A genetic association study of circulating coagulation factor VIII and von Willebrand factor levels

ABSTRACT

Coagulation factor VIII (FVIII) and its carrier protein von Willebrand factor (VWF) are critical to coagulation and platelet aggregation. We leveraged whole-genome sequence data from the Trans-Omics for Precision Medicine (TOPMed) program along with TOPMed-based imputation of genotypes in additional samples to identify genetic associations with circulating FVIII and VWF levels in a single-variant meta-analysis, including up to 45 289 participants. Gene-based aggregate tests were implemented in TOPMed. We identified 3 candidate causal genes and tested their functional effect on FVIII release from human liver endothelial cells (HLECs) and VWF release from human umbilical vein endothelial cells. Mendelian randomization was also performed to provide evidence for causal associations of FVIII and VWF with thrombotic outcomes. We identified associations (P < 5 × 10-9) at 7 new loci for FVIII (ST3GAL4, CLEC4M, B3GNT2, ASGR1, F12, KNG1, and TREM1/NCR2) and 1 for VWF (B3GNT2). VWF, ABO, and STAB2 were associated with FVIII and VWF in gene-based analyses. Multiphenotype analysis of FVIII and VWF identified another 3 new loci, including PDIA3. Silencing of B3GNT2 and the previously reported CD36 gene decreased release of FVIII by HLECs, whereas silencing of B3GNT2, CD36, and PDIA3 decreased release of VWF by HVECs. Mendelian randomization supports causal association of higher FVIII and VWF with increased risk of thrombotic outcomes. Seven new loci were identified for FVIII and 1 for VWF, with evidence supporting causal associations of FVIII and VWF with thrombotic outcomes. B3GNT2, CD36, and PDIA3 modulate the release of FVIII and/or VWF in vitro.

Staying Virtual: A Survey Study of the Virtual Lecture Experience in Academic Medicine

BACKGROUND

Increasing clinical demands can adversely impact academic advancement, including the ability to deliver lectures and disseminate scholarly work. The virtual lecture platform became mainstream during the height of the coronavirus-19 pandemic. Lessons learned from this period may offer insight into supporting academic productivity among physicians who must balance multiple demands, including high clinical workloads and family care responsibilities. We evaluated perceptions on delivering virtual lectures to determine whether virtual venues merit continuation beyond the pandemic's initial phase and whether these perceptions differ by gender and rank.

METHODS

In a survey study, faculty who spoke in 1 of 3 virtual lecture programs in the Departments of Anesthesiology and Critical Care Medicine, Otolaryngology, and Radiology at a university hospital in 2020 to 2022 were queried about their experience. Speakers' motivations to lecture virtually and the perceived advantages and disadvantages of virtual and in-person lectures were analyzed using descriptive statistics and qualitative analyses.

RESULTS

Seventy-two of 95 (76%) faculty members responded (40% women, 38% men, and 22% gender undisclosed). Virtual lectures supported the speakers "a lot" to "extremely" with the following goals: enhancing one's reputation and credibility (76%), networking (70%), receiving feedback (63%), and advancing prospects for promotion (59%). Virtual programs also increased the speakers' sense of accomplishment (70%) and professional optimism (61%) by at least "a lot," including instructors and assistant professors who previously had difficulty obtaining invitations to speak outside their institution. Many respondents had declined prior invitations to speak in-person due to clinical workload (66%) and family care responsibilities (58%). Previous opportunities to lecture in-person were also refused due to finances (39%), teaching (26%), and research (19%) requirements, personal medical conditions or disabilities (9%), and religious obligations (5%). Promotion was a stronger motivating factor to lecture virtually for instructors and assistant professors than for associate and full professors. By contrast, disseminating work and ideas was a stronger motivator for associate and full professors. Associate and full professors also reported greater improvement in work-related well-being than earlier career faculty from the virtual lecture experience. Very few differences were found by gender.

CONCLUSIONS

Virtual lecture programs support faculty who might not otherwise have the opportunity to lecture in-person due to multiple constraints. To increase the dissemination of scholarly work and expand opportunities to all faculty, virtual lectures should continue even as in-person venues are reestablished.

Association of Preoperative Immune Checkpoint Inhibitor Therapy With Cardiopulmonary Instability and Organ Injury After High-Risk Surgery

OBJECTIVES

To assess the relationship between prior exposure to immune checkpoint inhibitors (ICIs) and the risk of postoperative complications in cancer patients.

DESIGN

Single-center retrospective cohort study.

INTERVENTIONS

The main exposure was treatment with an FDA-approved ICI within 6 months before surgery.

MEASUREMENTS AND MAIN RESULTS

Exposure to ICIs and covariates was determined from the electronic health record. The primary outcome was a composite of postoperative complications, including prolonged pressor or oxygen dependence, kidney injury, or myocardial injury. Secondary outcomes included each subcomponent of the primary outcome. Of 7674 subjects with cancer admitted to the ICU after surgery, 247 were exposed to one or more ICIs in the 6 months before surgery. After propensity score matching, 197 ICI-exposed subjects were matched to 777 nonexposed. The composite outcome occurred in 70 of 197 (35.5%) ICI-exposed subjects and 251 of 777 (32.3%) nonexposed. There was no difference between exposed and nonexposed groups in the primary composite outcome (odds ratio [OR], 1.12; 95% CI, 0.80-1.58) by conditional logistic regression. Risk of the secondary outcome of prolonged pressor dependence was significantly higher in ICI-exposed subjects (OR, 1.64; 95% CI, 1.01-2.67). Risks of oxygen dependence (OR, 1.13; 95% CI, 0.75-1.73), kidney injury (OR, 1.15; 95% CI, 0.77-1.71), and myocardial injury (OR, 1.76; 95% CI, 1.00-3.10) were not significantly different. There was no difference between groups in the time to hospital discharge alive (p = 0.62).

CONCLUSIONS

Exposure to ICIs within 6 months before high-risk surgery was not associated with the composite outcome of cardiopulmonary instability or organ injury in patients with cancer. The potential for an association with the secondary outcomes of cardiac instability and injury is worthy of future study.

Low-Volume Acute Normovolemic Hemodilution Does Not Reduce Allogeneic Red Blood Cell Transfusion in Cardiac Surgery in the Modern Era of Patient Blood Management: A Propensity Score-Matched Cohort Study

OBJECTIVES

Patients undergoing cardiac surgery often require blood transfusions, which are associated with increased morbidity and mortality. Patient blood management (PBM) strategies, including acute normovolemic hemodilution (ANH), have been implemented to minimize allogeneic transfusion requirements. Older studies suggested that ANH is associated with reduced transfusions; however, its effectiveness in the modern era of PBM remains unclear.

DESIGN

This was a retrospective cohort study.

SETTING

The study was held at a single university hospital.

PARTICIPANTS

542 patients who underwent elective cardiac surgery with cardiopulmonary bypass (CPB) using low-priming-volume circuits between January 2017 and March 2022.

INTERVENTIONS

Patients who received ANH were matched with those who did not receive ANH, using propensity scores.

MEASUREMENTS AND MAIN RESULTS

The primary outcome was the proportion of patients who received perioperative red blood cell (RBC) transfusion. Of the 542 eligible patients, 49 ANH cases were propensity-score matched to 97 controls. The median ANH volume was 450 mL (IQR, 400-800 mL). There was no significant difference in perioperative RBC transfusion rates between the 2 groups (24.5% in the ANH group vs 30.9% in the control group, p = 0.42). The odds ratio for perioperative RBC transfusion in the ANH group versus the control group was 0.72 (95% CI, 0.32-1.55, p = 0.42).

CONCLUSIONS

Low-volume ANH was not associated with a significant reduction in perioperative allogeneic RBC transfusion during cardiac surgery with CPB using low-priming-volume circuits. The benefits of low-volume ANH in reducing the requirement for RBC transfusion in the modern era of PBM may be smaller than reported previously.

Whole Genome Sequencing Based Analysis of Inflammation Biomarkers in the Trans-Omics for Precision Medicine (TOPMed) Consortium

Inflammation biomarkers can provide valuable insight into the role of inflammatory processes in many diseases and conditions. Sequencing based analyses of such biomarkers can also serve as an exemplar of the genetic architecture of quantitative traits. To evaluate the biological insight, which can be provided by a multi-ancestry, whole-genome based association study, we performed a comprehensive analysis of 21 inflammation biomarkers from up to 38,465 individuals with whole-genome sequencing from the Trans-Omics for Precision Medicine (TOPMed) program. We identified 22 distinct single-variant associations across 6 traits - E-selectin, intercellular adhesion molecule 1, interleukin-6, lipoprotein-associated phospholipase A2 activity and mass, and P-selectin - that remained significant after conditioning on previously identified associations for these inflammatory biomarkers. We further expanded upon known biomarker associations by pairing the single-variant analysis with a rare variant set-based analysis that further identified 19 significant rare variant set-based associations with 5 traits. These signals were distinct from both significant single variant association signals within TOPMed and genetic signals observed in prior studies, demonstrating the complementary value of performing both single and rare variant analyses when analyzing quantitative traits. We also confirm several previously reported signals from semi-quantitative proteomics platforms. Many of these signals demonstrate the extensive allelic heterogeneity and ancestry-differentiated variant-trait associations common for inflammation biomarkers, a characteristic we hypothesize will be increasingly observed with well-powered, large-scale analyses of complex traits.

