Whole-exome sequencing reveals a role of HTRA1 and EGFL8 in brain white matter hyperintensities

White matter hyperintensities (WMH) are among the most common radiological abnormalities in the ageing population and an established risk factor for stroke and dementia. While common variant association studies have revealed multiple genetic loci with an influence on their volume, the contribution of rare variants to the WMH burden in the general population remains largely unexplored. We conducted a comprehensive analysis of this burden in the UK Biobank using publicly available whole-exome sequencing data (n up to 17 830) and found a splice-site variant in GBE1, encoding 1,4-alpha-glucan branching enzyme 1, to be associated with lower white matter burden on an exome-wide level [c.691+2T>C, β = -0.74, standard error (SE) = 0.13, P = 9.7 × 10-9]. Applying whole-exome gene-based burden tests, we found damaging missense and loss-of-function variants in HTRA1 (frequency of 1 in 275 in the UK Biobank population) to associate with an increased WMH volume (P = 5.5 × 10-6, false discovery rate = 0.04). HTRA1 encodes a secreted serine protease implicated in familial forms of small vessel disease. Domain-specific burden tests revealed that the association with WMH volume was restricted to rare variants in the protease domain (amino acids 204-364; β = 0.79, SE = 0.14, P = 9.4 × 10-8). The frequency of such variants in the UK Biobank population was 1 in 450. The WMH volume was brought forward by ∼11 years in carriers of a rare protease domain variant. A comparison with the effect size of established risk factors for WMH burden revealed that the presence of a rare variant in the HTRA1 protease domain corresponded to a larger effect than meeting the criteria for hypertension (β = 0.26, SE = 0.02, P = 2.9 × 10-59) or being in the upper 99.8% percentile of the distribution of a polygenic risk score based on common genetic variants (β = 0.44, SE = 0.14, P = 0.002). In biochemical experiments, most (6/9) of the identified protease domain variants resulted in markedly reduced protease activity. We further found EGFL8, which showed suggestive evidence for association with WMH volume (P = 1.5 × 10-4, false discovery rate = 0.22) in gene burden tests, to be a direct substrate of HTRA1 and to be preferentially expressed in cerebral arterioles and arteries. In a phenome-wide association study mapping ICD-10 diagnoses to 741 standardized Phecodes, rare variants in the HTRA1 protease domain were associated with multiple neurological and non-neurological conditions including migraine with aura (odds ratio = 12.24, 95%CI: 2.54-35.25; P = 8.3 × 10-5]. Collectively, these findings highlight an important role of rare genetic variation and the HTRA1 protease in determining WMH burden in the general population.

Mendelian Randomization Studies in Stroke: Exploration of Risk Factors and Drug Targets With Human Genetic Data

Elucidating the causes of stroke is key to developing effective preventive strategies. The Mendelian randomization approach leverages genetic variants related to an exposure of interest to investigate the effects of varying that exposure on disease risk. The random allocation of genetic variants at conception reduces confounding from environmental factors and thus strengthens causal inference, analogous to treatment allocation in a randomized controlled trial. With the recent explosion in the availability of human genetic data, Mendelian randomization has proven a valuable tool for studying risk factors for stroke. In this review, we provide an overview of recent developments in the application of Mendelian randomization to unravel the pathophysiology of stroke subtypes and identify therapeutic targets for clinical translation. The approach has offered novel insight into the differential effects of risk factors and antihypertensive, lipid-lowering, and anticoagulant drug classes on risk of stroke subtypes. Analyses have further facilitated the prioritization of novel drug targets, such as for inflammatory pathways underlying large artery atherosclerotic stroke and for the coagulation cascade that contributes to cardioembolic stroke. With continued methodological advances coupled with the rapidly increasing availability of genetic data related to a broad range of stroke phenotypes, the potential for Mendelian randomization in this context is expanding exponentially.

Does Sodium Intake Induce Systemic Inflammatory Response? A Systematic Review and Meta-Analysis of Randomized Studies in Humans

