring in 75 live neonates (0-28 days), enrolled in the Italian Registry of Pediatric Thrombosis from neonatology centers between January 2007 and July 2013.

RESULTS

Among 75 events, 41 (55%) were VT, 22 (29%) AT, and 12 (16%) ICT; males represented 65%, and 71% were preterm. In 19 (25%), thromboembolism was diagnosed on the first day of life. In this "early onset" group, prenatal-associated risk conditions (maternal/placental disease) were reported in 70% and inherited thrombophilia in 33%. Postnatal risk factors were present in 73%; infections and central vascular catheters in 56% and 54% VT, respectively, and in 67% ICT vs 27% AT (<.05). Overall mortality rate was 15% and significant thromboembolism-related sequelae were reported in 16% of discharged patients.

CONCLUSIONS

This report from the Registro Italiano Trombosi Infantili, although limited by representing an uncontrolled case series, can be used to develop future clinical trials on appropriate management and prevention of neonatal thrombosis, focusing on obstetrical surveillance and monitoring of critically ill neonates with vascular access. A thrombosis risk prediction rule specific for the neonatal population should be developed through prospective controlled studies.

[Haemostatic disorders in children]

Haemorrhagic and thrombotic events occur in both children and adults. The underlying causes are congenital or acquired disorders. In contrast to haemorrhagic disorders, inherited thrombotic disorders nearly exclusively in association with additional external risk factors lead to thrombotic events predominantly during the newborn period and adolescence. It is necessary to be aware of age-specific properties of coagulation in order to correctly interpret clinical and laboratory findings and to provide optimal care for children with haemorrhagic and thrombotic complications.

Fetal hydrocephalus and neonatal stroke as the first presentation of protein C deficiency

Severe protein C-deficiency is a rare heritable thrombophilia of the newborn. Infants with biallelic PROC mutations present purpura fulminans and intracranial thromboembolism, while the prenatal onset of mutated heterozygotes remains unclear. We herewith present the first case of fetal ventriculomegaly and neonatal stroke associated with heterozygous PROC mutation. The infant was born to a healthy mother at 38 gestational weeks. The fetal growth had been normal, but the routine ultrasound screening had indicated mild hydrocephalus at 28 weeks of gestation. He developed convulsions two days after birth. Computed tomography of the brain revealed multiple hemorrhagic infarctions and ventriculomegaly. Dissociated levels of the plasma activity between protein C (21%) and protein S (42%) reached to determine the heterozygote of PROC c.574_576delAAG, a common thrombophilic predisposition in Asian ancestries. PC-mutant heterozygotes may have a limited high risk of cerebral thromboembolism during the perinatal course.

Age-specific onset and distribution of the natural anticoagulant deficiency in pediatric thromboembolism

BACKGROUND

The early diagnosis of inherited thrombophilia in children is challenging because of the rarity and hemostatic maturation.

METHODS

We explored protein C (PC), protein S (PS), and antithrombin (AT) deficiencies in 306 thromboembolic patients aged ≤20 y using the screening of plasma activity and genetic analysis.

RESULTS

Reduced activities were determined in 122 patients (40%). Low PC patients were most frequently found in the lowest age group (0-2 y, 45%), while low PS or low AT patients were found in the highest age group (16-20 y; PS: 30% and AT: 20%). Genetic study was completed in 62 patients having no other causes of thromboembolism. Mutations were determined in 18 patients (8 PC, 8 PS, and 2 AT genes). Six of eight patients with PC gene mutation were found in age 0-2 y (75%), while six of eight patients with PS gene mutation were in 7-20 y. Two AT gene-mutated patients were older than 4 y. Four PC-deficient and two PS-deficient patients carried compound heterozygous mutations. All but one PC gene-mutated patient suffered from intracranial thromboembolism, while PS/AT gene-mutated patients mostly developed extracranial venous thromboembolism.

CONCLUSION

Stroke in low PC infants and deep vein thrombosis in low PS/AT school age children could be targeted for genetic screening of pediatric thrombophilias.

High prevalence of protein C, protein S, antithrombin deficiency, and Factor V Leiden mutation as a cause of hereditary thrombophilia in patients of venous thromboembolism and cerebrovascular accident

OBJECTIVES

To determine the frequency of Protein C, Protein S (PC & PS), antithrombin deficiency (AT III) and Factor V Leiden mutation (FVL) as a cause of thrombophilia in the patients with venous thromboembolism (VTE) and cerebrovascular accident (CVA).

METHODS

It was an observational study conducted at Department of Haematology, Armed Forces Institute of Pathology (AFIP), Rawalpindi, Pakistan. All patients referred for thrombophilia screening from July 2009 to June 2012 were screened. Patients with evidence of VTE or CVA were screened for PC & PS, AT III deficiency, and FVL.

RESULTS

Total 404 patients of age between 1-71 years mean 33 ± 14 with male to female ratio of 2.4:1 had evidence of thrombophilia. Two hundred eighteen (54%) patients presented with CVA, 116 (29%) with deep vein thrombosis (DVT), 42 (10.5%) with pulmonary embolism (PE), and 28 (7.5%) with portal or mesenteric vein thrombosis (PV). Protein C & S deficiency was detected in 35/404 (8.7%), ATIII in 9/404 (2%), and FVL in 25/173 patients (14.5%). The findings were suggestive of a significant association of FVL mutation for developing DVT (OR=11.0, 95% C I 4.6-26.3), CVA (OR=5.7, 95% C I 2.1-15.1), and PV (OR=5.4, 95% C I 1.3-21.9). PC & PS deficiency was a significant risk factor for developing PE (OR=3, 95% C I 0.8-11.4).

