Evaluation of Inherited Prothrombotic Risk Factors in Children with Acute Lymphoblastic Leukemia.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 3953-3953
Author(s):  
Valerie Li Thiao Te ◽  
Remi Favier ◽  
Jeanne-Yvonne Borg ◽  
Estelle Cadet ◽  
Jacqueline Reynaud ◽  
...  

Abstract This retrospective study was designed to determine the prevalence of inherited prothrombotic risk factors (Factor V Leiden (FV) G1691A and prothrombin G20210A mutations, TT677 genotype of the methylenetetrahydrofolate reductase (MTHFR), protein C, protein S, antithrombin deficiencies) in a population of children with ALL treated according to the FRALLE 2000 study Protocol (High Risk and Standard Risk groups). The study was performed in 5 French Centers including Amiens, Angers, Paris Trousseau, Rouen and Saint-Etienne. From December 2000 to March 2006, 354 children aged 1 to 18 years old were consecutively admitted for ALL and were enrolled in the FRALLE 2000 Protocol. Among them, 281 patients were investigated for hereditary prothrombotic defects at the time of ALL diagnosis. Informed parental consent was required for gene analysis. Abnormal test results for protein S (functional activity and free protein S antigen concentration), protein C and antithrombin were controlled on a second blood sample after induction. In the population studied, the prevalence of one established prothrombotic risk factor was 19,2%: the FV G1691A mutation was diagnosed in 10 patients (3.6%), all heterozygous, 10 patients (3.6%) showed the heterozygous prothrombin G20210A mutation, the TT677 MTHFR genotype was found in 34 children (12.7%), 1 patient showed protein C deficiency (0.4%). No antithrombin deficiency was detected. The prevalence of inherited protein S deficiency could not be evaluated because of missing data in the family medical history. Combined prothrombotic defects were found in 2 patients (0.71%): heterozygous FV G1691A mutation combined with heterozygous prothrombin G20210A mutation in 1 patient and combined with TT677 MTHFR genotype in the second patient. Except for TT677 MTHFR genotype, the prevalence of hereditary prothrombotic risk factors in children with ALL in France were found within the prevalence reported for children treated for ALL (table 1) and comparable to the prevalence in healthy Europeans (Junker et al. 1999, Margaglione et al 2001, Mueller et al. 2005). Comparison of the prevalence of inherited prothrombotic risk factors in children with ALL Country Population FV G1691A +/− ++ PT G20210A +/− +/+ MTHFR TT677 AT PC AT: antithrombin deficiency ; PC: protein C deficiency ; NE : non evaluated NowakGöttl et al 1999 (n=301) Germany ALL children 5.3% 0.3% 2% 0% 7.7% 0.7% 2.3% Mauz-Körholz et al. 2000 (n=108) Germany ALL children 5.6% 0% 2.8% 0% 5.6% 0% 2.7% Mitchell et al. 2002 (n=60) Canada ALL children 3.3% 0% 2% 0% NE NE NE Present study (n=281) France ALL children 3.6% 0% (n=277) 3.6% 0%(n=279) 2.7% (n=268) 0% 0.4%

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 23-24
Author(s):  
Ruben Rhoades

