Genetics of hemostasis: differential effects of heritability and household components influencing lipid concentrations and clotting factor levels in 282 pediatric stroke families

Quantile-specific heritability of plasma fibrinogen concentrations

Background

Fibrinogen is a moderately heritable blood protein showing different genetic effects by sex, race, smoking status, pollution exposure, and disease status. These interactions may be explained in part by “quantile-dependent expressivity”, where the effect size of a genetic variant depends upon whether the phenotype (e.g. plasma fibrinogen concentration) is high or low relative to its distribution.

Purpose

Determine whether fibrinogen heritability (h²) is quantile-specific, and whether quantile-specific h² could account for fibrinogen gene-environment interactions.

Methods

Plasma fibrinogen concentrations from 5689 offspring-parent pairs and 1932 sibships from the Framingham Heart Study were analyzed. Quantile-specific heritability from offspring-parent (β_OP, h² = 2β_OP/(1+r_spouse)) and full-sib regression slopes (β_FS, h² = {(1+8r_spouseβ_FS)^0.05–1}/(2r_spouse)) were robustly estimated by quantile regression with nonparametric significance assigned from 1000 bootstrap samples.

Results

Quantile-specific h² (±SE) increased with increasing percentiles of the offspring’s age- and sex-adjusted fibrinogen distribution when estimated from β_OP (P_trend = 5.5x10^-6): 0.30±0.05 at the 10^th, 0.37±0.04 at the 25^th, 0.48±0.05 at the 50^th, 0.61±0.06 at the 75^th, and 0.65±0.08 at the 90^th percentile, and when estimated from β_FS (P_trend = 0.008): 0.28±0.04 at the 10^th, 0.31±0.04 at the 25^th, 0.36±0.03 at the 50^th, 0.41±0.05 at the 75^th, and 0.50±0.06 at the 90^th percentile. The larger genetic effect at higher average fibrinogen concentrations may contribute to fibrinogen’s greater heritability in women than men and in Blacks than Whites, and greater increase from smoking and air pollution for the FGB -455G>A A-allele. It may also explain greater fibrinogen differences between: 1) FGB -455G>A genotypes during acute phase reactions than usual conditions, 2) GTSM1 and IL-6 -572C>G genotypes in smokers than nonsmokers, 3) FGB -148C>T genotypes in untreated than treated diabetics, and LPL PvuII genotypes in macroalbuminuric than normoalbuminuric patients.

Conclusion

Fibrinogen heritability is quantile specific, which may explain or contribute to its gene-environment interactions. The analyses do not disprove the traditional gene-environment interpretations of these examples, rather quantile-dependent expressivity provides an alternative explanation that warrants consideration.

Whole-Genome Approach Discovers Novel Genetic and Nongenetic Variance Components Modulated by Lifestyle for Cardiovascular Health

Background

Both genetic and nongenetic factors can predispose individuals to cardiovascular risk. Finding ways to alter these predispositions is important for cardiovascular disease prevention.

Methods and Results

We used a novel whole‐genome approach to estimate the genetic and nongenetic effects on—and hence their predispositions to—cardiovascular risk and determined whether they vary with respect to lifestyle factors such as physical activity, smoking, alcohol consumption, and dietary intake. We performed analyses on the ARIC (Atherosclerosis Risk in Communities) Study (N=6896–7180) and validated findings using the UKBB (UK Biobank, N=14 076–34 538). Lifestyle modulation was evident for many cardiovascular traits such as body mass index and resting heart rate. For example, alcohol consumption modulated both genetic and nongenetic effects on body mass index, whereas smoking modulated nongenetic effects on heart rate, pulse pressure, and white blood cell count. We also stratified individuals according to estimated genetic and nongenetic effects that are modulated by lifestyle factors and showed distinct phenotype–lifestyle relationships across the stratified groups. Finally, we showed that neglecting lifestyle modulations of cardiovascular traits would on average reduce single nucleotide polymorphism heritability estimates of these traits by a small yet significant amount, primarily owing to the overestimation of residual variance.

Conclusions

Lifestyle changes are relevant to cardiovascular disease prevention. Individual differences in the genetic and nongenetic effects that are modulated by lifestyle factors, as shown by the stratified group analyses, implies a need for personalized lifestyle interventions. In addition, single nucleotide polymorphism–based heritability of cardiovascular traits without accounting for lifestyle modulations could be underestimated.

