Fine mapping of quantitative trait nucleotides underlying thrombin-activatable fibrinolysis inhibitor antigen levels by a transethnic study

Thrombin Activatable Fibrinolysis Inhibitor (TAFI): An Updated Narrative Review

Thrombin activatable fibrinolysis inhibitor (TAFI), a proenzyme, is converted to a potent attenuator of the fibrinolytic system upon activation by thrombin, plasmin, or the thrombin/thrombomodulin complex. Since TAFI forms a molecular link between coagulation and fibrinolysis and plays a potential role in venous and arterial thrombotic diseases, much interest has been tied to the development of molecules that antagonize its function. This review aims at providing a general overview on the biochemical properties of TAFI, its (patho)physiologic function, and various strategies to stimulate the fibrinolytic system by interfering with (activated) TAFI functionality.

Thrombin-Activatable Fibrinolysis Inhibitor Polymorphisms and Cerebral Venous Thrombosis in Mexican Mestizo Patients

Thrombin-activatable fibrinolysis inhibitor (TAFI) gene polymorphisms have been proposed as a predisposing factor for cerebral venous thrombosis (CVT). We analyzed the association between CVT and TAFI single-nucleotide polymorphisms (rs3742264, rs2146881, and rs1926447) compared to healthy controls. Mexico Mestizo confirmed cases with CVT and age- and sex-matched controls with no history of venous thrombotic events were recruited from July 2006 to July 2015. Demographic, clinical, and imaging information was included in the analysis. Genotyping single-nucleotide polymorphisms were performed by allele-specific polymerase chain reaction. Allelic univariate analysis, haplotype association, and Hardy-Weinberg equilibrium were assessed. A total of 113 CVT cases (94 females [83.2%]; median age 35 years [interquartile range 27-43 years]) and 134 age- and sex-matched controls were included. The main risk factors for CVT were pregnancy/puerperium (30.9%), oral contraceptive use (19.5%), and hereditary thrombophilia (7.1%). We found no significant association for heterozygous and homozygous models for rs3742264 ( P = .30 and P = .69, respectively), rs2146881 ( P = .90 and P = .17, respectively), or rs1926447 ( P = .40 and P = .52, respectively) compared to controls; these findings were consistent in subgroup and haplotype analyses. In conclusion, TAFI rs3742264, rs2146881, and rs1926447 polymorphisms do not increase the risk of CVT in comparison to healthy controls.

A Genome-wide Study of Common and Rare Genetic Variants Associated with Circulating Thrombin Activatable Fibrinolysis Inhibitor

Thrombin-activatable fibrinolysis inhibitor (TAFI) plays a central role in haemostasis, and plasma TAFI concentrations are heritable. Candidate gene studies have identified several variants within the gene encoding TAFI, CPB2 , that explain part of the estimated heritability. Here, we describe an exploratory genome-wide association study to identify novel variants within and outside of the CPB2 locus that influence plasma concentrations of intact TAFI and/or the extent of TAFI activation (measured by released TAFI activation peptide, TAFI-AP) amongst 3,260 subjects from Southern Sweden. We also explored the role of rare variants on the HumanExome BeadChip. We confirmed the association with previously reported common variants in CPB2 for both intact TAFI and TAFI-AP, and discovered novel associations with variants in putative CPB2 enhancers. We identified a gene-based association with intact TAFI at CPB2 ( P_SKAT-O  = 2.8 × 10 ⁻⁸ ), driven by two novel rare nonsynonymous single nucleotide polymorphisms (SNPs; I420N and D177G). Carriers of the rare variant of D177G (rs140446990; MAF 0.2%) had lower intact TAFI and TAFI-AP concentrations compared with non-carriers (intact TAFI, geometric mean 53 vs. 78%, P_T-test   =  5 × 10 ⁻⁷ ; TAFI-AP 63 vs. 99%, P_T-test  = 7.2 × 10 ⁻⁴ ). For TAFI-AP, we identified a genome-wide significant association at an intergenic region of chromosome 3p14.1 and five gene-based associations (all P_SKAT-O  < 5 × 10 ⁻⁶ ). Using well-characterized assays together with a genome-wide association study and a rare-variant approach, we verified CPB2 to be the primary determinant of TAFI concentrations and identified putative secondary loci (candidate variants and genes) associated with intact TAFI and TAFI-AP that require independent validation.

Pro-inflammatory cytokines reduce human TAFI expression via tristetraprolin-mediated mRNA destabilisation and decreased binding of HuR

Thrombin activatable fibrinolysis inhibitor (TAFI) is the zymogen form of a basic carboxypeptidase (TAFIa) with both anti-fibrinolytic and anti-inflammatory properties. The role of TAFI in inflammatory disease is multifaceted and involves modulation both of specific inflammatory mediators as well as of the behaviour of inflammatory cells. Moreover, as suggested by in vitro studies, inflammatory mediators are capable of regulating the expression of CPB2, the gene encoding TAFI. In this study we addressed the hypothesis that decreased TAFI levels observed in inflammation are due to post-transcriptional mechanisms. Treatment of human HepG2 cells with pro-inflammatory cytokines TNFα, IL-6 in combination with IL-1β, or with bacterial lipopolysaccharide (LPS) decreased TAFI protein levels by approximately two-fold over 24 to 48 hours of treatment. Conversely, treatment of HepG2 cells with the anti-inflammatory cytokine IL-10 increased TAFI protein levels by two-fold at both time points. We found that the mechanistic basis for this modulation of TAFI levels involves binding of tristetraprolin (TTP) to the CPB2 3′-UTR, which mediates CPB2 mRNA destabilisation. In this report we also identified that HuR, another ARE-binding protein but one that stabilises transcripts, is capable of binding the CBP2 3’UTR. We found that pro-inflammatory mediators reduce the occupancy of HuR on the CPB2 3’-UTR and that the mutation of the TTP binding site in this context abolishes this effect, although TTP and HuR appear to contact discrete binding sites. Interestingly, all of the mediators tested appear to increase TAFI protein expression in THP-1 macrophages, likewise through effects on CPB2 mRNA stability.