Testing for inherited thrombophilias following venous and arterial thrombotic events remains controversial. These conditions are associated with an increased risk of initial and recurrent venous thromboembolism (VTE) and, in some cases, arterial events such as strokes and myocardial infarctions. However, testing for them in unselected patients with thrombotic events is not associated with lower recurrence rates, and other risk factors may be more clinically useful for determining whether and for how long to anticoagulate. Further, these tests are expensive and in the setting of an acute thrombosis, many may result in false positives. As such, the American Society of Hematology and American Society for Clinical Pathology recommended in their Choosing Wisely campaigns to not test for inherited thrombophilias after a provoked VTE or in the acute setting, respectively. The AHA/ASA determined that the utility of thrombophilia screening in stroke patients was unknown in its 2014 guidelines. This single institution, retrospective study reviewed all instances of inpatient inherited thrombophilia testing in 2019 at Thomas Jefferson University Hospitals, including its 3 primary hospitals in Philadelphia, PA. Tests included those to evaluate the following conditions: Factor V Leiden (FVL); prothrombin G20210A mutation; Protein C, S, and antithrombin deficiency; hyperhomocysteinemia; and plasminogen activator inhibitor-1 (PAI-1) elevation. The study included 231 patients, among whom a total of 872 tests were sent. Tests sent for non-thrombotic indications, such as homocysteine for B12 or folate deficiency, or in patients with a known deficiency were excluded. Median age of the patients was 50.8 years (IQR 38-63) and 129 (55.8%) were female. Diagnoses for which testing was sent and predisposing risk factors are summarized in Table 1. Arterial events were most common (54.5%), followed by VTE (26.0%). 14.7% of patients had no documented thrombosis, ischemic event, or pregnancy complication. Arterial events primarily included stroke/TIA (74.6%), and 76.7% of patients had at least one documented risk factor for these conditions. VTE was associated with a major transient risk factor or cancer in 32.8% of patients. Among all inherited thrombophilia tests sent, the most common were for the evaluation of FVL (20.9%), hyperhomocysteinemia (17.0%), Protein S deficiency (16.5%), prothrombin G20210A mutation (15.1%), Protein C deficiency (14.8%), and antithrombin deficiency (14.3%) (Table 2). Overall, 83.3% of tests were normal. Tests that were most frequently abnormal included MTHFR mutation (76.0%), antithrombin (36.0%), Protein C antigen (40.0%), PAI-1 (33.3%), and total Protein S (22.2%). Given our lab's references ranges, values for antithrombin, and Protein C antigen and function, and total Protein S that fell below normal but >60% were deemed "borderline positive." The likelihood of an abnormal result was not significantly different in cases of unprovoked VTE or arterial event without a risk factor, compared to those with risk factors. All charts were reviewed, including both inpatient and outpatient notes, to determine short- and long-term clinical decision-making. Importantly, among all positive tests, clinical management was not definitively changed in response to the test result in a single case. In two patients, it was unclear whether anticoagulation was continued based upon the test result. Both patients had heterozygous FVL mutations. Most positive results were deemed by the treating clinicians to be due to the acute thrombotic episode. Last, the hospital's chargemaster was queried, showing that these tests were associated with $398,912 in total charges. This single-institution retrospective study of inpatient inherited thrombophilia tests reveals the limited benefit of thrombophilia testing in the acute setting. Arterial ischemic/thrombotic events were the most common indication for testing, yet over 3/4 of patients had at least one risk factor. Nearly a third of patients with VTE had a major provoking factor, patients in whom thrombophilia testing is not recommended. While nearly 17% of tests returned abnormal, not one was associated with a clear change in clinical management. Despite limited clinical utility, costs of these tests are high. These data justify education and pathway implementation aimed at decreasing inpatient utilization of thrombophilia tests. Disclosures No relevant conflicts of interest to declare.


Blood ◽  
1999 ◽  
Vol 93 (5) ◽  
pp. 1595-1599 ◽  
Author(s):  
Ulrike Nowak-Göttl ◽  
Cornelia Wermes ◽  
Ralf Junker ◽  
Hans-Georg Koch ◽  
Rosmarie Schobess ◽  
...  