Experimental studies suggest that sodium induced inflammation might be another missing link leading to atherosclerosis. To test the hypothesis that high daily sodium intake induces systemic inflammatory response in humans, we performed a systematic review according to PRISMA guidelines of randomized controlled trials (RCTs) that examined the effect of high versus low sodium dose (HSD vs. LSD), as defined per study, on plasma circulating inflammatory biomarkers. Eight RCTs that examined CRP, TNF-a and IL-6 were found. Meta-analysis testing the change of each biomarker in HSD versus LSD was possible for CRP (n = 5 studies), TNF-a (n = 4 studies) and IL-6 (n = 4 studies). The pooled difference (95% confidence intervals) per biomarker was for: CRP values of 0.1(−0.3, 0.4) mg/L; TNF-a −0.7(−5.0, 3.6) pg/mL; IL-6 −1.1(−3.3 to 1.1) pg/mL. Importantly, there was inconsistency between RCTs regarding major population characteristics and the applied methodology, including a very wide range of LSD (460 to 6740 mg/day) and HSD (2800 to 7452 mg/day). Although our results suggest that the different levels of daily sodium intake are not associated with significant changes in the level of systemic inflammation in humans, this outcome may result from methodological issues. Based on these identified methodological issues we propose that future RCTs should focus on young healthy participants to avoid confounding effects of comorbidities, should have three instead of two arms (very low, “normal” and high) of daily sodium intake with more than 100 participants per arm, whereas an intervention duration of 14 days is adequate.

Association of Vitamin D Receptor Gene Polymorphisms with Serum Vitamin D Levels in a Greek Rural Population (Velestino Study)

BACKGROUND/AIM

An alarming increase in vitamin D deficiency even in sunny regions highlights the need for a better understanding of the genetic background of the vitamin D endocrine system and the molecular mechanisms of gene polymorphisms of the vitamin D receptor (VDR). In this study, the serum levels of 25(OH)D3 were correlated with common VDR polymorphisms (ApaI, BsmI, FokI, and TaqI) in 98 subjects of a Greek homogeneous rural population.

METHODS

25(OH)D3 concentration was measured by ultra-HPLC, and the VDR gene polymorphisms were identified by quantitative real-time PCR followed by amplicon high-resolution melting analysis.

RESULTS

Subjects carrying either the B BsmI (OR: 0.52, 95% CI: 0.27-0.99) or t TaqI (OR: 2.06, 95%: 1.06-3.99) allele presented twice the risk for developing vitamin D deficiency compared to the reference allele. Moreover, subjects carrying 1, 2, or all 3 of these genotypes (BB/Bb, Tt/tt, and FF) demonstrated 2-fold (OR: 2.04, 95% CI: 0.42-9.92), 3.6-fold (OR: 3.62, 95% CI: 1.07-12.2), and 7-fold (OR: 6.92, 95% CI: 1.68-28.5) increased risk for low 25(OH)D3 levels, respectively.

CONCLUSIONS

Our findings reveal a cumulative effect of specific VDR gene polymorphisms that may regulate vitamin D concentrations explaining, in part, the paradox of vitamin D deficiency in sunny regions, with important implications for precision medicine.

Circulating biomarkers of immunity and inflammation, risk of Alzheimer's disease, and hippocampal volume: a Mendelian randomization study

The aim of this study was to explore the association between genetically predicted circulating levels of immunity and inflammation, and the risk of Alzheimer's disease (AD) and hippocampal volume, by conducting a two-sample Mendelian Randomization Study. We identified 12 markers of immune cells and derived ratios (platelet count, eosinophil count, neutrophil count, basophil count, monocyte count, lymphocyte count, platelet-to-lymphocyte ratio, monocyte-to-lymphocyte ratio, CD4 count, CD8 count, CD4-to-CD8 ratio, and CD56) and 5 signaling molecules (IL-6, fibrinogen, CRP, and Lp-PLA2 activity and mass) as primary exposures of interest. Other genetically available immune biomarkers with a weaker a priori link to AD were considered secondary exposures. Associations with AD were evaluated in The International Genomics of Alzheimer's Project (IGAP) GWAS dataset (21,982 cases; 41,944 controls of European ancestry). For hippocampal volume, we extracted data from a GWAS meta-analysis on 33,536 participants of European ancestry. None of the primary or secondary exposures showed statistically significant associations with AD or with hippocampal volume following P-value correction for multiple comparisons using false discovery rate < 5% (Q-value < 0.05). CD4 count showed the strongest suggestive association with AD (odds ratio 1.32, P < 0.01, Q > 0.05). There was evidence for heterogeneity in the MR inverse variance-weighted meta-analyses as measured by Cochran Q, and weighted median and weighted mode for multiple exposures. Further cluster analyses did not reveal clusters of variants that could influence the risk factor in distinct ways. This study suggests that genetically predicted circulating biomarkers of immunity and inflammation are not associated with AD risk or hippocampal volume. Future studies should assess competing risk, explore in more depth the role of adaptive immunity in AD, in particular T cells and the CD4 subtype, and confirm these findings in other ethnicities.