Whole genome analysis of plasma fibrinogen reveals population-differentiated genetic regulators with putative liver roles

Genetic studies have identified numerous regions associated with plasma fibrinogen levels in Europeans, yet missing heritability and limited inclusion of non-Europeans necessitates further studies with improved power and sensitivity. Compared with array-based genotyping, whole genome sequencing (WGS) data provides better coverage of the genome and better representation of non-European variants. To better understand the genetic landscape regulating plasma fibrinogen levels, we meta-analyzed WGS data from the NHLBI's Trans-Omics for Precision Medicine (TOPMed) program (n=32,572), with array-based genotype data from the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium (n=131,340) imputed to the TOPMed or Haplotype Reference Consortium panel. We identified 18 loci that have not been identified in prior genetic studies of fibrinogen. Of these, four are driven by common variants of small effect with reported MAF at least 10% higher in African populations. Three ( SERPINA1, ZFP36L2 , and TLR10) signals contain predicted deleterious missense variants. Two loci, SOCS3 and HPN , each harbor two conditionally distinct, non-coding variants. The gene region encoding the protein chain subunits ( FGG;FGB;FGA ), contains 7 distinct signals, including one novel signal driven by rs28577061, a variant common (MAF=0.180) in African reference panels but extremely rare (MAF=0.008) in Europeans. Through phenome-wide association studies in the VA Million Veteran Program, we found associations between fibrinogen polygenic risk scores and thrombotic and inflammatory disease phenotypes, including an association with gout. Our findings demonstrate the utility of WGS to augment genetic discovery in diverse populations and offer new insights for putative mechanisms of fibrinogen regulation.

Key Points

Largest and most diverse genetic study of plasma fibrinogen identifies 54 regions (18 novel), housing 69 conditionally distinct variants (20 novel).Sufficient power achieved to identify signal driven by African population variant.Links to (1) liver enzyme, blood cell and lipid genetic signals, (2) liver regulatory elements, and (3) thrombotic and inflammatory disease.

Urine and Plasma Markers of Platelet Activation and Respiratory Symptoms in COPD

Introduction

Antiplatelet therapy has been associated with fewer exacerbations and reduced respiratory symptoms in chronic obstructive pulmonary disease (COPD). Whether platelet activation is associated with respiratory symptoms in COPD is unknown.

Methods

Former smokers with spirometry-confirmed COPD had urine 11-dehydro-thromboxane B2 (11dTxB2), plasma soluble CD40L (sCD40L), and soluble P-selectin (sP-selectin) repeatedly measured during a 6- to 9-month study period. Multivariate mixed-effects models adjusted for demographics, clinical characteristics, and medication use evaluated the association of each biomarker with respiratory symptoms, health status, and quality of life.

Results

Among 169 participants (average age 66.5±8.2 years, 51.5% female, 47.5±31 pack years, forced expiratory volume in 1 second percent predicted 53.8±17.1), a 100% increase in 11dTxB2 was associated with worse respiratory symptoms reflected by higher scores on the COPD Assessment Test (β 0.77, 95% confidence interval [CI]: 0.11-1.4) and Ease of Cough and Sputum Clearance Questionnaire β 0.77, 95%CI: 0.38-1.2, worse health status (Clinical COPD Questionnaire β 0.13, 95%CI: 0.03-0.23) and worse quality of life (St George's Respiratory Questionnaire β 1.9, 95%CI: 0.39-3.4). No statistically significant associations were observed for sCD40L or sP-selectin. There was no consistent statistically significant effect modification of the relationship between urine 11dTxB2 and respiratory outcomes by history of cardiovascular disease, subclinical coronary artery disease, antiplatelet therapy, or COPD severity.

Conclusions

In stable moderate-severe COPD, elevated urinary11dTxB2, a metabolite of the platelet activation product thromboxane A2, was associated with worse respiratory symptoms, health status, and quality of life.

Dendrimer nanotherapy for severe COVID-19 attenuates inflammation and neurological injury markers and improves outcomes in a phase2a clinical trial

Hyperinflammation triggered by SARS-CoV-2 is a major cause of disease severity, with activated macrophages implicated in this response. OP-101, a hydroxyl-polyamidoamine dendrimer-N-acetylcysteine conjugate that specifically targets activated macrophages, improves outcomes in preclinical models of systemic inflammation and neuroinflammation. In this multicenter, randomized, double-blind, placebo-controlled, adaptive phase 2a trial, we evaluated safety and preliminary efficacy of OP-101 in patients with severe COVID-19. Twenty-four patients classified as having severe COVID-19 with a baseline World Health Organization seven-point ordinal scale of ≥5 were randomized to receive a single intravenous dose of placebo (n = 7 patients) or OP-101 at 2 (n = 6), 4 (n = 6), or 8 mg/kg (n = 5 patients). All study participants received standard of care, including corticosteroids. OP-101 at 4 mg/kg was better than placebo at decreasing inflammatory markers; OP-101 at 4 and 8 mg/kg was better than placebo at reducing neurological injury markers, (neurofilament light chain and glial fibrillary acidic protein). Risk for the composite outcome of mechanical ventilation or death at 30 and 60 days after treatment was 71% (95% CI: 29%, 96%) for placebo and 18% (95% CI: 4%, 43%; P = 0.021) for the pooled OP-101 treatment arms. At 60 days, 3 of 7 patients given placebo and 14 of 17 OP-101-treated patients were surviving. No drug-related adverse events were reported. These data show that OP-101 was well tolerated and may have potential to treat systemic inflammation and neuronal injury, reducing morbidity and mortality in hospitalized patients with severe COVID-19.

Selected Transesophageal Echocardiographic Parameters of Left Ventricular Diastolic Function Predict Length of Stay Following Coronary Artery Bypass Graft-A Prospective Observational Study

(1) Importance: Abnormal left ventricular (LV) diastolic function, with or without a diagnosis of heart failure, is a common finding that can be easily diagnosed by intra-operative transesophageal echocardiography (TEE). The association of diastolic function with duration of hospital stay after coronary artery bypass (CAB) is unknown. (2) Objective: To determine if selected TEE parameters of diastolic dysfunction are associated with length of hospital stay after coronary artery bypass surgery (CAB). (3) Design: Prospective observational study. (4) Setting: A single tertiary academic medical center. (5) Participants: Patients with normal systolic function undergoing isolated CAB from September 2017 through June 2018. (6) Exposures: LV function during diastole, as assessed by intra-operative TEE prior to coronary revascularization. (7) Main Outcomes and Measures: The primary outcome was duration of postoperative hospital stay. Secondary intermediate outcomes included common postoperative cardiac, respiratory, and renal complications. (8) Results: The study included 176 participants (mean age 65.2 ± 9.2 years, 73% male); 105 (60.2%) had LV diastolic dysfunction based on selected TEE parameters. Median time to hospital discharge was significantly longer for subjects with selected parameters of diastolic dysfunction (9.1/IQR 6.6−13.5 days) than those with normal LV diastolic function (6.5/IAR 5.3−9.7 days) (p < 0.001). The probability of hospital discharge was 34% lower (HR 0.66/95% CI 0.47−0.93) for subjects with diastolic dysfunction based on selected TEE parameters, independent of potential confounders, including a baseline diagnosis of heart failure. There was a dose−response relation between severity of diastolic dysfunction and probability of discharge. LV diastolic dysfunction based on those selected TEE parameters was also associated with postoperative cardio-respiratory complications; however, these complications did not fully account for the relation between LV diastolic dysfunction and prolonged length of hospital stay. (9) Conclusions and Relevance: In patients with normal systolic function undergoing CAB, diastolic dysfunction based on selected TEE parameters is associated with prolonged duration of postoperative hospital stay. This association cannot be explained by baseline comorbidities or common post-operative complications. The diagnosis of diastolic dysfunction can be made by TEE.

Association Between Left Ventricular Relative Wall Thickness and Acute Kidney Injury After Noncardiac Surgery

BACKGROUND

Acute kidney injury (AKI) after major noncardiac surgery is commonly attributed to cardiovascular dysfunction. Identifying novel associations between preoperative cardiovascular markers and kidney injury may guide risk stratification and perioperative intervention. Increased left ventricular relative wall thickness (RWT), routinely measured on echocardiography, is associated with myocardial dysfunction and long-term risk of heart failure in patients with preserved left ventricular ejection fraction (LVEF); however, its relationship to postoperative complications has not been studied. We evaluated the association between preoperative RWT and AKI in high-risk noncardiac surgical patients with preserved LVEF.

METHODS

Patients ≥18 years of age having major noncardiac surgery (high-risk elective intra-abdominal or noncardiac intrathoracic surgery) between July 1, 2016, and June 30, 2018, who had transthoracic echocardiography in the previous 12 months were eligible. Patients with preoperative creatinine ≥2 mg/dL or reduced LVEF (<50%) were excluded. The association between RWT and AKI, defined as an increase in serum creatinine by 0.3 mg/dL from baseline within 48 hours or by 50% within 7 days after surgery, was assessed using multivariable logistic regression adjusted for preoperative covariates. An additional model adjusted for intraoperative covariates, which are strongly associated with AKI, especially hypotension. RWT was modeled continuously, associating the change in odds of AKI for each 0.1 increase in RWT.

RESULTS

The study included 1041 patients (mean ± standard deviation [SD] age 62 ± 15 years; 59% female). A total of 145 subjects (13.9%) developed AKI within 7 days. For RWT quartiles 1 through 4, respectively, 20 of 262 (7.6%), 40 of 259 (15.4%), 39 of 263 (14.8%), and 46 of 257 (17.9%) developed AKI. Log-odds and proportion with AKI increased across the observed RWT values. After adjusting for confounders (demographics, American Society of Anesthesiologists [ASA] physical status, comorbidities, baseline creatinine, antihypertensive medications, and left ventricular mass index), each RWT increase of 0.1 was associated with an estimated 26% increased odds of developing AKI (odds ratio [OR]; 95% confidence interval [CI]) of 1.26 (1.09-1.46; P = .002). After adjusting for intraoperative covariates (length of surgery, presence of an arterial line, intraoperative hypotension, crystalloid administration, transfusion, and urine output), RWT remained independently associated with the odds of AKI (OR; 95% CI) of 1.28 (1.13-1.47; P = .001). Increased RWT was also independently associated with hospital length of stay and adjusted hazard ratio (HR [95% CI]) of 0.94 (0.89-0.99; P = .018).