Abstract The reported incidence of thromboembolism in children with acute lymphoblastic leukemia (ALL) treated with L-asparaginase, vincristine, and prednisone varies from 2.4% to 11.5%. The present study was designed to prospectively evaluate the role of the TT677 methylenetetrahydrofolate reductase (MTHFR) genotype, the prothrombin G20210A mutation, the factor V G1691A mutation, deficiencies of protein C, protein S, antithrombin, and increased lipoprotein (a) concentrations in leukemic children treated according to the ALL-Berlin-Frankfurt-Muenster (BFM) 90/95 study protocols with respect to the onset of vascular events. Three hundred and one consecutive leukemic children were enrolled in this study. Fifty-five of these 301 subjects investigated had one established single prothrombotic risk factor: 20 children showed the TT677 MTHFR genotype; 5 showed the heterozygous prothrombin G20210A variant; 11 were carriers of the factor V G1691A mutation (heterozygous, n = 10; homozygous, n = 1); 4 showed familial protein C, 4 protein S, and 2 antithrombin type I deficiency; 9 patients were suffering from familially increased lipoprotein (a) [Lp(a)] concentrations (>30 mg/dL). In addition, combined prothrombotic defects were found in a further 10 patients: the FV mutation was combined with the prothrombin G20210A variant (n = 1), increased Lp(a) (n = 3), protein C deficiency (n = 1), and homozygosity for the C677T MTHFR gene mutation (n = 1). Lp(a) was combined with protein C deficiency (n = 2) and the MTHFR TT 677 genotype (n = 2). Two hundred eighty-nine of the 301 patients were available for thrombosis-free survival analysis. In 32 (11%) of these 289 patients venous thromboembolism occurred. The overall thrombosis-free survival in patients with at least one prothrombotic defect was significantly reduced compared with patients without a prothrombotic defect within the hemostatic system (P < .0001). In addition, a clear-cut positive correlation (P < .0001) was found between thrombosis and the use of central lines. However, because the prothrombotic defects diagnosed in the total childhood population studied were all found within the prevalences reported for healthy Caucasian individuals, the interaction between prothrombotic risk factors, ALL treatment, and further environmental factors is likely to cause thrombotic manifestations.


Blood ◽  
1999 ◽  
Vol 93 (5) ◽  
pp. 1595-1599 ◽  
Author(s):  
Ulrike Nowak-Göttl ◽  
Cornelia Wermes ◽  
Ralf Junker ◽  
Hans-Georg Koch ◽  
Rosmarie Schobess ◽  
...  

The reported incidence of thromboembolism in children with acute lymphoblastic leukemia (ALL) treated with L-asparaginase, vincristine, and prednisone varies from 2.4% to 11.5%. The present study was designed to prospectively evaluate the role of the TT677 methylenetetrahydrofolate reductase (MTHFR) genotype, the prothrombin G20210A mutation, the factor V G1691A mutation, deficiencies of protein C, protein S, antithrombin, and increased lipoprotein (a) concentrations in leukemic children treated according to the ALL-Berlin-Frankfurt-Muenster (BFM) 90/95 study protocols with respect to the onset of vascular events. Three hundred and one consecutive leukemic children were enrolled in this study. Fifty-five of these 301 subjects investigated had one established single prothrombotic risk factor: 20 children showed the TT677 MTHFR genotype; 5 showed the heterozygous prothrombin G20210A variant; 11 were carriers of the factor V G1691A mutation (heterozygous, n = 10; homozygous, n = 1); 4 showed familial protein C, 4 protein S, and 2 antithrombin type I deficiency; 9 patients were suffering from familially increased lipoprotein (a) [Lp(a)] concentrations (>30 mg/dL). In addition, combined prothrombotic defects were found in a further 10 patients: the FV mutation was combined with the prothrombin G20210A variant (n = 1), increased Lp(a) (n = 3), protein C deficiency (n = 1), and homozygosity for the C677T MTHFR gene mutation (n = 1). Lp(a) was combined with protein C deficiency (n = 2) and the MTHFR TT 677 genotype (n = 2). Two hundred eighty-nine of the 301 patients were available for thrombosis-free survival analysis. In 32 (11%) of these 289 patients venous thromboembolism occurred. The overall thrombosis-free survival in patients with at least one prothrombotic defect was significantly reduced compared with patients without a prothrombotic defect within the hemostatic system (P < .0001). In addition, a clear-cut positive correlation (P < .0001) was found between thrombosis and the use of central lines. However, because the prothrombotic defects diagnosed in the total childhood population studied were all found within the prevalences reported for healthy Caucasian individuals, the interaction between prothrombotic risk factors, ALL treatment, and further environmental factors is likely to cause thrombotic manifestations.


Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 5355-5355
Author(s):  
Aysegul Unuvar ◽  
Arzu Akcay ◽  
Ebru T Saribeyoglu ◽  
Deniz Tugcu ◽  
Zeynep Karakas ◽  
...  

Abstract Pediatric patients with malignancy are at high risk of thromboembolic complications due to complex interactions of a variety of factors such as the malignancy, chemotherapy, central venous catheters (CVCs), infections, dehydration, and hereditary thrombophilia. In this study, deficiencies of protein C (PC), protein S (PS), and antithrombin (AT), activated protein C resistance (APCR), the factor V G1691A mutation, the prothrombin G20210A mutation, and increased factor VIII, IX, fasting homocysteine levels were assessed at the diagnosis of leukemia, retrospectively. The aim was to evaluate the role of the thrombophilic risk factors on vascular events during treatment period. Thirty children (11 F, 19 M) with leukemia (24 patients with ALL, 4 AML, one biphenotypic leukemia, one infant leukemia) were enrolled in this study. The median age of the patients was 56 months (range 7–215 months). All patients had CVCs, and thromboprophylaxis was not given to the any patients. We detected main prothrombotic risk factors at the diagnosis of leukemia as following: low PC (8/30), PS (11/30), AT activity (3/25), APCR (5/22), increased FVIII (5/22), FIX (2/22), and homocysteine levels (2/8), and FV Leiden mutation (1/24; heterozygous). The prothrombin G20210A mutation was not detected in any patient. The parents of these patients with abnormal test results were also evaluated to discriminate congenital or acquired deficiencies. In addition; PC, PS, AT levels were followed-up, and MTHFR genotype for the patients with high homocysteine levels was studied, also. In spite of, 24 of these 30 patients had at least one abnormal laboratory test result at the diagnosis of leukemia, venous thrombosis (7 with CVC-related venous thrombosis, one CVC-related jugular vein thrombosis and VOD, one vena saphena parva thrombosis) developed in 9 of 24 patients. In conclusion, leukemic children with at least one prothrombotic risk factor have high venous thrombosis risk. Further trials are needed to clarify the necessarity of screening program for thrombophilia and thromboprophylaxis in children with leukemia and CVCs, and, especially for the patients carrying hereditary prothrombotic risk factors.


2001 ◽  
Vol 86 (10) ◽  
pp. 1012-2001 ◽  
Author(s):  
Rüdiger von Kries ◽  
Ralf Junker ◽  
Doris Oberle ◽  
Andrea Kosch ◽  
Ulrike Nowak-Göttl

SummaryPlacental infarction is frequently observed in low birth weight children. To evaluate whether low birth weight in healthy term neonates is associated with foetal inherited prothrombotic risk factors this retrospective study was conducted. Outcome measures were “birth weight in the lowest quartile” and “birth weight in the lowest decile” in singletons with a gestational age of ≥37 weeks.The analyses were based on 375 Caucasian children screened at the Münster childhood thrombophilia centre with complete data for all prothrombotic risk factors (factor V G1691A, prothrombin G20210A, elevated lipoprotein (a), protein C-, protein S-, antithrombin-deficiency). The proportion of children in the lowest birth weight quartile increased from 23.7% to 30.5% to 48.0% for children with no, only single heterozygous and multiple or homozygous defects respectively. The respective adjusted odds ratios (95% confidence intervals) of thrombophilia for birth weight in the lowest quartile (lowest decile) were 1.53 (0.76-3.08) in carriers of one prothrombotic risk factor and 4.01 (1.48-10.84) in subjects carrying multiple or homozygous defects. We identified foetal thrombophilia as an additional cause of low birth weight.


Blood ◽  
2003 ◽  
Vol 102 (5) ◽  
pp. 1686-1692 ◽  
Author(s):  
Rory R. Koenen ◽  
Guido Tans ◽  
René van Oerle ◽  
Karly Hamulyák ◽  
Jan Rosing ◽  
...  

