Genetic variants associated with type 2 diabetes and adiposity and risk of intracranial and abdominal aortic aneurysms

Associations between Type 2 Diabetes Mellitus, Metabolic Traits, and Abdominal Aortic Aneurysm: A Cross-Ethnic Mendelian Randomization Analysis

BACKGROUND

Evidence suggests that type 2 diabetes mellitus (T2DM) may protect from abdominal aortic aneurysm (AAA). However, it is unclear whether a causal relationship exists between these 2 conditions and, if so, whether it remains consistent among racial groups.

METHODS

Cross-ethnic Mendelian randomization (MR) was used to examine the causal relationships between T2DM, metabolic traits, and AAA. Inverse variance weighted (IVW) was the primary analysis tool, supplemented by MR-Egger, weighted median, and MR Pleiotropy RESidual Sum and Outlier. Heterogeneity and horizontal pleiotropy were assessed using the Cochran's Q test and MR-Egger intercept, respectively.

RESULTS

According to IVW, an inverse correlation between T2DM and AAA was detected in Europeans (odds ratio [OR] 0.91, 95% confidence interval [CI] 0.84-0.99; P = 0.034) and East Asians (OR 0.87, 95% CI 0.77-0.99; P = 0.038). Fasting glucose was inversely associated with AAA in Europeans (OR 0.56, 95% CI 0.33-0.96; P = 0.034) but not in East Asians. In Europeans, fasting insulin was a risk factor for AAA (OR 3.03, 95% CI 1.53-6.01; P = 0.001), while 2-hour glucose was protective (OR 0.67, 95% CI 0.49-0.91; P = 0.011). Glycated hemoglobin (HbA1c) had no effect. Insufficient instrumental variables prevented the evaluation of the relationships of fasting insulin, HbA1c, and 2-hour glucose with AAA in East Asians.

CONCLUSIONS

T2DM protects against AAA in Europeans and East Asians. The effects of different glucose metabolism characteristics on AAA may inform AAA treatment.

Editor's Choice - Glycaemic Status and Risk of Abdominal Aortic Aneurysm: A Nationwide Cohort Study of Four Million Adults using Korean National Health Screening Data

OBJECTIVE

This retrospective cohort study aimed to confirm the previously reported inverse association between diabetes mellitus (DM) and abdominal aortic aneurysm (AAA) using large population based data. It also investigated the associations between AAA and impaired fasting glucose (IFG) and new onset DM (not yet treated).

METHODS

A representative dataset was obtained from the Korean National Health Insurance Service. Participants who were aged ≥ 50 years and received a national health examination in 2009 were included and followed until 31 December 2019. Glycaemic status was defined based on fasting plasma glucose level and the relevant diagnostic codes. AAA was ascertained using medical facility use records with relevant diagnostic codes or aneurysm repair surgery. A Cox proportional hazards model was used to examine the association between glycaemic status and AAA, with adjustment for confounders. Additionally, the interactions between glycaemic status and subgroups based on baseline characteristics were examined.

RESULTS

The study population comprised 4 162 640 participants. Participants with IFG or DM were significantly more likely to be male, older, and have comorbidities compared with normoglycaemic participants at baseline. The incidence of AAA was lower in participants with IFG or DM compared with normoglycaemic participants. The AAA risk was lower in patients with DM than in patients with IFG, and decreased linearly according to glycaemic status: the adjusted hazard ratio was 0.88 (95% confidence interval [CI] 0.85 - 0.91) for IFG, 0.72 (95% CI 0.67 - 0.78) for newly diagnosed DM, 0.65 (95% CI 0.61 - 0.69) for DM duration < 5 years, and 0.47 (95% CI 0.44 - 0.51) for DM duration ≥ 5 years compared with the normoglycaemia group. Both IFG and DM were related to reduced AAA risk in all subgroups, suggesting an independent association.

CONCLUSION

Both IFG and DM, even when not treated with antihyperglycaemic medication, were associated with a lower incidence of AAA. The AAA risk decreased linearly according to DM duration.

Type 2 diabetes has a protective causal association with thoracic aortic aneurysm: a Mendelian randomization study

BACKGROUND

Observational studies have reported an inverse association of type 2 diabetes (T2D) with thoracic aortic aneurysm (TAA). However, the causality of the association has not been established yet. The present study aims to clarify the causal relationship between T2D and TAA via a Mendelian randomization (MR) approach.