Sex-specific effect of CPB2 Ala147Thr but not Thr325Ile variants on the risk of venous thrombosis: A comprehensive meta-analysis

BACKGROUND

Thrombin activatable fibrinolysis inhibitor (TAFI), encoded by the Carboxypeptidase B2 gene (CPB2), is an inhibitor of fibrinolysis and plays a role in the pathogenesis of venous thrombosis. Experimental findings support a functional role of genetic variants in CPB2, while epidemiological studies have been unable to confirm associations with risk of venous thrombosis. Sex-specific effects could underlie the observed inconsistent associations between CPB2 genetic variants and venous thrombosis.

METHODS

A comprehensive literature search was conducted for associations between Ala147Thr and Thr325Ile variants with venous thrombosis. Authors were contacted to provide sex-specific genotype counts from their studies. Combined and sex-specific random effects meta-analyses were used to estimate a pooled effect estimate for primary and secondary genetic models.

RESULTS

A total of 17 studies met the inclusion criteria. A sex-specific meta-analysis applying a dominant model supported a protective effect of Ala147Thr on venous thrombosis in females (OR = 0.81, 95%CI: 0.68,0.97; p = 0.018), but not in males (OR = 1.06, 95%CI:0.96-1.16; p = 0.263). The Thr325Ile did not show a sex-specific effect but showed variation in allele frequencies by geographic region. A subgroup analysis of studies in European countries showed decreased risk, with a recessive model (OR = 0.83, 95%CI:0.71-0.97, p = 0.021) for venous thrombosis.

CONCLUSIONS

A comprehensive literature review, including unpublished data, provided greater statistical power for the analyses and decreased the likelihood of publication bias influencing the results. Sex-specific analyses explained apparent discrepancies across genetic studies of Ala147Thr and venous thrombosis. While, careful selection of genetic models based on population genetics, evolutionary and biological knowledge can increase power by decreasing the need to adjust for testing multiple models.

Association between thrombin-activatable fibrinolysis inhibitor gene polymorphisms and venous thrombosis risk: a meta-analysis

Thrombin-activatable fibrinolysis inhibitor (TAFI) is an important antifibrinolytic factor that has been shown in increased concentrations to be associated with an increased risk for venous thrombosis. However, the effect of TAFI gene polymorphisms on the risk of venous thrombosis remains debatable. The aim of the current study was to evaluate the association of three single nucleotide polymorphisms: 505G>A (rs3742264), 1040 C>T (rs1926447) and -438G>A (rs2146881) with venous thrombosis risk using a meta-analysis. A systematic literature search for eligible studies published before 20 January 2015 was conducted in PubMed, EMBASE, Web of Science, WanFang database and Chinese National Knowledge Infrastructure. We assessed the possible association by pooled odds ratio and its 95% confidence interval. A total of 14 independent case-control studies including 2970 cases and 3049 controls were enrolled in the final meta-analysis. A significant reduction of venous thrombosis risk in the 505G>A polymorphism was observed under allele comparison, homozygote comparison and recessive models, but opposite results were seen in Asians. Likewise, there was a significant decreased susceptibility to venous thrombosis in the 1040C>T polymorphism in homozygote comparison and recessive models. In the subgroup analysis, the nonvenous thromboembolism disease group showed a significantly increased venous thrombosis risk. Pooled estimates did not show evidence of association between -438G>A and venous thrombosis risk in any genetic model. This meta-analysis suggested that although the -438G>T polymorphism is not correlated with venous thrombosis risk in all models, a trend toward reduced risk still could be observed. The A allele and AA genotype of 505G>A in whites and the TT genotype of 1040C>T were significantly associated with a decreased risk of venous thrombosis, except in the non-venous thromboembolism group.

Impact of genetic polymorphisms in thrombin activatable fibrinolysis inhibitor (TAFI) on venous thrombosis disease: A meta-analysis

BACKGROUND

Reported studies have showed that Thrombin Activatable Fibrinolysis Inhibitor (TAFI) may be associated with an increased risk of venous thromboembolism. But the relation of VT with TAFI gene SNPs could not be clearly demonstrated. Thus, we conducted a meta-analysis to analyze the associations between three TAFI variants -438G/A, 505G/A and 1040C/T and the risk of venous thrombosis.

METHODS

We carried out a systematic search to obtain all the eligible studies published before 30th October 2014. Pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) were computed to assess the association.

RESULTS

13 eligible studies were enrolled including 2321 patients and 2464 controls. There was a significant association between 505G/A and the risk of VTD under all models except recessive model (G vs. A: OR=1.13, 95% CI: 1.02, 1.26; GG vs. AA:OR=1.47, 95% CI: 1.14, 1.88; GA vs. AA: OR=1.36, 95% CI: 1.06, 1.73; GG+GA vs. AA: OR=1.41, 95% CI: 1.12, 1.77). Similarly, obvious relationship was observed in subgroup analyses in light of type of disease and ethnicity. Likewise, for 1040C/T variant, significant associations were identified under homozygote, heterozygote and dominant models (CC vs. TT: OR=1.65, 95% CI: 1.06, 2.59; CT vs. TT: OR=1.55, 95% CI: 1.19, 2.03; CC+CT vs. TT: OR=1.55, 95% CI: 1.20, 2.00). Sub-analysis presented significant associations in non-CVT and non-Asian group under homozygote, heterozygote, and dominant models and CVT group in recessive model.

CONCLUSION

This meta-analysis showed that -438G/A variant was not associated with the incidence of venous thrombosis. But in non-Asian populations, G allele and GG genotype of 505G/A may increase the risk of venous thrombosis diseases. GG genotype of 505G/A and one C carrier (CC and CT) of 1040C/T gave rise to the development of venous thrombosis diseases except CVT. Additionally, the heterozygote CT may be a potential contributing factor of gene effect in venous thrombosis.

