Objective: To determine whether endogenous testosterone has a causal role in thromboembolism, heart failure, and myocardial infarction. Design: Two sample mendelian randomisation study using genetic variants as instrumental variables, randomly allocated at conception, to infer causality as additional randomised evidence. Setting: Reduction by Dutasteride of Prostate Cancer Events (REDUCE) randomised controlled trial, UK Biobank, and CARDIoGRAMplusC4D 1000 Genomes based genome wide association study. Participants: 3225 men of European ancestry aged 50-75 in REDUCE; 392 038 white British men and women aged 40-69 from the UK Biobank; and 171 875 participants of about 77% European descent, from CARDIoGRAMplusC4D 1000 Genomes based study for validation. Main outcome measures: Thromboembolism, heart failure, and myocardial infarction based on self reports, hospital episodes, and death. Results: Of the UK Biobank participants, 13 691 had thromboembolism (6208 men, 7483 women), 1688 had heart failure (1186, 502), and 12 882 had myocardial infarction (10 136, 2746). In men, endogenous testosterone genetically predicted by variants in the JMJD1C gene region was positively associated with thromboembolism (odds ratio per unit increase in log transformed testosterone (nmol/L) 2.09, 95% confidence interval 1.27 to 3.46) and heart failure (7.81, 2.56 to 23.8), but not myocardial infarction (1.17, 0.78 to 1.75). Associations were less obvious in women. In the validation study, genetically predicted testosterone (based on JMJD1C gene region variants) was positively associated with myocardial infarction (1.37, 1.03 to 1.82). No excess heterogeneity was observed among genetic variants in their associations with the outcomes. However, testosterone genetically predicted by potentially pleiotropic variants in the SHBG gene region had no association with the outcomes. Conclusions: Endogenous testosterone was positively associated with thromboembolism, heart failure, and myocardial infarction in men. Rates of these conditions are higher in men than women. Endogenous testosterone can be controlled with existing treatments and could be a modifiable risk factor for thromboembolism and heart failure.

OBJECTIVE: Glycated hemoglobin (HbA1c) is positively associated with cardiovascular disease (CVD), although evidence is primarily observational. Mendelian randomization studies have only examined its relation with subtypes of CVD. We examined the relation of HbA1c with CVD and its subtypes in the UK Biobank using Mendelian randomization. RESEARCH DESIGN AND METHODS: We used 38 genetic variants strongly and independently related to HbA1c (n = 123,665) applied to the UK Biobank (n = 392,038). We used inverse variance weighting (IVW) to obtain the associations of HbA1c with CVD, coronary artery disease (CAD), and stroke (overall and stroke subtypes). Sensitivity analyses included Mendelian randomization (MR)-Egger, a weighted median, and exclusion of potentially invalid single nucleotide polymorphisms (SNPs). We also applied the same genetic instruments to CARDIoGRAMplusC4D (Coronary ARtery DIsease Genome wide Replication and Meta-analysis [CARDIoGRAM] plus The Coronary Artery Disease [C4D] Genetics) 1000 Genomes–based genome-wide association study (n = 184,305) as a validation for CAD. RESULTS: In the UK Biobank, HbA1c was not associated with CVD using IVW (odds ratio [OR] 1.11 per %, 95% CI 0.83–1.48). However, HbA1c was associated with increased CAD risk (OR 1.50 per %, 95% CI 1.08–2.11) with directionally consistent results from MR-Egger and weighted median. The positive association with CAD was more pronounced when we excluded potentially invalid SNPs (OR 2.24 per %, 95% CI 1.55–3.25). The positive association was replicated in CARDIoGRAM (OR 1.52 per %, 95% CI 1.03–2.26). The association of HbA1c with stroke and its subtypes was less clear given the low number of cases. CONCLUSIONS: HbA1c likely causes CAD. The underlying mechanisms remain to be elucidated.