METHODS

Causality of associations were assessed using a two-sample MR framework. Genome-wide association study (GWAS) summary statistics were obtained for T2D, glycated hemoglobin (HbA1c), fasting glucose (FG) and fasting insulin (FI) as exposures, and TAA, ascending aortic diameter (AAoD) and descending aortic diameter (DAoD) as outcomes. Four different methods (inverse variance weighted [IVW], weight median, MR-Egger and MR-PRESSO) were used to calculate causal estimates. Heterogeneity and horizontal pleiotropy were assessed using Cochran Q test and MR-Egger regression intercept, respectively.

RESULTS

Genetically predicted T2D was inversely associated with the risk of TAA (OR: 0.931, 95% CI 0.870 to 0.997, p = 0.040, IVW method) and AAoD (Beta: -0.065, 95%CI -0.099 to  - 0.031, p = 1.7e-04, IVW method), but not with DAoD (p > 0.05). Genetically predicted FG level was inversely associated with AAoD (Beta: -0.273, 95% CI -0.396 to -0.150, p = 1.41e-05, IVW method) and DAoD (Beta: -0.166, 95% CI -0.281 to -0.051, p = 0.005, IVW method), but not with TAA (p > 0.05). The effect of genetically predicted HbA1c and FI on TAA, AAoD and DAoD did not reach statistical significance (p > 0.05).

CONCLUSIONS

Genetic predisposition to T2D decreases the risk of TAA. Genetically predicted T2D is inversely associated with AAoD, but not with DAoD. Genetically predicted FG level was inversely associated with AAoD and DAoD.

A Guide for Selection of Genetic Instruments in Mendelian Randomization Studies of Type 2 Diabetes and HbA1c: Toward an Integrated Approach

In this study we examine the instrument selection strategies currently used throughout the type 2 diabetes and HbA1c Mendelian randomization (MR) literature. We then argue for a more integrated and thorough approach, providing a framework to do this in the context of HbA1c and diabetes. We conducted a literature search for MR studies that have instrumented diabetes and/or HbA1c. We also used data from the UK Biobank (UKB) (N = 349,326) to calculate instrument strength metrics that are key in MR studies (the F statistic for average strength and R2 for total strength) with two different methods ("individual-level data regression" and Cragg-Donald formula). We used a 157-single nucleotide polymorphism (SNP) instrument for diabetes and a 51-SNP instrument (with partition into glycemic and erythrocytic as well) for HbA1c. Our literature search yielded 48 studies for diabetes and 22 for HbA1c. Our UKB empirical examples showed that irrespective of the method used to calculate metrics of strength and whether the instrument was the main one or included partition by function, the HbA1c genetic instrument is strong in terms of both average and total strength. For diabetes, a 157-SNP instrument was shown to have good average strength and total strength, but these were both substantially lesser than those of the HbA1c instrument. We provide a careful set of five recommendations to researchers who wish to genetically instrument type 2 diabetes and/or HbA1c. In MR studies of glycemia, investigators should take a more integrated approach when selecting genetic instruments, and we give specific guidance on how to do this.

Association of cardiovascular risk factors and lifestyle behaviors with aortic aneurysm: A Mendelian randomization study

Objective: To examine the causality between hypertension, diabetes, other cardiovascular risk factors, lifestyle behaviors, and the aortic aneurysm among patients of European ancestry.

Methods: We performed two-sample Mendelian randomization (MR) analysis to investigate the causality of 12 modifiable risk factors with aortic aneurysm, including hypertension, body mass index (BMI), waist–hip ratio (WHR), diabetes, tobacco smoking, alcohol and coffee consumption, physical activity, and sleep duration. Genome-wide significant genetic instruments (p < 5 × 10^–8) for risk factors were extracted from European-descent genome-wide association studies, whereas aortic aneurysm genetic instruments were selected from the UK Biobank and FinnGen cohort. The inverse-variance weighted MR was used as the main analysis, and MR-Egger (MRE), weighted median MR, MR pleiotropy residual sum and outlier, and Phenoscanner searching were performed as sensitivity analyses. Furthermore, we calculated MRE intercept to detect pleiotropy and Cochran’s Q statistics to assess heterogeneity and conducted bidirectional MR and MR Steiger tests to exclude the possibility of reverse causality.