AbstractProtein S exhibits anticoagulant activity independent of activated protein C (APC). An automated factor Xa–based one-stage clotting assay was developed that enables quantification of the APC-independent activity of protein S in plasma from the ratio of clotting times (protein S ratio [pSR]) determined in the absence and presence of neutralizing antibodies against protein S. The pSR was 1.62 ± 0.16 (mean ± SD) in a healthy population (n = 60), independent of plasma levels of factors V, VIII, IX, and X; protein C; and antithrombin, and not affected by the presence of factor V Leiden. The pSR strongly correlates with the plasma level of protein S and is modulated by the plasma prothrombin concentration. In a group of 16 heterozygous protein S–deficient patients, the observed mean pSR (1.31 ± 0.09) was significantly lower than the mean pSR of the healthy population, as was the pSR of plasma from carriers of the prothrombin G20210A mutation (1.47 ± 0.21; n = 46). We propose that the decreased APC-independent anticoagulant activity of protein S in plasma with elevated prothrombin levels may contribute to the thrombotic risk associated with the prothrombin G20210A mutation.


Blood ◽  
1995 ◽  
Vol 85 (10) ◽  
pp. 2756-2761 ◽  
Author(s):  
T Koster ◽  
FR Rosendaal ◽  
E Briet ◽  
FJ van der Meer ◽  
LP Colly ◽  
...  

A deficiency of protein C (PC), antithrombin, or protein S is strongly associated with deep-vein thrombosis in selected patients and their families. However, the strength of the association with venous thrombosis in the general population is unknown. This study was a population-based, patient-control study of 474 consecutive outpatients, aged less than 70 years, with a first, objectively diagnosed, episode of venous thrombosis and without an underlying malignant disease, and 474 healthy controls who matched for age and sex. Relative risks were estimated as matched odds ratios. Based on a single measurement, there were 22 (4.6%) patients with a PC deficiency (PC activity, less than 0.67 U/mL or PC antigen, less than 0.33 U/mL when using coumarins). Among the controls, the frequency was 1.5% (seven subjects). Thus, there is a threefold increase in risk of thrombosis in subjects with PC levels below 0.67 or 0.33 U/mL [matched odds ratio, 3.1; 95% confidence interval (CI), 1.4 to 7.0]. When a PC deficiency was based on two repeated measurements, the relative risk for thrombosis increased to 3.8 (95% CI, 1.3 to 10); when it was based on DNA-confirmation, the relative risk increased further to 6.5 (95% CI, 1.8 to 24). In addition, there was a gradient in thrombosis risk, according to PC levels. The results for antithrombin are similar to those for PC, although less pronounced (relative risk, 2.2; 95% CI, 1.0 to 4.7). We could not find an association between reduced total protein S (relative risk, 0.7; 95% CI, 0.3 to 1.8) or free protein S levels (relative risk, 1.6; 95% CI, 0.6 to 4.0) and thrombosis risk. Although not very frequent, PC and antithrombin deficiency are clearly associated with an increase in thrombosis risk.


2016 ◽  
Vol 23 (2) ◽  
pp. 105-115 ◽  
Author(s):  
S. Moussaoui ◽  
P. Saussoy ◽  
J. Ambroise ◽  
J. P. Defour ◽  
R. Zouitene ◽  
...  

