Marieke C.H. de Visser

ABO blood group genotypes, plasma von Willebrand factor levels and loading of von Willebrand factor with A and B antigens

ABO blood group is a genetic determinant of von Willebrand factor (VWF) levels. We investigated the effect of ABO genotypes on VWF and factor VIII (FVIII) levels and on the degree to which VWF is loaded with A- and B-antigens, expressed as normalized ratios, nA-ratio and nB-ratio, respectively, in the Leiden Thrombophilia Study, a large case-control study on venous thrombosis. We found that the ABO locus had an allele-specific, dosage dependent effect on VWF and FVIII levels and on the loading of VWF with A-antigen and B-antigen. The highest mean nA- and nB-ratios were found in A(1)A(1) and BB genotypes, respectively. Four A(1)O carriers had four 43-bp repeats in the minisatellite region of the ABO gene in stead of the expected one repeat. All had a reduced nA-ratio compared to A(1)O carriers with one repeat in their A(1) allele. The amount of A- and B-antigens expressed onVWF (nA-ratio and nB-ratio) explained about 18% (R(2)) of the variation in VWF levels.

Haplotypes of the interleukin-1 receptor antagonist gene, interleukin-1 receptor antagonist mRNA levels and the risk of myocardial infarction

BACKGROUND The overall effect of the major pro-inflammatory cytokine interleukin-1 (IL-1) on coagulation and fibrinolysis is prothrombotic. We recently found that haplotype 5 (H5) of the gene (IL1RN) coding for the interleukin-1 receptor antagonist (IL-1Ra), the natural inhibitor of IL-1, is associated with an increased risk of venous thrombosis. It is unclear whether variations in IL1RN affect the risk of myocardial infarction. OBJECTIVES The aim of this study was to investigate the effect of the five most common haplotype groups of IL1RN on the risk of myocardial infarction and on IL1RN mRNA levels. PATIENTS/METHODS We genotyped 5 single nucleotide polymorphisms (SNPs) in IL1RN in 560 male patients and 646 male control subjects of a population-based case-control study on myocardial infarction, enabling us to tag the five common haplotype groups of IL1RN. For all haplotype groups the relationship with the risk of myocardial infarction and IL1RN mRNA levels was determined. RESULTS An increased risk of myocardial infarction was found for haplotype 3 (H3) carriers (tagged by SNP 13760T/C, odds ratio=1.3; 95% confidence interval: 1.1-1.7) compared to non-H3 carriers. No effect on myocardial infarction risk was found for the other haplotypes. H3 carriers had decreased IL1RN mRNA levels compared to non-H3 carriers (p<0.01), whereas mRNA levels were higher in H2 carriers compared to non-H2 carriers (p<0.01). CONCLUSIONS We found that H3 carriership increases the risk of myocardial infarction. This effect could be explained by the reduced IL1RN expression in H3 carriers, which is expected to result in reduced levels of IL-1Ra, the principal antagonist of IL-1.

Haplotypes of IL1B, IL1RN, IL1R1, and IL1R2 and the Risk of Venous Thrombosis

Objective—It has been suggested that the overall effect of the major proinflammatory cytokine interleukin-1 (IL-1) on coagulation and fibrinolysis is prothrombotic. The aim of this study was to investigate whether common variations in IL1B, IL1RN, IL1R1, and IL1R2 influence the risk of venous thrombosis. Methods and Results—In a case–control study on the causes of deep venous thrombosis, the Leiden Thrombophilia Study (LETS), we genotyped 18 single nucleotide polymorphisms (SNPs) in IL1B, IL1RN, IL1R1, and IL1R2, enabling us to tag a total of 25 haplotype groups. Overall testing of the haplotype frequency distribution in patients and controls indicated that a recessive effect was present in IL1RN (P=0.031). Subsequently the risk of venous thrombosis was calculated for each haplotype of IL1RN. Increased thrombotic risk was found for homozygous carriers of haplotype 5 (H5, tagged by SNP 13888T/G, rs2232354) of IL1RN (Odds ratio=3.9; 95% confidence interval: 1.6 to 9.7; P=0.002). No risk was associated with haplotype 3 of IL1RN, which contains the frequently examined allele 2 variant of the intron 2 VNTR. Conclusions—We found that IL1RN–H5H5 carriership increases the risk of venous thrombosis.

Frequency of the TAFI – 438 G/A and factor XIIIA Val34Leu polymorphisms in patients with objectively proven pulmonary embolism

Deep vein thrombosis (DVT) and pulmonary embolism (PE) are considered to be two forms of the same disease, however it is not fully understood what determines their clinical presentation. Proteins encoded by the FXIIIA and TAFI genes are involved in stabilizing the fibrin clot and in making it more lysis resistant. The FXIIIA 34Leu and TAFI -438A alleles might protect against DVT. Information on such an association with PE is either contradictory or missing. We hypothesized that both polymorphisms might influence the formation and fate of emboli and accordingly the risk of PE. We determined the frequencies of both polymorphisms in patients with objectively demonstrated PE. The frequency of FXIIIA Leu34Leu in PE patients and non-PE patients was 4.5% and 8.8%, [OR 0.5 (95% CI: 0.1 to 1.9)], respectively. For -438 A/A TAFI genotype the frequency was 1.5% and 8.1% [OR 0.1 (95% CI: 0.02 to 1.1)], respectively.