CONCLUSIONS

Left ventricular RWT is a novel cardiovascular factor associated with AKI within 7 days after high-risk noncardiac surgery among patients with preserved LVEF. Application of this commonly available measurement of risk stratification or perioperative intervention warrants further investigation.

Whole genome sequence analysis of platelet traits in the NHLBI Trans-Omics for Precision Medicine (TOPMed) initiative

Platelets play a key role in thrombosis and hemostasis. Platelet count (PLT) and mean platelet volume (MPV) are highly heritable quantitative traits, with hundreds of genetic signals previously identified, mostly in European ancestry populations. We here utilize whole genome sequencing (WGS) from NHLBI's Trans-Omics for Precision Medicine initiative (TOPMed) in a large multi-ethnic sample to further explore common and rare variation contributing to PLT (n = 61 200) and MPV (n = 23 485). We identified and replicated secondary signals at MPL (rs532784633) and PECAM1 (rs73345162), both more common in African ancestry populations. We also observed rare variation in Mendelian platelet-related disorder genes influencing variation in platelet traits in TOPMed cohorts (not enriched for blood disorders). For example, association of GP9 with lower PLT and higher MPV was partly driven by a pathogenic Bernard-Soulier syndrome variant (rs5030764, p.Asn61Ser), and the signals at TUBB1 and CD36 were partly driven by loss of function variants not annotated as pathogenic in ClinVar (rs199948010 and rs571975065). However, residual signal remained for these gene-based signals after adjusting for lead variants, suggesting that additional variants in Mendelian genes with impacts in general population cohorts remain to be identified. Gene-based signals were also identified at several genome-wide association study identified loci for genes not annotated for Mendelian platelet disorders (PTPRH, TET2, CHEK2), with somatic variation driving the result at TET2. These results highlight the value of WGS in populations of diverse genetic ancestry to identify novel regulatory and coding signals, even for well-studied traits like platelet traits.

Secondary analyses for genome-wide association studies using expression quantitative trait loci

Genome-wide association studies (GWAS) have successfully identified thousands of single nucleotide polymorphisms (SNPs) associated with complex traits; however, the identified SNPs account for a fraction of trait heritability, and identifying the functional elements through which genetic variants exert their effects remains a challenge. Recent evidence suggests that SNPs associated with complex traits are more likely to be expression quantitative trait loci (eQTL). Thus, incorporating eQTL information can potentially improve power to detect causal variants missed by traditional GWAS approaches. Using genomic, transcriptomic, and platelet phenotype data from the Genetic Study of Atherosclerosis Risk family-based study, we investigated the potential to detect novel genomic risk loci by incorporating information from eQTL in the relevant target tissues (i.e., platelets and megakaryocytes) using established statistical principles in a novel way. Permutation analyses were performed to obtain family-wise error rates for eQTL associations, substantially lowering the genome-wide significance threshold for SNP-phenotype associations. In addition to confirming the well known association between PEAR1 and platelet aggregation, our eQTL-focused approach identified a novel locus (rs1354034) and gene (ARHGEF3) not previously identified in a GWAS of platelet aggregation phenotypes. A colocalization analysis showed strong evidence for a functional role of this eQTL.

Whole-genome sequencing in diverse subjects identifies genetic correlates of leukocyte traits: The NHLBI TOPMed program

Many common and rare variants associated with hematologic traits have been discovered through imputation on large-scale reference panels. However, the majority of genome-wide association studies (GWASs) have been conducted in Europeans, and determining causal variants has proved challenging. We performed a GWAS of total leukocyte, neutrophil, lymphocyte, monocyte, eosinophil, and basophil counts generated from 109,563,748 variants in the autosomes and the X chromosome in the Trans-Omics for Precision Medicine (TOPMed) program, which included data from 61,802 individuals of diverse ancestry. We discovered and replicated 7 leukocyte trait associations, including (1) the association between a chromosome X, pseudo-autosomal region (PAR), noncoding variant located between cytokine receptor genes (CSF2RA and CLRF2) and lower eosinophil count; and (2) associations between single variants found predominantly among African Americans at the S1PR3 (9q22.1) and HBB (11p15.4) loci and monocyte and lymphocyte counts, respectively. We further provide evidence indicating that the newly discovered eosinophil-lowering chromosome X PAR variant might be associated with reduced susceptibility to common allergic diseases such as atopic dermatitis and asthma. Additionally, we found a burden of very rare FLT3 (13q12.2) variants associated with monocyte counts. Together, these results emphasize the utility of whole-genome sequencing in diverse samples in identifying associations missed by European-ancestry-driven GWASs.

An exploratory data quality analysis of time series physiologic signals using a large-scale intensive care unit database

Physiological data, such as heart rate and blood pressure, are critical to clinical decision-making in the intensive care unit (ICU). Vital signs data, which are available from electronic health records, can be used to diagnose and predict important clinical outcomes; While there have been some reports on the data quality of nurse-verified vital sign data, little has been reported on the data quality of higher frequency time-series vital signs acquired in ICUs, that would enable such predictive modeling. In this study, we assessed the data quality issues, defined as the completeness, accuracy, and timeliness, of minute-by-minute time series vital signs data within the MIMIC-III data set, captured from 16009 patient-ICU stays and corresponding to 9410 unique adult patients. We measured data quality of four time-series vital signs data streams in the MIMIC-III data set: heart rate (HR), respiratory rate (RR), blood oxygen saturation (SpO2), and arterial blood pressure (ABP). Approximately, 30% of patient-ICU stays did not have at least 1 min of data during the time-frame of the ICU stay for HR, RR, and SpO2. The percentage of patient-ICU stays that did not have at least 1 min of ABP data was ∼56%. We observed ∼80% coverage of the total duration of the ICU stay for HR, RR, and SpO2. Finally, only 12.5%%, 9.9%, 7.5%, and 4.4% of ICU lengths of stay had ≥ 99% data available for HR, RR, SpO2, and ABP, respectively, that would meet the three data quality requirements we looked into in this study. Our findings on data completeness, accuracy, and timeliness have important implications for data scientists and informatics researchers who use time series vital signs data to develop predictive models of ICU outcomes.

Gene and protein expression in human megakaryocytes derived from induced pluripotent stem cells

BACKGROUND

There is interest in deriving megakaryocytes (MKs) from pluripotent stem cells (iPSC) for biological studies. We previously found that genomic structural integrity and genotype concordance is maintained in iPSC-derived MKs.

OBJECTIVE

To establish a comprehensive dataset of genes and proteins expressed in iPSC-derived MKs.

METHODS

iPSCs were reprogrammed from peripheral blood mononuclear cells (MNCs) and MKs were derived from the iPSCs in 194 healthy European American and African American subjects. mRNA was isolated and gene expression measured by RNA sequencing. Protein expression was measured in 62 of the subjects using mass spectrometry.

RESULTS AND CONCLUSIONS

MKs expressed genes and proteins known to be important in MK and platelet function and demonstrated good agreement with previous studies in human MKs derived from CD34+ progenitor cells. The percent of cells expressing the MK markers CD41 and CD42a was consistent in biological replicates, but variable across subjects, suggesting that unidentified subject-specific factors determine differentiation of MKs from iPSCs. Gene and protein sets important in platelet function were associated with increasing expression of CD41/42a, while those related to more basic cellular functions were associated with lower CD41/42a expression. There was differential gene expression by the sex and race (but not age) of the subject. Numerous genes and proteins were highly expressed in MKs but not known to play a role in MK or platelet function; these represent excellent candidates for future study of hematopoiesis, platelet formation, and/or platelet function.

Whole-genome sequencing association analysis of quantitative red blood cell phenotypes: The NHLBI TOPMed program

Whole-genome sequencing (WGS), a powerful tool for detecting novel coding and non-coding disease-causing variants, has largely been applied to clinical diagnosis of inherited disorders. Here we leveraged WGS data in up to 62,653 ethnically diverse participants from the NHLBI Trans-Omics for Precision Medicine (TOPMed) program and assessed statistical association of variants with seven red blood cell (RBC) quantitative traits. We discovered 14 single variant-RBC trait associations at 12 genomic loci, which have not been reported previously. Several of the RBC trait-variant associations (RPN1, ELL2, MIDN, HBB, HBA1, PIEZO1, and G6PD) were replicated in independent GWAS datasets imputed to the TOPMed reference panel. Most of these discovered variants are rare/low frequency, and several are observed disproportionately among non-European Ancestry (African, Hispanic/Latino, or East Asian) populations. We identified a 3 bp indel p.Lys2169del (g.88717175_88717177TCT[4]) (common only in the Ashkenazi Jewish population) of PIEZO1, a gene responsible for the Mendelian red cell disorder hereditary xerocytosis (MIM: 194380), associated with higher mean corpuscular hemoglobin concentration (MCHC). In stepwise conditional analysis and in gene-based rare variant aggregated association analysis, we identified several of the variants in HBB, HBA1, TMPRSS6, and G6PD that represent the carrier state for known coding, promoter, or splice site loss-of-function variants that cause inherited RBC disorders. Finally, we applied base and nuclease editing to demonstrate that the sentinel variant rs112097551 (nearest gene RPN1) acts through a cis-regulatory element that exerts long-range control of the gene RUVBL1 which is essential for hematopoiesis. Together, these results demonstrate the utility of WGS in ethnically diverse population-based samples and gene editing for expanding knowledge of the genetic architecture of quantitative hematologic traits and suggest a continuum between complex trait and Mendelian red cell disorders.

