Thrombophilic Families Research Articles

Antithrombin Deficiency: Frequency in Patients with Thrombosis and Thrombophilic Families

Purpose: Antithrombin (AT) deficiency is a well-known inherited risk factor for venous thromboembolism (VTE). However, F V Leiden and F II20210a mutations have drawn much more attention in the recent years. Therefore, we have decided to analyze the frequency of antithrombin deficiency in different cohorts of patients and tried to formulate indications for its testing. Results: Antithrombin deficiency was found in 4% of patients with recurrent VTE ≤ 50 years of age with, in 1% of patients with splanchnic vein thrombosis and in 2% of cases associated with combined oral contraceptives (COC) use or pregnancy. In patients with central venous thrombosis, antithrombin deficiency was not found. Recommendation: We consider antithrombin testing useful in patients with thrombosis occuring up to 45 years of age without any risk factors. Namely, females with VTE in pregnancy and puerperium should be tested as well as females with thrombosis on COC, if VTE occurred within the first year of their use. Conclusion: In spite of degressive interest in thrombophilia work up, we still consider antithrombin testing useful in defined clinical situations.

A thrombophilia family with protein S deficiency due to protein translation disorders caused by a Leu607Ser heterozygous mutation in PROS1

BackgroundProtein S deficiency (PSD) is an autosomal dominant hereditary disease. In 1984, familial PSD was reported to be prone to recurrent thrombosis. Follow-up studies have shown that heterozygous protein S (PROS1) mutations increase the risk of thrombosis. More than 300 PROS1 mutations have been identified; among them, only a small number of mutations have been reported its possible mechanism to reduce plasma protein S (PS) levels. However, whether PROS1 mutations affect protein structure and why it can induce PSD remains unknown.MethodsThe clinical phenotypes of the members of a family with thrombosis were collected. Their PS activity was measured using the coagulation method, whereas their protein C and antithrombin III activities were measured using methods such as the chromogenic substrate method. The proband and her parents were screened for the responsible mutation using second-generation whole exon sequencing, and the members of the family were verified for suspected mutations using Sanger sequencing. Mutant and wild type plasmids were constructed and transfected into HEK293T cells to detect the mRNA and protein expression of PROS1.ResultsIn this family, the proband with venous thrombosis of both lower extremities, the proband’s mother with pulmonary embolism and venous thrombosis of both lower extremities, and the proband’s younger brother had significantly lower PS activity and carried a PROS1 c. 1820 T > C:p.Leu607Ser heterozygous mutation (NM_000313.3). However, no such mutations were found in family members with normal PS activity. The PS expression in the cell lysate and supernatant of the Leu607Ser mutant cells decreased, while mRNA expression increased. Immunofluorescence localization showed that there was no significant difference in protein localization before and after mutation.ConclusionsThe analysis of family phenotype, gene association, and cell function tests suggest that the PROS1 Leu607Ser heterozygous mutation may be a pathogenic mutation. Serine substitution causes structural instability of the entire protein. These data indicate that impaired PS translation and synthesis or possible secretion impairment is the main pathogenesis of this family with hereditary PSD and thrombophilia.

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

AbstractHigh 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.

Lifestyle Moderates Genetic Risk of Venous Thromboembolism: The ARIC Study.

Venous thromboembolism (VTE) is a common disease that has a genetic basis. Lifestyle factors contribute to risk, but it is unknown whether healthy lifestyle can mitigate the genetic risk. We studied whether greater adherence to the American Heart Association's cardiovascular health metric, Life's Simple 7 (LS7), is associated with lower incidence of VTE in individuals across categories of a genetic risk score (GRS) for VTE. Approach AND RESULTS: We followed 9026 White participants from the ARIC (Atherosclerosis Risk in Communities) Study, a prospective cohort enrolled in 1987 to 1989 until 2015. We tested the joint associations with VTE of a validated VTE GRS comprising 5 well-known gene variants and baseline LS7 categories. There were 466 incident VTE events over 22.8 years. Participants with an optimal LS7 score had a lower incidence of VTE (3.9%) than those with inadequate LS7 (5.7%). Compared with the high GRS and inadequate LS7 group (hazard ratio=1), those with high GRS and optimal LS7 indeed had a reduced hazard ratio of VTE: 0.65 (95% CI, 0.48-0.89). The group with low GRS and optimal LS7 had the lowest hazard ratio of VTE (0.39 [95% CI, 0.25-0.61]). Of the LS7 components, in all GRS groups, the factor most strongly protective for VTE was normal weight. Among people at low or high genetic risk for VTE, healthier lifestyle factors, particularly normal weight, were associated with a lower incidence of VTE. Further studies should determine the impact of lifestyle changes among patients at high genetic risk of VTE, such as in thrombophilic families.