Thrombin-activatable fibrinolysis inhibitor Thr325Ile polymorphism and plasma level in breast cancer: A pilot study

This study aimed to investigate thrombin-activatable fibrinolysis inhibitor (TAFI) Thr325Ile polymorphism and TAFI antigen (Ag) levels in breast cancer (BC) in the Egyptian population to clarify their role in relation to BC. A group of 300 females was recruited in this study; of these 150 unrelated patients with different stages of BC and 150 age-matched healthy controls. Plasma TAFI Ag was measured by ELISA and TAFI Thr325Ile (rs1926447) polymorphism was genotyped using TaqMan single nucleotide polymorphism (SNP) genotyping assay. The results showed the genotypes of the minor allele; Thr/Ile (CT) and Ile/Ile (TT) were significantly more frequent in patients compared to control group (50.0% and 22.0% vs. 42.0% and 13.3%, respectively) and were also associated with BC susceptibility [OR = 1.9 and 2.6; 95% CI: (1.1–3.3) and (1.3–5.5), respectively P = 0.01]. Ile325 allele carriers were more frequent in cases than in controls (47.0% vs. 34.0%) [OR = 1.7, (95% CI = 1.2–2.4), P = 0.001]. However, TAFI Thr325Ile polymorphism was not associated with BC stage or other clincopathological characteristics. TAFI Ag levels were correlated with advanced stages of BC, poor prognosis and risk of recurrence (P = 0.02, P = 0.04 and P  < 0.001, respectively) and Thr325Ile SNP was significantly correlated with TAFI antigen levels with the C/C genotype corresponding to the highest and the T/T genotype to the lowest TAFI antigen levels (P < 0.001) in the study groups. In conclusion, this study showed for the first time that TAFI Thr325Ile polymorphism could have a contribution to BC susceptibility in our population. Furthermore, high TAFI plasma levels may serve as a predictor of poor prognosis in patients with BC.

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TAFI Thr325Ile polymorphism associated with breast cancer in studied population

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TAFI Thr325Ile polymorphism was significantly correlated with TAFI antigen levels.

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High TAFI antigen levels were correlated with advanced stages of breast cancer.

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High TAFI plasma level could be used to recognize tumor prognosis and risk of recurrence.

Genetic variations in the thrombin-activatable fibrinolysis inhibitor gene and risk of cardiovascular disease: a systematic review and meta-analysis

BACKGROUND

An imbalance between coagulation and fibrinolytic system plays an important role in the pathogenesis of arterial thrombosis. It has been identified that elevated plasma thrombin-activatable fibrinolysis inhibitor (TAFI) concentration, an anti-fibrinolytic factor, is associated with an increased risk of cardiovascular disease (CVD). But the effect of genetic variations in TAFI gene on the risk of CVD is inconclusive.

OBJECTIVES

To investigate the associations between two variants Ala147Thr(rs3742264) and Thr325Ile(rs1926447) in TAFI and the risk of CVD.

METHODS

Systematic review and meta-analysis of eligible studies published before January 2014. Coronary heart disease(CHD) and stroke are regarded as end-points of CVD.

RESULTS

A total of 18 articles including 23 studies were enrolled. Among these articles were 19 studies of Ala147Thr and 15 of Thr325Ile variants, comprising 4,977 CVD patients and 8,082 controls together with 4,890 cases and 8,311 controls, respectively. There were no significant associations between Ala147Thr variant and CVD under allele, dominant, recessive genetic models. Similar results were observed when end-point, ethnicity, sample size, genotyping method were taken into account. Likewise, meta-analysis of Thr325Ile variant did not show significant associations with CVD under three genetic models. Nevertheless, in sub-analysis based on end-point, the TT(Ile/Ile) genotype was associated with a 25% higher risk of coronary heart disease(CHD) (OR=1.25, 95%CI, 1.02-1.54; P=0.03) compared with TC+CC(Thr/Ile+Thr/Thr) genotype(recessive model).

CONCLUSIONS

The present meta-analysis failed to confirm the influence of Ala147Thr and Thr325Ile variants on the susceptibility to CVD. However, potentially increased risk of CHD was detected in Ile325 allele carriers under recessive model.

Association between polymorphisms in the flanking region of the TAFI gene and atherosclerotic cerebral infarction in a Chinese population

Background

Atherosclerosis is the leading etiologic factor of Atherosclerotic Cerebral Infarction (ACI). Previous studies have shown that thrombin activatable fibrinolysis inhibitor (TAFI) may play an important role in the occurrence of acute cerebral infarction, and the levels of TAFI are affected by several single nucleotide polymorphisms (SNPs) located in the regulatory and coding regions of the gene encoding TAFI. The present study aimed to determine whether polymorphisms (TAFI –2345 2G/1G, –1690 A/G, –438 A/G, +1583 A/T) of the TAFI gene were associated with ACI in a Han Chinese population.

Methods

The variant genotypes were identified by restriction fragment length polymorphism (RFLP) and allele-specific polymerase chain reactions (AS-PCR) in 225 patients with ACI and 184 age-matched healthy individuals.

Results

There was a significant difference in the genotype and allele frequencies of TAFI –2345 2G/1G and −1690 A/G polymorphisms between the ACI and control subjects. Further stratification analysis by gender revealed that the presence of the –438 AA genotype and the A allele conferred a higher risk of developing ACI in male patients (p < 0.05). Haplotype analysis demonstrated that four haplotypes of TAFI are significantly associated with ACI.

Conclusions

Our study provides preliminary evidence that the TAFI –2345 2G/1G and –1690 A/G polymorphisms are associated with ACI susceptibility in a Han Chinese population.