CONCLUSION

FVL mutation and Protein C & S are the leading causes of thrombophilia with strong association of Factor V Leiden mutation as risk for developing DVT.

Venous thromboembolism at uncommon sites in neonates and children

We retrospectively analyzed the data of 24 children (whereof 11 neonates), with non-central venous line-related and nonmalignancy-related venous thromboembolism (VTE) at uncommon sites, referred to our Unit from January 1999 to January 2012. Thirty patients who also suffered deep vein thrombosis, but in upper/low extremities, were not included in the analysis. The location of rare site VTE was: portal (n=7), mesenteric (n=2) and left facial vein (n=1), spleen (n=3), lung (n=3), whereas 10 neonates developed renal venous thrombosis. The majority of patients (91.7%) had at least 1 risk factor for thrombosis. Identified thrombophilic factors were: antiphospholipid antibodies (n=2), FV Leiden heterozygosity (n=6), MTHFR C677T homozygosity (n=4), protein S deficiency (n=2), whereas all neonates had age-related low levels of protein C and protein S. All but 6 patients received low-molecular-weight heparin, followed by warfarin in 55% of cases, for 3 to 6 months. Prolonged anticoagulation was applied in selected cases. During a median follow-up period of 6 years, the clinical outcome was: full recovery in 15 patients, evolution to both chronic portal hypertension and esophageal varices in 2 children, and progression to renal failure in 7 of 10 neonates. Neonates are greatly vulnerable to complications after VTE at uncommon sites, particularly renal. Future multicentre long-term studies on neonatal and pediatric VTE at unusual sites are considered worthwhile.

Clinical and laboratory characteristics of paediatric and adolescent index cases with venous thromboembolism and antithrombin deficiency. An observational multicentre cohort study

Venous thromboembolism [TE] is a multifactorial disease and antithrombin deficiency [ATD] constitutes a major risk factor. In the present study the prevalence of ATD and the clinical presentation at TE onset in a cohort of paediatric index cases are reported. In 319 unselected paediatric patients (0.1-18 years) from 313 families, recruited between July 1996 and December 2013, a comprehensive thrombophilia screening was performed along with recording of anamnestic data. 21 of 319 paediatric patients (6.6%), corresponding to 16 of 313 families (5.1%), were AT-deficient with confirmed underlying AT gene mutations. Mean age at first TE onset was 14 years (range 0.1 to 17). Thrombotic locations were renal veins (n=2), cerebral veins (n=5), deep veins (DVT) of the leg (n=9), DVT & pulmonary embolism (n=4) and pelvic veins (n=1). ATD co-occurred with the factor-V-Leiden mutation in one and the prothrombin G20210A mutation in two children. In 57.2% of patients a concomitant risk factor for TE was identified, whereas 42.8% of patients developed TE spontaneously. A second TE event within primarily healthy siblings occurred in three of 313 families and a third event among siblings was observed in one family. In an unselected cohort of paediatric patients with symptomatic TE, the prevalence of ATD adjusted for family status was 5.1%. Given its clinical implication for patients and family members, thrombophilia testing should be performed and the benefit of medical or educational interventions should be evaluated in this high risk population.

Impact of the type of SERPINC1 mutation and subtype of antithrombin deficiency on the thrombotic phenotype in hereditary antithrombin deficiency

Mutations in the antithrombin (AT) gene can impair the capacity of AT to bind heparin (AT deficiency type IIHBS), its target proteases such as thrombin (type IIRS), or both (type IIPE). Type II AT deficiencies are almost exclusively caused by missense mutations, whereas type I AT deficiency can originate from missense or null mutations. In a retrospective cohort study, we investigated the impact of the type of mutation and type of AT deficiency on the manifestation of thromboembolic events in 377 patients with hereditary AT deficiencies (133 from our own cohort, 244 reported in the literature). Carriers of missense mutations showed a lower risk of venous thromboembolism (VTE) than those of null mutations (adjusted hazard ratio [HR] 0.39, 95% confidence interval [CI] 0.27-0.58, p<0.001), and the risk of VTE was significantly decreased among patients with type IIHBS AT deficiency compared to patients with other types of AT deficiency (HR 0.23, 95%CI 0.13-0.41, p<0.001). The risk of pulmonary embolism complicating deep-vein thrombosis was lower in all type II AT deficiencies compared to type I AT deficiency (relative risk 0.69, 95%CI 0.56-0.84). By contrast, the risk of arterial thromboembolism tended to be higher in carriers of missense mutations than in those with null mutations (HR 6.08-fold, 95%CI 0.74-49.81, p=0.093) and was 5.9-fold increased (95%CI 1.22-28.62, p=0.028) in type IIHBS versus other types of AT deficiency. Our data indicate that the type of inherited AT defect modulates not only the risk of thromboembolism but also the localisation and encourage further studies to unravel this phenomenon.

Thrombophilia screening: whom to test?

In this issue of Blood, Holzhauer et al have determined a novel method of identifying patients with protein C, protein S, and antithrombin deficiency who are at increased risk of developing venous thromboembolism (VTE; see figure). Children with VTE and their relatives were screened for inherited thrombophilia including proteins C and S and antithrombin deficiency; and Factor (F)V G1691A and FII G20210A. Their study demonstrates that relatives with proteins C and S and antithrombin deficiency are at a significantly higher risk of developing VTE compared with those without inherited thrombophilia.