Nasal Microbiota and Infectious Complications After Elective Surgical Procedures

IMPORTANCE

The association of the nasal microbiome with outcomes in surgical patients is poorly understood.

OBJECTIVE

To characterize the composition of nasal microbiota in patients undergoing clean elective surgical procedures and to examine the association between characteristics of preoperative nasal microbiota and occurrence of postoperative infection.

DESIGN, SETTING, AND PARTICIPANTS

Using a nested matched case-control design, 53 individuals who developed postoperative infection were matched (approximately 3:1 by age, sex, and surgical procedure) with 144 individuals who were not infected (ie, the control group). The 2 groups were selected from a prospective cohort of patients undergoing surgical procedures at 2 tertiary care university hospitals in Baltimore, Maryland, who were at high risk for postoperative infectious complications. Included individuals were aged 40 years or older; had no history of autoimmune disease, immunocompromised state, immune-modulating medication, or active infection; and were scheduled to undergo elective cardiac, vascular, spinal, or intracranial surgical procedure. Data were analyzed from October 2015 through September 2020.

EXPOSURES

Nasal microbiome cluster class served as the main exposure. An unsupervised clustering method (ie, grades of membership modeling) was used to classify nasal microbial samples into 2 groups based on features derived from 16S ribosomal RNA gene sequencing. The microbiome cluster groups were derived independently and agnostic of baseline clinical characteristics and infection status.

MAIN OUTCOMES AND MEASURES

Composite of surgical site infection, bacteremia, and pneumonia occurring within 6 months after surgical procedure.

RESULTS

Among 197 participants (mean [SD] age, 64.1 [10.6] years; 63 [37.7%] women), 553 bacterial taxa were identified from preoperative nasal swab samples. A 2-cluster model (with 167 patients in cluster 1 and 30 patients in cluster 2) accounted for the largest proportion of variance in microbial profiles using grades of membership modeling and was most parsimonious. After adjusting for potential confounders, the probability of assignment to cluster 2 was associated with 6-fold higher odds of infection after surgical procedure (odds ratio [OR], 6.18; 95% CI, 3.33-11.7; P < .001) independent of baseline clinical characteristics, including nasal carriage of Staphylococcus aureus. Intrasample (ie, α) diversity was inversely associated with infectious outcome in both clusters (OR, 0.57; 95% CI, 0.42-0.75; P < .001); however, probability of assignment to cluster 2 was associated with higher odds of infection independent of α diversity (OR, 4.61; 95% CI, 2.78-7.86; P < .001).

CONCLUSIONS AND RELEVANCE

These findings suggest that the nasal microbiome was an independent risk factor associated with infectious outcomes among individuals who underwent elective surgical procedures and may serve as a biomarker associated with infection susceptibility in this population.

Racial differences in platelet serotonin polymorphisms in acute coronary syndrome

INTRODUCTION

Genetic differences between races have been hypothesized to contribute to differences in outcome from acute coronary syndromes (ACS). Our objective was to assess racial differences in genetic variations in the platelet serotonin transporter (5HTT) and receptor in patients with ACS.

MATERIALS AND METHODS

127 consecutive patients, African Americans (AA) = 27; Caucasian (C) =100, admitted with ACS were evaluated for platelet function by serotonin (5HT) induced platelet activation. All patients were genotyped for two polymorphisms in the serotonin-transporter-linked polymorphic region (5-HTTLPR) S/L and L_G/L_A and one polymorphism of the serotonin 2A receptor (5-HT2A, T102C) gene. All patients were followed for major and minor adverse cardiac events at 12 months.

RESULTS

AA when compared to C had a lower prevalence of the HTTLPR S allele (21% vs 45%, p = 0.0003) and a higher prevalence of the L_G allele (24% vs 4.5%, p = 0.0001). Allelic frequency of the 5-HT2A T102C allele was not significantly different between the races. Platelet activation was lower in AA compared to C, median EC50 5HT was 12.08 μg vs 2.14 μg (p = 0.001). The 5-HTTLPR and the 5-HT2A polymorphisms were not associated with platelet functional responses to serotonin. There were no significant differences in major or minor adverse cardiac events in patients with serotonin transporter or receptor polymorphisms.

CONCLUSION

We found a lower prevalence of the S allele and a higher prevalence of the G allele in AA with ACS. We also found decreased platelet activation in AA which did not correlate with serotonin-related platelet polymorphisms. It is unclear if other contributing factors may explain these platelet functional differences.

Use of >100,000 NHLBI Trans-Omics for Precision Medicine (TOPMed) Consortium whole genome sequences improves imputation quality and detection of rare variant associations in admixed African and Hispanic/Latino populations

Most genome-wide association and fine-mapping studies to date have been conducted in individuals of European descent, and genetic studies of populations of Hispanic/Latino and African ancestry are limited. In addition, these populations have more complex linkage disequilibrium structure. In order to better define the genetic architecture of these understudied populations, we leveraged >100,000 phased sequences available from deep-coverage whole genome sequencing through the multi-ethnic NHLBI Trans-Omics for Precision Medicine (TOPMed) program to impute genotypes into admixed African and Hispanic/Latino samples with genome-wide genotyping array data. We demonstrated that using TOPMed sequencing data as the imputation reference panel improves genotype imputation quality in these populations, which subsequently enhanced gene-mapping power for complex traits. For rare variants with minor allele frequency (MAF) < 0.5%, we observed a 2.3- to 6.1-fold increase in the number of well-imputed variants, with 11-34% improvement in average imputation quality, compared to the state-of-the-art 1000 Genomes Project Phase 3 and Haplotype Reference Consortium reference panels. Impressively, even for extremely rare variants with minor allele count <10 (including singletons) in the imputation target samples, average information content rescued was >86%. Subsequent association analyses of TOPMed reference panel-imputed genotype data with hematological traits (hemoglobin (HGB), hematocrit (HCT), and white blood cell count (WBC)) in ~21,600 African-ancestry and ~21,700 Hispanic/Latino individuals identified associations with two rare variants in the HBB gene (rs33930165 with higher WBC [p = 8.8x10-15] in African populations, rs11549407 with lower HGB [p = 1.5x10-12] and HCT [p = 8.8x10-10] in Hispanics/Latinos). By comparison, neither variant would have been genome-wide significant if either 1000 Genomes Project Phase 3 or Haplotype Reference Consortium reference panels had been used for imputation. Our findings highlight the utility of the TOPMed imputation reference panel for identification of novel rare variant associations not previously detected in similarly sized genome-wide studies of under-represented African and Hispanic/Latino populations.

Diabetes and Platelet Response to Low-Dose Aspirin

CONTEXT

Previous studies have suggested less cardioprotective benefit of aspirin in adults with diabetes, raising concerns about "aspirin resistance" and potentially reduced effectiveness for prevention of cardiovascular disease (CVD).

OBJECTIVE

To examine differences in platelet response to aspirin by diabetes status.

DESIGN, SETTING, PARTICIPANTS

We examined platelet response before and after aspirin (81 mg/day for 14 days) in 2113 adults (175 with diabetes, 1,938 without diabetes), in the Genetic Study of Aspirin Responsiveness cohort, who had family history of early-onset CVD.

MAIN OUTCOME MEASURES

In vivo platelet activation (urinary thromboxane B2), in vitro platelet aggregation to agonists (arachidonic acid, adenosine diphosphate, collagen), and platelet function analyzer-100 closure time.

RESULTS

Although adults with diabetes had higher in vivo platelet activation before aspirin, the reduction in in vivo platelet activation after aspirin was similar in those with vs without diabetes. Likewise, the reduction in multiple in vitro platelet measures was similar after aspirin by diabetes status. In regression analyses adjusted for age, sex, race, BMI, smoking, platelet counts, and fibrinogen levels, in vivo platelet activation remained higher in adults with vs without diabetes after aspirin (P = 0.04), but this difference was attenuated after additional adjustment for preaspirin levels (P = 0.10). No differences by diabetes status were noted for any of the in vitro platelet measures after aspirin in fully adjusted models that also accounted for preaspirin levels.

CONCLUSIONS

In vitro platelet response to aspirin does not differ by diabetes status, suggesting no intrinsic differences in platelet response to aspirin. Instead, factors extrinsic to platelet function should be investigated to give further insights into aspirin use for primary prevention in diabetes.

The Effects of Bedrest on Circadian Changes in Hemostasis

Venous stasis occurs when people are at bedrest, because of altered venous flow characteristics. This is commonly believed to be one etiology behind the development of deep venous thrombosis (DVT). The hemostatic effects of bedrest and their possible role in DVT development have not been fully examined. We hypothesized that bedrest would lead to increases in hemostatic function and that these increases could be important in the development of DVT.

Twelve non-smoking volunteers were studied during supine positioning for 36 hours. Platelet reactivity and plasma concentrations of fibrinogen, a2-antiplasmin, plasminogen, thromboxane (32, plasminogen activator inhibitor-1, tissue plasminogen activator and neuroendocrine hormones (cortisol, epinephrine and norepinephrine) were measured at 8:00 a.m., 10:00 a.m., 4:00 p.m. and 8:00 a.m.

Cortisol demonstrated an early morning increase while catecholamines were unchanged throughout. Fibrinogen, a2-antiplasmin, plasminogen and platelet reactivity were no different at any time point. Fibrinolytic proteins changed over time, manifested by decreased PAI-1 antigen and activity levels at 24 h.

Based upon the parameters measured, bedrest causes no increase in hemostatic function. In fact, bedrest causes the potential for enhanced fibrinolysis, that differs from that previously reported for normal activity over 24 h. This may represent a protective mechanism to counter the effects of stasis from bedrest.