Association of Circulating Monocyte Chemoattractant Protein-1 Levels With Cardiovascular Mortality: A Meta-analysis of Population-Based Studies

Importance

Human genetics and studies in experimental models support a key role of monocyte-chemoattractant protein-1 (MCP-1) in atherosclerosis. Yet, the associations of circulating MCP-1 levels with risk of coronary heart disease and cardiovascular death in the general population remain largely unexplored.

Objective

To explore whether circulating levels of MCP-1 are associated with risk of incident coronary heart disease, myocardial infarction, and cardiovascular mortality in the general population.

Data Sources and Selection

Population-based cohort studies, identified through a systematic review, that have examined associations of circulating MCP-1 levels with cardiovascular end points.

Data Extraction and Synthesis

Using a prespecified harmonized analysis plan, study-specific summary data were obtained from Cox regression models after excluding individuals with overt cardiovascular disease at baseline. Derived hazard ratios (HRs) were synthesized using random-effects meta-analyses.

Main Outcomes and Measures

Incident coronary heart disease (myocardial infarction, coronary revascularization, and unstable angina), nonfatal myocardial infarction, and cardiovascular death (from cardiac or cerebrovascular causes).

Results

The meta-analysis included 7 cohort studies involving 21 401 individuals (mean [SD] age, 53.7 [10.2] years; 10 012 men [46.8%]). Mean (SD) follow-up was 15.3 (4.5) years (326 392 person-years at risk). In models adjusting for age, sex, and race/ethnicity, higher MCP-1 levels at baseline were associated with increased risk of coronary heart disease (HR per 1-SD increment in MCP-1 levels: 1.06 [95% CI, 1.01-1.11]; P = .01), nonfatal myocardial infarction (HR, 1.07 [95% CI, 1.01-1.13]; P = .02), and cardiovascular death (HR, 1.12 [95% CI, 1.05-1.20]; P < .001). In analyses comparing MCP-1 quartiles, these associations followed dose-response patterns. After additionally adjusting for vascular risk factors, the risk estimates were attenuated, but the associations of MCP-1 levels with cardiovascular death remained statistically significant, as did the association of MCP-1 levels in the upper quartile with coronary heart disease. There was no significant heterogeneity; the results did not change in sensitivity analyses excluding events occurring in the first 5 years after MCP-1 measurement, and the risk estimates were stable after additional adjustments for circulating levels of interleukin-6 and high-sensitivity C-reactive protein.

Conclusions and Relevance

Higher circulating MCP-1 levels are associated with higher long-term cardiovascular mortality in community-dwelling individuals free of overt cardiovascular disease. These findings provide further support for a key role of MCP-1-signaling in cardiovascular disease.

Monocyte-Chemoattractant Protein-1 Levels in Human Atherosclerotic Lesions Associate With Plaque Vulnerability

[Figure: see text].

Relationship Between Blood Pressure and Incident Cardiovascular Disease: Linear and Nonlinear Mendelian Randomization Analyses

Supplemental Digital Content is available in the text.

Observational studies exploring whether there is a nonlinear effect of blood pressure on cardiovascular disease (CVD) risk are hindered by confounding. This limitation can be overcome by leveraging randomly allocated genetic variants in nonlinear Mendelian randomization analyses. Based on their association with blood pressure traits in a genome-wide association study of 299 024 European ancestry individuals, we selected 253 genetic variants to proxy the effect of modifying systolic and diastolic blood pressure. Considering the outcomes of incident coronary artery disease, stroke and the combined outcome of CVD, linear and nonlinear Mendelian randomization analyses were performed on 255 714 European ancestry participants without a history of CVD or antihypertensive medication use. There was no evidence favoring nonlinear relationships of genetically proxied systolic and diastolic blood pressure with the cardiovascular outcomes over linear relationships. For every 10-mm Hg increase in genetically proxied systolic blood pressure, risk of incident CVD increased by 49% (hazard ratio, 1.49 [95% CI, 1.38–1.61]), with similar estimates obtained for coronary artery disease (hazard ratio, 1.50 [95% CI, 1.38–1.63]) and stroke (hazard ratio, 1.44 [95% CI, 1.22–1.70]). Genetically proxied blood pressure had a similar relationship with CVD in men and women. These findings provide evidence to support that even for individuals who do not have elevated blood pressure, public health interventions achieving persistent blood pressure reduction will be of considerable benefit in the primary prevention of CVD.

Dose-response relationship between genetically proxied average blood glucose levels and incident coronary heart disease in individuals without diabetes mellitus

AIMS/HYPOTHESIS

Our aim was to investigate the relationship between average blood glucose levels and incident CHD in individuals without diabetes mellitus.

