Ethnic differences in hypertension and blood pressure control in the UK.
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Adolescent↗
Biomedical subjects
D A Lane
Publications and source records attributed to D A Lane.
Haemostatic genetic risk factors in arterial thrombosis.
Haemostasis plays an integral role in arterial thrombotic disease. However, establishing which of the factors are risk factors has proven surprisingly difficult. Because of its technical simplicity and digital nature, the study of haemostatic polymorphisms as risk factors has grown in popularity. Once established as a risk factor, a genetic polymorphism has the potential to aid selective prophylaxis and therapy of disease. Numerous reports have now been published on polymorphisms of coagulation and fibrinolytic factors, of coagulation and fibrinolytic inhibitory proteins, and of platelet membrane glycoprotein receptors. This article describes the polymorphisms and evaluates the results of these studies using the premises of consistency of within-report genotype/phenotype/disease relationships and consistency of outcome between studies. Many studies have been only of association between polymorphisms and disease, a type of study that is prone to error. Furthermore, the collective outcome of these studies has primarily been inconsistent. It is concluded that despite the early promise of polymorphisms as risk factors, fresh approaches differing in scale and design are now required to clarify their possible importance.
Arteriosclerosis↗
Homozygous antithrombin deficiency type II (99 Leu to Phe mutation) and childhood thromboembolism.
We report 5 children from 3 families with homozygous antithrombin deficiency type II affecting the heparin binding site (99 Leu to Phe mutation). Four children had severe spontaneous thromboembolic events (deep leg or caval vein thrombosis, ischaemic stroke) at one week, 3 months, 13 and 14 years of age. The fifth patient, a 17 year-old boy was asymptomatic. Early manifestation of homozygous deficiency calls for prompt and accurate diagnosis. In doubtful cases genetic analysis is required. Long-term oral anticoagulation should be considered in affected individuals.
Adolescent↗
The endothelial cell protein C receptor: a candidate genetic risk factor for thrombosis.
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Animals↗
The factor XIII V34L polymorphism accelerates thrombin activation of factor XIII and affects cross-linked fibrin structure.
Factor XIII on activation by thrombin cross-links fibrin. A common polymorphism Val to Leu at position 34 in the FXIII A subunit is under investigation as a risk determinant of thrombosis. Because Val34Leu is close to the thrombin cleavage site, the hypothesis that it would alter the function of FXIII was tested. Analysis of FXIII subunit proteolysis by thrombin using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-performance liquid chromatography showed that FXIII 34Leu was cleaved by thrombin more rapidly and by lower doses than 34Val. Mass spectrometry of isolated activation peptides confirmed the predicted single methyl group difference and demonstrated that the thrombin cleavage site is unaltered by Val34Leu. Kinetic analysis of activation peptide release demonstrated that the catalytic efficiency (k(cat)/K(m)) of thrombin was 0.5 for FXIII 34Leu and 0.2 (micromol/L)(-1) x sec(-1) for 34Val. Presence of fibrin increased the catalytic efficiency to 4.8 and 2.2 (micromol/L)(-1) x sec(-1), respectively. Although the 34Leu peptide was released at a similar rate as fibrinopeptide A, the 34Val peptide was released more slowly than fibrinopeptide A but more quickly than fibrinopeptide B generation. Cross-linking of gamma- and alpha-chains appeared earlier when fibrin was incubated with FXIII 34Leu than with 34Val. Fully activated 34Leu and 34Val FXIII showed similar cross-linking activity. Analysis of fibrin clots prepared using plasma from FXIII 34Leu subjects by turbidity and permeability measurements showed reduced fiber mass/length ratio and porosity compared to 34Val. The structural differences were confirmed by electron microscopy. These results demonstrate that Val34Leu accelerates activation of FXIII by thrombin and consequently affects the structure of the cross-linked fibrin clot.
Blood Coagulation↗
Role of hemostatic gene polymorphisms in venous and arterial thrombotic disease.
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3' Untranslated Regions↗
Relationships between homocysteine, factor VIIa, and thrombin generation in acute coronary syndromes.