Gender Differences in Platelet GPIIb-IIIa Activation

Gender differences in the development of thrombotic diseases have been described in numerous clinical settings. Enhanced platelet reactivity in both sexes is associated with the development of vascular thromboses. Because activation of platelet GPIIb-IIIa receptors is a central event in thrombus formation, we examined GPIIb-IIIa function in normal male and female volunteers. Using flow cytometry, we quantitated gender differences in the number of binding sites for FITC-labeled fibrinogen (FITC-FGN) and FITC-labeled PAC-1 antibody (FITC-PAC-1). Washed platelets were incubated with either FITC-FGN or FITC-PAC-1 and activated with either ADP or thrombin receptor activating peptide (TRAP) prior to cytometric acquisition of data. The dissociation constant for FITC-FGN was the same in both sexes (approx. 1.6 x 10-7M), however, the number of GPIIb-IIIa receptors per platelet capable of binding fibrinogen was significantly greater in women than men in response to 20μM ADP (16,319 ± 1871 vs 9669±1994, p = 0.02), 20μM ADP (39,951 ± 4711 vs 25,948 ± 4953, p = 0.05) and 50μM TRAP (39,236 ± 3965 vs 21,848 ± 4159, p = 0.007). Similarly, the number of GPIIb-IIIa receptors capable of binding PAC-1 in response to ADP and TRAP was 50% to 80% greater in women than men. Binding experiments using specific anti-GPIIb-IIIa monoclonal antibodies (P2 and 10E5), as well as quantitative Western blotting experiments, showed no gender difference in the total number of GPIIb-IIIa molecules expressed. Analysis of data from female subgroups demonstrated an association of GPIIb-IIIa reactivity with menstrual phase. We conclude that GPIIb-IIIa receptors on platelets from premenopausal women are more “activatable” than those on platelets from young men. Variations in the serum concentrations of estrogens and/or progestins may modulate GPIIb-IIIa function.

Targeted deep sequencing of the PEAR1 locus for platelet aggregation in European and African American families

Coronary artery disease (CAD) remains a major cause of mortality and morbidity worldwide. The aggregation of activated platelets on a ruptured atherosclerotic plaque is a critical step in most acute cardiovascular events like myocardial infarction. Platelet aggregation both at baseline and after aspirin is highly heritable. Genome-wide association studies (GWAS) have identified a common variant within the first intron of the platelet endothelial aggregation receptor1 (PEAR1), to be robustly associated with platelet aggregation. In this study, we used targeted deep sequencing to fine-map the prior GWAS peak and identify additional rare variants of PEAR1 that account for missing heritability in platelet aggregation within the GeneSTAR families. In this study, 1709 subjects (1043 European Americans, EA and 666 African Americans, AA) from families in the GeneSTAR study were included. In vitro platelet aggregation in response to collagen, ADP and epinephrine was measured at baseline and 14 days after aspirin therapy (81 mg/day). Targeted deep sequencing of PEAR1 in addition to 2kb of upstream and downstream of the gene was performed. Under an additive genetic model, the association of single variants of PEAR1 with platelet aggregation phenotypes were examined. Additionally, we examined the association between the burden of PEAR1 rare non-synonymous variants and platelet aggregation phenotypes. Of 532 variants identified through sequencing, the intron 1 variant, rs12041331, was significantly associated with all platelet aggregation phenotypes at baseline and after platelet inhibition with aspirin therapy. rs12566888, which is in linkage disequilibrium with rs12041331, was associated with platelet aggregation phenotypes but to a lesser extent. In the EA families, the burden of PEAR1 missense variants was associated with platelet aggregation after aspirin therapy when the platelets were stimulated with epinephrine (p = 0.0009) and collagen (p = 0.03). In AAs, the burden of PEAR1 missense variants was associated, to a lesser degree, with platelet aggregation in response to epinephrine (p = 0.02) and ADP (p = 0.04). Our study confirmed that the GWAS-identified variant, rs12041331, is the strongest variant associated with platelet aggregation both at baseline and after aspirin therapy in our GeneSTAR families in both races. We identified additional association of rare missense variants in PEAR1 with platelet aggregation following aspirin therapy. However, we observed a racial difference in the contribution of these rare variants to the platelet aggregation, most likely due to higher residual missing heritability of platelet aggregation after accounting for rs12041331 in the EAs compared to AAs.

Separating fast and slow exchange transfer and magnetization transfer using off-resonance variable-delay multiple-pulse (VDMP) MRI

PURPOSE

To develop a method that can separate and quantify the fast (>1 kHz) and slow exchange transfer and magnetization transfer components in Z-spectra.

METHODS

Z-spectra were recorded as a function of mixing time using a train of selective pulses providing variable-delay multipulse build-up curves. Fast and slow transfer components in the Z-spectra were separated and quantified on a voxel-by-voxel basis by fitting the mixing time-dependent CEST signal using a 3-pool model.

RESULTS

Phantom studies of glutamate solution, bovine serum albumin solution, and hair conditioner showed the capability of the proposed method to separate fast and slow transfer components. In vivo mouse brain studies showed a strong contrast between white matter and gray matter in the slow-transferring map, corresponding to an asymmetric component of the conventional semisolid magnetization transfer contrast. In addition, a fast-transferring proton map was found that was homogeneous across the brain and attributed to the total contributions of the fast-exchanging protons from proteins, metabolites, and a symmetric magnetization transfer contrast component.

CONCLUSIONS

This new method provides a simple way to extract fast and slow transfer components from the Z-spectrum, leading to novel MRI contrasts, and providing insight into the different magnetization transfer contrast contributions.

Exome-chip meta-analysis identifies association between variation in ANKRD26 and platelet aggregation

Previous genome-wide association studies (GWAS) have identified several variants associated with platelet function phenotypes; however, the proportion of variance explained by the identified variants is mostly small. Rare coding variants, particularly those with high potential for impact on protein structure/function, may have substantial impact on phenotype but are difficult to detect by GWAS. The main purpose of this study was to identify low frequency or rare variants associated with platelet function using genotype data from the Illumina HumanExome Bead Chip. Three family-based cohorts of European ancestry, including ~4,000 total subjects, comprised the discovery cohort and two independent cohorts, one of European and one of African American ancestry, were used for replication. Optical aggregometry in platelet-rich plasma was performed in all the discovery cohorts in response to adenosine diphosphate (ADP), epinephrine, and collagen. Meta-analyses were performed using both gene-based and single nucleotide variant association methods. The gene-based meta-analysis identified a significant association (P = 7.13 × 10^-7) between rare genetic variants in ANKRD26 and ADP-induced platelet aggregation. One of the ANKRD26 SNVs - rs191015656, encoding a threonine to isoleucine substitution predicted to alter protein structure/function, was replicated in Europeans. Aggregation increases of ~20-50% were observed in heterozygotes in all cohorts. Novel genetic signals in ABCG1 and HCP5 were also associated with platelet aggregation to ADP in meta-analyses, although only results for HCP5 could be replicated. The SNV in HCP5 intersects epigenetic signatures in CD41+ megakaryocytes suggesting a new functional role in platelet biology for HCP5. This is the first study to use gene-based association methods from SNV array genotypes to identify rare variants related to platelet function. The molecular mechanisms and pathophysiological relevance for the identified genetic associations requires further study.

Association of Selective Serotonin Reuptake Inhibitors with Transfusion in Surgical Patients

BACKGROUND

The clinical relevance of chronic exposure to selective serotonin reuptake inhibitors (SSRIs) to transfusion in surgical patients is unclear.

METHODS

We conducted a prospective cohort study involving patients undergoing cardiac, vascular, spinal, and intracranial surgery at 2 academic medical centers. Medication use, demographics, comorbidities, and laboratory values were determined at baseline by patient interview and review of medical records. The primary outcome was transfusion of any hemostatic allogeneic blood product (i.e., fresh frozen plasma, platelets, and/or cryoprecipitate) through postoperative day 2.

RESULTS

The study sample consisted of 767 patients; 364 patients (47.5%) underwent cardiac surgery and the remainder underwent noncardiac surgery. Eighty-eight patients (11.5%) used SSRIs preoperatively. Among cardiac patients, the absolute number of allogeneic transfusions was higher for SSRI users than nonusers (2 [0-6] vs 0 [0-2], median [25%-75%], respectively, P = 0.008), and a similar trend was observed for noncardiac surgery. After adjusting for covariates using ordinal logistic regression, preoperative SSRI use was associated with an approximately 2-fold (odds ratio, 2.2; 95% confidence interval, 1.2-3.98) increase in odds of exposure to allogeneic hemostatic blood products; similar results were observed using propensity score adjustment (odds ratio, 1.85; 95% confidence interval, 1.11-3.07). A significant interaction between SSRI use and surgery type, age, sex, or concurrent antiplatelet therapy was not found; however, heterogeneity in magnitude of effect could not be excluded.

CONCLUSIONS

Preoperative use of SSRIs is associated with increased exposure to allogeneic hemostatic blood products in surgical patients at high risk for perioperative bleeding. Determining whether perioperative continuation or withdrawal of SSRIs produces a net clinical benefit requires randomized controlled trials.