METHODS

To investigate average blood glucose levels, we studied HbA_1c as predicted by 40 variants previously shown to be associated with both type 2 diabetes and HbA_1c. Linear and non-linear Mendelian randomisation analyses were performed to investigate associations with incident CHD risk in 324,830 European ancestry individuals from the UK Biobank without diabetes mellitus.

RESULTS

Every one mmol/mol increase in genetically proxied HbA_1c was associated with an 11% higher CHD risk (HR 1.11, 95% CI 1.05, 1.18). The dose-response curve increased at all levels of HbA_1c, and there was no evidence favouring a non-linear relationship over a linear one.

CONCLUSIONS/INTERPRETATIONS

In individuals without diabetes mellitus, lowering average blood glucose levels may reduce CHD risk in a dose-dependent way.

Diabetes Mellitus, Glycemic Traits, and Cerebrovascular Disease: A Mendelian Randomization Study

OBJECTIVE

We employed Mendelian randomization to explore the effects of genetic predisposition to type 2 diabetes (T2D), hyperglycemia, insulin resistance, and pancreatic β-cell dysfunction on risk of stroke subtypes and related cerebrovascular phenotypes.

METHODS

We selected instruments for genetic predisposition to T2D (74,124 cases, 824,006 controls), HbA1c levels (n = 421,923), fasting glucose levels (n = 133,010), insulin resistance (n = 108,557), and β-cell dysfunction (n = 16,378) based on published genome-wide association studies. Applying 2-sample Mendelian randomization, we examined associations with ischemic stroke (60,341 cases, 454,450 controls), intracerebral hemorrhage (1,545 cases, 1,481 controls), and ischemic stroke subtypes (large artery, cardioembolic, small vessel stroke), as well as with related phenotypes (carotid atherosclerosis, imaging markers of cerebral white matter integrity, and brain atrophy).

RESULTS

Genetic predisposition to T2D and higher HbA1c levels were associated with higher risk of any ischemic stroke, large artery stroke, and small vessel stroke. Similar associations were also noted for carotid atherosclerotic plaque, fractional anisotropy, a white matter disease marker, and markers of brain atrophy. We further found associations of genetic predisposition to insulin resistance with large artery and small vessel stroke, whereas predisposition to β-cell dysfunction was associated with small vessel stroke, intracerebral hemorrhage, lower gray matter volume, and total brain volume.

CONCLUSIONS

This study supports causal effects of T2D and hyperglycemia on large artery and small vessel stroke. We show associations of genetically predicted insulin resistance and β-cell dysfunction with large artery and small vessel stroke that might have implications for antidiabetic treatments targeting these mechanisms.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that genetic predisposition to T2D and higher HbA1c levels are associated with a higher risk of large artery and small vessel ischemic stroke.

Midlife vascular risk factors and risk of incident dementia: Longitudinal cohort and Mendelian randomization analyses in the UK Biobank

INTRODUCTION

Midlife clustering of vascular risk factors has been associated with late-life dementia, but causal effects of individual biological and lifestyle factors remain largely unknown.

METHODS

Among 229,976 individuals (mean follow-up 9 years), we explored whether midlife cardiovascular health measured by Life's Simple 7 (LS7) is associated with incident all-cause dementia and whether the individual components of the score are causally associated with dementia.

RESULTS

Adherence to the biological metrics of LS7 (blood pressure, cholesterol, glycemic status) was associated with lower incident dementia risk (hazard ratio = 0.93 per 1-point increase, 95% confidence interval [CI; 0.89-0.96]). In contrast, there was no association between the composite LS7 score and the lifestyle subscore (smoking, body mass index, diet, physical activity) and incident dementia. In Mendelian randomization analyses, genetically elevated blood pressure was associated with higher risk of dementia (odds ratio = 1.31 per one-standard deviation increase, 95% CI [1.05-1.60]).

DISCUSSION

These findings underscore the importance of blood pressure control in midlife to mitigate dementia risk.

Smoking and heart failure: a Mendelian randomization and mediation analysis

Aims

We performed a Mendelian randomization (MR) study to elucidate the associations of ever smoking, lifelong smoking duration, and smoking cessation with heart failure (HF) risk.