BACKGROUND: It has been suggested by clinical, epidemiological, and experimental in vitro studies that homocysteine potentiates thrombin generation. This prothrombotic effect however has not previously been demonstrated in patients presenting with acute coronary syndromes (ACS). METHODS AND RESULTS: Patients with ACS (n =117) presenting with confirmed acute myocardial infarction (MI) (n =57) or unstable angina pectoris (UAP) (n =60) were consecutively recruited together with patients (n =18) in whom the presenting chest pain was not of cardiac origin (NCP), included as controls. Plasma samples were collected on admission and before clinical intervention. Homocysteine was assayed by high performance liquid chromatography, and both Factor VIIa and prothrombin fragment F1+2 were analyzed by ELISA. There were significant elevations in F1+2 in MI (P<0.001) and UAP (P=0.003), and modest elevations in Factor VIIa in UAP (P<0.05) compared with NCP but no differences in homocysteine levels among those groups. On dividing patients with ACS into quartiles of homocysteine, there was a stepwise increase in F1+2 (P<0.0001) and of Factor VIIa (P<0.05). There were significant correlations in ACS between homocysteine and F1+2 (r=0.46, P<0.0001), homocysteine and Factor VIIa (r=0.24, P<0.01), and F1+2 and Factor VIIa (r=0.41, P<0.0001). There was no correlation between homocysteine and either F1+2 (r=-0.15, P=0.57) or Factor VIIa (r=0. 22, P=0.37) in the NCP patients. CONCLUSIONS: Elevated plasma homocysteine is associated with and may cause elevated Factor VIIa and thrombin generation in patients presenting with ACS. These findings suggest an explanation for the prothrombotic effect of homocysteine in ACS.
Acute Disease↗
Identification and characterization of a thrombomodulin gene mutation coding for an elongated protein with reduced expression in a kindred with myocardial infarction.
Thrombomodulin is an endothelial cell receptor for thrombin. It functions as a natural anticoagulant by greatly accelerating activation of protein C by thrombin. Using a direct gene screening strategy we identified a frameshift insertion mutation, insT 1689, in the thrombomodulin gene of a patient with myocardial infarction. The mutation predicts an elongated gene product because of substitution of the 12 C-terminal amino acids by 61 abnormal residues. Pedigree analysis showed that the mutation was also likely to have been present in a sibling who had had fatal myocardial infarction. Carriers of the mutant allele express significantly lower amounts of thrombomodulin on the surface of their monocytes detected by flow cytometry and have lower levels of soluble thrombomodulin in plasma. Wild type and the mutant thrombomodulin were expressed in COS-7 cells. Cellular distribution of the expressed proteins was evaluated by immunofluorescence microscopy, which showed reduced cell surface expression and intense juxtanuclear localization of the abnormal protein. This suggests impaired translocation through the endoplasmic reticulum/Golgi apparatus. Cells expressing abnormal thrombomodulin had reduced ability ( approximately 2.5-fold) to accelerate the thrombin mediated activation of protein C. This is the first demonstration of reduced expression arising from a natural thrombomodulin gene mutation. The results provide support for the suggestion that gene mutation of thrombomodulin may be important in the pathogenesis of some cases of occlusive thrombotic disease. (Blood. 2000;95:569-576)
Adult↗
Methylenetetrahydrofolate reductase 677 C-->T mutation and coronary heart disease risk in UK Indian Asians.
Plasma homocysteine concentrations are elevated in UK Indian Asians and may contribute to twice as many coronary heart disease (CHD) deaths in this group compared with European whites. The mechanisms underlying elevated homocysteine concentrations among Indian Asians are not well understood. In this study, we have investigated the extent to which the methylenetetrahydrofolate reductase (MTHFR) 677 C-->T mutation accounts for elevated plasma homocysteine and increased CHD risk in Indian Asians compared with European whites. We investigated 454 male cases (with myocardial infarction or angiographically proven CHD: 224 Indian Asians, 230 European whites) and 805 healthy male controls (381 Indian Asians, 424 European whites). Fasting homocysteine concentrations, MTHFR 677 C-->T genotype, and conventional CHD risk factors were measured. The prevalence of homozygous MTHFR 677T in Indian Asian controls was less than one third that in European white controls (3.1% versus 9. 7%, P<0.001). In Indian Asians, the TT MTHFR genotype was not associated with homocysteine concentrations and was not present in any of the Asian controls with hyperhomocysteinemia (>15 micromol/L). In contrast, among European whites, the TT MTHFR genotype was strongly related to elevated plasma homocysteine concentrations and was found in 27% of the European controls with hyperhomocysteinemia. Elevated homocysteine in Indian Asian compared with European white controls was accounted for by their reduced levels of B vitamins but not by the MTHFR 677T genotype. However, neither the TT MTHFR genotype nor B vitamin levels explained the elevated homocysteine concentrations in CHD cases compared with controls. TT MTHFR was not a risk factor for early-onset CHD in Indian Asians (odds ratio, 0.5; 95% confidence interval, 0.1 to 2.4; P=0.39), unlike in European whites (odds ratio, 2.1; 95% confidence interval, 1.1 to 4. 1; P=0.02). We conclude that the MTHFR 677T: mutation does not contribute to elevated plasma homocysteine concentrations or increased CHD risk in Indian Asians compared with European whites. Our results suggest that novel genetic defects and/or environmental factors influence homocysteine metabolism in Indian Asians residing in the United Kingdom.