The genetics of venous thromboembolism: a systematic review of thrombophilia families.

Genetic risk factors are important for the occurrence and prognosis of venous thromboembolism (VTE). The studies of thrombophilia families are important for dissecting the genetic background of the thrombotic disease. We conducted the systematic review of all published family-based studies on VTE genetics across all racial groups through PubMed and Embase prior to 13th April 2020. This systematic review of 287 families (including 225 Caucasian families, 52 East Asian families, and families of other ethnicities) revealed a total of 21 different genes; the five most reported mutated genes were F5 (88/287, 30.7%), SERPINC1 (67/287, 23.3%), PROC (65/287, 22.6%), F2 (40/287, 13.9%) and PROS1 (48/287, 16.7%). For Caucasian families, F5 mutations were most frequently reported at 37.8% (85/225), while PROS1 mutations were most frequently reported, at 40.4% (21/52), for East Asian families (Chinese, Japanese and Korean). Factor V Leiden was reported more frequently in Caucasians than in East Asians. Missense mutations were reported frequently in the SERPINC1, PROC and PROS1 genes. In conclusion, our study found the most likely mutated genes associated with VTE among different ethnic groups and provided indications for VTE genetic testing and research in the future.

Clinical Features of Visual Disturbances in Leiden Thrombophilia

The hereditary thrombophilias is a well-recognized important risk factor for a systemic and local thromboembolic events development. The case of Leiden thrombophilia family inheritance concomitant by the visual disturbances development are shown in this аrticle. Most commonly in hereditary thrombophilias, venous thrombembolias occur, arterial occlusions which have been reported in the recent literature only as individual clinical cases occur more rarely. In the European population hereditary thrombophilias are associated with a prothrombotic mutation in the coagulation factor V gene (Leiden factor) in a greater degree; herewith the risk of thrombotic complications is increasing significantly in homozygous polymorphism forms. Presence of combined mutations in several clotting factors also leads to risk of thrombembolias increase. Consequence of the Leiden mutation is a V activator resistance to the resolving action of the activated protein C which is a natural endogenous anticoagulant protein. Resistance development leads to a deceleration of V factor inactivation and to increasing of the thrombin amount. In the work presented here, development of the consistent bilateral occlusion of the central retinal artery (CRA) in a middle-aged patient with a heterozygous form of Leiden thrombophilia is the subject of interest. Along with the hereditary hemostatic system abnormality, the patient also had cardiovascular risk factors (hypertensive disease, atherosclerosis) which had a potentiating effect on the occlusion development. Taking into account the autosomal dominant nature of the Leiden mutation inheritance, the patient’s only daughter was examined; brief episodes of amaurosis fugax against the background of headaches similar to migraine were detected due to ophthalmological abnormalities. For verification of the Leiden thrombophilia diagnosis, both patients underwent molecular genetic diagnostics. Currently there are no large prospective studies showing the optimal and economically viable approach for identification of thrombophilia genetic polymorphisms in patients with retinal vascular occlusions in daily clinical experience. Possible additional risk factors for thrombembolias development, prevention services for manifest and recurrent vascular occlusions in patients with hereditary blood coagulation system abnormalities and their relatives are discussed in this article.

Mitigation of Venous Thromboembolism Risk through Favorable Lifestyle: The ARIC Study