Factor IX-R338L (Factor IX Padua) screening in a Dutch population of sibpairs with early onset venous thromboembolism.

A new missense mutation in exon 8 of the F9 gene that results in a substitution of an arginine to a leucine at position 338 (R338L) was described by Simioni et al. [1]. Thismutation, called factor IX Padua,was discovered in a 23 year-old man presenting with a spontaneous venous thromboembolism (VTE). Established genetic risk factors for VTE were not present in this patient. The patient had a normal factor IX antigen level but his factor IX activity level was approximately eight times the normal level. Factor IX Padua was shown to be a gain-of-function mutation resulting in an elevation of the factor IX activity. Screening for the factor IX Padua mutation in 200 controls and 200 patients with a documented VTE and normal factor IX activity levels resulted in no additional cases. Factor IX Padua was also not found in a small study including 19 VTE patients with high factor IX activity and/or high factor IX activity/antigen ratio, and 132 healthy individuals, as reported by Mazetto et al. [2]. We studied the factor IX Paduamutation in the Genetics In Familial Thrombosis (GIFT) study [3]. This study consists of 201 Dutch sibships with 2, 3, or 4 affected siblings with at least one objectively confirmed VTE (n=438). The 201 index patients experienced VTE at a young age (≤45 years). Compared to unselected VTE patients, the prevalence of established genetic risk factors for VTE is higher in the GIFT study. Factor V Leiden was found in only 15.3% [4] of unselected VTE patients and in 36.8% of index patients from the GIFT study. In a large part of the GIFT cases none or only one established genetic risk factor for VTE has been found. As familial thrombophilia is assumed to be a multigenic disorder, the GIFT population might be suitable for the discovery of novel genetic risk factors for VTE. We hypothesized that the factor IX Paduamutation could be one of these additional genetic risk factors for VTE. Therefore, we determined the frequency of the factor IX Padua mutation in the GIFT study by sequencing the first part of exon 8 of the F9 gene. Factor IX Padua was not detected in the patients from the GIFT study.

Estimation of genetic effects in multiple cases family studies using penalized maximum likelihood methodology

Family studies are often used in genetic research to explore associations between genetic markers and various phenotypes. A commonly used design oversamples families enriched with the disease under study for efficient data collection and estimation. For instance, in a multiple cases family study, families are selected based on the number of affected relatives. In such cases, valid inference for the model parameters relies on the proper modeling of both the within family correlations and the outcome-dependent sampling, also known as ascertainment. A flexible modeling approach is the ascertainment-corrected mixed-effects model, but it is known to only be asymptotically identifiable, because in small samples the available data do not provide sufficient information to estimate both the intercept and the genetic variance. To deal with this issue, we propose a penalized maximum likelihood estimation procedure which reliably estimates the model parameters in small family studies by using external population-based information.

Generalizing Terwilliger's likelihood approach: a new score statistic to test for genetic association.

Background:In this paper, we propose a one degree of freedom test for association between a candidate gene and a binary trait. This method is a generalization of Terwilligers likelihood ratio statistic and is especially powerful for the situation of one associated haplotype. As an alternative to the likelihood ratio statistic, we derive a score statistic, which has a tractable expression. For haplotype analysis, we assume that phase is known.Results:By means of a simulation study, we compare the performance of the score statistic to Pearsons chi-square statistic and the likelihood ratio statistic proposed by Terwilliger. We illustrate the method on three candidate genes studied in the Leiden Thrombophilia Study.Conclusion:We conclude that the statistic follows a chi square distribution under the null hypothesis and that the score statistic is more powerful than Terwilligers likelihood ratio statistic when the associated haplotype has frequency between 0.1 and 0.4 and has a small impact on the studied disorder. With regard to Pearsons chi-square statistic, the score statistic has more power when the associated haplotype has frequency above 0.2 and the number of variants is above five.

The effect of plasma caeruloplasmin levels on the sensitivity for activated protein C

Summary.  The effect of caeruloplasmin levels on the sensitivity for activated protein C (APC), measured by a clotting assay based on the activated partial thromboplastin time, was investigated in a large group of healthy individuals without factor V Leiden. A modest inverse association between caeruloplasmin and normalized APC sensitivity ratio was found (regression coefficient β = −0·33 × 10−2; 95% confidence interval, −0·42 × 10−2 to −0·24 × 10−2). After adjustment for sex and oral contraceptive use, this association weakened (β = −0·19 × 10−2; 95% CI: −0·34 × 10−2 to −0·05 × 10−2). After additional adjustment for factor VIII levels, which are known to influence the assay, the effect of caeruloplasmin on APC sensitivity completely disappeared.