Results: We observed significantly higher risks for the aortic aneurysm in hypertension [pooled OR: 4.30 (95% CI 2.84–6.52)], BMI [OR: 1.58 (95% CI 1.37–1.81)], WHR [OR: 1.51 (95% CI 1.21–1.88)], WHR adjusted for BMI (WHRadjBMI) [OR: 1.35 (95% CI 1.12–1.63)], age of smoking initiation [OR: 1.63 (95% CI 1.18–2.26)], and tobacco use (initiation, cessation, and heaviness) [OR: 2.88 (95% CI 1.85–2.26)]. In sensitivity analysis, the causal effects of hypertension, BMI, WHRadjBMI, and tobacco use (initiation, cessation, and heaviness) remained robust.

Conclusion: There was a positive causal relationship between hypertension, BMI, WHR, and WHRadjBMI and aortic aneurysm.

A two-sample Mendelian randomization analysis of modifiable risk factors and intracranial aneurysms

We aimed to investigate the causality between potentially modifiable risk factors and the risk of intracranial aneurysm. Genetic instruments for 51 modifiable factors and intracranial aneurysm data were obtained from recently published genome-wide association studies. We applied two-sample Mendelian randomization methods to investigate their causal relationships. Genetically predicted cigarettes per day, smoking initiation, systolic blood pressure, hypertension and body fat percentage were significantly associated with an increased risk of intracranial aneurysm [odds ratios (OR) 2.67, 95% confidence interval (CI) 1.75–4.07, p = 5.36 × 10^–6, OR 1.53, 95% CI 1.32–1.77, p = 9.58 × 10^–9, OR 1.05, 95% CI 1.02–1.08, p = 1.18 × 10^–3, OR 1.65, 95% CI 1.19–2.28, p = 2.56 × 10^–3 and OR 1.29, 95% CI 1.11–1.52, p = 1.33 × 10^–3, respectively]. Type 2 diabetes mellitus was significantly associated with a decreased risk of intracranial aneurysm (OR 0.89, 95% CI 0.83–0.95, p = 8.54 × 10^–4). Body fat percentage was significantly associated with subarachnoid haemorrhage (p = 5.70 × 10^–5). This study provided genetic evidence of causal effects of smoking, blood pressure, type 2 diabetes mellitus and obesity on the risk of intracranial aneurysm.

Modifiable risk factors for intracranial aneurysms: Evidence from genetic studies

Background:

Intracranial aneurysm (IA) is a crucial health concern with limited strategies for prevention and treatment.

Aim:

To identify potentially modifiable risk factors, such as socioeconomic, behaviors, dietary, and cardiometabolic factors, for IA and its subtypes.

Methods:

Summary statistics for IA were derived from a genome-wide association study with an overall 79,429 participants. Single nucleotide polymorphisms associated with modifiable risk factors at genome-wide significance ( P = 5 × 10–8) were used as instrumental variables. The inverse-variance-weighted method, weighted-median method, Mendelian randomization (MR)-Egger regression, MR-Pleiotropy RESidual Sum and Outlier, and multivariable MR analyses were performed to evaluate the effect estimates.

Results:

Genetically predicted educational attainment, insomnia, smoking, and systolic and diastolic blood pressure (SBP and DBP) were significantly associated with the risk of IA. The odds ratios (ORs) were 0.44 (95% confidence interval (CI): 0.37–0.52) for educational attainment, 1.15 (95% CI: 1.08–1.23) for insomnia, 1.56 (95% CI: 1.38–1.75) for smoking initiation, 2.69 (95% CI: 1.77–4.07) for cigarette per day, 2.65 (95% CI: 1.72–4.08) for lifetime smoking, 1.07 (95% CI: 1.06–1.09), and 1.06 (95% CI: 1.04–1.10) for SBP and DBP, respectively. Similar effect estimates were observed for unruptured IAs and aneurysmal subarachnoid hemorrhage.

Conclusions:

This study provided genetic evidence that several modifiable risk factors, including blood pressure, smoking, educational attainment, and insomnia were associated with the risk of IA.

Causal role of high body mass index in multiple chronic diseases: a systematic review and meta-analysis of Mendelian randomization studies

BACKGROUND

Obesity is a worldwide epidemic that has been associated with a plurality of diseases in observational studies. The aim of this study was to summarize the evidence from Mendelian randomization (MR) studies of the association between body mass index (BMI) and chronic diseases.