Background: Venous thromboembolism (VTE) is a common disease with a strong genetic basis. Unhealthy lifestyle factors contribute to risk, but it is unknown whether healthier lifestyle can mitigate the risk for VTE in those at high genetic risk. We studied whether greater adherence to the American Heart Association's (AHA's) cardiovascular health metric called Life's Simple 7 (LS7) is associated with a lower rate of VTE in individuals with high genetic risk score (GRS) for VTE. Methods: We followed 9,026 middle-aged white participants from the Atherosclerosis Risk in Communities (ARIC) Study, a prospective cohort of 15,792 individuals enrolled in 1987-89. A validated GRS was used, comprising 5 well known genetic conditions associated with VTE (factor V Leiden, prothrombin 20210A, non-O blood group, factor XI rs4241824, and fibrinogen gamma FGG rs2066865). Only white participants were included, as the GRS did not predict VTE in others. AHA's LS7 categories of inadequate, average, and optimal health were determined based on smoking status, body mass index, physical activity, diet, total cholesterol, blood pressure, and fasting glucose. VTE events were adjudicated by expert medical record review. We calculated hazard ratios (HRs) and 95% confidence intervals (CI) of incident VTE by LS7 categories, stratified by GRS (low, intermediate, high), adjusting for age, sex, and education. HRs were also calculated for individual LS7 components stratified by GRS. Results: There were 466 incident VTE over 22.8 years of follow-up. Compared to those with optimal health, those with inadequate LS7 score had higher rates of VTE (5.7% vs. 3.9%). In Figure 1, compared to the high GRS / inadequate LS7 group, the HR of VTE in the low GRS group with optimal health was lowest at 0.39 (95% CI 0.25-0.61), but moreover, the HR in the high GRS group with optimal health was also attenuated to 0.65 (95% CI 0.48-0.89). The pattern of association was similar for provoked and unprovoked VTE. Of the LS7 components, obesity was most strongly related to VTE. In Figure 2, compared to obese / high GRS participants, the HR of VTE with normal weight / low GRS was 0.36 (95% CI 0.23-0.57), while the HR in high GRS / normal weight participants was reduced by 45%, at 0.55 (95% CI 0.4-0.76). Conclusion: Among all participants, even those at high genetic risk, healthier lifestyle factors, particularly obesity, were associated with decreased incidence of VTE. Further studies should determine the impact of lifestyle change among patients at high genetic risk of VTE, such as in thrombophilic families. Disclosures Heckbert: National Institutes of Health: Other: Grants.

Analysis of PROC and PROS1 single nucleotide polymorphisms in a thrombophilia family

The aim of this study was to assess the association of single nucleotide polymorphisms (SNPs) in protein C (PROC) and protein S (PROS1) genes with deep venous thrombosis (DVT) in a thrombophilia family. DNA were extracted from blood of participants. Five PROC SNPs and 11 PROS1 SNPs were selected from the Hapmap and 1000 Genomes databases. The minor allele frequencies (MAFs) of SNPs in the thrombophilia family (Group I) and healthy controls (Group II) were detected. SNPs were analysed by Chi-square, logistic regression and linkage disequilibrium patterns. MAFs for all 16 SNPs were greater than 0.05. Chi-square analysis showed significant differences between Group I and Group II in the frequency of mutant alleles of rs1799808, rs5936, rs6123, rs12634349, rs6441600 and rs13062355 SNPs (P<.05). Logistic regression analysis found that mutant alleles of rs1799808, rs6441600 and rs13062355 SNPs may contribute to DVT in this family (OR>1, L95>1). Linkage disequilibrium was found among 15 of the PROC and PROS SNPs. Single nucleotide polymorphisms (SNPs) of PROC and PROS1 may be closely associated with DVT in this thrombophilia family. Mutant alleles of rs1799808, rs6441600 and rs13062355 SNPs may contribute to DVT, whereas mutant alleles of rs1799810, rs6123 and rs12634349 may protect individuals from DVT. With the exception of rs9681204, there was linkage disequilibrium between PROC and PROS1 SNPs. We found that 12 haplotypes were in linkage disequilibrium, but linkage disequilibrium was strong in only eight of these (frequency>5%).

Biochemical and cellular consequences of the antithrombin p.Met1? mutation identified in a severe thrombophilic family.

Nature is always the best inspiration for basic research. A family with severe thrombosis and antithrombin deficiency, the strongest anticoagulant, carried a new mutation affecting the translation-start codon of SERPINC1, the gene encoding antithrombin. Expression of this variant in a eukaryotic cell system produced three different antithrombins. Two downstream methionines were used as alternative initiation codons, generating highly expressed small aglycosylated antithrombins with cytoplasmic localization. Wild-type antithrombin was generated by the use of the mutated AUU as initiation codon. Actually, any codon except for the three stop codons might be used to initiate translation in this strong Kozak context.We show unexpected consequences of natural mutations affecting translation-start codons. Downstream alternative initiation AUG codons may be used when the start codon is mutated, generating smaller molecules with potential different cell localization, biochemical features and unexplored consequences. Additionally, our data further support the use of other codons apart from AUG for initiation of translation in eukaryotes.