Many genetic risk factors have been identified for causing venous thromboembolism (VTE). Most of them affect the function of natural anticoagulant pathways, particularly the protein C system, although recent studies suggest a role of components of the hematopoietic pathway in the etiology of venous thrombosis. In this case–control study, we aimed to determine the frequency of prothrombin G20210A and factor V Leiden (FVL) G1691A polymorphisms and protein C, protein S, and antithrombin III deficiencies in the East Algerian population and to investigate whether these genetic factors are associated with VTE. On the other hand, our study tends to evaluate the status of JAK2V617F and calreticulin (CALR) mutations among these cases. The participants consisted of 121 cases with VTE and 146 healthy controls. Polymorphisms of FVL G1691A and prothrombin G20210A were genotyped by polymerase chain reaction (PCR) restriction fragment length polymorphism. JAK2-V617F and calreticulin mutations were analyzed by quantitative PCR and PCR followed by capillary electrophoresis sequencing, respectively. Protein C, protein S, and antithrombin levels were determined and then hereditary deficiencies were identified. Of all cases and controls, none was a carrier of the antithrombin III deficiency, prothrombin gene G20210A, and CALR mutations. Only 1 case reported having a positive JAK2 mutation (mutant allele burden was 15%). The FVL mutation (GA/AA) was found in 14 (11.6%) cases and 2 (1.4%) controls and it was significantly different between both the groups ( P = .001). Deficiencies of protein S and protein C were detected in 17 (18.8%) cases. The univariate analysis resulted in a significant impact of FVL (odds ratio [OR] = 9.4, 95% confidence interval [CI] = 2.1-42.3; P = .003) and of protein S deficiency (OR = 16.9, 95% CI =2.1-132.8, P = .007) on the VTE status. Both factors stayed significant after adjustment for sex and age. The OR of the protein C deficiency was slightly elevated (OR = 6.4, 95% CI = 0.7-55.5), but it did not reach the level of statistical significance ( P = .091), and it was therefore not considered as a risk factor. In conclusion, coagulant factor V gene G1691A mutation and protein S deficiency constitute important genetic risk factors in patients with VTE in Eastern Algeria. The somatic mutation of JAK2 V617F and CALR mutations are less frequent causes of VTE, thus routine testing for these mutations is not recommended.


Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 4048-4048
Author(s):  
Mario C. Aggio ◽  
Pablo A. Martinez

Abstract Anderson-Fabry disease (AFD), described independently in the 1890s by William Anderson and Johann Fabry, is the second most frequent lysosomal storage disorder (after Gaucher disease). AFD is a pan-ethnic disorder due to a deficiency of the lysosomal enzime alpha-galactosidase A (alpha-GAL), with an estimated frequency of 1 in 117,000 male births, although recent studies suggest that the incidence may be underestimated, as certain patients with residual alpha-GAL activity (5 to 35% of normal levels) have disease too. Increased incidence of thrombotic events has been demonstrated in AFD. We evaluated the prevalence of prothrombotic risk factors in Argentine patients. Patients/methods: 36 patients (15 hemizygous and 21 heterozygous from 3 families) were studied for: protein C pathway (PCSys), antithrombin (AT), protein C (PC), protein S (PS), activated protein C resistance (APCR), lupus anticoagulant (LA), total plasma homocysteine (tHcy), anticardiolipin antibodies (ACA), and antiphosphatidylserine antibodies (APA). Results: The evaluation of PCSys, APCR, plasmatic levels of PC, PS, AT and APA were normal in all patients. Elevated levels of tHcy were found in 19.4% (n=7). Positive for LA were 38.9% (n=14) and for ACA 8.3% (n=3). Conclusions: 1) Our results confirm data from the literature reporting elevated homocysteinemia in AFD patients. Nutritional deficiencies, renal failure and metabolic disturbances are probable etiologic factors. 2) Thrombophilia was more frequent in hemizygous (13 patients, 86.7%) than in heterozygous (8 patients, 38.1%). Four hemizygous patients showed coexistence of two risk factors. 3) We found an unexpected high incidence of procoagulant autoantibodies. This association has also been reported and might contribute to thrombophilia in AFD: as in Gaucher disease, the accumulation of immunogenic glucocerebrosides might induce chronic immunostimulation.


1999 ◽  
Vol 82 (08) ◽  
pp. 662-666 ◽  
Author(s):  
Sandra J. Hasstedt ◽  
Mark F. Leppert ◽  
George L. Long ◽  
Edwin G. Bovill

