Using genetics to examine the overall and sex-specific associations of branch-chain amino acids and the valine metabolite, 3-hydroxyisobutyrate, with ischemic heart disease and diabetes: A two-sample Mendelian randomization study

Obesity and Cardiometabolic Disease: Insights From Genetic Studies

Obesity is a highly prevalent chronic disease and major driver of both atherosclerotic heart disease and heart failure. Obesity is also a heritable neuronal disease with heritability estimates of up to 70%. In this work I review how common genetic variants, usually with small effect sizes, contribute to the risk for developing obesity and cardiometabolic disease in the majority of people and how this can be further modulated by environmental factors. In some individuals, rare genetic variants with large effect sizes can influence the risk of developing obesity, in some cases in a Mendelian manner. I also address how identification of these rare variants has led to fundamental biologic insights into how satiety and reward are biologic processes, has led to more personalized treatments, and has identified potential novel drug treatments. Biologic insights derived from genetic studies of obesity have also improved our understanding of the causal mediators between obesity and cardiovascular disease. A major limitation of studies to date is that they involved mostly people of European ancestry. Studying more diverse populations will improve our understanding of obesity and cardiometabolic disease. Lessons derived from genetic studies make a compelling case for increasing accessibility to therapies that have sustained efficacy in managing obesity and improving health. This increased knowledge must also inform public health initiatives that will reduce the prevalence of obesity in the coming decades.

Analyses of potential causal contributors to increased waist/hip ratio-associated cardiometabolic disease: A combined and sex-stratified Mendelian randomization study

BACKGROUND

Increased waist/hip ratio (WHR) contributes to type 2 diabetes, fatty liver, dyslipidaemia, hypertension and coronary artery disease, with potential sex-differential effects. Postulated mediators include increased lipid flux, branched-chain amino acids, glycine and glycoprotein acetyl, but their relative contributions and sex-specific impact on WHR-associated cardiometabolic disease (CMD) are not established.

METHODS

We therefore undertook combined and sex-stratified Mendelian randomization (MR) to assess the relative causal contributions of these mediators to WHR-associated CMD using summary statistics from the largest genome-wide association studies in European ancestries.

RESULTS

In sex-combined MR analyses, increased WHR significantly reduces high-density lipoprotein (beta = -0.416, SE = 0.029, p = 2.87E-47), increases triglyceride (beta = 0.431, SE = 0.029, p = 1.87E-50), type 2 diabetes (odds ratio = 2.747, SE = 0.09, p = 26E-23), coronary artery disease (odds ratio = 1.478, SE = 0.045, p = 6.96E-18), alanine transaminase (beta = 0.062, SE = 0.004, p = 6.88E-67), and systolic (beta = 0.134, SE = 0.022, p = 7.81E-10) and diastolic blood pressure (beta = 0.162, SE = 0.026, p = 5.38E-10). Adjustment for the mediators attenuated WHR's effects, but the associations remained significant with concordant results in females. In males, a similar pattern was seen, except after adjusting for the effect of the ratio of monounsaturated fatty acid to total free fatty acid, the potential causal effect of WHR was no longer significant: high-density lipoprotein (beta = -0.117, SE = 0.069, p = .09) and triglyceride (beta = 0.051, SE = 0.068, p = .459).

CONCLUSIONS

MR suggests WHR increases the risk of CMD independent of these mediators, with the exception of dyslipidaemia in males, which is largely driven by the monounsaturated fatty acid to total free fatty acid ratio.

A two-sample Mendelian randomization study explores metabolic profiling of different glycemic traits

We assessed the causal relation of four glycemic traits and type 2 diabetes liability with 167 metabolites using Mendelian randomization with various sensitivity analyses and a reverse Mendelian randomization analysis. We extracted instruments for fasting glucose, 2-h glucose, fasting insulin, and glycated hemoglobin from the Meta-Analyses of Glucose and Insulin-related traits Consortium (n = 200,622), and those for type 2 diabetes liability from a meta-analysis of multiple cohorts (148,726 cases, 965,732 controls) in Europeans. Outcome data were from summary statistics of 167 metabolites from the UK Biobank (n = 115,078). Fasting glucose and 2-h glucose were not associated with any metabolite. Higher glycated hemoglobin was associated with higher free cholesterol in small low-density lipoprotein. Type 2 diabetes liability and fasting insulin were inversely associated with apolipoprotein A1, total cholines, lipoprotein subfractions in high-density-lipoprotein and intermediate-density lipoproteins, and positively associated with aromatic amino acids. These findings indicate hyperglycemia-independent patterns and highlight the role of insulin in type 2 diabetes development. Further studies should evaluate these glycemic traits in type 2 diabetes diagnosis and clinical management.