The impact of a male or female thrombotic family history on contraceptive counseling: a cohort study

Essentials It is unknown if a male or female thrombotic family history influences risk in female relatives. We assessed thrombotic risk in female relatives of male and female patients with thrombosis. A hormonally related female thrombotic family history further increases risk in female relatives. This information could be important in counseling women on contraceptive options. Click to hear Prof. Rosendaal's perspective on venous thrombosis: etiology, pathogenesis, and prognosis Background Women from thrombophilic families have increased risk of venous thromboembolism (VTE), which increases further during oral contraceptive (COC) use and pregnancy-postpartum. Whether this additional risk differs between relatives of male and female patients, or is different when that female patient had a hormonally related VTE (during COC use/pregnancy), is unknown. Methods One thousand five female relatives of consecutive patients with VTE from a family-based cohort were retrospectively followed for incident VTE from ages 15 to 50, first VTE, or study inclusion. Absolute and relative VTE risks adjusted for factors of patients (sex, age) and relatives (thrombophilia, COC use, pregnancy) were estimated in relatives of female and male patients and in relatives of female patients with and without hormonally related VTE. Results Absolute risk in relatives of female (0.32 [95% confidence interval [CI] 0.23-0.43]) vs. male patients (0.39 [95% CI 0.28-0.53]) was comparable. However, the heterogeneity analysis of risk estimates suggested that in relatives of female vs. male patients, the contribution of pregnancy-postpartum (hazard ratio [HR] 11.6 [95% CI 6.3-21.3] vs. HR6.6 [95% CI 2.8-15.2]) and, to a lesser extent, COC use (HR3.6 [95% CI 1.8-7.1] vs. HR2.7 [95% CI 1.5-5.0]) to the VTE risk differs. Absolute risk was significantly higher in relatives of female patients with hormonally related VTE (0.43 [95% CI 0.3-0.6]) vs. relatives of female patients without hormonally related VTE (0.13 [95% CI 0.05-0.27]), HR3.28 [95% CI 1.5-7.9]). The higher contribution of pregnancy-postpartum and COC use to the VTE risk was mainly observed in relatives of patients with hormonally related VTE. Conclusions These findings suggest that a family history from a female patient, especially when VTE was hormonally related, may further increase VTE risk in her female relatives. This information could be important in counseling women on contraceptive options.

Antithrombin resistance: a new mechanism of inherited thrombophilia

Venous thromboembolism is a multifactorial disease resulting from complex interactions among genetic and environmental factors. To date, numerous genetic defects have been found in families with hereditary thrombophilia, but there may still be many undiscovered causative gene mutations. We investigated a possible causative gene defect in a large Japanese family with inherited thrombophilia, and found a novel missense mutation in the prothrombin gene (p.Arg596Leu) resulting in a variant prothrombin (prothrombin Yukuhashi). The mutant prothrombin had moderately lower activity than wild type prothrombin in clotting assays, but formation of the thrombin-antithrombin (TAT) complex was substantially impaired resulting in prolonged thrombin activity. A thrombin generation assay revealed that the peak activity of the mutant prothrombin was fairly low, but its inactivation was extremely slow in reconstituted plasma. The Leu596 substitution caused a gain-of-function mutation in the prothrombin gene, resulting in resistance to antithrombin and susceptibility to thrombosis. We also showed the effects of the prothrombin Yukuhashi mutation on the thrombomodulin-protein C anticoagulation system, recent development of a laboratory test detecting antithrombin resistance in plasma, and another antithrombin resistant mutation found in other thrombophilia families.