Methods and results

We extracted genetic variants associated with smoking initiation, age at initiation of regular smoking, cigarettes per day, and smoking cessation from the genome‐wide association study and Sequencing Consortium of Alcohol and Nicotine use (1.2 million individuals), as well as a composite lifetime smoking index from the UK Biobank (462 690 individuals). The associations between smoking phenotypes and HF were explored in the Heart Failure Molecular Epidemiology for Therapeutic Targets Consortium (47 309 cases; 930 014 controls) employing inverse variance‐weighted meta‐analysis and multivariable MR. The mediation effects of coronary artery disease and atrial fibrillation on smoking–HF risk were explored using mediation analysis. The odds ratios (ORs) for HF were 1.28 [95% confidence interval (CI), 1.22–1.36; P = 1.5 × 10⁻¹⁸] for ever regular smokers compared with never smokers and 1.25 (95% CI, 1.09–1.44; P = 1.6 × 10⁻³) for current smokers vs. former smokers. Genetic liability to smoking more cigarettes per day (OR, 1.37; 95% CI, 1.20–1.58; P = 6.4 × 10⁻⁶) and a higher composite lifetime smoking index (OR, 1.49; 95% CI, 1.31–1.70; P = 2.5 × 10⁻⁹) were associated with a higher risk of HF. The results were robust and consistent in all sensitivity analyses and multivariable MR after adjusting for HF risk factors, and their associations were independent of coronary artery disease and atrial fibrillation.

Conclusions

Genetic liability to ever smoking and a higher lifetime smoking burden are associated with a higher risk of HF.

Abstract P771: Monocyte-Chemoattractant Protein-1 Levels in Human Carotid Atherosclerosis Associate With Hallmarks of Plaque Vulnerability

Background: Monocyte chemoattractant protein-1 (MCP-1) is a chemokine recruiting monocytes to the atherosclerotic plaque. Experimental, genetic, and epidemiological data support a key role of MCP-1 in atherosclerosis. Yet, the translational potential of targeting MCP-1 signaling for lowering vascular risk is limited by the lack of data on plaque MCP-1 activity in human atherosclerosis.

Methods: We measured MCP-1 levels in human plaque samples from 1,199 patients undergoing carotid endarterectomy from the Athero-Express Biobank. We explored associations of plaque MCP-1 levels with histopathological features of plaque vulnerability, clinical plaque instability (symptomatic vs. asymptomatic plaque), molecular markers of plaque inflammation and remodeling, and with incident vascular events up to three years after plaque removal.

Results: MCP-1 plaque levels were associated with individual histopathological hallmarks of plaque vulnerability (large lipid core, low collagen, high macrophage burden, low smooth muscle cell burden, intraplaque hemorrhage), as well as with a cumulative vulnerability index (range 0-5, beta: 0.42, 95%CI: 0.30-0.53, p=5.4x10 -13 ) independently of age, sex, and conventional vascular risk factors. Furthermore, MCP-1 levels were higher among patients with symptomatic, as compared to asymptomatic plaques (p=0.0001) and were associated with the levels of pro-inflammatory cytokines involved in leukocyte adhesion, as well as with matrix metalloproteinase activity in the plaque. In the follow-up analyses, MCP-1 levels were associated with a higher risk of peri-procedural events (up to 30 days after surgery).

Conclusions: Our findings highlight a role of MCP-1 in human plaque vulnerability, the leading mechanism underlying vascular events like stroke and myocardial infarction. As such, they suggest that interfering with MCP-1 signaling in patients with established atherosclerosis could lower vascular risk.

Prediction of Long-term Cognitive Function After Minor Stroke Using Functional Connectivity

OBJECTIVE

To determine whether functional MRI connectivity can predict long-term cognitive function 36 months after minor stroke.

METHODS

Seventy-two participants with first-ever stroke were included at baseline and followed up for 36 months. A ridge regression machine learning algorithm was developed and used to predict cognitive scores 36 months poststroke on the basis of the functional networks measured using MRI at 6 months (referred to here as the poststroke cognitive impairment [PSCI] network). The prediction accuracy was evaluated in 4 domains (memory, attention/executive, language, and visuospatial functions) and compared with clinical data and other functional networks. The models' statistical significance was probed with permutation tests. The potential involvement of cortical atrophy was assessed 6 months poststroke. A second, independent dataset (n = 40) was used to validate the results and assess their generalizability.

RESULTS

Based on the PSCI network, a machine learning model was able to predict memory, attention, visuospatial functions, and language functions 36 months poststroke (r 2: 0.67, 0.73, 0.55, and 0.48, respectively). The PSCI-based model was at least as accurate as models based on other functional networks or clinical data. Specific patterns were demonstrated for the 4 cognitive domains, with involvement of the left superior frontal cortex for memory, attention, and visuospatial functions. The cortical thickness 6 months poststroke was not correlated with cognitive function 36 months poststroke. The independent validation dataset gave similar results.