Resequencing and fine-mapping of the chromosome 12q13-14 locus associated with multiple sclerosis refines the number of implicated genes

Multiple sclerosis (MS) is a common chronic inflammatory disease of the central nervous system. Susceptibility to the disease is affected by both environmental and genetic factors. Genetic factors include haplotypes in the histocompatibility complex (MHC) and over 50 non-MHC loci reported by genome-wide association studies. Amongst these, we previously reported polymorphisms in chromosome 12q13-14 with a protective effect in individuals of European descent. This locus spans 288 kb and contains 17 genes, including several candidate genes which have potentially significant pathogenic and therapeutic implications. In this study, we aimed to fine-map this locus. We have implemented a two-phase study: a variant discovery phase where we have used next-generation sequencing and two target-enrichment strategies [long-range polymerase chain reaction (PCR) and Nimblegen's solution phase hybridization capture] in pools of 25 samples; and a genotyping phase where we genotyped 712 variants in 3577 healthy controls and 3269 MS patients. This study confirmed the association (rs2069502, P = 9.9 × 10(-11), OR = 0.787) and narrowed down the locus of association to an 86.5 kb region. Although the study was unable to pinpoint the key-associated variant, we have identified a 42 (genotyped and imputed) single-nucleotide polymorphism haplotype block likely to harbour the causal variant. No evidence of association at previously reported low-frequency variants in CYP27B1 was observed. As part of the study we compared variant discovery performance using two target-enrichment strategies. We concluded that our pools enriched with Nimblegen's solution phase hybridization capture had better sensitivity to detect true variants than the pools enriched with long-range PCR, whilst specificity was better in the long-range PCR-enriched pools compared with solution phase hybridization capture enriched pools; this result has important implications for the design of future fine-mapping studies.

Genome-wide haplotype analysis of cis expression quantitative trait loci in monocytes

In order to assess whether gene expression variability could be influenced by several SNPs acting in cis, either through additive or more complex haplotype effects, a systematic genome-wide search for cis haplotype expression quantitative trait loci (eQTL) was conducted in a sample of 758 individuals, part of the Cardiogenics Transcriptomic Study, for which genome-wide monocyte expression and GWAS data were available. 19,805 RNA probes were assessed for cis haplotypic regulation through investigation of ~2,1 × 10(9) haplotypic combinations. 2,650 probes demonstrated haplotypic p-values >10(4)-fold smaller than the best single SNP p-value. Replication of significant haplotype effects were tested for 412 probes for which SNPs (or proxies) that defined the detected haplotypes were available in the Gutenberg Health Study composed of 1,374 individuals. At the Bonferroni correction level of 1.2 × 10(-4) (~0.05/412), 193 haplotypic signals replicated. 1000 G imputation was then conducted, and 105 haplotypic signals still remained more informative than imputed SNPs. In-depth analysis of these 105 cis eQTL revealed that at 76 loci genetic associations were compatible with additive effects of several SNPs, while for the 29 remaining regions data could be compatible with a more complex haplotypic pattern. As 24 of the 105 cis eQTL have previously been reported to be disease-associated loci, this work highlights the need for conducting haplotype-based and 1000 G imputed cis eQTL analysis before commencing functional studies at disease-associated loci.

Genetic variation in thrombin-activatable fibrinolysis inhibitor is associated with the risk of diabetic nephropathy

Diabetic nephropathy is a kidney disease or damage that results as a complication of diabetes, especially Type 2 diabetes, while albuminuria is an early marker for diabetic nephropathy as it can predict cardiovascular events and mortality in diabetic patients. A potent inhibitor of fibrinolysis, the thrombin-activatable fibrinolysis inhibitor (TAFI) has been isolated and characterized from human plasma. We investigated the associations of the activity-related variants in the TAFI coding gene (505A/G,1040C/T) with the risk of diabetic nephropathy by examining 297samples including 140 health controls and 157 confirmed diabetic nephropathy patients. Diabetic nephropathy grades were further categorized by the urine albumin excretion (UAE)-to-creatinine ratios (ACR). We found little difference that was statistically significant in terms of 505A/G among patients and controls. While at 1040C/T, the detected frequency for the T allele in the group of diabetic nephropathy patients was significantly smaller than that of the control group (15.6% vs 25.7%, respectively; p<0.05). This was due to the relative decrease of T/T homozygotes in the patients (p<0.05, 95% odds ratio 0.28, confidence interval 0.11-0.70). Surprisingly, the difference was only observed with initial diabetic nephropathy stages. This study clearly indicates that, at 1040C/T, the frequency for the T allele is strongly associated with increased risk for diabetic nephropathy in a subset of the general population, implying that the T allele confers protection against the onset of diabetic nephropathy only in homozygosity and may function as a recessive trait.

Identification of tristetraprolin as a factor that modulates the stability of the TAFI transcript through binding to the 3'-untranslated region

BACKGROUND

Thrombin-activatable fibrinolysis inhibitor (TAFI) is a basic carboxypeptidase zymogen encoded by the human gene CPB2. TAFI constitutes a molecular link between coagulation and fibrinolysis, and between coagulation and inflammation. The 3'-untranslated region (UTR) of the human CPB2 mRNA plays a key role in regulating CPB2 mRNA abundance, but the exact mechanisms that mediate this regulation are largely unexplored.

OBJECTIVES

To pinpoint cis-acting elements in the CPB2 3'-UTR that act as stability determinants and to identify protein factors binding to these sites.

METHODS

We constructed a series of plasmids encoding mRNAs containing rabbit β-globin sequences (as a reporter) fused to sequences of the CPB2 3'-UTR (encompassing 5' and internal deletions). These plasmids were transfected into HepG2 (human hepatoma) cells and the stability of the fusion transcripts measured. We performed a series of gel mobility shift analyses using RNA probes encompassing putative (in)stability elements.

RESULTS

We identified one element conferring stability and three elements conferring instability. Supershift assays identified the protein bound to the site between the second and third polyadenylation sites as tristetraprolin (TTP). Mutation of the TTP site abolished TTP binding in gel mobility shift assays and also stabilized β-globin/CPB2 fusion transcripts. TTP knockdown stabilized the fusion transcript containing the TTP site, but not a fusion transcript in which this site was mutated.

CONCLUSIONS

Our findings are indicative of a role for TTP in constitutive, and perhaps regulated, control of CPB2 mRNA stability and hence abundance.

Finding genes and variants for lipid levels after genome-wide association analysis

PURPOSE OF REVIEW

We review the main findings from genome-wide association studies (GWAS) for levels of HDL-cholesterol, LDL-cholesterol and triglycerides, including approaches to identify the functional variant(s) or gene(s). We discuss study design and challenges related to whole genome or exome sequencing to identify novel genes and variants.

