Mendelian randomization confirms association BMI and cardio-metabolic diseases

Background

Correlations between high BMI and cardiometabolic disease risk usually arise from observational studies. However, these studies are unable to fully account for confounding by shared risk factors, which, in contrast, can be achieved by mendelian randomization studies.

Studies comparing observational with mendelian randomization estimates of the association between BMI and coronary heart disease (CHD), stroke and type 2 diabetes mellitus (T2DM), reported discrepant ORs and showed inconsistency in terms of finding significant associations with CHD and stroke [1-3].

In this study, 119,859 usable data of the UK Biobank with was used to explore whether a true association exists between BMI and cardio-metabolic diseases in a large cohort with detailed measurements of covariates and, if so, whether BMI has a causal relationship with other health-related phenotypes.

For this, all participants completed physical, sociodemographic and medical assessments from 2006 to 2010. Non-white Europeans, participants with a relatedness coefficient >0.0442 (e.g. first cousins), cases with mismatch between reported and genetic gender or with failure at the UK Biobank quality controlling as well as individuals without genetic data, were excluded from the analysis.

A 93 single-nucleotide polymorphism (SNP) polygenic risk (PGR) score based on a genome-wide association study with 97 BMI-related loci of 339,224 individuals, including 56 newly discovered SNPs, was used [4]. Conventional mendelian randomization as well as the mendelian randomization (MR)-Egger method was used [5].

Main results

• In the fully adjusted models of the observational analyses, an SD increase in BMI (4.83 kg/m2) was associated with risk of stroke (OR 1.26, 95% CI 1.21-1.31, P=2.0*10−29), CHD (OR 1.43, 95% CI 1.40-1.46, P=2.0*10−184), type 2 diabetes (OR 1.97, 95% CI 1.93-2.02, P <4.51*10−308), hypertension (OR 1.75, 95% CI 1.73-1.78, P <4.51*10−308), higher SBP (β=3.02 mmHg, 95% CI 2.91-3.13 mmHg, P <4.5*10−308), higher DBP (β=2.82 mmHg, 95% CI 2.76-2.89 mmHg, P <4.5*10−308) and higher pulse rate (β=1.86 beats/min, 95% CI 1.79-1.94 beats/min, P <4.5*10−308).
• The conventional mendelian randomization analyses using individual participant data showed generally similar effect sizes compared with the observational analyses for hypertension (OR 1.64, 95% CI 1.48-1.83, P=1.1*10−19) and CHD (OR 1.35, 95% CI 1.09-1.69, P=0.007). On the other hand, the association with T2DM increased in magnitude compared to the observational OR (mendelian OR 2.53, 95% CI 2.04-3.13). There was no association between BMI and stroke (P=0.93).
• Using MR-Egger, analyses did not identify evidence of unbalanced horizontal pleiotropy. Furthermore, the associations with SBP and DBP remained significant, but pulse rate did not. And results were similar in the partially vs fully adjusted models.
• All findings remained unchanged for T2DM, CHD and hypertension, after removing participants who reported their age at diagnosis as unknown, chose not to answer or had an age ≤10 years at diagnosis as well as after including physical activity in the final models.

Conclusion

References

Find this article online at JAMA Cardiol