Importance of thrombophilia screening

Thrombophilia testing denotes a test battery for inherited or acquired features associated with a tendency for clot formation. Currently, it is being used in a frequency and to an extent which is not supported by evidence. In order to protect patients from unnecessary worry and stigmatization, but also for reasons of cost effectiveness, thrombophilia testing should be reduced to a very small number of medically justifiable indications which are outlined in this review.Those indications include the following: secondary prevention of venous thromboembolism in patients from a thrombophilic family, i.e., with two or more first degree relatives with venous thromboembolism (VTE), or patients with suspected antiphospholipid syndrome; women prior to oral contraception or planning to become pregnant if they had no prior VTE but have one or more first-degree relatives with VTE-provided they are willing to follow the consequences of positive test results; women with recurrent miscarriage. The inappropriate indications are discussed as well.The test panel for inherited thrombophilias includes deficiencies of antithrombin, protein C and protein S, factor V Leiden and prothrombin 20210 mutation. Patients with suspicion of antiphospholipid syndrome have to be tested for lupus anticoagulans, anti-cardiolipin antibodies, and anti-β2-glycoprotein I-antibodies. It is important to do the blood sampling at an appropriate point in time.

Staphylococcal endocarditis as the first manifestation of heritable protein S deficiency in childhood

A 12-year-old Japanese girl developed infective endocarditis and central nervous system disease. The previously healthy girl showed altered consciousness and abnormal behaviors along with the classical signs of septic emboli. Staphylococcus aureus was isolated from peripheral blood, but not, the pleocytotic cerebrospinal fluid. Diagnostic imaging studies revealed a vegetative structure in the morphologically normal heart, and multiple thromboembolisms in the brain and spleen. Low plasma activity of protein S (12%) and thrombophilic family history allowed the genetic study, demonstrating that she carried a heterozygous mutation of PROS1 (exon 13; 1689C>T, p.R474C). Surgical intervention of the thrombotic fibrous organization and subsequent anticoagulant therapy successfully managed the disease. There are no reports of infective endocarditis in childhood occurring as the first presentation of heritable thrombophilia. Protein S deficiency might be a risk factor for the development or exacerbation of infective endocarditis in children having no pre-existing heart disease.

Protein S levels and the risk of venous thrombosis: results from the MEGA case-control study

AbstractIn thrombophilic families, protein S deficiency is clearly associated with venous thrombosis. We aimed to determine whether the same holds true in a population-based case-control study (n = 5317). Subjects were regarded protein S deficient when protein S levels were <2.5th percentile of the controls. Free and total protein S deficiency was not associated with venous thrombosis: free protein S < 53 U/dL, odds ratio [OR] 0.82 (95% confidence interval [CI], 0.56-1.21) and total protein S < 68 U/dL, OR 0.90 (95% CI, 0.62-1.31). When lower cutoff values were applied, it appeared that subjects at risk of venous thrombosis could be identified at levels <0.10th percentile of free protein S (<33 U/dL, OR 5.4; 95% CI, 0.61-48.8). In contrast, even extremely low total protein S levels were not associated with venous thrombosis. PROS1 was sequenced in 48 subjects with free protein S level <1st percentile (<46 U/dL), and copy number variations were investigated in 2718 subjects, including all subjects with protein S (free or total) <2.5th percentile. Mutations in PROS1 were detected in 5 patients and 5 controls reinforcing the observation that inherited protein S deficiency is rare in the general population. Protein S testing and PROS1 testing should not be considered in unselected patients with venous thrombosis.Key Points

Genome‐wide linkage scan in affected sibling pairs identifies novel susceptibility region for venous thromboembolism: Genetics In Familial Thrombosis study

Venous thromboembolism (VTE) is a multicausal disorder involving environmental and genetic risk factors. In many thrombophilic families the clustering of thrombotic events cannot be explained by known genetic risk factors, indicating that some remain to be discovered. We aimed to identify novel thrombosis susceptibility alleles in a large panel of small thrombophilic families: the Genetics In Familial Thrombosis (GIFT) study. In the GIFT study, 201 families were recruited consisting of 438 siblings with an objectively confirmed VTE at a young age. Multipoint linkage analysis (402 SSR markers) and fine mapping were performed, followed by genotyping of tagging SNPs in positional candidate genes. Established genetic risk factors such as factor V Leiden, ABO blood group non-O, prothrombin 20210A, fibrinogen gamma 10034T and deficiencies of antithrombin, protein C and protein S were more frequent in GIFT patients than in unselected VTE patients. Linkage supported the presence of novel thrombosis susceptibility loci on 7p21.3-22.2 (LOD score=3.23) and Xq24-27.3 (LOD score=1.95). Simulation analysis showed that the chr7 signal was genome-wide statistically significant (P=0.022). Tagging SNPs (n=157) in eight positional candidate genes (LOD drop 1.5 regions) were genotyped in GIFT patients and 332 healthy controls. Five chr7 SNPs associated with VTE. SNP THSD7A rs2074597 was responsible for part of the chr7 signal. The GIFT panel is rich in established genetic risk factors for VTE, but genetic factors remain unidentified in many families. Genome-wide linkage failed to identify the previously established genetic risk factors for VTE, but identified a novel VTE susceptibility locus on chr7.