Whole exome sequencing in the Framingham Heart Study identifies rare variation in HYAL2 that influences platelet aggregation

Inhibition of platelet reactivity is a common therapeutic strategy in secondary prevention of cardiovascular disease. Genetic and environmental factors influence inter-individual variation in platelet reactivity. Identifying genes that contribute to platelet reactivity can reveal new biological mechanisms and possible therapeutic targets. Here, we examined rare coding variation to identify genes associated with platelet reactivity in a population-based cohort. To do so, we performed whole exome sequencing in the Framingham Heart Study and conducted single variant and gene-based association tests against platelet reactivity to collagen, adenosine diphosphate (ADP), and epinephrine agonists in up to 1,211 individuals. Single variant tests revealed no significant associations (p<1.44×10^-7), though we observed a suggestive association with previously implicated MRVI1 (rs11042902, p = 1.95×10^-7). Using gene-based association tests of rare and low-frequency variants, we found significant associations of HYAL2 with increased ADP-induced aggregation (p = 1.07×10^-7) and GSTZ1 with increased epinephrine-induced aggregation (p = 1.62×10^-6). HYAL2 also showed suggestive associations with epinephrine-induced aggregation (p = 2.64×10^-5). The rare variants in the HYAL2 gene-based association included a missense variant (N357S) at a known N-glycosylation site and a nonsense variant (Q406*) that removes a glycophosphatidylinositol (GPI) anchor from the resulting protein. These variants suggest that improper membrane trafficking of HYAL2 influences platelet reactivity. We also observed suggestive associations of AR (p = 7.39×10^-6) and MAPRE1 (p = 7.26×10^-6) with ADP-induced reactivity. Our study demonstrates that gene-based tests and other grouping strategies of rare variants are powerful approaches to detect associations in population-based analyses of complex traits not detected by single variant tests and possible new genetic influences on platelet reactivity.

Platelet glycoproteins associated with aspirin-treatment upon platelet activation

Platelet glycoproteins are known to play central roles in hemostasis and vascular integrity and have pathologic roles in vascular occlusive diseases such as myocardial infarction and stroke. Characterizing glycoproteins within and secreted by platelets can provide insight into the mechanisms that underlie vascular pathologies and the therapeutic benefits or failure of anti-platelet agents. To study the impact of aspirin, which is commonly prescribed for primary and secondary cardiovascular prevention, on the platelet glycoproteome, we evaluated washed platelets from ten donors. The platelet glycoproteome, was studied using an iTRAQ in resting and stimulated states and with and without aspirin treatment. Using solid phase extraction of glycosite-containing peptides (SPEG), we were able to identify 799 unique N-linked glycosylation sites (glycosites) in platelets, representing the largest and the most comprehensive analysis to date. We were able to identity a number of glycoproteins impacted by aspirin treatment, which we validated using global proteomics analysis of platelets and their secreted proteins. In our analyses, metallopeptidase inhibitor 1 (TIMP1) was the single most significantly affected glycoprotein by aspirin treatment. ELISA assays confirmed proteomic results and validated our strategy. Functional analysis demonstrated that TIMP1 levels were highly correlated with platelet reactivity in vitro, with a correlation coefficient of -0.5. The release of TIMP1 from platelets, which was previously unknown to be affected by aspirin treatment, may play important roles in hemostasis and/or vascular integrity. If validated, our findings may be useful for developing assays that assess platelet response to aspirin or other anti-platelet therapies.

Integrity of Induced Pluripotent Stem Cell (iPSC) Derived Megakaryocytes as Assessed by Genetic and Transcriptomic Analysis

Previously, we have described our feeder-free, xeno-free approach to generate megakaryocytes (MKs) in culture from human induced pluripotent stem cells (iPSCs). Here, we focus specifically on the integrity of these MKs using: (1) genotype discordance between parent cell DNA to iPSC cell DNA and onward to the differentiated MK DNA; (2) genomic structural integrity using copy number variation (CNV); and (3) transcriptomic signatures of the derived MK lines compared to the iPSC lines. We detected a very low rate of genotype discordance; estimates were 0.0001%-0.01%, well below the genotyping error rate for our assay (0.37%). No CNVs were generated in the iPSCs that were subsequently passed on to the MKs. Finally, we observed highly biologically relevant gene sets as being upregulated in MKs relative to the iPSCs: platelet activation, blood coagulation, megakaryocyte development, platelet formation, platelet degranulation, and platelet aggregation. These data strongly support the integrity of the derived MK lines.

Large-Scale Exome-wide Association Analysis Identifies Loci for White Blood Cell Traits and Pleiotropy with Immune-Mediated Diseases

White blood cells play diverse roles in innate and adaptive immunity. Genetic association analyses of phenotypic variation in circulating white blood cell (WBC) counts from large samples of otherwise healthy individuals can provide insights into genes and biologic pathways involved in production, differentiation, or clearance of particular WBC lineages (myeloid, lymphoid) and also potentially inform the genetic basis of autoimmune, allergic, and blood diseases. We performed an exome array-based meta-analysis of total WBC and subtype counts (neutrophils, monocytes, lymphocytes, basophils, and eosinophils) in a multi-ancestry discovery and replication sample of ∼157,622 individuals from 25 studies. We identified 16 common variants (8 of which were coding variants) associated with one or more WBC traits, the majority of which are pleiotropically associated with autoimmune diseases. Based on functional annotation, these loci included genes encoding surface markers of myeloid, lymphoid, or hematopoietic stem cell differentiation (CD69, CD33, CD87), transcription factors regulating lineage specification during hematopoiesis (ASXL1, IRF8, IKZF1, JMJD1C, ETS2-PSMG1), and molecules involved in neutrophil clearance/apoptosis (C10orf54, LTA), adhesion (TNXB), or centrosome and microtubule structure/function (KIF9, TUBD1). Together with recent reports of somatic ASXL1 mutations among individuals with idiopathic cytopenias or clonal hematopoiesis of undetermined significance, the identification of a common regulatory 3' UTR variant of ASXL1 suggests that both germline and somatic ASXL1 mutations contribute to lower blood counts in otherwise asymptomatic individuals. These association results shed light on genetic mechanisms that regulate circulating WBC counts and suggest a prominent shared genetic architecture with inflammatory and autoimmune diseases.

Platelet-Related Variants Identified by Exomechip Meta-analysis in 157,293 Individuals

Platelet production, maintenance, and clearance are tightly controlled processes indicative of platelets' important roles in hemostasis and thrombosis. Platelets are common targets for primary and secondary prevention of several conditions. They are monitored clinically by complete blood counts, specifically with measurements of platelet count (PLT) and mean platelet volume (MPV). Identifying genetic effects on PLT and MPV can provide mechanistic insights into platelet biology and their role in disease. Therefore, we formed the Blood Cell Consortium (BCX) to perform a large-scale meta-analysis of Exomechip association results for PLT and MPV in 157,293 and 57,617 individuals, respectively. Using the low-frequency/rare coding variant-enriched Exomechip genotyping array, we sought to identify genetic variants associated with PLT and MPV. In addition to confirming 47 known PLT and 20 known MPV associations, we identified 32 PLT and 18 MPV associations not previously observed in the literature across the allele frequency spectrum, including rare large effect (FCER1A), low-frequency (IQGAP2, MAP1A, LY75), and common (ZMIZ2, SMG6, PEAR1, ARFGAP3/PACSIN2) variants. Several variants associated with PLT/MPV (PEAR1, MRVI1, PTGES3) were also associated with platelet reactivity. In concurrent BCX analyses, there was overlap of platelet-associated variants with red (MAP1A, TMPRSS6, ZMIZ2) and white (PEAR1, ZMIZ2, LY75) blood cell traits, suggesting common regulatory pathways with shared genetic architecture among these hematopoietic lineages. Our large-scale Exomechip analyses identified previously undocumented associations with platelet traits and further indicate that several complex quantitative hematological, lipid, and cardiovascular traits share genetic factors.

Abstract W P236: Role of Leukocyte Cathepsin G in an Atherothrombotic Stroke Model

The majority of ischemic strokes in humans are caused by atheroemboli that originate from extracranial vessels, activate platelets and produce thrombi that occlude intracranial vessels. Most of the current stroke models do not simulate the mechanisms of endogenous thrombus interaction with blood elements, the vascular wall and its extracellular matrix, and thus do not translate well for the study of atherothrombotic mechanisms. To overcome these shortcomings, we developed an atherothrombotic stroke model. We used this model to determine the pathophysiologic role of leukocyte cathepsin G, a serine protease with pro-thrombotic properties, in stroke and to determine its suitability as a molecular target for therapy. We hypothesized that deficiency of cathepsin G will reduce intravascular thrombus formation, decrease infarct volume and improve neurobehavioral deficit in a mouse atherothrombotic stroke model.

Male C57Bl/6 (WT) and cathepsin G knockout mice (CG-/-) were used. A PE8 catheter was advanced into the ICA near the MCA origin and a reduction in cortical laser-Doppler flow was induced after a series of intra-arterial injections of collagen, a platelet activator and component of ruptured atherosclerotic plaque. Mice were sacrificed 3h post-collagen injection for histologic examination, or 48h post-collagen for infarct volume quantification and neurobehavioral assessment.

Gross examination of excised brains 3h post-collagen revealed thrombi within the main ICA in 71% (5/7) of WT mice and 0% of CG-/- mice (p=0.005), branches of the ICA in 0 WT mice and 29% (2/7) of CG-/- mice (p=0.13), in the main MCA in 43% (3/7) of WT mice and 0 CG-/- mice (p=0.05), and distal branches of the MCA in 100% (7/7) of WT and CG-/- mice. Immunofluorescence microscopy confirmed that platelets and fibrin were major components of these thrombi. Cerebral infarct in WT mice was 33% ± 9% of hemispheric volume and 19% ± 1% in CG-/- mice (p=0.02). Neurobehavioral deficit 48h post-collagen was reduced in CG-/- mice compared to WT.

Using a novel atherothrombotic stroke model, these data reveal an important role of cathepsin G in cerebrovascular thrombus formation and a novel mechanism linking inflammatory cells to ischemic brain injury- a link commonly observed in human clinical studies.

A novel atherothrombotic model of ischemic stroke induced by injection of collagen into the cerebral vasculature

BACKGROUND

Most ischemic strokes in humans are caused by ruptured arterial atheroma, which activate platelets and produce thrombi that occlude cerebral vessels.