IntroductionNearly 150 years ago, Virchow postulated that thrombosis was caused by changes in the flow of blood, the vessel wall, or the composition of blood. This concept created the foundation for subsequent investigation of hereditary and acquired hypercoagulable states. This review will focus on an example of the use of modern genetic epidemiologic analysis to evaluate the multigenic pathogenesis of the syndrome of juvenile thrombophilia.Juvenile thrombophilia has been observed clinically since the time of Virchow and is characterized by venous thrombosis onset at a young age, recurrent thrombosis, and a positive family history for thrombosis. The pathogenesis of juvenile thrombophilia remained obscure until the Egeberg observation, in 1965, of a four generation family with juvenile thrombophilia associated with a heterozygous antithrombin deficiency subsequently identified as antithrombin Oslo (G to A in the triplet coding for Ala 404).1,2 The association of a hereditary deficiency of antithrombin III with thrombosis appeared to support the hypothesis, first put forward by Astrup in 1958, of a thrombohemorrhagic balance.3 He postulated that there is a carefully controlled balance between clot formation and dissolution and that changes in conditions, such as Virchow’s widely encompassing triad, could tip the balance toward thrombus formation.The importance of the thrombohemorrhagic balance in hypercoagulable states has been born out of two lines of investigation: evidence supporting the tonic activation of the hemostatic mechanism and the subsequent description of additional families with antithrombin deficiency and other genetically abnormal hemostatic proteins associated with inherited thrombophilia. Assessing the activation of the hemostatic mechanism in vivo is achieved by a variety of measures, including assays for activation peptides generated by coagulation enzyme activity. Activation peptides, such as prothrombin fragment1+2, are measurable in normal individuals, due to tonic hemostatic activity and appear elevated in certain families with juvenile thrombophilia.4 In the past 25 years since Egeberg’s description of antithrombin deficiency, a number of seemingly monogenic, autosomal dominant, variably penetrant hereditary disorders have been well established as risk factors for venous thromboembolic disease. These disorders include protein C deficiency, protein S deficiency, antithrombin III deficiency, the presence of the factor V Leiden mutation, and the recently reported G20210A prothrombin polymorphism.5,6 These hereditary thrombophilic syndromes exhibit considerable variability in the severity of their clinical manifestations. A severe, life-threatening risk for thrombosis is conferred by homozygous protein C or protein S deficiency, which if left untreated, leads to death.7,8 Homozygous antithrombin III deficiency has not been reported but is also likely to be a lethal condition. Only a moderate risk for thrombosis is conferred by the homozygous state for factor V Leiden or the G20210A polymorphism.9,10 In contrast to homozygotes, the assessment of risk in heterozygotes, with these single gene disorders, has been complicated by variable clinical expression in family members with identical genotypes.11 Consideration of environmental interactions has not elucidated the variability of clinical expression. Consequently, it has been postulated that more than one genetic risk factor may co-segregate with a consequent cumulative or synergistic effect on thrombotic risk.12 A number of co-segregating risk factors have been described in the past few years. Probably the best characterized interactions are between the common factor V Leiden mutation, present in 3% to 6% of the Caucasian population,13,14 and the less common deficiencies of protein C, protein S, and antithrombin III. The factor V Leiden mutation does not, by itself, confer increased risk of thrombosis. The high prevalence of the mutation, however, creates ample opportunity for interaction with other risk factors when present.The G20210A prothrombin polymorphism has a prevalence of 1% to 2% in the Caucasian population and, thus, may play a similar role to factor V Leiden. A number of small studies have documented an interaction of G20210A with other risk factors.15-17 A limited evaluation of individuals with antithrombin III, protein C, or protein S deficiency revealed a frequency of 7.9% for the G20210A polymorphism, as compared to a frequency of 0.7% for controls.18 The G20210A polymorphism was observed in only 1 of the 6 protein C-deficient patients.18 In the present state, the elucidation of risk factors for venous thromboembolic disease attests to the effectiveness of the analytical framework constructed from the molecular components of Virchow’s triad, analyzed in the context of the thrombohemorrhagic balance hypothesis. Two investigative strategies have been used to study thromobophilia: clinical case-control studies and genetic epidemiologic studies. The latter strategy has gained considerable utility, based on the remarkable advances in molecular biology over the past two decades. Modern techniques of genetic analysis of families offer important opportunities to identify cosegregation of risk factors with disease.19 The essence of the genetic epidemiologic strategy is the association of clinical disease with alleles of specific genes. It is achieved either by the direct sequencing of candidate genes or by demonstration of linkage to genetic markers.


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