Genetic variants associated with protein C levels

Normal protein C (PC) plasma levels range widely in the general population. Factors influencing normal PC levels are thought to influence the risk of venous thrombosis. Little is known about the underlying genetic variants. We performed a genome scan of normal PC levels to identify genes that regulate normal PC levels. We performed a variance components linkage analysis for normal PC levels in 275 individuals from a single, large family. We then sequenced candidate genes under the identified linkage peak in eight family members: four with high and four with low, but normal, PC levels. For variants showing a difference in carriers between those with high and low PC levels, we re-evaluated linkage in the 275 family members conditional on the measured genotype effect. Genotype-specific mean PC levels were determined using likelihood analysis. Findings were replicated in the Leiden Thrombophilia Study (LETS). We identified a quantitative trait locus at chromosome 5q14.1 affecting normal PC plasma level variability. Next-generation sequencing of 113 candidate genes under the linkage peak revealed four SNPs in BHMT2, ACOT12, SSBP2 and XRCC4, which significantly increased PC levels in our thrombophilic family, but not in LETS. We identified four genes at chromosome 5q14.1 that might influence normal PC levels. BHMT2 seems the most likely candidate to regulate PC levels via homocysteine, a competitive inhibitor to thrombin. Failure to replicate our findings in LETS might be due to differences between the studies in genetic background and linkage disequilibrium patterns.

Cell adhesion molecule 1 (CADM1) is ubiquitously present in the endothelium and smooth muscle cells of the human macro- and micro-vasculature

Cell adhesion molecule 1 (CADM1) is a member of the immunoglobulin cell adhesion molecule family. Recently, we identified CADM1 to be a novel risk factor for venous thrombosis in a large, protein C deficient, thrombophilic family and showed, for the first time, the expression of CADM1 in endothelial cells (Hasstedt et al. in Blood 114:3084-3091, 2009). To further investigate its role in venous thrombosis, as well as other vasculopathies, we undertook a systematic confocal microscopic investigation for the presence of CADM1 in the vasculature of 28 different human tissues. Paraffin embedded tissue sections were dual immunostained with an antibody against CADM1, together with an antibody against either von Willebrand factor (to identify endothelial cells), or α-smooth muscle actin (to identify smooth muscle cells). The results showed that CADM1 was ubiquitously present in endothelial cells and smooth muscle cells in the vasculature from all 28 tissues, though its representation in the various classes of vessels was tissue dependent.

ABO Blood Group and von Willebrand Factor Levels Partially Explained the Incomplete Penetrance of Congenital Thrombophilia

We aimed to study the association among ABO blood group, von Willebrand factor, factor VIII plasma levels, and the risk of venous thrombosis (VT) in a cohort of 1774 relatives from 500 families with inherited thrombophilia. One hundred sixty-one of the 1774 relatives had a VT. Different risk groups were formed: no, low-(factor V Leiden or F2G20210A heterozygous carriers), and high-risk thrombophilia (antithrombin, protein C, protein S, factor V Leiden, or F2G20210A homozygous carriers and combined defects). Compared with group O, AB blood group was associated with increased risk of VT: hazard ratio (HR)=3.8 (2.0-7.2). The effect of blood group A and B was milder (HR=1.6 [1.1-2.5] and 1.8 [1.0-3.3], respectively). An increased risk of VT was observed with increasing levels of von Willebrand factor and factor VIII plasma levels (HR=2.96 [1.92-4.56] and HR=2.60 [1.92-4.56] for third versus first tertile of von Willebrand factor and factor VIII plasma levels, respectively). In multivariate analysis, AB group (HR=2.3 [1.1-4.8]), high-risk thrombophilia (HR=2.8 [1.6-4.6]), and high von Willebrand factor levels (HR=2.3 [1.3-4.0]) were significantly associated with increased risk of VT. The risk of VT in individuals with high-risk thrombophilia and AB group was 14.4× higher than in those without thrombophilia and O group (5.0-41.4). ABO blood group modifies the risk of VT in families with hereditary thrombophilia. Phenotyping of the ABO blood group should be performed to better assess the risk of VT in asymptomatic individuals from thrombophilic families.