METHODS

To simulate these events, we threaded a catheter through the internal carotid artery toward the middle cerebral artery (MCA) orifice and injected collagen directly into the cerebral circulation of male C57Bl/6 mice and Wistar rats.

RESULTS

Laser-Doppler flowmetry demonstrated reductions in cerebral blood flow (CBF) of ∼80% in mice and ∼60% in rats. CBF spontaneously increased but remained depressed after catheter withdrawal. Magnetic resonance imaging showed that ipsilateral CBF was reduced at 3h after collagen injection and markedly improved at 48 h. Micro-computed tomography revealed reduced blood vessel density in the ipsilateral MCA territory at 3 h. Gross examination of excised brains revealed thrombi within ipsilateral cerebral arteries at 3 h, but not 24 h, after collagen injection. Immunofluorescence microscopy confirmed that platelets and fibrinogen/fibrin were major components of these thrombi at both macrovascular and microvascular levels. Cerebral infarcts comprising ∼30% of hemispheric volume and neurobehavioral deficits were observed 48 h after ischemic injury in both mice and rats.

COMPARISON WITH EXISTING METHODS

Collagen injection caused brain injury that was similar in magnitude and variability to mechanical MCA occlusion or injection of a pre-formed clot; however, alterations in CBF and the mechanism of vascular occlusion were more consistent with clinical ischemic stroke.

CONCLUSION

This novel rodent model of ischemic stroke has pathophysiologic characteristics consistent with clinical atherothrombotic stroke, is technically feasible, and creates reproducible brain injury.

Greater collagen-induced platelet aggregation following cyclooxygenase 1 inhibition predicts incident acute coronary syndromes

Greater ex vivo platelet aggregation to agonists may identify individuals at risk of acute coronary syndromes (ACS). However, increased aggregation to a specific agonist may be masked by inherent variability in other activation pathways. In this study, we inhibited the cyclooxygenase-1 (COX1) pathway with 2-week aspirin therapy and measured residual aggregation to collagen and ADP to determine whether increased aggregation in a non-COX1 pathway is associated with incident ACS. We assessed ex vivo whole blood platelet aggregation in 1,699 healthy individuals with a family history of early-onset coronary artery disease followed for 6±1.2 years. Incident ACS events were observed in 22 subjects. Baseline aggregation was not associated with ACS. After COX1 pathway inhibition, collagen-induced aggregation was significantly greater in participants with ACS compared with those without (29.0 vs. 23.6 ohms, p < 0.001). In Cox proportional hazards models, this association remained significant after adjusting for traditional cardiovascular risk factors (HR = 1.10, 95%CI = 1.06-1.15; p < 0.001). In contrast, ADP-induced aggregation after COX1 inhibition was not associated with ACS. After COX1 pathway inhibition, subjects with greater collagen-induced platelet aggregation demonstrated a significant excess risk of incident ACS. These data suggest that platelet activation related to collagen may play an important role in the risk of ACS.

Abstract 536: RNA-Seq Identifies Differential Expression of Platelet Transcripts Between People With Hyper- and Hypoaggregation to Collagen

Background: Platelet aggregation plays an important role in the pathogenesis of myocardial infarction, and high platelet aggregability is associated with increased risk of events. We hypothesized that inter-individual variability in platelet function is associated with differences in the mRNA transcripts found in platelets from hyper-aggregators and hypo-aggregators.

Methods: Eight African American (discovery cohort) and four European American (validation cohort) males with family history of early onset coronary artery disease were enrolled. Individuals were divided into hyper- and hypo-aggregators based on maximal aggregation to collagen using whole blood impedance aggregometry. RNA was extracted from leukocyte-depleted platelet-rich plasma and approximately 70 million 100bp paired-end reads per sample were obtained using an Illumina HiSeq 2500. RNA-seq analysis was performed using Bowtie/TopHat/Cufflinks software pipeline. Genes with expression ≥ 1 fragments per kilobase of transcript per million reads (FPKM) were considered to be expressed. On log2 scale, ≥ 2-fold (discovery cohort) and ≥ 1-fold (replication cohort) change in gene expression were considered to be significantly differentially expressed.

Results: Among the 9,373 expressed genes, the most highly expressed nonubiquitous genes included GP1BB, GP9, PPBP, PF4, & TUBB1, confirming our methods. Hyper-aggregability was associated with up-regulation of 239 genes and down-regulation of 29 genes in the discovery cohort (44 and 2 replicated in validation cohort respectively). Pathway analysis found that genes related to sphingosine-1P3 (such as RHOA [ras homolog family member A], GNAZ [G protein, alpha z polypeptide], VEGFA [vascular endothelial growth factor A]) and platelet aggregation pathways (such as GP9 [platelet glycoprotein IX], TLN1 [talin 1], ITGB3 [platelet glycoprotein IIIa]) were up-regulated in hyper-aggregators.

Conclusion: RNA-seq and pathway analyses found that hyper- and hypo-aggregators have significant differences in gene expression. Increased expression of sphingosine-1P3 and platelet aggregation pathway genes in hyper-aggregators highlights the relationship of signal transduction with increased platelet aggregation.

Cathepsin G-dependent modulation of platelet thrombus formation in vivo by blood neutrophils

Neutrophils are consistently associated with arterial thrombotic morbidity in human clinical studies but the causal basis for this association is unclear. We tested the hypothesis that neutrophils modulate platelet activation and thrombus formation in vivo in a cathepsin G-dependent manner. Neutrophils enhanced aggregation of human platelets in vitro in dose-dependent fashion and this effect was diminished by pharmacologic inhibition of cathepsin G activity and knockdown of cathepsin G expression. Tail bleeding time in the mouse was prolonged by a cathepsin G inhibitor and in cathepsin G knockout mice, and formation of neutrophil-platelet conjugates in blood that was shed from transected tails was reduced in the absence of cathepsin G. Bleeding time was highly correlated with blood neutrophil count in wildtype but not cathepsin G deficient mice. In the presence of elevated blood neutrophil counts, the anti-thrombotic effect of cathepsin G inhibition was greater than that of aspirin and additive to it when administered in combination. Both pharmacologic inhibition of cathepsin G and its congenital absence prolonged the time for platelet thrombus to form in ferric chloride-injured mouse mesenteric arterioles. In a vaso-occlusive model of ischemic stroke, inhibition of cathepsin G and its congenital absence improved cerebral blood flow, reduced histologic brain injury, and improved neurobehavioral outcome. These experiments demonstrate that neutrophil cathepsin G is a physiologic modulator of platelet thrombus formation in vivo and has potential as a target for novel anti-thrombotic therapies.

Targeted deep resequencing identifies coding variants in the PEAR1 gene that play a role in platelet aggregation

Platelet aggregation is heritable, and genome-wide association studies have detected strong associations with a common intronic variant of the platelet endothelial aggregation receptor1 (PEAR1) gene both in African American and European American individuals. In this study, we used a sequencing approach to identify additional exonic variants in PEAR1 that may also determine variability in platelet aggregation in the GeneSTAR Study. A 0.3 Mb targeted region on chromosome 1q23.1 including the entire PEAR1 gene was Sanger sequenced in 104 subjects (45% male, 49% African American, age = 52±13) selected on the basis of hyper- and hypo- aggregation across three different agonists (collagen, epinephrine, and adenosine diphosphate). Single-variant and multi-variant burden tests for association were performed. Of the 235 variants identified through sequencing, 61 were novel, and three of these were missense variants. More rare variants (MAF<5%) were noted in African Americans compared to European Americans (108 vs. 45). The common intronic GWAS-identified variant (rs12041331) demonstrated the most significant association signal in African Americans (p = 4.020×10(-4)); no association was seen for additional exonic variants in this group. In contrast, multi-variant burden tests indicated that exonic variants play a more significant role in European Americans (p = 0.0099 for the collective coding variants compared to p = 0.0565 for intronic variant rs12041331). Imputation of the individual exonic variants in the rest of the GeneSTAR European American cohort (N = 1,965) supports the results noted in the sequenced discovery sample: p = 3.56×10(-4), 2.27×10(-7), 5.20×10(-5) for coding synonymous variant rs56260937 and collagen, epinephrine and adenosine diphosphate induced platelet aggregation, respectively. Sequencing approaches confirm that a common intronic variant has the strongest association with platelet aggregation in African Americans, and show that exonic variants play an additional role in platelet aggregation in European Americans.

Genetic variation in PEAR1 is associated with platelet aggregation and cardiovascular outcomes

BACKGROUND- Aspirin or dual antiplatelet therapy with aspirin and clopidogrel is a standard therapy for patients who are at increased risk for cardiovascular events. However, the genetic determinants of variable response to aspirin (alone and in combination with clopidogrel) are not known. METHODS AND RESULTS- We measured ex vivo platelet aggregation before and after dual antiplatelet therapy in individuals (n=565) from the Pharmacogenomics of Anti-Platelet Intervention (PAPI) Study and conducted a genome-wide association study of drug response. Significant findings were extended by examining genotype and cardiovascular outcomes in 2 independent aspirin-treated cohorts: 227 percutaneous coronary intervention patients and 1000 patients of the International Verapamil SR/Trandolapril Study (INVEST) Genetic Substudy (INVEST-GENES). Results from the genome-wide association study revealed a strong association between single-nucleotide polymorphisms on chromosome 1q23 and post-dual antiplatelet therapyplatelet aggregation. Further genotyping revealed rs12041331 in the platelet endothelial aggregation receptor-1 (PEAR1) gene to be most strongly associated with dual antiplatelet therapy response (P=7.66×10(-9)). In white and black patients undergoing percutaneous coronary intervention, A-allele carriers of rs12041331 were more likely to experience a cardiovascular event or death compared with GG homozygotes (hazard ratio, 2.62; 95% confidence interval, 0.96-7.10; P=0.059; and hazard ratio, 3.97; 95% confidence interval, 1.10-14.31; P=0.035, respectively). In aspirin-treated INVEST-GENES patients, rs12041331 A-allele carriers had significantly increased risk of myocardial infarction compared with GG homozygotes (odds ratio, 2.03; 95% confidence interval, 1.01-4.09; P=0.048). CONCLUSION- Common genetic variation in PEAR1 may be a determinant of platelet response and cardiovascular events in patients on aspirin alone or in combination with clopidogrel. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifiers: NCT00799396 and NCT00370045.