RECENT FINDINGS

GWAS have detected approximately 100 loci associated with one or more lipid trait. Fine mapping of several loci for LDL-cholesterol demonstrated that the trait variance explained may double when the functional variants responsible for the association signals are identified. Experimental follow-up of three loci identified by GWAS has identified functional genes GALNT2, TRIB1, and SORT1, and a functional variant at SORT1.

SUMMARY

The goal of genetic studies for lipid levels is to improve treatment and ultimately reduce the prevalence of heart disease. Many signals identified by GWAS have modest effect sizes, useful for identifying novel biologically relevant genes, but less useful for personalized medicine. Whole genome or exome sequencing studies may fill this gap by identifying rare variants of larger effect associated with lipid levels and heart disease.

Genome scan of clot lysis time and its association with thrombosis in a protein C-deficient kindred

BACKGROUND

 Previously, we found increased clot-lysis time (CLT), as measured with a plasma-based assay, to increase the risk of venous thrombosis in two population-based case-control studies. The genes influencing CLT are as yet unknown.

PATIENTS/METHODS

 We tested CLT as risk factor for venous thrombosis in Kindred Vermont II (n = 346), a pedigree suffering from a high thrombosis risk, partially attributable to a type I protein C deficiency. Furthermore, we tested for quantitative trait loci (QTLs) for CLT, using variance component linkage analysis.

RESULTS

 Protein C-deficient family members had shorter CLTs than non-deficient members (median CLT 67 min vs. 75 min). One standard deviation increase in CLT increased the risk of venous thrombosis 2.4-fold in non-deficient family members. Protein C deficiency without elevated CLT increased the risk 6.9-fold. Combining both risk factors yielded a 27.8-fold increased risk. The heritability of CLT was 42-52%. We found suggestive evidence of linkage on chromosome 11 (62 cM), partly explained by the prothrombin 20210A mutation, and on chromosome 13 (52 cM). Thrombin-activatable fibrinolysis inhibitor genotypes did not explain the variation in CLT.

CONCLUSION

Hypofibrinolysis appears to increase thrombosis risk in this family, especially in combination with protein C deficiency. Protein C deficiency is associated with short CLT. CLT is partly genetically regulated. Suggestive QTLs were found on chromosomes 11 and 13.

Association between genotype and plasma levels of thrombin-activated fibrinolysis inhibitor (TAFI) in the development of preeclampsia

INTRODUCTION

The objective was to evaluate if thrombin-activated fibrinolysis inhibitor (TAFI) polymorphisms (G505A, C1040T, and G-438A), and TAFIa plasma levels are associated with preeclampsia.

MATERIALS AND METHODS

In a case-control study design, we evaluated preeclampsia patients and women with uncomplicated pregnancies. The TAFI polymorphisms were determined by real-time PCR method, and TAFIa plasma levels were established with a chromogenic assay.

RESULTS

We included 87 women in each group. The TAFIa levels in the preeclampsia group were 20.4 μg/mL (CI 95% 17.3-23.5), while in the control group, they were significantly lower: 13.3 μg/mL (12.0-14.5, p 0.003). There were no differences in the genotype distribution or allelic frequency of TAFI polymorphisms between the two groups. In preeclampsia patients and controls heterozygous for the G505A polymorphism, the TAFIa values were 22.8 (16.7-28.9 μg/mL) and 13.2 (11.3-15.0 μg/mL, p 0.019), respectively. In G505A homozygous polymorphism the TAFIa values were 25.7 (18.7-32.6 μg/mL) and 13.5 (1.6-21.9 μg/mL, p 0.041), respectively. In the C1040T and G-438A TAFI wild type polymorphisms, the TAFIa values were 18.3 (12.5-23.9 μg/mL) and 11.5 (9.9-35.0, p 0.033), and 19.4 (10.9-27.9 μg/mL) and 12.5 (10.8-14.2 μg/mL, p 0.006), respectively, without differences in other genotypes.

CONCLUSIONS

Preeclampsia by itself may be responsible for the increase in TAFIa values rather than the presence of polymorphisms.

Thrombin activatable fibrinolysis inhibitor

Thrombin activatable fibrinolysis inhibitor (TAFI) was discovered two decades ago as a consequence of the identification of an unstable carboxypeptidase (CPU), which was formed upon thrombin activation of the respective pro-enzyme (proCPU). The antifibrinolytic function of the activated form (TAFIa, CPU) is directly linked to its capacity to remove C-terminal lysines from the surface of the fibrin clot. No endogenous inhibitors have been identified, but TAFIa activity is regulated by its intrinsic temperature-dependent instability with a half-life of 8 to 15 min at 37 °C. A variety of studies have demonstrated a role for TAFI/TAFIa in venous and arterial diseases. In addition, a role in inflammation and cell migration has been shown. Since an elevated level of TAFIa it is a potential risk factor for thrombotic disorders, many inhibitors, both at the level of activation or at the level of activity, have been developed and were proven to exhibit a profibrinolytic effect in animal models. Pharmacologically active inhibitors of the TAFI/TAFIa system may open new ways for the prevention of thrombotic diseases or for the establishment of adjunctive treatments during thrombolytic therapy.

Childhood maltreatment, the corticotropin-releasing hormone receptor gene and adult depression in the general population

Dysregulations of the hypothalamic-pituitary-adrenal (HPA) axis have been implicated in the pathogenesis of depressive disorders and the corticotropin-releasing hormone (CRH) was found to modulate emotional memory consolidation. Recently, two studies have reported an interaction between childhood abuse and the TAT-haplotype of the CRH-Receptor Gene (CRHR1) connecting childhood adversities and genetic susceptibility to adult depression. We tested the hypothesis of an interaction of childhood maltreatment with single nucleotide polymorphisms (SNPs) and haplotypes of the CRHR1 gene not previously investigated. Caucasian subjects (n = 1,638) from the German general population (Study of Health in Pomerania, SHIP) were analyzed. As in the previous studies, childhood abuse and neglect were assessed with the Childhood Trauma Questionnaire (CTQ) and depression with the Beck Depression Inventory (BDI-2). The CRHR1-SNPs were genotyped on the Affymetrix Genome-Wide Human SNP Array 6.0 platform. We identified an interaction between the TAT-haplotype and childhood physical neglect. The interaction with physical neglect showed significant (P < 0.05) results in 23 of the 28 SNPs, with rs17689882 (P = 0.0013) reaching "gene-wide" significance. Although we did not replicate the specific interaction of abuse and the TAT-haplotype of the CRHR1 gene we confirmed the relevance of an interplay between variants within the CRHR1 gene and childhood adversities in the modulation of depression in adults. The largest effect was found for rs17689882, a SNP previously not analyzed. Relevant sample differences between this and prior studies like lower BDI-2 scores, less childhood maltreatment and higher psychosocial functioning may account for the differences in gene-environment interaction findings. © 2010 Wiley-Liss, Inc.

