A Guide for Selection of Genetic Instruments in Mendelian randomisation (MR) studies of Type-2 diabetes and HbA1c: towards an integrated approach

This study examines the instrument selection strategies currently employed throughout the type-2 diabetes and HbA1c 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 Mendelian randomisation studies that have instrumented diabetes and/or HbA1c. We also used data from the UK Biobank (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-SNP instrument for diabetes and a 51-SNP instrument (as well as partitioned into glycaemic and erythrocytic) 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 was partitioned 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 and total strength, but these were both substantially smaller 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. MR studies of glycaemia should take a more integrated approach when selecting genetic instruments and we give specific guidance on how to do this. </p

Data_Sheet_1_Antihypertensive Medication Use and Its Effects on Blood Pressure and Haemodynamics in a Tri-ethnic Population Cohort: Southall and Brent Revisited (SABRE).docx

Objectives:We characterised differences in BP control and use of antihypertensive medications in European (EA), South Asian (SA) and African-Caribbean (AC) people with hypertension and investigated the potential role of type 2 diabetes (T2DM), reduced arterial compliance (Ca), and antihypertensive medication use in any differences.Methods:Analysis was restricted to individuals with hypertension [age range 59–85 years; N = 852 (EA = 328, SA = 356, and AC =168)]. Questionnaires, anthropometry, BP measurements, echocardiography, and fasting blood assays were performed. BP control was classified according to UK guidelines operating at the time of the study. Data were analysed using generalised structural equation models, multivariable regression and treatment effect models.Results:SA and AC people were more likely to receive treatment for high BP and received a greater average number of antihypertensive agents, but despite this a smaller proportion of SA and AC achieved control of BP to target [age and sex adjusted odds ratio (95% confidence interval) = 0.52 (0.38, 0.72) and 0.64 (0.43, 0.96), respectively]. Differences in BP control were partially attenuated by controlling for the higher prevalence of T2DM and reduced Ca in SA and AC. There was little difference in choice of antihypertensive agent by ethnicity and no evidence that differences in efficacy of antihypertensive regimens contributed to ethnic differences in BP control.Conclusions:T2DM and more adverse arterial stiffness are important factors in the poorer BP control in SA and AC people. More effort is required to achieve better control of BP, particularly in UK ethnic minorities.</p

Data_Sheet_1_A Double-Blind Placebo-Controlled Crossover Study of the Effect of Beetroot Juice Containing Dietary Nitrate on Aortic and Brachial Blood Pressure Over 24 h.docx

Dietary inorganic nitrate in beetroot can act as a source of nitric oxide and has been reported to lower brachial blood pressure (BP). This study examined the effect of inorganic nitrate in beetroot juice on aortic (central) BP acutely and over the subsequent 24-h period. A double blind, randomized, placebo-controlled crossover trial was performed in fifteen healthy, normotensive men and women (age 22–40 years). Participants were randomized to receive beetroot juice containing nitrate (6.5–7.3 mmol) or placebo beetroot juice from which nitrate had been removed (<0.06 mmol nitrate). Effects on aortic systolic BP were measured at 30 min (primary endpoint), 60 min and over a subsequent 24 h period using an ambulatory BP monitor. Carotid-femoral pulse wave velocity (cfPWV) was also measured at 30 min. Following a washout period, the procedure was repeated within 7 days with crossover to the opposite arm of the trial. Compared with placebo, ingestion of beetroot juice containing nitrate lowered aortic systolic BP at 30 min by 5.2 (1.9–8.5) mmHg [mean (95% confidence interval); p < 0.01]. A smaller effect on aortic systolic BP was observed at 60 min. There were minimal effects on brachial BP or cfPWV. Effects on aortic systolic BP were not sustained over the subsequent 24 h and there were no effects on other hemodynamic parameters during ambulatory monitoring. A single dose of beetroot juice containing nitrate lowers aortic BP more effectively than brachial BP in the short term, but the effects are comparatively short-lived and do not persist over the course of the same day.</p

Characteristics of the two ethnic groups.

<p>Values are % (n), mean ± SD, or median (25th, 75th percentile) for skewed data; p values were calculated using the Student’s t-test or the Mann-Whitney U-test for continuous variables and the Chi-squared test for categorical variables. Abbreviations: BMI, body mass index; BP, blood pressure; HbA1c, glycosylated haemoglobin; HDL, high density lipoprotein, HOMA-IR, homeostasis model of the assessment of insulin resistance; WHR, waist hip ratio.</p

The incremental prognostic value of 3D-EF, 3D-GLS, and 3D-PTS over FRS.

The incremental prognostic value of 3D-EF, 3D-GLS, and 3D-PTS over FRS.</p

S1 –S4 Tables and S1 & S2 Figs.

3D-speckle tracking echocardiography(3D-STE) allows simultaneous assessment of ejection fraction(EF) and multidirectional strains, but its prognostic utility in the general population is unknown. We investigated if 3D-STE strains predicted a composite of major cardiac endpoints(MACE) beyond cardiovascular risk factors(CVDRF), and whether they were superior to 3D-EF. 529 participants in SABRE, a UK-based tri-ethnic general population cohort (69±6y; 76.6% male) with acceptable 3D-STE imaging were studied. Associations between 3D-EF or multidirectional myocardial strains and MACE(coronary heart disease(fatal/non-fatal), heart failure hospitalization, new-onset arrhythmia and cardiovascular mortality) were determined using Cox regression including adjustment for CVDRF and 2D-EF. Whether 3D-EF, global longitudinal strain(3D-GLS) and principle tangential strain(3D-PTS/3D-strain) improved cardiovascular risk stratification over CVDRF was investigated using a likelihood ratio test on a series of nested Cox proportional hazards models and Harrell’s C statistics. During follow-up(median, 12y), there were 92 events. 3D-EF, 3D-GLS and 3D-PTS and 3D-RS were associated with MACE in unadjusted and models adjusted for CVDRF but not CVDRF+2D-EF. Compared to 3D-EF, both 3D-GLS and 3D-PTS slightly improved the predictive value over CVDRF for MACE, but the improvement was modest(C statistic increased from 0.698(0.647, 0.749) to 0.715(0.663, 0.766) comparing CVDRF with CVDRF +3D-GLS). 3D-STE-derived LV myocardial strains predicted MACE in a multi-ethnic general population sample of elderly individuals from the UK; however the added prognostic value of 3D-STE myocardial strains was small.</div

Unadjusted survival analysis of predictors.

Nelson-Aalen cumulative hazard curves by medians of 3D-STE LV indices (major adverse cardiac endpoint). Dashed line = ≥median, solid line = </p

Flow diagram of the study population.

Abbreviations: FR, frame rate; 3DE, 3D echocardiography; 3D-STE, 3D speckle-tracking echocardiography; LV, left ventricular.</p

Associations between major adverse cardiovascular endpoints ((n = 92) and 3D-STE LV functional indices in the overall population.

Associations between major adverse cardiovascular endpoints ((n = 92) and 3D-STE LV functional indices in the overall population.</p

Associations between major adverse cardiac endpoints (n = 68) and 3D-STE LV functional indices in the overall population without prior history of CHD (n = 475).

Associations between major adverse cardiac endpoints (n = 68) and 3D-STE LV functional indices in the overall population without prior history of CHD (n = 475).</p