Adult↗
The maternal perspective on prenatal ultrasound.
BACKGROUND: Most women in the United States will have a routine sonogram during pregnancy. The medical necessity of this is debatable. The goal of our study was to examine maternal beliefs about prenatal sonography. METHODS: We surveyed 150 prenatal patients at their point of entry to maternity care at a large military medical center. The main outcome measures were the patient's desire for a prenatal sonogram, the reasons for wanting a sonogram, the number of sonograms wanted, and the patient's willingness to pay for the examination. RESULTS: Of the 150 eligible subjects, 137 (91%) participated and 135 (98%) wanted a prenatal sonogram. Fifty-one (37%) of the respondents were willing to pay for the sonogram if it was not ordered by their provider. The reasons for wanting a sonogram (to determine the sex of the fetus, to ensure that the fetus was healthy, general maternal reassurance, and to ensure adequate fetal growth) were similar across age, race, and income (military rank). CONCLUSIONS: Our study indicates that most women want a sonogram during pregnancy, and many are willing to pay for the examination. Women appear to want sonograms for reasons that may not assist their provider with immediate clinical decision making. This is a potentially important disagreement between cost-saving and patient satisfaction that maternity care providers must consider when deciding whether to perform prenatal sonography for women with low-risk pregnancies.
California↗
Tissue factor is rapidly elevated in plasma collected from the pericardial cavity during cardiopulmonary bypass.
There is growing evidence that the tissue factor/factor VIIa pathway of coagulation is enhanced during cardiopulmonary bypass. Hitherto, available evidence has suggested that upregulated monocyte bound tissue factor is made available, either in the blood collected from the site of surgery or on circulating cells. However, cellular upregulation is slow, while generation of factor VIIa in blood collected from the pericardial cavity is rapid. We have therefore investigated the possibility of an alternative source of tissue factor, plasma (as opposed to cellular) tissue factor in blood samples taken from the central vein catheter (systemic circulation) and collected from the pericardial cavity during cardiopulmonary bypass. Six patients undergoing first time cardiopulmonary bypass grafting were studied. Tissue factor antigen was found to be rapidly elevated (by 15 min) in the pericardial plasma, approximately 5-fold above systemic levels (p <0.004). Similar elevations were found in markers of coagulation activation, factor VIIa antigen (p = 0.066), prothrombin fragment F(1+2) (p <0.003) and thrombin-antithrombin complex (p <0.03). To explore whether plasma tissue factor was (or had been) functionally active, factor VIIa was measured also with the soluble tissue factor functional assay after removal of heparin. Functional factor VIIa activity fell significantly in the systemic circulation, probably due to the heparin-induced increase (approximately 15-fold) in tissue factor pathway inhibitor (TFPI), but was elevated in pericardial blood compared with that taken from the central line catheter (p <0.006). These results demonstrate that both components of the activation complex for the extrinsic pathway of coagulation are rapidly generated in pericardial blood during bypass.
Aged↗
Structural and functional implications of the intron/exon organization of the human endothelial cell protein C/activated protein C receptor (EPCR) gene: comparison with the structure of CD1/major histocompatibility complex alpha1 and alpha2 domains.
The endothelial cell protein C/activated protein C receptor (EPCR) is located primarily on the surface of the large vessels of the vasculature. In vitro studies suggest that it is involved in the protein C anticoagulant pathway. We report the organization and nucleotide sequence of the human EPCR gene. It spans approximately 6 kbp of genomic DNA, with a transcription initiation point 79 bp upstream of the translation initiation (Met) codon in close proximity to a TATA box and other promoter element consensus sequences. The human EPCR gene has been localized to 20q11.2 and consists of four exons interrupted by three introns, all of which obey the GT-AG rule. Exon I encodes the 5' untranslated region and the signal peptide, and exon IV encodes the transmembrane domain, the cytoplasmic tail, and the 3' untranslated region. Exons II and III encode most of the extracellular region of the EPCR. These exons have been found to correspond to those encoding the alpha1 and alpha2 domains of the CD1/major histocompatibility complex (MHC) class I superfamily. Flanking and intervening introns are of the same phase (phase I) and the position of the intervening intron is identically located. Secondary structure prediction for the amino acid sequence of exons II and III corresponds well with the actual secondary structure elements determined for the alpha1 and alpha2 domains of HLA-A2 and murine CD1.1 from crystal structures. These findings suggest that the EPCR folds with a beta-sheet platform supporting two alpha-helical regions collectively forming a potential binding pocket for protein C/activated protein C.