Emergency cardiac surgery in patients with acute coronary syndromes: a review of the evidence and perioperative implications of medical and mechanical therapeutics

Patients with acute coronary syndromes who require emergency cardiac surgery present complex management challenges. The early administration of antiplatelet and antithrombotic drugs has improved overall survival for patients with acute myocardial infarction, but to achieve maximal benefit, these drugs are given before coronary anatomy is known and before the decision to perform percutaneous coronary interventions or surgical revascularization has been made. A major bleeding event secondary to these drugs is associated with a high rate of death in medically treated patients with acute coronary syndrome possibly because of subsequent withholding of antiplatelet and antithrombotic therapies that otherwise reduce the rate of death, stroke, or recurrent myocardial infarction. Whether the added risk of bleeding and blood transfusion in cardiac surgical patients receiving such potent antiplatelet or antithrombotic therapy before surgery specifically for acute coronary syndromes affects long-term mortality has not been clearly established. For patients who do proceed to surgery, strategies to minimize bleeding include stopping the anticoagulation therapy and considering platelet and/or coagulation factor transfusion and possibly recombinant-activated factor VIIa administration for refractory bleeding. Mechanical hemodynamic support has emerged as an important option for patients with acute coronary syndromes in cardiogenic shock. For these patients, perioperative considerations include maintaining appropriate anticoagulation, ensuring suitable device flow, and periodically verifying correct device placement. Data supporting the use of these devices are derived from small trials that did not address long-term postoperative outcomes. Future directions of research will seek to optimize the balance between reducing myocardial ischemic risk with antiplatelet and antithrombotics versus the higher rate perioperative bleeding by better risk stratifying surgical candidates and by assessing the effectiveness of newer reversible drugs. The effects of mechanical hemodynamic support on long-term patient outcomes need more stringent analysis.

Lack of association between the Trp719Arg polymorphism in kinesin-like protein-6 and coronary artery disease in 19 case-control studies

OBJECTIVES

We sought to replicate the association between the kinesin-like protein 6 (KIF6) Trp719Arg polymorphism (rs20455), and clinical coronary artery disease (CAD).

BACKGROUND

Recent prospective studies suggest that carriers of the 719Arg allele in KIF6 are at increased risk of clinical CAD compared with noncarriers.

METHODS

The KIF6 Trp719Arg polymorphism (rs20455) was genotyped in 19 case-control studies of nonfatal CAD either as part of a genome-wide association study or in a formal attempt to replicate the initial positive reports.

RESULTS

A total of 17,000 cases and 39,369 controls of European descent as well as a modest number of South Asians, African Americans, Hispanics, East Asians, and admixed cases and controls were successfully genotyped. None of the 19 studies demonstrated an increased risk of CAD in carriers of the 719Arg allele compared with noncarriers. Regression analyses and fixed-effects meta-analyses ruled out with high degree of confidence an increase of ≥2% in the risk of CAD among European 719Arg carriers. We also observed no increase in the risk of CAD among 719Arg carriers in the subset of Europeans with early-onset disease (younger than 50 years of age for men and younger than 60 years of age for women) compared with similarly aged controls as well as all non-European subgroups.

CONCLUSIONS

The KIF6 Trp719Arg polymorphism was not associated with the risk of clinical CAD in this large replication study.

Association of single nucleotide polymorphisms on chromosome 9p21.3 with platelet reactivity: a potential mechanism for increased vascular disease

BACKGROUND

Genome-wide association studies have identified a locus on chromosome 9p21.3 to be strongly associated with myocardial infarction/coronary artery disease and ischemic stroke. To gain insights into the mechanisms underlying these associations, we hypothesized that single nucleotide polymorphisms (SNPs) in this region would be associated with platelet reactivity across multiple populations.

METHODS AND RESULTS

Subjects in the initial population included 1402 asymptomatic Amish adults in whom we measured platelet reactivity (n=788) and coronary artery calcification (CAC) (n=939). Platelet reactivity on agonist stimulation was measured by impedance aggregometry, and CAC was measured by electron beam CT. Twenty-nine SNPs at the 9p21.3 locus were genotyped using the Affymetrix 500K array. Twelve correlated SNPs in the locus were significantly associated with platelet reactivity (all P≤0.001). The SNP most strongly associated with platelet reactivity, rs10965219 (P=0.0002), also was associated with CAC (P=0.002) along with 9 other SNPs (all P<0.004). Association of rs10965219 with platelet reactivity persisted after adjustment for CAC, a measure of underlying atherosclerotic burden known to affect platelet reactivity. We then tested rs10965219 for association with platelet function in 2364 subjects from the Framingham Heart Study and 1169 subjects from the Genetic Study of Aspirin Responsiveness. The rs10965219 G allele (frequency ≈51% across all 3 populations) was significantly associated with higher platelet reactivity in the Framingham Heart Study (P=0.001) and trended toward higher reactivity in the Genetic Study of Aspirin Responsiveness (P=0.087); the combined P value for metaanalysis was 0.0002.

CONCLUSIONS

These results suggest that risk alleles at 9p21.3 locus may have pleiotropic effects on myocardial infarction/coronary artery disease and stroke risk, possibly through their influence on platelet reactivity.

Genome-wide meta-analyses identifies seven loci associated with platelet aggregation in response to agonists

Platelet function mediates both beneficial and harmful effects on human health, but few genes are known to contribute to variability in this process. We tested association of 2.5 million SNPs with platelet aggregation responses to three agonists (ADP, epinephrine and collagen) in two cohorts of European ancestry (N Collapse

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MESH Headings

• Adenosine Diphosphate/pharmacology
• Adrenergic alpha-Agonists/pharmacology
• Cohort Studies
• Collagen/pharmacology
• Epinephrine/pharmacology
• Female
• Genome-Wide Association Study
• Genotype
• Humans
• Male
• Meta-Analysis as Topic
• Phenotype
• Platelet Aggregation/drug effects
• Platelet Aggregation/genetics
• Polymorphism, Single Nucleotide
• Prospective Studies

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Grants

• R01 HL087698 NHLBI NIH HHS
• R01 HL087698-03 NHLBI NIH HHS
• M01 RR000052-46 NCRR NIH HHS
• N01 HC025195 NHLBI NIH HHS
• N02 HL64278 NHLBI NIH HHS
• R01 HL048157 NHLBI NIH HHS
• M01-RR000052 NCRR NIH HHS
• M01 RR000052 NCRR NIH HHS
• U01 HL72518 NHLBI NIH HHS
• U01 HL072518 NHLBI NIH HHS
• N02-HL-6-4278 NHLBI NIH HHS
• N01-HC-25195 NHLBI NIH HHS
• R01 HL087698-01 NHLBI NIH HHS
• N01HC25195 NHLBI NIH HHS
• Z99 HL999999 Intramural NIH HHS
• U01 HL072518-06 NHLBI NIH HHS
• M01 RR005280-08 NCRR NIH HHS

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Affiliation(s)

Andrew D Johnson National Heart, Lung, and Blood Institute's The Framingham Heart Study, Framingham, Massachusetts, USA.
Lisa R Yanek
Ming-Huei Chen
Nauder Faraday
Martin G Larson
Geoffrey Tofler
Shiow J Lin
Aldi T Kraja
Michael A Province
Qiong Yang
Diane M Becker
Christopher J O'Donnell
Lewis C Becker

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A combined genome-wide linkage and association approach to find susceptibility loci for platelet function phenotypes in European American and African American families with coronary artery disease

Background

The inability of aspirin (ASA) to adequately suppress platelet aggregation is associated with future risk of coronary artery disease (CAD). Heritability studies of agonist-induced platelet function phenotypes suggest that genetic variation may be responsible for ASA responsiveness. In this study, we leverage independent information from genome-wide linkage and association data to determine loci controlling platelet phenotypes before and after treatment with ASA.

Methods

Clinical data on 37 agonist-induced platelet function phenotypes were evaluated before and after a 2-week trial of ASA (81 mg/day) in 1231 European American and 846 African American healthy subjects with a family history of premature CAD. Principal component analysis was performed to minimize the number of independent factors underlying the covariance of these various phenotypes. Multi-point sib-pair based linkage analysis was performed using a microsatellite marker set, and single-SNP association tests were performed using markers from the Illumina 1 M genotyping chip from deCODE Genetics, Inc. All analyses were performed separately within each ethnic group.

Results

Several genomic regions appear to be linked to ASA response factors: a 10 cM region in African Americans on chromosome 5q11.2 had several STRs with suggestive (p-value < 7 × 10^-4) and significant (p-value < 2 × 10^-5) linkage to post aspirin platelet response to ADP, and ten additional factors had suggestive evidence for linkage (p-value < 7 × 10^-4) to thirteen genomic regions. All but one of these factors were aspirin response variables. While the strength of genome-wide SNP association signals for factors showing evidence for linkage is limited, especially at the strict thresholds of genome-wide criteria (N = 9 SNPs for 11 factors), more signals were considered significant when the association signal was weighted by evidence for linkage (N = 30 SNPs).

Conclusions

Our study supports the hypothesis that platelet phenotypes in response to ASA likely have genetic control and the combined approach of linkage and association offers an alternative approach to prioritizing regions of interest for subsequent follow-up.