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

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

Fibrinogen alpha and beta gene polymorphisms in pediatric stroke--case-control and family based study

BACKGROUND/PURPOSE

Data on the role of the -455G > A polymorphism of the gene encoding β fibrinogen subunit (FGB) and the Thr312Ala polymorphism of the gene for the α fibrinogen subunit (FGA) in childhood ischemic stroke are insufficient. Therefore the aim of the study was to evaluate a possible association between these two polymorphisms and arterial ischemic stroke.

METHODS

The study group consisted of 85 children after ischemic stroke, 146 of their parents and 159 controls. Both polymorphisms were genotyped using the restriction fragment length polymorphism method. Two study designs were used: a case-control model and a family-based transmission-disequilibrium test. Statistica 7.1 and EpiInfo 6 softwares were used in all analyses.

RESULTS

In the TDT test, a tendency to a higher transmission of the 312Ala allele of the FGA gene and the -455A allele of the FGB gene was observed, however, it was statistically non-significant. The frequencies of alleles and genotypes of both FGA and FGB genes polymorphisms did not differentiate children from both groups also in the case-control model. Additive or synergistic effects between FGA and FGB genes polymorphisms were not observed.

CONCLUSION

An analysis of the results obtained in this study and a critical review of previously published data indicate that examined gene polymorphisms are not related to ischemic stroke in children.

The role of biochemical risk factors in the etiology of AIS in children and adults

Stroke is an abrupt onset of both focal and global neurological deficits secondary to a vascular event lasting more than 24 h and with a vascular background as its only cause. It can be triggered by a rupture of a blood vessel, aneurysm (hemorrhagic stroke, HS), thrombosis or embolisms (ischemic stroke, IS). In developed countries, it is the third most common cause of death in the adult population. Stroke in children is a rare disorder with a reported frequency of about 3 cases per 100,000 children per year. The history of acute brain ischemia is burdened with neurological complications such as motor impairment, speech impairment and intellectual delay. Moreover, in children after AIS seizures and epilepsy are also quite common. Stroke is a heterogeneous disorder; its risk factors in adults are well known, however, in pediatrics, in more than 20% cases, the cause of stroke is impossible to determine. Due to the fact that stroke usually arises as a consequence of the cerebral thrombosis, many of the mechanisms responsible for its occurrence can be considered as risk factors. We have reviewed the recent case-control studies conducted on pediatric patients regarding biochemical risk factors such as elevated levels of homocysteine, fibrinogen, protein C, protein S, antithrombin III, lipoprotein(a), cholesterol and its fractions, and compared them with the results obtained from adult patients.

Genetic variants in PLG, LPA, and SIGLEC 14 as well as smoking contribute to plasma plasminogen levels

Plasminogen is the precursor of the serine protease plasmin, a central enzyme of the fibrinolytic system. Plasma levels of plasminogen vary by almost 2-fold among healthy individuals, yet little is known about its heritability or genetic determinants in the general population. In order to identify genetic factors affecting the natural variation of plasminogen levels, we performed a genome-wide association study and linkage analysis in a sample of 3456 young healthy individuals who participated in the Genes and Blood Clotting Study (GABC) or the Trinity Student Study (TSS). Heritability of plasminogen levels was 48.1% to 60.0%. Tobacco smoking and female sex were associated with higher levels of plasminogen. In the meta-analysis, 11 single-nucleotide polymorphisms (SNPs) in 2 regions reached genome-wide significance (P < 5.0E-8). Of these, 9 SNPs were near the PLG or LPA genes on Chr6q26, whereas 2 were on Chr19q13 and 5' upstream of SIGLEC14. These 11 SNPs represented 4 independent signals and collectively explained 6.8% of plasminogen level variation in the study populations. The strongest association was observed for a nonsynonymous SNP in the PLG gene (R523W). Individuals bearing an additional copy of this allele had an average decrease of 13.4% in plasma plasminogen level.