CONCLUSIONS

A machine learning model based on the PSCI network can predict long-term cognitive outcome after stroke.

Mendelian randomization for studying the effects of perturbing drug targets

Drugs whose targets have genetic evidence to support efficacy and safety are more likely to be approved after clinical development. In this paper, we provide an overview of how natural sequence variation in the genes that encode drug targets can be used in Mendelian randomization analyses to offer insight into mechanism-based efficacy and adverse effects. Large databases of summary level genetic association data are increasingly available and can be leveraged to identify and validate variants that serve as proxies for drug target perturbation. As with all empirical research, Mendelian randomization has limitations including genetic confounding, its consideration of lifelong effects, and issues related to heterogeneity across different tissues and populations. When appropriately applied, Mendelian randomization provides a useful empirical framework for using population level data to improve the success rates of the drug development pipeline.

Modifiable Lifestyle Factors and Risk of Stroke: A Mendelian Randomization Analysis

BACKGROUND AND PURPOSE

Assessing whether modifiable risk factors are causally associated with stroke risk is important in planning public health measures, but determining causality can be difficult in epidemiological data. We evaluated whether modifiable lifestyle factors including educational attainment, smoking, and body mass index are causal risk factors for ischemic stroke and its subtypes and hemorrhagic stroke.

METHODS

We performed 2-sample and multivariable Mendelian randomization to assess the causal effect of 12 lifestyle factors on risk of stroke and whether these effects are independent.

RESULTS

Genetically predicted years of education was inversely associated with ischemic, large artery, and small vessel stroke, and intracerebral hemorrhage. Genetically predicted smoking, body mass index, and waist-hip ratio were associated with ischemic and large artery stroke. The effects of education, body mass index, and smoking on ischemic stroke were independent.

CONCLUSIONS

Our findings support the hypothesis that reduced education and increased smoking and obesity increase risk of ischemic, large artery, and small vessel stroke, suggesting that lifestyle modifications addressing these risk factors will reduce stroke risk.

Dissecting the Association Between Inflammation, Metabolic Dysregulation, and Specific Depressive Symptoms: A Genetic Correlation and 2-Sample Mendelian Randomization Study

IMPORTANCE

Observational studies highlight associations of C-reactive protein (CRP), a general marker of inflammation, and interleukin 6 (IL-6), a cytokine-stimulating CRP production, with individual depressive symptoms. However, it is unclear whether inflammatory activity is associated with individual depressive symptoms and to what extent metabolic dysregulation underlies the reported associations.

OBJECTIVE

To explore the genetic overlap and associations between inflammatory activity, metabolic dysregulation, and individual depressive symptoms.

GWAS DATA SOURCES

Genome-wide association study (GWAS) summary data of European individuals, including the following: CRP levels (204 402 individuals); 9 individual depressive symptoms (3 of which did not differentiate between underlying diametrically opposite symptoms [eg, insomnia and hypersomnia]) as measured with the Patient Health Questionnaire 9 (up to 117 907 individuals); summary statistics for major depression, including and excluding UK Biobank participants, resulting in sample sizes of 500 199 and up to 230 214 individuals, respectively; insomnia (up to 386 533 individuals); body mass index (BMI) (up to 322 154 individuals); and height (up to 253 280 individuals).

DESIGN

In this genetic correlation and 2-sample mendelian randomization (MR) study, linkage disequilibrium score (LDSC) regression was applied to infer single-nucleotide variant-based heritability and genetic correlation estimates. Two-sample MR tested potential causal associations of genetic variants associated with CRP levels, IL-6 signaling, and BMI with depressive symptoms. The study dates were November 2019 to April 2020.

RESULTS

Based on large GWAS data sources, genetic correlation analyses revealed consistent false discovery rate (FDR)-controlled associations (genetic correlation range, 0.152-0.362; FDR P = .006 to P < .001) between CRP levels and depressive symptoms that were similar in size to genetic correlations of BMI with depressive symptoms. Two-sample MR analyses suggested that genetic upregulation of IL-6 signaling was associated with suicidality (estimate [SE], 0.035 [0.010]; FDR plus Bonferroni correction P = .01), a finding that remained stable across statistical models and sensitivity analyses using alternative instrument selection strategies. Mendelian randomization analyses did not consistently show associations of higher CRP levels or IL-6 signaling with other depressive symptoms, but higher BMI was associated with anhedonia, tiredness, changes in appetite, and feelings of inadequacy.