METHODS

PubMed and Embase were searched for MR studies on adult BMI in relation to major chronic diseases, including diabetes mellitus; diseases of the circulatory, respiratory, digestive, musculoskeletal, and nervous systems; and neoplasms. A meta-analysis was performed for each disease by using results from published MR studies and corresponding de novo analyses based on summary-level genetic data from the FinnGen consortium (n = 218,792 individuals).

RESULTS

In a meta-analysis of results from published MR studies and de novo analyses of the FinnGen consortium, genetically predicted higher BMI was associated with increased risk of type 2 diabetes mellitus, 14 circulatory disease outcomes, asthma, chronic obstructive pulmonary disease, five digestive system diseases, three musculoskeletal system diseases, and multiple sclerosis as well as cancers of the digestive system (six cancer sites), uterus, kidney, and bladder. In contrast, genetically predicted higher adult BMI was associated with a decreased risk of Dupuytren's disease, osteoporosis, and breast, prostate, and non-melanoma cancer, and not associated with Alzheimer's disease, amyotrophic lateral sclerosis, or Parkinson's disease.

CONCLUSIONS

The totality of the evidence from MR studies supports a causal role of excess adiposity in a plurality of chronic diseases. Hence, continued efforts to reduce the prevalence of overweight and obesity are a major public health goal.

Investigating Causal Relationships Between Psychiatric Traits and Intracranial Aneurysms: A Bi-directional Two-Sample Mendelian Randomization Study

Background Despite psychiatric traits were associated with intracranial aneurysms (IAs) in observational studies, their causal relationships remain largely undefined. We aimed to assess the causality between psychiatric traits and IAs.

Methods We firstly collected the genome-wide association statistics of IAs (sample size, n = 79,429) and ten psychiatric traits from Europeans, including insomnia (n = 1,331,010), mood instability (n = 363,705), anxiety disorder (n = 83,566), major depressive disorder (MDD) (n = 480,359), subjective wellbeing (n = 388,538), attention deficit/hyperactivity disorder (ADHD) (n = 53,293), autism spectrum disorder (ASD) (n = 46,350), bipolar disorder (BIP) (n = 51,710), schizophrenia (SCZ) (n = 105,318), and neuroticism (n = 168,105). We then conducted a series of bi-directional two-sample Mendelian randomization (MR) analyses, of which the Robust Adjusted Profile Score (RAPS) was the primary method to estimate the causal effects between these psychiatric traits and IAs.

Results We found that insomnia exhibited a significant risk effect on IAs with the odds ratio (OR) being 1.22 (95% CI: 1.11–1.34, p = 4.61 × 10^–5) from the RAPS method. There was suggestive evidence for risk effect of mood instability on IAs (RAPS, OR = 4.16, 95% CI: 1.02–17.00, p = 0.047). However, no clear evidence of causal effects on IAs for the rest eight psychiatric traits (anxiety disorder, MDD, subjective wellbeing, ADHD, ASD, BIP, SCZ, and neuroticism) was identified. In the reverse MR analyses, no causal effects of IAs on psychiatric traits were found.

Conclusions Our findings provide strong evidence for a causal risk effect of insomnia on IAs and suggestive evidence for mood instability as a causal risk effect on IAs. These results could inform the prevention and clinical intervention of IAs.

Genetics of Intracranial Aneurysms

Rupture of an intracranial aneurysm leads to aneurysmal subarachnoid hemorrhage, a severe type of stroke which is, in part, driven by genetic variation. In the past 10 years, genetic studies of IA have boosted the number of known genetic risk factors and improved our understanding of the disease. In this review, we provide an overview of the current status of the field and highlight the latest findings of family based, sequencing, and genome-wide association studies. We further describe opportunities of genetic analyses for understanding, prevention, and treatment of the disease.

Systematic review and Meta-Analysis of Mendelian randomisation analyses of Abdominal aortic aneurysms

INTRODUCTION

Mendelian randomisation (MR) has been suggested to be able to overcome biases of observational studies, but no meta-analysis is available on MR studies on abdominal aortic aneurysm (AAA). This systematic review and Meta-analysis examined the evidence of causal risk factors for AAA identified in MR studies.