The role of genetic risk factors in arterial ischemic stroke in pediatric and adult patients: a critical review

The incidence of arterial ischemic stroke (AIS) in childhood (about 2-13 per 100,000 children a year) is much lower than the incidence in the adult population. Still, adverse outcomes of acute brain ischemia in childhood include death (10% of AIS children), neurological sequel, epileptic seizures (over 50%) and recurrence (over 20%). The knowledge of childhood stroke etiopathogenesis is still insufficient and the diagnostic and therapeutic procedures--controversial. Risk factors for childhood stroke differ from those observed in adults due to differing exposure to external risk factors. The most frequently reported risk factors for pediatric ischemic stroke are cerebral arteriopathies and vascular malformations, cardiac diseases, infections, traumas and metabolic diseases. Because of its multifactorial etiology pediatric AIS probably has a multigenic inheritance pattern. The genetic susceptibility to AIS may be determined by specific polymorphic variants encoding markers of hemostasis regulation and they are some of the most important targets in searching for genetic determinants in pediatric AIS. The authors have reviewed the recent literature on risk factors of childhood ischemic stroke with the focus on genetic factors like polymorphisms of genes encoding coagulation factors II, V, VII and XIII, MTHFR, fibrinogen beta, and compared them with the results performed in adult patients.

Advances in understanding stroke risk in children--a geneticist's view

The advent of the genomic era has provided novel insights into the genetic architecture of common complex diseases, such as thrombophilia and stroke. Since 2006, a growing number of genome wide association studies (GWAS) for common complex diseases have revealed new candidate loci and genomic regions that play an important role in disease aetiology and progression. While GWAS on the above mentioned traits are abundant in adults, similar studies in paediatric study cohorts are lagging behind. However, genetic research in this important clinical area has gained momentum and starts to provide us with exciting insights into the genetic underpinnings of stroke with paediatric onset. Here we review recent advances in genetic association studies underlying stroke in children and aim to translate the results to clinical utility. These studies comprise candidate gene approaches and GWAS, and represent the current status on what we have learnt about the genetic architecture underlying paediatric stroke, and how this may affect medical practice in the years to come.

Review of lipid and lipoprotein(a) abnormalities in childhood arterial ischemic stroke

National organizations recommend cholesterol screening in children to prevent vascular disease in adulthood. There are currently no recommendations for cholesterol and lipoprotein (a) testing in children who experience an arterial ischemic stroke. While dyslipidemia and elevated lipoprotein (a) are associated with ischemic stroke in adults, the role of atherosclerotic risk factors in childhood arterial ischemic stroke is not known. A review of the literature was performed from 1966 to April 2012 to evaluate the association between childhood arterial ischemic stroke and dyslipidemia or elevated lipoprotein (a). Of 239 citations, there were 16 original observational studies in children (with or without neonates) with imaging-confirmed arterial ischemic stroke and data on cholesterol or lipoprotein (a) values. Three pairs of studies reported overlapping subjects, and two were eliminated. Among 14 studies, there were data on cholesterol in 7 and lipoprotein (a) in 10. After stroke, testing was performed at >three-months in nine studies, at ≤three-months in four studies, and not specified in one study. There were five case-control studies: four compared elevated lipoprotein (a) and one compared abnormal cholesterol in children with arterial ischemic stroke to controls. A consistent positive association between elevated lipoprotein (a) and stroke was found [Mantel-Haenszel OR 4·24 (2·94-6·11)]. There was no association in one study on total cholesterol, and a positive association in one study on triglycerides. The literature suggests that elevated lipoprotein (a) may be more likely in children with arterial ischemic stroke than in control children. The absence of confirmatory study on dyslipidemia should be addressed with future research.

Role of reduced ADAMTS13 in arterial ischemic stroke: a pediatric cohort study

OBJECTIVE

Previous studies in adults and mice have implicated ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), also known as von Willebrand factor (VWF)-cleaving protease, as a protective factor for stroke. Here we investigated ADAMTS13 in 208 pediatric patients with arterial ischemic stroke (AIS) and 125 population-based control children in a frequency-matched case-control study.

METHODS

The proportion of patients/controls with ADAMTS13 activity levels below and above the 10th percentile was compared. Additionally, in a quintile comparison, the proportion of patients versus controls in the lowest ADAMTS13 quintile was compared to those in the 2nd to 5th quintiles. Adjustment was performed for VWF antigen (VWF:Ag), factor VIII activity (FVIII:C), blood group, and age.