CONCLUSIONS AND RELEVANCE

This study reports coheritability between CRP levels and individual depressive symptoms, which may result from the potentially causal association of metabolic dysregulation with anhedonia, tiredness, changes in appetite, and feelings of inadequacy. The study also found that IL-6 signaling is associated with suicidality. These findings may have clinical implications, highlighting the potential of anti-inflammatory approaches, especially IL-6 blockade, as a putative strategy for suicide prevention.

Mendelian randomization for studying the effects of perturbing drug targets

Drugs whose targets have genetic evidence to support efficacy and safety are more likely to be approved after clinical development. In this paper, we provide an overview of how natural sequence variation in the genes that encode drug targets can be used in Mendelian randomization analyses to offer insight into mechanism-based efficacy and adverse effects. Large databases of summary level genetic association data are increasingly available and can be leveraged to identify and validate variants that serve as proxies for drug target perturbation. As with all empirical research, Mendelian randomization has limitations including genetic confounding, its consideration of lifelong effects, and issues related to heterogeneity across different tissues and populations. When appropriately applied, Mendelian randomization provides a useful empirical framework for using population level data to improve the success rates of the drug development pipeline.

Genetically Predicted Blood Pressure and Risk of Atrial Fibrillation

Observational studies have shown an association between hypertension and atrial fibrillation (AF). Aggressive blood pressure management in patients with known AF reduces overall arrhythmia burden, but it remains unclear whether hypertension is causative for AF. To address this question, this study explored the relationship between genetic predictors of blood pressure and risk of AF. We secondarily explored the relationship between genetically proxied use of antihypertensive drugs and risk of AF. Two-sample Mendelian randomization was performed using an inverse-variance weighted meta-analysis with weighted median Mendelian randomization and Egger intercept tests performed as sensitivity analyses. Summary statistics for systolic blood pressure, diastolic blood pressure, and pulse pressure were obtained from the International Consortium of Blood Pressure and the UK Biobank discovery analysis and AF from the 2018 Atrial Fibrillation Genetics Consortium multiethnic genome-wide association studies. Increases in genetically proxied systolic blood pressure, diastolic blood pressure, or pulse pressure by 10 mm Hg were associated with increased odds of AF (systolic blood pressure: odds ratio [OR], 1.17 [95% CI, 1.11-1.22]; P=1×10^-11; diastolic blood pressure: OR, 1.25 [95% CI, 1.16-1.35]; P=3×10^-8; pulse pressure: OR, 1.1 [95% CI, 1.0-1.2]; P=0.05). Decreases in systolic blood pressure by 10 mm Hg estimated by genetic proxies of antihypertensive medications showed calcium channel blockers (OR, 0.66 [95% CI, 0.57-0.76]; P=8×10^-9) and β-blockers (OR, 0.61 [95% CI, 0.46-0.81]; P=6×10^-4) decreased the risk of AF. Blood pressure-increasing genetic variants were associated with increased risk of AF, consistent with a causal relationship between blood pressure and AF. These data support the concept that blood pressure reduction with calcium channel blockade or β-blockade could reduce the risk of AF.

Genetic Liability to Depression and Risk of Coronary Artery Disease, Myocardial Infarction, and Other Cardiovascular Outcomes

Background

Observational studies have indicated that depression is associated with coronary artery disease (CAD) and myocardial infarction. Nevertheless, causal associations between depression and cardiovascular diseases remain controversial. Hence, we conducted a Mendelian randomization and mediation analysis to evaluate the associations of depression‐related genetic variants with CAD and myocardial infarction.

Methods and Results

Summary statistics from genome‐wide association studies of depression (807 553 individuals), and CAD (60 801 cases, including 43 676 with myocardial infarction, and 123 504 controls) were used. We pooled Mendelian randomization estimates using a fixed‐effects inverse‐variance weighted meta‐analysis and multivariable Mendelian randomization. The mediation effects of potential cardiovascular risk factors on depression‐CAD and myocardial infarction risk were investigated by using mediation analysis. We also explored the relationship of genetic liability to depression with heart failure, atrial fibrillation, and ischemic stroke. Genetic liability to depression was associated with higher CAD (odds ratio [OR], 1.14; 95% CI, 1.06–1.24; P=1.0×10⁻³) and myocardial infarction (OR, 1.21; 95% CI, 1.11–1.33; P=4.8×10⁻⁵) risks. Results were consistent in all sensitivity analyses. Type 2 diabetes mellitus and smoking demonstrated significant mediation effects. Furthermore, our Mendelian randomization analyses revealed that the genetic liability to depression was associated with higher risks of heart failure and small vessel stroke.