METHODS

Publicly available databases were systematically searched for MR studies that reported any causal risk factors for AAA diagnosis. Meta-analyses were performed using random effect models and reported as odds ratio (OR) and 95% confidence intervals (CI). Study quality was assessed using a modified version of Strengthening the Reporting of Mendelian Randomisation Studies (STROBE-MR) guidelines.

RESULTS

Sixteen MR studies involving 34,050 patients with AAA and 2,205,894 controls were included. Meta-analyses suggested that one standard deviation increase in high density lipoprotein (HDL) significantly reduced (OR: 0.66, 95% CI: 0.61, 0.72) and one standard deviation increase in low density lipoprotein (LDL) significantly increased the risk (OR: 1.68, 95%, CI: 1.55, 1.82) of AAA. One standard deviation increase in triglycerides did not significantly increase the risk of AAA (OR: 1.21, 95% CI: 0.86, 1.71). Quality assessment suggested that ten and five studies were of low and moderate risk of bias respectively, with one study considered as high risk of bias.

CONCLUSION

This meta-analysis suggests LDL and HDL are positive and negative casual risk factors for AAA.

Evaluating marginal genetic correlation of associated loci for complex diseases and traits between European and East Asian populations

Genome-wide association studies (GWASs) have successfully identified a large amount of single-nucleotide polymorphisms associated with many complex phenotypes in diverse populations. However, a comprehensive understanding of the genetic correlation of associated loci of phenotypes across populations remains lacking and the extent to which associations discovered in one population can be generalized to other populations or can be utilized for trans-ethnic genetic prediction is also unclear. By leveraging summary statistics, we proposed MAGIC to evaluate the trans-ethnic marginal genetic correlation (r_m) of per-allele effect sizes for associated SNPs (P < 5E-8) under the framework of measurement error models. We confirmed the methodological advantage of MAGIC over general approaches through simulations and demonstrated its utility by analyzing 34 GWAS summary statistics of phenotypes from the East Asian (N_max = 254,373) and European (N_max = 1,220,901) populations. Among these phenotypes, r_m was estimated to range from 0.584 (se = 0.140) for breast cancer to 0.949 (se = 0.035) for age of menarche, with an average of 0.835 (se = 0.045). We also uncovered that the trans-ethnic genetic prediction accuracy for phenotypes in the target population would substantially become low when using associated SNPs identified in non-target populations, indicating that associations discovered in the one population cannot be simply generalized to another population and that the accuracy of trans-ethnic phenotype prediction is generally dissatisfactory. Overall, our study provides in-depth insight into trans-ethnic genetic correlation and prediction for complex phenotypes across diverse populations.

Diabetes mellitus and abdominal aortic aneurysms: A review of the mechanisms underlying the negative relationship

INTRODUCTION

Diabetes mellitus appears to be negatively associated with abdominal aortic aneurysm; however, the mechanisms underlying this relationship remain poorly understood. The aim of this article is to provide a comprehensive review of the currently understood biological pathways underlying this relationship.

METHODS

A review of the literature ('diabetes' OR 'hyperglycaemia' AND 'aneurysm') was performed and relevant studies grouped into biological pathways.

RESULTS

This review identified a number of biological pathways through which diabetes mellitus may limit the presence, growth and rupture of abdominal aortic aneurysms. These include those influencing extracellular matrix volume, extracellular matrix glycation, the formation of advanced glycation end-products, inflammation, oxidative stress and intraluminal thrombus biology. In addition, there is an increasing evidence to suggest that the medications used to treat diabetes can also limit the development and progression of abdominal aortic aneurysms.

CONCLUSION

The negative association between diabetes and abdominal aortic aneurysm is robust. Future studies should attempt to target the pathways identified in this review to develop novel therapeutic agents aimed at slowing or even halting aneurysm progression.

Genetically determined schizophrenia is not associated with impaired glucose homeostasis

Here, we used data from large genome-wide association studies to test the presence of causal relationships, conducting a Mendelian randomization analysis; and shared molecular mechanisms, calculating the genetic correlation, among schizophrenia, type 2 diabetes (T2D), and impaired glucose homeostasis. Although our Mendelian randomization analysis was well-powered, no causal relationship was observed between schizophrenia and T2D, or traits related to glucose impaired homeostasis. Similarly, we did not observe any global genetic overlap among these traits. These findings indicate that there is no causal relationships or shared mechanisms between schizophrenia and impaired glucose homeostasis.