On the use of phylogeny-based tests to detect association between quantitative traits and haplotypes

With the increasing availability of genetic data, several SNPs in a candidate gene can be combined into haplotypes to test for association with a quantitative trait. When the number of SNPs increases, the number of haplotypes can become very large and there is a need to group them together. The use of the phylogenetic relationships between haplotypes provides a natural and efficient way of grouping. Moreover, it allows us to identify disease or quantitative trait-related loci. In this article, we describe ALTree-q, a phylogeny-based approach to test for association between quantitative traits and haplotypes and to identify putative quantitative trait nucleotides (QTN). This study focuses on ALTree-q association test which is based on one-way analyses of variance (ANOVA) performed at the different levels of the tree. The statistical properties (type-one error and power rates) were estimated through simulations under different genetic models and were compared to another phylogeny-based test, TreeScan, (Templeton, 2005) and to a haplotypic omnibus test consisting in a one-way ANOVA between all haplotypes. For dominant and additive models ALTree-q is usually the most powerful test whereas TreeScan performs better under a recessive model. However, power depends strongly on the recurrence rate of the QTN, on the QTN allele frequency, and on the linkage disequilibrium between the QTN and other markers. An application of the method on Thrombin Activatable Fibronolysis Inhibitor Antigen levels in European and African samples confirms a possible association with polymorphisms of the CPB2 gene and identifies several QTNs.

The role of thrombin activatable fibrinolysis inhibitor in arterial thrombosis at a young age: the ATTAC study

BACKGROUND AND OBJECTIVES

Thrombin activatable fibrinolysis inhibitor (TAFI) attenuates fibrinolysis and may therefore contribute to the pathophysiology of arterial thrombosis. The aim of the present study was to elucidate the pathogenetic role of TAFI levels and genotypes in young patients with arterial thrombosis.

PATIENTS AND METHODS

In a case-control study, 327 young patients with a recent first-ever event of coronary heart disease (CHD subgroup) or cerebrovascular disease (ischemic stroke subgroup) and 332 healthy young controls were included. TAFI levels [intact TAFI, activation peptide (TAFI-AP) and (in)activated TAFI (TAFIa(i)] and TAFI activity were measured and genetic variations in the TAFI gene (-438G/A, 505G/A and 1040C/T) were determined.

RESULTS

In the total group of patients, TAFIa(i) levels were higher (145.1 +/- 37.5%) than in controls (137.5 +/- 31.3%, P = 0.02). Plasma levels of intact TAFI, TAFI-AP and TAFI activity were similar in patients and controls. In the CHD subgroup (n = 218), intact TAFI levels were higher (109.4 +/- 23.0%) than in controls (102.8 +/- 20.7%, P = 0.02). In 325Ile/Ile homozygotes, lower TAFI levels and a decreased risk of arterial thrombosis were observed (OR 0.58, 95% CI 0.34-0.99) compared with patients with the common 325Thr/Thr genotype. This association was most evident in CHD patients (OR 0.48, 95% CI 0.26-0.90). Haplotype analyses supported a role for the Thr325Ile polymorphism.

CONCLUSIONS

TAFIa(i) levels were higher in patients with cardiovascular disease. Furthermore, the TAFI 325Thr/Ile polymorphism was associated with lower TAFI levels and with the risk of cardiovascular disease in young patients, especially in CHD.

Low thrombin activatable fibrinolysis inhibitor activity levels are associated with an increased risk of a first myocardial infarction in men

BACKGROUND

Studies on the relation between thrombin activatable fibrinolysis inhibitor (TAFI) and arterial thrombosis have produced conflicting results. TAFI regulates fibrinolysis, but other roles of this inhibitor, including anti-inflammatory properties, have also been demonstrated.

DESIGN AND METHODS

We investigated the association between TAFI activity and the risk of myocardial infarction. Additionally, we studied the association of common single nucleotide polymorphisms in the TAFI gene with levels of the TAFI protein and risk of myocardial infarction.We included 554 men under 70 years old with a first myocardial infarction and 643 controls participating in the Study of Myocardial Infarctions Leiden (SMILE), a case-control study.

RESULTS

We found odds ratios (95% confidence intervals) of a first myocardial infarction of 2.4 (1.6-3.6), 3.2 (2.1-4.7) and 3.4 (2.3-5.1) for subjects whose TAFI levels were in the third, second and first quartiles (lowest TAFI levels), respectively, compared with the fourth quartile, after adjusting for arterial disease risk factors. The rare -438A and 1040T alleles were associated with lower, and the rare 505G allele with higher TAFI levels than the common alleles. Carriers of the -438A allele had an increased risk of myocardial infarction (odds ratio 1.6 (1.0-2.5) for AA; odds ratio 1.2 (0.9-1.5) for AG compared with GG). The other single nucleotide polymorphisms were not associated with myocardial infarction.

CONCLUSIONS

Low TAFI activity levels are associated with increased risk of a first myocardial infarction in men. The results on the association between TAFI single nucleotide polymorphisms and myocardial infarction were inconsistent.