Amino Acid Sequence↗
Familial overexpression of beta antithrombin caused by an Asn135Thr substitution.
We have investigated the basis of antithrombin deficiency in an asymptomatic individual (and family) with borderline levels (approximately 70% antigen and activity) of antithrombin. Direct sequencing of amplified DNA showed a mutation in codon 135, AAC to ACC, predicting a heterozygous Asn135Thr substitution. This substitution alters the predicted consensus sequence for glycosylation, Asn-X-Ser, adjacent to the heparin interaction site of antithrombin. The antithrombin isolated from plasma of the proband by heparin-Sepharose chromatography contained amounts of beta antithrombin (the very high affinity fraction) greatly increased (approximately 20% to 30% of total) above the trace levels found in normals. Expression of the residue 135 variant in both a cell-free system and COS-7 cells confirmed altered glycosylation arising as a consequence of the mutation. Wild-type and variant protein were translated and exported from COS-7 cells with apparently equal efficiency, in contrast to the reduced level of variant observed in plasma of the affected individual. This case represents a novel cause of antithrombin deficiency, removal of glycosylation concensus sequence, and highlights the potentially important role of beta antithrombin in regulating coagulation.
Adult↗
Determining exposure underreporting in pharmacoepidemiologic case-control studies: methods and example.
Many pharmacoepidemiologic case-control studies have to rely on what their subjects relate about the drugs to which they have been exposed and the durations of exposure. There is often good reason to suppose that not all exposures are actually reported and to suspect reporting rates may differ between cases and controls. We introduce two procedures designed to determine the extent of underreporting of exposures. These procedures make use of data from the case-control study itself, as well as sales, demographic and market research data for a reference population to which study subjects belong. We apply these procedures to data from the International Primary Pulmonary Hypertension Study (IPPHS) linking anorexigens with PPH. We show that exposures to the anorectic agent dexfenfluramine beginning in or before 1989 were highly significantly underrepresented in the data for IPPHS controls, relative to exposures beginning after 1989 (P<0.01); there is no corresponding evidence for relative underrepresentation of early exposure for IPPHS cases. However, data on control exposures from 1990 to 1992 are consistent with the hypothesis that these exposures were not underreported to the IPPHS. Subject to certain key modeling assumptions and the availability of some supplemental data, it is possible to investigate the extent of underreporting of exposure in a pharmacoepidemiologic case-control study and in particular to determine if study results are likely to have been affected by recall bias.
Adolescent↗
Two-chain factor VIIa generated in the pericardium during surgery with cardiopulmonary bypass : relationship to increased thrombin generation and heparin concentration.
Several recent studies have proposed that coagulation is triggered during cardiopulmonary bypass surgery by extrinsic pathway activation involving factor VIIa generation, but the methodology was indirect. Therefore, 12 patients were studied during routine cardiac and cardiopulmonary bypass surgery. Samples were taken before, during, and after bypass from the perfusate, from the aorta (retrograde cardiac drainage), pericardium, and collected suction fluid originating from the whole operative field. These samples were analyzed by enzyme-linked immunosorbent assay for 2-chain factor VIIa, by prothrombin F1+2 assay, by thrombin-antithrombin (TAT) assay, and for heparin concentration. Factor VIIa, F1+2, and TAT levels in samples from the pericardium were greatly elevated (mean, 0.92 to 1.01, 227 to 334, and 399 to 526 microg/L, respectively; preoperative mean, 0.33, 32.3, and 1.90 microg/L, respectively; P<0. 05 for all), whereas levels in suction fluid were less consistently high. Factor VIIa and both F1+2 and thrombin-antithrombin levels in samples from the aorta, pericardium, and suction fluid were significantly correlated (r=0.57, P<0.001, n=111; and r=0.51, P<0. 001, n=105, respectively), and all were inversely correlated with heparin levels (r>-0.35, P<0.001, n>92). There was no evidence of factor VIIa generation in the circuit during bypass surgery, and both F1+2 and thrombin-antithrombin levels rose only approximately 2-fold, probably because heparin levels were higher than they were in the pericardium (P<0.05). We concluded that appreciable activation of factor VII occurs on the pericardium and that this is associated with increased thrombin generation. Ineffective local heparinization may be partly responsible. These results suggest that pericardium-induced activation of factor VII should be the target of anticoagulant strategies during cardiopulmonary bypass surgery.
Aged↗
Impaired cotranslational processing as a mechanism for type I antithrombin deficiency.