Testosterone supplementation has been linked to increased cardiovascular disease risk in some observational studies. The causal role of testosterone can be investigated using a Mendelian randomization approach. We assessed genetic associations of variants in two gene regions (SHBG and JMJD1C) with several cardiovascular risk factors (lipids, adiponectin, blood pressure, anthropometric traits) plus male pattern baldness, including control outcomes and potential mediators. We assessed genetic associations with coronary artery disease (CAD) risk in the CARDIoGRAMplusC4D consortium (171,191 individuals including 60,801 cases), and associations with CAD and ischaemic stroke risk in the UK Biobank (367,643 individuals including 25,352 CAD cases and 3650 ischaemic stroke cases). Genetic predictors of increased serum testosterone were associated with lipids, blood pressure, and height. There was some evidence of an association with risk of CAD (SHBG gene region: odds ratio (OR) 0.95 per 1 unit increase in log-transformed testosterone [95% confidence interval: 0.81-1.12, p = 0.55]; JMJD1C gene region: OR 1.24 [1.01-1.51, p = 0.04]) and ischaemic stroke both overall (SHBG: OR 1.05 [0.64, 1.73, p = 0.83]; JMJD1C: OR 2.52 [1.33, 4.77, p = 0.005]) and in men. However, associations with some control outcomes were in the opposite direction to that expected. Sex hormone-related mechanisms appear to be relevant to cardiovascular risk factors and for stroke (particularly for men). However, the extent that these findings are specifically informative about endogenous testosterone or testosterone supplementation is unclear. These findings underline a fundamental limitation for the use of Mendelian randomization where biological knowledge about the function of genetic variants is uncertain.

Background: To summarize modifiable factors for coronavirus disease 2019 (COVID-19) suggested by Mendelian randomization studies. Methods: In this systematic review, we searched PubMed, EMBASE and MEDLINE, from inception to 15 November 2021, for Mendelian randomization studies in English. We selected studies that assessed associations of genetically predicted exposures with COVID-19-related outcomes (severity, hospitalization and susceptibility). Risk of bias of the included studies was evaluated based on the consideration of the three main assumptions for instrumental variable analyses. Results: We identified 700 studies through systematic search, of which 50 Mendelian randomization studies were included. Included studies have explored a wide range of socio-demographic factors, lifestyle attributes, anthropometrics and biomarkers, predisposition to diseases and druggable targets in COVID-19 risk. Mendelian randomization studies suggested that increases in smoking, obesity and inflammatory factors were associated with higher risk of COVID-19. Predisposition to ischaemic stroke, combined bipolar disorder and schizophrenia, attention-deficit and hyperactivity disorder, chronic kidney disease and idiopathic pulmonary fibrosis was potentially associated with higher COVID-19 risk. Druggable targets, such as higher protein expression of histo-blood group ABO system transferase (ABO), interleukin (IL)-6 and lower protein expression of 2′-5′ oligoadenylate synthetase 1 (OAS1) were associated with higher risk of COVID-19. There was no strong genetic evidence supporting the role of vitamin D, glycaemic traits and predisposition to cardiometabolic diseases in COVID-19 risk. Conclusion: This review summarizes modifiable factors for intervention (e.g. smoking, obesity and inflammatory factors) and proteomic signatures (e.g. OAS1 and IL-6) that could help identify drugs for treating COVID-19.

This study explored the associations of genetic susceptibility and adherence to a healthy lifestyle with incident coronary heart disease (CHD) and stroke in individuals with hypertension. This study included 258 531 European descendants with hypertension at baseline from UK Biobank. Genetic risk of CHD and stroke was estimated using polygenic risk scores derived from 300 and 87 single-nucleotide polymorphisms, respectively. Lifestyle scores were calculated based on 4 lifestyle components (no obesity, no current smoking, regular physical activity and healthy diet). Cox regression with age as the underlying timescale was fit for incident CHD (n = 7470) and stroke (n = 5015), separately. A favourable lifestyle (3–4 lifestyle components) was associated with 37% and 30% lower hazards of CHD (95% confidence intervals, 32–42%) and stroke (23–37%), compared with an unfavourable lifestyle (0–1 lifestyle component), at all levels of genetic risk. Evidence of interaction between genetic susceptibility and lifestyle adherence was found for stroke (P = 0.036): no evidence of interaction for CHD (P = 0.524). A favourable lifestyle at high genetic risk had lower 12-year absolute risk of CHD and stroke, compared with an unfavourable lifestyle at low-to-intermediate genetic (exception: an unfavourable lifestyle at low CHD genetic risk). Adhering to a healthy lifestyle is associated with lower CHD and stroke risk regardless of genetic risk among individuals with hypertension. Risk of CHD and stroke for those at high genetic risk but adhering to a healthy lifestyle was generally lower than for those at low-to-intermediate genetic risk but adhering to an unhealthy lifestyle.