RESULTS

Forty-six of 208 patients (22%) showed ADAMTS13 levels below the 10th percentile, compared with 5 of 125 controls (4%; p < 0.001). Odds ratios/95% confidence intervals were 7.30/2.73-19.50 for the lowest percentile and 2.44/1.15-5.16 in the quintile comparison after adjustment for VWF:Ag, FVIII:C, blood group, and age. Comparing the proportion of patients with ADAMTS13 activity below the 10th percentile within the different stroke subtypes (undetermined, cardioembolic, steno-occlusive arteriopathies), no statistically significant differences were found (undetermined, 16 of 89; cardioembolic, 6 of 40; steno-occlusive arteriopathies, 24 of 79; p = 0.08). ADAMTS13 levels did not significantly differ among stroke subtypes (p = 0.29).

INTERPRETATION

Our findings implicate reduced ADAMTS13 activity as a risk factor for pediatric AIS, and support the concept that ADAMTS13 has a role in the pathogenesis of pediatric AIS.

Genetic regulation of inflammation-mediated activation of haemostasis: family-based approaches in population studies

Blood coagulation and inflammation play a key role in atherosclerosis and thrombosis. Candidate gene and genome wide association studies have identified potential specific genes that might have a causal role in these pathogenic processes. The analysis of quantitative traits is more powerful as they are closer to direct gene action than disease phenotypes. Thus linkage-based studies on extended families might be useful both to estimate the heritability and to map the genetic loci responsible for the regulation of the trait. Family-based studies may estimate high heritability for thrombosis and quantitative traits regarding both platelet aggregation and blood coagulation. Some specific loci relevant to thrombosis have been identified, with some of them showing a direct pleiotropic effect on the risk of thrombosis. Haemostasis factors can be activated by inflammatory stimuli. Fibrinogen level is genetically correlated with C-reactive protein levels with a link for both traits on chromosomes 12 and 21. Genes related to prostanoid biosynthesis, involved both in inflammation and thrombosis, show high heritability levels in both enzyme expression and prostanoid production. Considering that few large family-based linkage studies have as yet been performed on haemostasis and inflammation-related traits, additional studies are highly needed. We are performing a family-based linkage study on large pedigrees (750 subjects from 23 families with juvenile myocardial infarction and 31 control families), to identify genes responsible for quantitative traits involved in the pathway progressively going from inflammation to haemostasis, cell activation, thrombus formation and cardiovascular events.

Plasma glutathione peroxidase in pediatric stroke families

BACKGROUND/OBJECTIVES

Promoter polymorphisms in the plasma glutathione peroxidase gene (GPX3), which encodes a major antioxidant enzyme implicated in post-translational modification of fibrinogen, have been implicated as risk factors for arterial ischemic stroke (AIS) and cerebral sinovenous thrombosis (CSVT) in young adults. However, the contribution of these polymorphisms could not be confirmed by other studies.

PATIENTS/METHODS

The aim of the present study was to investigate the association of three haplotype-tagging single-nucleotide polymorphisms (htSNPs) in GPX3 in a large family-based study sample comprising 268 nuclear families with different pediatric AIS subtypes, i.e. arteriopathy stroke (AS) and thromboembolic stroke (TS). In addition, an independent study sample comprising 154 nuclear families of pediatric CSVT was investigated. Single-point and haplotype association was assessed with the transmission disequilibrium test implemented in haploview.

RESULTS

Single-point analysis revealed that the G allele of htSNP rs8177412 was significantly overtransmitted to affected AS children (T/U = 25 : 11, χ(2) = 5.54, P = 0.019), but not to affected TS children (T/U = 49 : 40, χ(2) = 0.91, P = 0.34). The corresponding GG haplotype (H2: frequency 0.18) was also significantly overtransmitted to AS children (T/U = 23 : 11, χ(2) = 4.28, P= 0.03), but not to TS children or in children with CSVT. These results remained significant following 10,000 bootstrap permutations. Our findings indicate that genetic variants of GPX3 are risk factors for AS, but not for thromboembolic AIS or CSVT, in children.

CONCLUSIONS

Our results further highlight the need to analyze the contribution of genetic variants to pediatric AS, TS or CSVT separately, as these subcategories probably result from different combinations of risk-conferring and protective genetic variations.