Free and Total Protein S Antigen Levels on the Risk of Venous Thrombosis: Results From the MEGA Study

Abstract 538 Context:Conflicting data have been reported on the risk for venous thrombosis in individuals with low total protein S levels (i.e. type I protein S deficiency) and low free protein S levels with normal total protein S levels (i.e. type III protein S deficiency). This may be due to small numbers, wrong cut off level or inclusion of individuals with mild transitory decrements in protein S levels. Most studies that showed that type I and type III protein S deficiency were related with an increased risk for venous thrombosis, have been performed in thrombophilic families, suggesting that these deficiencies are inherited. As the prevalence of inherited type I or type III protein S deficiency is not known, the relevance of these findings within normal populations remain to be established. Objectives:To assess the risk of first venous thrombosis in persons with low levels of free protein S or total protein S in a large population-based case–control study. Design:MEGA study, 4956 consecutive patients aged 18 to 70 years with a first episode of venous thrombosis were included. Age- and sex-matched controls were partners of patients (n=3297) or individuals recruited by random digit dialing (n=3000). DNA was obtained by standard methods and was available for 4485 patients and 4889 control subjects. Citrated plasma was available for 2471 patients and 2940 controls. Molecular basis for protein S deficiency was investigated by analysis of copy number variation of PROS1 and sequencing of individuals with the lowest levels of protein S in attempt to explain the different findings in risk estimates between families and population studies. Statistical analysis:Odds ratios were adjusted for age and sex (matching factors) for levels of free/total protein S and their 95% confidence levels (95% CIs) with the use of logistic regression. The 2.5th-97.5th percentile of both total and free protein S in control subjects that did not use vitamin K antagonists (VKA) at time of blood draw were considered as the reference range. Individuals that used VKA at time of blood draw were excluded when calculating relative risk estimates. Furthermore, a preplanned sensitivity analysis was performed where we excluded estrogen users and pregnant women at time of blood draw. Results:Individuals with low free protein S levels or low total protein S levels (<2.5th percentile) were not at increased risk of venous thrombosis as compared to individuals with protein S levels in the 2.5th-97.5th percentile; odds ratio 0.82 (95% CI, 0.56–1.21) and 0.90 (95% CI, 0.62–1.31) respectively. Excluding all women who used estrogens or were pregnant/puerperic at time of venous thrombosis or at time of blood sampling increased the odds ratios slightly to 1.55 (95% CI, 0.84–2.88) for individuals with low free protein S levels and to 1.28 (95% CI, 0.70–2.35) in individuals with low total protein S levels. We subsequently compared decreasing cut off values of free and total protein S levels on the risk of venous thrombosis as compared to the same reference group. Although numbers became small, it appeared that a free protein S cut off level of < 0.20th or < 0.10th percentile could identify individuals at high risk of venous thrombosis (odds ratios 2.01; 95% CI, 0.57–7.15, and 5.44; 95% CI, 0.61–48.78, respectively). Even extremely low (<0.10th percentile) total protein S levels were not associated with venous thrombosis. Only one patient had a copy number variation of PROS1 in 2270 consecutive samples tested. Currently, we are sequencing the PROS1 gene in all individuals with protein S levels <1st percentile of which results will be available before the ASH conference of 2011. Conclusion:Low free protein S and low total protein S levels could not identify individuals at risk for venous thrombosis in a population based study. Although extremely low free protein S levels were associated with an increased risk for venous thrombosis, numbers were too small to support testing on free protein S in an unselected group of venous thrombosis patients. Disclosures:No relevant conflicts of interest to declare.

Thrombophilia in Childhood: To Test or Not to Test

Inherited thrombophilia is defined as a genetically determined tendency to develop venous thromboembolism. In children, inherited thrombophilia contributes to the development of pediatric thromboembolic disease. As a consequence, pediatric hematologists are increasingly requested to test thrombophilia in pediatric patients with thrombosis or asymptomatic children from thrombophilic families. This article reviews the benefits and limitations of testing for thrombophilic disorders, for example, factor V Leiden, prothrombin mutation, and deficiencies of antithrombin, protein C, or protein S in childhood.