Thrombin activatable fibrinolysis inhibitor gene polymorphisms are associated with antigenic levels in the Asian-Indian population but may not be a risk for stroke

Thrombin activatable fibrinolysis inhibitor [carboxypeptidase B2 (plasma), CPB2] is a basic carboxypeptidase, which inhibits fibrinolysis by cleaving the C-terminal lysine residues on plasmin-modified partially degraded fibrin. Plasma CPB2 concentrations have been reported to be under the control of numerous single nucleotide polymorphisms located in the regulatory and coding regions of the gene encoding CPB2 (CPB2). High functional CPB2 levels have been found to be associated with an increased risk for ischemic stroke. The present study investigated CPB2 antigen levels and associated CPB2 polymorphisms in an acute onset non-cardioembolic stroke population compared with an age- and sex-matched healthy control population. This is, to the best of our knowledge, the first such study done in an Asian Indian population. CPB2 antigen levels were significantly associated with the disease phenotype (P < 0.001) and with CPB2 polymorphisms (P < 0.001). The haplotypes generated on analysis of the genotypic data accounted for 21% of the natural variation in the CPB2 antigenic levels. However none of the haplotype combinations generated showed any association with disease phenotype and therefore could not explain for the difference in CPB2 antigen levels between cases and controls.

Activated thrombin activatable fibrinolysis inhibitor levels are associated with the risk of cardiovascular death in patients with coronary artery disease: the AtheroGene study

BACKGROUND

Thrombin activatable fibrinolysis inhibitor (TAFI) attenuates fibrinolysis. Results on the association between TAFI levels and the risk of coronary artery disease (CAD) are inconsistent.

OBJECTIVES

We investigated the association between TAFI levels and the risk of cardiovascular events in CAD.

PATIENTS/METHODS

1668 individuals with angiographically proven CAD at baseline were followed for a median of 2.3 years, as part of the prospective AtheroGene cohort. Fifty-six deaths from cardiovascular (CV) causes and 35 non-fatal CV events were observed.

RESULTS

At baseline, three TAFI measurements were available: one evaluating the total amount of TAFI (t-TAFI), one measuring the TAFIa/TAFIai amount, and the last the released activated peptide (TAFI-AP). TAFIa/TAFIai levels were associated with increased risk of CV death [hazard ratio (HR) for one tertile increase, 2.38 (1.56-3.63); P < 10(-4)]. This association remained significant after adjustment for conventional risk factors, CRP levels, white blood count and markers of thrombin generation and fibrinolysis [HR = 1.69 (1.07-2.67); P = 0.01]. In addition, CPB2 gene polymorphisms explained 12%, 6%, and 3% of t-TAFI, TAFIa/TAFIai and TAFI-AP levels, respectively, but none was associated with CV events.

CONCLUSIONS

The amount of activated TAFI, measured by TAFIa/TAFIai ELISA, but not of the t-TAFI is independently associated with the risk of CV death.

Assessment of fibrinolytic activity by measuring the lysis time of a tissue-factor-induced clot: a feasibility evaluation

A clot lysis time assay in which a tissue factor-induced fibrin clot is lysed by exogenously added tissue plasminogen activator has been recently reported. We evaluated the feasibility of clot lysis time in a routine hemostasis laboratory, and its correlation with thrombin activatable fibrinolysis inhibitor and plasminogen activator inhibitor-1 levels and changes with aging in 185 healthy participants. Clot lysis time was assessed by monitoring changes in turbidity during clot formation and subsequent lysis using a computerized kinetic spectrophotometric microtiter plate. After preliminary experiments, 100 and 160 ng/mL tissue plasminogen activator concentrations were chosen for the study. Clot lysis time was calculated by a new mathematical analysis of the lysis curve based on discrete derivative. Clot lysis time, thrombin activatable fibrinolysis inhibitor, and plasminogen activator inhibitor-1 plasma levels showed a normal distribution. For both concentrations of tissue plasminogen activator, clot lysis time progressively increased with increase in age (P < .0001) and was significantly correlated with thrombin activatable fibrinolysis inhibitor antigen, thrombin activatable fibrinolysis inhibitor activity, and plasminogen activator inhibitor-1 antigen (at least P < .01). During linear regression analysis, thrombin activatable fibrinolysis inhibitor and plasminogen activator inhibitor-1 antigen were found to significantly influence clot lysis time (at least P < .01). Clot lysis time determination has a good laboratory performance. Our new method of calculation is independent of the time of reading and allows a more accurate and consistent detection of both short and prolonged lysis times. Our data suggest the feasibility of the use of this test in the work of routine hemostasis laboratory.

TAFI antigen level variability in young healthy Asian Indians; first report from Asia

Thrombin Activatable Fibrinolytic Inhibitor (TAFI) is a plasma protein, which inhibits fibrinolysis by removing carboxyterminal lysine residues from partially degraded fibrin thereby decreasing plasminogen binding on its surface. In this study we have investigated the antigenic level variability (Inter and Intraindividual) of Thrombin Activatable Fibrinolysis Inhibitor in 120 healthy Asian Indians since no data on this is available regarding this population. TAFI antigen levels did not show a normal distribution in our population (p<0.001). Median TAFI antigen levels were found to be 11.683 microg/ml. It ranged from 33.9-202.5%of normal pool plasma (3.9-23.5 microg/ml). TAFI antigenic level showed high level of variability in the Indian population (coefficient of variation: 37.4%). TAFI antigenic levels were stable intraindividually (p=0.218).

Common variants in the GDF5-UQCC region are associated with variation in human height

Identifying genetic variants that influence human height will advance our understanding of skeletal growth and development. Several rare genetic variants have been convincingly and reproducibly associated with height in mendelian syndromes, and common variants in the transcription factor gene HMGA2 are associated with variation in height in the general population. Here we report genome-wide association analyses, using genotyped and imputed markers, of 6,669 individuals from Finland and Sardinia, and follow-up analyses in an additional 28,801 individuals. We show that common variants in the osteoarthritis-associated locus GDF5-UQCC contribute to variation in height with an estimated additive effect of 0.44 cm (overall P < 10(-15)). Our results indicate that there may be a link between the genetic basis of height and osteoarthritis, potentially mediated through alterations in bone growth and development.