Conclusions

Genetic liability to depression is associated with higher CAD and myocardial infarction risks, partly mediated by type 2 diabetes mellitus and smoking. The potential preventive value of depression treatment on cardiovascular diseases should be investigated in the future.

Small vessel disease more than Alzheimer's disease determines diffusion MRI alterations in memory clinic patients

INTRODUCTION

Microstructural alterations as assessed by diffusion tensor imaging (DTI) are key findings in both Alzheimer's disease (AD) and small vessel disease (SVD). We determined the contribution of each of these conditions to diffusion alterations.

METHODS

We studied six samples (N = 365 participants) covering the spectrum of AD and SVD, including genetically defined samples. We calculated diffusion measures from DTI and free water imaging. Simple linear, multivariable random forest, and voxel-based regressions were used to evaluate associations between AD biomarkers (amyloid beta, tau), SVD imaging markers, and diffusion measures.

RESULTS

SVD markers were strongly associated with diffusion measures and showed a higher contribution than AD biomarkers in multivariable analysis across all memory clinic samples. Voxel-wise analyses between tau and diffusion measures were not significant.

DISCUSSION

In memory clinic patients, the effect of SVD on diffusion alterations largely exceeds the effect of AD, supporting the value of diffusion measures as markers of SVD.

Gender-affirming hormone treatment and cognitive function in transgender young adults: a systematic review and meta-analysis

BACKGROUND

Previous studies have examined whether steroid hormone treatment in transgender individuals may affect cognitive function; yet, their limited power does not allow firm conclusions to be drawn. We leveraged data from to-date literature aiming to explore the effect of gender-affirming hormone administration on cognitive function in transgender individuals.

METHODS

A search strategy of MEDLINE was developed (through June 1, 2019) using the key terms transgender, hormone therapy and cognitive function. Eligible were (i) cohort studies examining the longitudinal effect of hormone therapy on cognition, and (ii) cross-sectional studies comparing the cognitive function between treated and non-treated individuals. Standardized mean differences (Hedges' g) were pooled using random-effects models. Study quality was evaluated using the Newcastle-Ottawa Scale.

OUTCOMES

Ten studies (seven cohort and three cross-sectional) were eligible representing 234 birth-assigned males (aM) and 150 birth-assigned females (aF). The synthesis of cohort studies (n = 5) for visuospatial ability following hormone treatment showed a statistically significant enhancement among aF (g = 0.55, 95% confidence intervals [CI]: 0.29, 0.82) and an improvement with a trend towards statistical significance among aM (g = 0.28, 95%CI: -0.01, 0.58). By contrast, no adverse effects of hormone administration were shown. No heterogeneity was evident in most meta-analyses.

INTERPRETATION

Current evidence does not support an adverse impact of hormone therapy on cognitive function, whereas a statistically significant enhancing effect on visuospatial ability was shown in aF. New longitudinal studies with longer follow-up should explore the long-term effects of hormone therapy, especially the effects on younger individuals, where there is greater scarcity of data.

Genetically determined blood pressure, antihypertensive drug classes, and risk of stroke subtypes

OBJECTIVE

We employed Mendelian randomization to explore whether the effects of blood pressure (BP) and BP-lowering through different antihypertensive drug classes on stroke risk vary by stroke etiology.

METHODS

We selected genetic variants associated with systolic and diastolic BP and BP-lowering variants in genes encoding antihypertensive drug targets from genome-wide association studies (GWAS) on 757,601 individuals. Applying 2-sample Mendelian randomization, we examined associations with any stroke (67,162 cases; 454,450 controls), ischemic stroke and its subtypes (large artery, cardioembolic, small vessel stroke), intracerebral hemorrhage (ICH, deep and lobar), and the related small vessel disease phenotype of white matter hyperintensities (WMH).

RESULTS

Genetic predisposition to higher systolic and diastolic BP was associated with higher risk of any stroke, ischemic stroke, and ICH. We found associations between genetically determined BP and all ischemic stroke subtypes with a higher risk of large artery and small vessel stroke compared to cardioembolic stroke, as well as associations with deep, but not lobar ICH. Genetic proxies for calcium channel blockers, but not β-blockers, were associated with lower risk of any stroke and ischemic stroke. Proxies for calcium channel blockers showed particularly strong associations with small vessel stroke and the related radiologic phenotype of WMH.

CONCLUSIONS

This study supports a causal role of hypertension in all major stroke subtypes except lobar ICH. We find differences in the effects of BP and BP-lowering through antihypertensive drug classes between stroke subtypes and identify calcium channel blockade as a promising strategy for preventing manifestations of cerebral small vessel disease.