Introduction

Mendelian randomization (MR) is a statistical method used in genetic epidemiology to examine the causal relationship between a modifiable exposure and an outcome. This tutorial provides an overview of the underlying theory and assumptions for various MR methods and step-by-step guidance on how to implement them using R.

Sugested Readings

These resources provide a good starting point for understanding the basic concepts and methods of MR, as well as the current best practices and software tools available for conducting MR studies.

Genome-wide association studies

  1. Uffelmann, E. et al. Genome-wide association studies. Nat Rev Methods Primers 1, 59 (2021).
  2. Marees, A. T. et al. A tutorial on conducting genome‐wide association studies: Quality control and statistical analysis. Int J Method Psych 27, e1608 (2018).
  3. MacArthur, J. A. L. et al. Workshop proceedings: GWAS summary statistics standards and sharing. Cell Genom 1, 100004 (2021).

Mendelian Randomization

  1. Sanderson, E. et al. Mendelian randomization. Nat Rev Methods Primers 2, 6 (2022).
  2. Davies, N. M., Holmes, M. V. & Smith, G. D. Reading Mendelian randomisation studies: a guide, glossary, and checklist for clinicians. Bmj 362, k601 (2017).
  3. Hemani, G. et al. The MR-Base platform supports systematic causal inference across the human phenome. Elife 7, e34408 (2018).
  4. Skrivankova, V. W. et al. Strengthening the Reporting of Observational Studies in Epidemiology Using Mendelian Randomization. Jama 326, 1614–1621 (2021).
  5. Skrivankova, V. W. et al. Strengthening the reporting of observational studies in epidemiology using mendelian randomisation (STROBE-MR): explanation and elaboration. Bmj 375, n2233 (2021).

Multivariable Mendelian Randomization

  1. Sanderson, E. Multivariable Mendelian Randomization and Mediation. Csh Perspect Med 11, a038984 (2020).
  2. Carter, A. R. et al. Mendelian randomisation for mediation analysis: current methods and challenges for implementation. Eur J Epidemiol 36, 465–478 (2021).

R packages, tutorials, and databases

  • GWAS Catalog: A database of genome-wide association studies and loci-trait associsation discovered.
  • PhenoScanner: A database of human genotype-phenotype associations.
  • MungeSumstats: Tutorial for standardizing GWAS summary statistics using the MungeSumstats R package.
  • TwoSampleMR: Tutorial for conducting Two-Sample Mendelian randomization using the TwoSampleMR R package
  • MVMR: Tutorial for conducting multivariable Mendelian ranomization using the MVMR R package.
  • MendelianRandomization: Vignette for the MendelianRandomization R package.
  • MR Dictionary: The definitive list of terms for Mendelian randomization research