Examining the causal association of fasting glucose with blood pressure in healthy children and adolescents: a Mendelian randomization study employing common genetic variants of fasting glucose

Type 2 Diabetes and Hypertension

RATIONALE

In observational studies, type 2 diabetes mellitus (T2D) has been associated with an increased risk of hypertension, and vice versa; however, the causality between these conditions remains to be determined.

OBJECTIVES

This population-based prospective cohort study sought to investigate the bidirectional causal relations of T2D with hypertension, systolic and diastolic blood pressure (BP) using Mendelian randomization (MR) analysis.

METHODS AND RESULTS

After exclusion of participants free of a history of heart failure, cardiovascular disease, cardiac procedures, and non-T2D diabetes mellitus, a total of 318 664 unrelated individuals with qualified genotyping data of European descent aged 37 to 73 from UK Biobank were included. The genetically instrumented T2D and hypertension were constructed using 134 and 233 single nucleotide polymorphisms, respectively. Seven complementary MR methods were applied, including inverse-variance weighted method, 2 median-based methods (simple and weighted), MR-Egger, MR-robust adjusted profile scores, MR-Pleiotropy Residual Sum and Outlier, and multivariate MR. The genetically instrumented T2D was associated with risk of hypertension (odds ratio, 1.07 [95% CI, 1.04-1.10], P=3.4×10^-7), whereas the genetically determined hypertension showed no relationship with T2D (odds ratio, 0.96 [0.88-1.04], P=0.34). Our MR estimates from T2D to BP showed that the genetically instrumented T2D was associated with a 0.67 mm Hg higher systolic BP (95% CI, 0.41-0.93, P=5.75×10^-7) but not with a higher diastolic BP. There was no clear evidence showing a causal effect of elevated systolic BP or diastolic BP on T2D risk. Positive pleiotropic bias was indicated in the hypertension→T2D relation (odds ratio, of MR-Egger intercept 1.010 [1.004-1.016], P=0.001) but not from T2D to hypertension (1.001 [0.998-1.004], P=0.556).

CONCLUSIONS

T2D may causally affect hypertension, whereas the relationship from hypertension to T2D is unlikely to be causal. These findings suggest the importance of keeping an optimal glycemic profile in general populations, and BP screening and monitoring, especially systolic BP, in patients with T2D.

Correlates of elevated blood pressure in healthy children: a systematic review

The prevalence of hypertension in children is increasing globally. Addressing this will require a robust understanding of associated risk factors. To this end, we conducted a systematic review to identify correlates of elevated blood pressure (BP) in children. Literature searches were conducted using pre-defined search terms from three academic databases. The abstract and full text of identified studies were screened for eligibility by two independent reviewers. A total of 100 studies were included in this systematic review. An assessment tool was first used to assess study quality; a narrative synthesis was then performed. We found a broad range of physiological, social and behavioural factors associated with elevated BP in children. The most common correlate observed was adiposity, suggesting that childhood obesity may be implicated in the increased prevalence of hypertension observed in children. However, the broad range of other factors identified underscores the multi-factorial aetiology of hypertension. Data from a broad range of studies showed that the correlates of hypertension in children are multi-factorial. Therefore, approaches aimed at preventing hypertension must in turn be multi-factorial to ensure that the burden of hypertension in childhood is addressed.

Mendelian randomisation in type 2 diabetes and coronary artery disease

Type 2 diabetes, coronary artery disease and hypertension are associated with anthropometric and biomarker traits, including waist-to-hip-ratio, body mass index and altered glucose and insulin levels. Clinical trials, for example of weight-loss interventions, show these factors are causal, but lifelong impact of subtle changes in body mass index and body fat distribution are less clear. The use of human genetics can quantify the causal effects of long-term exposure to subtle changes of modifiable risk factors. Mendelian randomisation (MR) uses human genetic variants associated with the risk factor to quantify the relationship between risk factor and disease outcome. The last two years have seen an increase in the number of MR studies investigating the relationship between anthropometric traits and metabolic diseases. This review provides an overview of these recent MR studies in relation to type 2 diabetes, coronary artery disease and hypertension. MR provides evidence for causal associations of waist-to-hip-ratio, body mass index and altered glucose levels with type 2 diabetes, coronary artery disease and hypertension.