Most secretory proteins, including antithrombin (AT), are synthesized with a signal peptide, which is cleaved before the mature protein is exported from the cell. The signal peptide is important in the process whereby nascent protein is recognized as requiring subsequent modification within the endoplasmic reticulum (ER). We have identified a novel mutation, 2436T-->C L(-10)P, which affects the central hydrophobic domain of the AT signal peptide, in a proband presenting with venous thrombotic disease and type I AT deficiency. We investigated the basis of the phenotype by examining expression in mammalian cells of a range of variant AT cDNAs with mutations affecting the -10 residue. Glycosylated AT was secreted from COS-7 cells transfected with wild-type AT, -10L deletion, -10V or -10M variants, but not variants with P, T, R, or G at -10. Cell-free expression of wild-type and variant AT cDNAs was then performed in the presence of canine pancreatic microsomes, as a substitute for ER. Variant AT proteins with P, T, R, or G at residue -10 did not undergo posttranslational glycosylation, and their susceptibility to trypsin digestion suggested they had not been translocated into microsomes. Our results suggest that the ability of AT signal peptide to direct the protein to ER for cotranslational processing events appears to be critically dependent on maintaining the hydrophobic nature of the region including residue -10. The investigations have defined impaired cotranslational processing as a hitherto unrecognized cause of hereditary AT deficiency.
Adult↗
Clarification of the risk for venous thrombosis associated with hereditary protein S deficiency by investigation of a large kindred with a characterized gene defect.
BACKGROUND: Protein S is an important regulatory protein of the coagulation cascade. The risk for venous thrombosis associated with protein S deficiency has been uncertain because all previous risk estimates used phenotypic evaluation alone, which can be ambiguous. OBJECTIVE: To quantitate the risk for thrombosis associated with a characterized protein S gene mutation that causes a Gly295-->Val substitution and protein S deficiency. DESIGN: Retrospective study of a single extended family. SETTING: University hospital referral center. PARTICIPANTS: A 122-member protein S-deficient family, in which 44 members had a recently characterized gene defect. MEASUREMENTS: Comprehensive history of thrombosis, history of exposure to acquired risk factors for thrombosis, levels of total and free protein S antigen, and genotype for the mutation causing the Gly295-->Val substitution. RESULTS: Kaplan-Meier analysis of thrombosis-free survival showed that the probability of remaining free of thrombosis at 30 years of age is 0.5 (95% CI, 0.33 to 0.66) for carriers of the Gly295-->Val mutation compared with 0.97 (CI, 0.93 to 1.0) for normal family members (P < 0.001). In a multivariate Cox regression model that included smoking and obesity, the mutation was a strong independent risk factor for thrombosis (hazard ratio, 11.5 [CI, 4.33 to 30.6]; P < 0.001). For free (but not total) protein S antigen levels, the distributions of persons with and persons without the mutation did not overlap. CONCLUSIONS: Protein S deficiency, as defined by the presence of a causative gene mutation or a reduced level of free protein S antigen, is a strong independent risk factor for venous thrombosis in a clinical affected family.
Adolescent↗
Academic calculations versus clinical judgments: practicing physicians' use of quantitative measures of test accuracy.
PURPOSE: To determine how often practicing physicians use the customarily recommended quantitative methods that include sensitivity, specificity, and likelihood ratio indexes; receiver operator characteristic (ROC) curves; and Bayesian diagnostic calculations. PARTICIPANTS AND METHODS: A random sample of 300 practicing physicians (stratified by specialty to include family physicians, general internists, general surgeons, pediatricians, obstetrician/gynecologists, and internal medicine subspecialists) were briefly interviewed in a telephone survey. They were asked about the frequency with which they used the formal methods, the reasons for non-use, and if they employed alternative strategies when appraising tests' diagnostic accuracy. RESULTS: Of the 300 surveyed physicians, 8 (3%) used the recommended formal Bayesian calculations, 3 used ROC curves, and 2 used likelihood ratios. The main reasons cited for non-use included impracticality of the Bayesian method (74%), and nonfamiliarity with ROC curves and likelihood ratios (97%). Of the 174 physicians who said they used sensitivity and specificity indexes, 165 (95%) did not do so in the recommended formal manner. Instead, the physicians directly estimated tests' diagnostic accuracy by determining how often the test results were correct in groups of patients later found to have, or to be free of, the selected disease. CONCLUSIONS: The results indicate that most practicing physicians do not use the formal recommended quantitative methods to appraise tests' diagnostic accuracy, and instead report using an alternative direct approach. Although additional training might make physicians use the formal methods more often, the physicians' direct method merits further evaluation as a potentially pragmatic tool for the determination of tests' diagnostic accuracy in clinical practice.
Adult↗