The 1040C/T polymorphism influencing thermal stability and activity of thrombin activatable fibrinolysis inhibitor is associated with risk for oral cancer

No studies thus far have investigated the contribution of thrombin activatable fibrinolysis inhibitor (TAFI) to oral oncogenesis. We studied the activity-related 1040C/T polymorphism in 150 patients with oral cancer and 138 healthy controls matched by age, gender, and ethnicity. The increased-activity T allele frequency was significantly reduced in patients compared with controls (28.7% vs. 37.0%, P < 0.05). T/T homozygotes had about half the probability of developing oral cancer (O.R. 0.39, 95%C.I. 0.13-1.14), while no significant difference was observed in C/T heterozygotes. The observed prophylactic effect of increased TAFI activity might result from reduction of plasmin and inhibition of extracellular matrix dissolution.

Effect of single nucleotide polymorphisms on expression of the gene encoding thrombin-activatable fibrinolysis inhibitor: a functional analysis

Thrombin-activable fibrinolysis inhibitor (TAFI) is a plasma zymogen that acts as a molecular link between coagulation and fibrinolysis. Numerous single nucleotide polymorphisms (SNPs) have been identified in CPB2, the gene encoding TAFI, and are located in the 5'-flanking region, in the coding sequences, and in the 3'-untranslated region (UTR) of the CPB2 mRNA transcript. Associations between CPB2 SNPs and variation in plasma TAFI antigen concentrations have been described, but the identity of SNPs that are causally linked to this variation is not known. In the current study, we investigated the effect of the SNPs in the 5'-flanking region on CPB2 promoter activity and SNPs in the 3'-UTR on CPB2 mRNA stability. Whereas the 5'-flanking region SNPs (with 2 exceptions) did not have a significant effect on promoter activity, either alone or in haplotypic combinations seen in the human population, all of the 3'-UTR SNPs substantially affected mRNA stability. We speculate that these SNPs, in part, contribute to variation in plasma TAFI concentrations via modulation of CPB2 gene expression through an effect on mRNA stability.

Plasma coagulation factor levels in venous thrombosis

High plasma levels of several coagulation factors have been described to be associated with an increased risk of venous thrombosis. However, the mechanisms underlying these associations, as well as those involved in the regulation of plasma levels of coagulation factors, are mostly unknown. Whether these factors should be included in the workup of patients with venous thrombosis remains to be determined. In this review, we discuss the present knowledge on the effects of plasma levels of coagulation factors on the development of venous thrombosis. Furthermore, we review recent findings and ideas on the mechanisms through which elevated plasma coagulation factor levels may influence thrombosis. Finally, we enter into the matter of the possible determinants of elevated plasma levels of coagulation factors.

A new JAVA interface implementation of THESIAS: testing haplotype effects in association studies

THESIAS (Testing Haplotype EffectS In Association Studies) is a popular software for carrying haplotype association analysis in unrelated individuals. In addition to the command line interface, a graphical JAVA interface is now proposed allowing one to run THESIAS in a user-friendly manner. Besides, new functionalities have been added to THESIAS including the possibility to analyze polychotomous phenotype and X-linked polymorphisms.

AVAILABILITY

The software package including documentation and example data files is freely available at http://genecanvas.ecgene.net. The source codes are also available upon request.

Thrombin activatable fibrinolysis inhibitor activation peptide shows association with all major subtypes of ischemic stroke and with TAFI gene variation

OBJECTIVE

Thrombin activatable fibrinolysis inhibitor (TAFI) attenuates fibrinolysis. The aim of the present study was to investigate the possible association between TAFI and overall ischemic stroke and ischemic stroke subtypes.

METHODS AND RESULTS

The Sahlgrenska Academy Study on Ischemic Stroke (SAHLSIS) comprises 600 cases (18 to 69 years) and 600 matched population controls. Stroke subtype was defined by the Trial of Org 10172 in Acute Stroke Treatment (TOAST) classification. TAFI was investigated at the protein level, by analyzing plasma levels of intact TAFI and released activation peptide [AP], and at the genetic level, by genotyping a selection of eleven single nucleotide polymorphisms. After adjustment for traditional risk factors, both TAFI measurements showed association with overall ischemic stroke (AP: odds ratio, 2.22; 95% confidence interval, 1.89 to 2.61; intact TAFI: odds ratio, 1.21; 95% confidence interval, 1.06 to 1.38; for 1-SD increase in AP and intact TAFI, respectively). AP showed associations with all 4 major subtypes of ischemic stroke and intact TAFI to large vessel disease and cryptogenic stroke. TAFI genotypes and haplotypes showed significant associations with both TAFI measurements. In contrast, no association was observed between genetic variants and overall ischemic stroke.

CONCLUSION

TAFI levels show independent association with overall ischemic stroke. This association is stronger for released AP than for intact TAFI, and for released AP, it is present in all ischemic stroke subtypes.

Curiouser and curiouser: recent advances in measurement of thrombin-activatable fibrinolysis inhibitor (TAFI) and in understanding its molecular genetics, gene regulation, and biological roles

The thrombin-activatable fibrinolysis inhibitor (TAFI) pathway defines a novel molecular connection between blood coagulation and both fibrinolysis and inflammation. TAFI is a plasma zymogen that can be activated by thrombin, the thrombin-thrombomodulin complex, or plasmin. The activated form of TAFI (TAFIa) attenuates fibrinolysis by removing the carboxyl-terminal lysine residues from partially degraded fibrin that mediate positive feedback in the fibrinolytic cascade. A role for TAFIa in modulating inflammation is suggested by the ability of this enzyme to down-regulate pericellular plasminogen activation and to inactivate the inflammatory peptides bradykinin and the anaphylatoxins C3a and C5a. The focus of this review is on recent advances in the clinical measurement of the TAFI pathway in human subjects and what this has revealed in terms of the molecular genetics of TAFI, the biological variation in plasma TAFI antigen levels, potential regulators of expression of the gene encoding TAFI, and the TAFI pathway as a risk factor for the development of vascular diseases. Although this field is in its infancy, much recent progress has been made and the available data suggest that the TAFI pathway is an intriguing new player in a variety of physiological and pathophysiological contexts.