Crossing the blood-brain barrier: clinical interactions between neurologists and hematologists in pediatrics - advances in childhood arterial ischemic stroke and cerebral venous thrombosis

PURPOSE OF REVIEW

The past year has marked a period of growing awareness of the need for improved diagnosis and treatment in children with arterial ischemic stroke (AIS) and cerebral sinus venous thrombosis (CSVT). Here we review these conditions, highlighting the importance of the intersection between hematologic abnormalities and pediatric stroke as they impact clinical management.

RECENT FINDINGS

Recent multicenter cohort studies are beginning to clarify the incidence, risk factors, clinical course and outcomes of AIS and CSVT in children. Key findings include: diagnosis rests on adequate neuroimaging and is often delayed more than 24 h after symptom onset; multiple risk factors and inciting events are often involved; one or more prothrombotic risk factors are common; recurrence is common; and selected groups of patients benefit from anticoagulation, and less frequently, thrombolytic therapies.

SUMMARY

Progress in caring for children with AIS and CSVT requires greatly improved awareness of cerebrovascular disease among primary providers, who are most often the first point of contact, more rapid and specific diagnosis using appropriate advanced neuroimaging technologies, comprehensive hematologic evaluation for inherited and acquired thrombophilias, and multidisciplinary approaches to treatment. Additional large cohort studies and clinical trials are greatly needed to further clarify these issues.

Fibrinogen alpha and gamma genes and factor VLeiden in children with thromboembolism: results from 2 family-based association studies

Previous case-control studies showed that genetic variation in the fibrinogen gamma gene (FGG) increased the risk for deep vein thrombosis (VT) in adults. We investigated the association between the fibrinogen alpha (FGA) and FGG haplotypes, the factor V(Leiden)-mutation, and pediatric VT and thromboembolic stroke (TS) in 2 independent study samples. Association analysis revealed that the FGA-H1 and FGG-H2 haplotypes were significantly overtransmitted to VT patients (FGA-H1, P = .05; FGG: H2, P = .032). In contrast, the FGG-H3 haplotype was undertransmitted (P = .022). In an independent study sample, FGA-H1 (P = .008) and FGG-H2 (P = .05) were significantly associated with TS. The association of FGA and FGG haplotypes with VT was more pronounced in FV(Leiden)-negative families (FGA-H1, P = .001; FGG-H2, P = .001), indicating a genetic interaction between both risk factors. The risk-conferring FGG-H2 and the protective FGG-H3 haplotypes correlated with low (FGG-H2) and high (FGG-H3) levels of the gamma' chain variant, respectively. These results provide independent and novel evidence that FGA-H1 and FGG-H2 variants are associated with an increased risk of VT and TS in children. The observed negative correlation of genetic VT risk with the plasma levels of the fibrinogen gamma' variant suggests that FGG-H2 and -H3 haplotypes modify thrombosis risk by controlling the level of this FGG splice isoform.

Association of the protein Z ATG haplotype with symptomatic nonvascular stroke or thromboembolism in white children: a family-based cohort study

To clarify the role of protein Z (PZ) in children with stroke/thromboembolism (TE), the present haplotype (HT)–based family study was performed. We genotyped 365 pediatric stroke/TE families (stroke n = 216; TE n = 149) for 4 single nucleotide polymorphisms (SNPs; rs3024718, rs3024731, rs3024772, and rs3024778) to assess the association between genetic variation within a conserved block of linkage disequilibrium harboring the PZ gene and pediatric TE. Association was assessed with use of the transmission disequilibrium test (TDT), corrected for multiple testing (permutation testing: HAPLOVIEW). In addition, PZ antigen was determined and correlated with carriership of PZ haplotypes and the FV G1691A mutation. Rs3024718, rs3024731, and rs3024772 are in tight linkage disequilibrium (LD) and define 4 haplotypes, capturing 97% of the genetic variation for this LD block. HT1 (ATG) was significantly overtransmitted from parents to affected offspring (HT frequency 73.5%, T:U 122:80, χ2 = 8.791, P = .003). The ATG risk haplotype was significantly correlated with greater PZ antigen levels. Multivariate analysis adjusted for age, sex, established thrombophilias, smoking, fibrinogen, and PZ levels revealed a significant association of the ATG haplotype and TE in children (odds ratio [OR] 1.4; 95% confidence interval [95% CI] 1.08-1.93). Our results suggest that the ATG haplotype of the PZ gene is a genetic marker for symptomatic TE in white German children.