Associations between vitamin D and autoimmune diseases: Mendelian randomization analysis

OBJECTIVE

The VITAL trial of vitamin D supplementation suggested a possible protective effect for autoimmune diseases but uncertainties remain. We investigated potential causal effects of vitamin D on composite and individual autoimmune diseases using Mendelian randomization.

METHODS

We used data from 332,984 participants of the UK Biobank of whom 23,089 had at least one autoimmune disease defined using ICD code and/or self-report. Diseases were further considered in mechanistic subgroups driven by "autoimmunity" (n = 12,774) or "autoinflammation" (n = 11,164), then individually. We selected variants within gene regions implicated in vitamin D biology to generate a weighted genetic score. We performed population-wide analysis using the ratio method, then examined non-linear effects across five quantiles based on 25-hydroxycholecalciferol levels.

RESULTS

Genetically-predicted vitamin D was associated with lower risk of diseases in the autoinflammation group (OR 0.95 per 10 ng/ml increase in 25-hydroxycholecalciferol; 95%CI 0.91-0.99; p = 0.03) but not the autoimmunity group (OR 0.99; 95%CI 0.95-1.03; p = 0.64) or combined. When considering individual diseases, genetically-predicted vitamin D was associated with lower risk of psoriasis (OR 0.91; 95%CI 0.85-0.97; p = 0.005), the most common disease in the autoinflammation group, and suggestively with systemic lupus erythematosus (OR 0.84; 95%CI 0.69-1.02; p = 0.08); results were replicated using data from independent studies. We found no evidence for a plausible non-linear relationship between vitamin D and any outcome.

CONCLUSIONS

We found genetic evidence to support a causal link between 25-hydroxycholecalciferol concentrations and psoriasis and systemic lupus erythematosus. These results have implications for potential disease prevention strategies, and the interpretation and design of vitamin D supplementation trials.

Cardiovascular safety of genetically proxied interleukin-5 inhibition: A mendelian randomization study

Interleukin-5 (IL-5) inhibitors have revolutionized the management of eosinophilic asthma. However, IL-5 is thought to play a protective role in atherosclerosis, and cardiovascular safety data for IL-5i are scarce. We used population-level data to examine the association between genetically proxied IL-5i and the risk of cardiovascular diseases. Genetic instruments for IL-5i were selected from a genome-wide association study of eosinophil count in 563,946 individuals. Genetic association data for coronary artery disease were obtained from 60,801 cases, 40,585 stroke cases, 7988 venous thromboembolism cases, and up to 406,111 controls. We used the inverse-variance weighted method and a series of sensitivity analyses. Nine genetic variants were selected to instrument IL-5i. Genetically proxied IL-5i was not associated with the risk of coronary heart disease (OR 0.82, 95%CI 0.65-1.03), stroke (OR 1.10; 0.95-1.27), or venous thromboembolism (OR 0.87; 0.64-1.17). We found no genetic evidence to suggest that IL-5i affects the risk of adverse cardiovascular and thromboembolic events.

Genome-wide identification of genes regulating DNA methylation using genetic anchors for causal inference

BACKGROUND

DNA methylation is a key epigenetic modification in human development and disease, yet there is limited understanding of its highly coordinated regulation. Here, we identify 818 genes that affect DNA methylation patterns in blood using large-scale population genomics data.

RESULTS

By employing genetic instruments as causal anchors, we establish directed associations between gene expression and distant DNA methylation levels, while ensuring specificity of the associations by correcting for linkage disequilibrium and pleiotropy among neighboring genes. The identified genes are enriched for transcription factors, of which many consistently increased or decreased DNA methylation levels at multiple CpG sites. In addition, we show that a substantial number of transcription factors affected DNA methylation at their experimentally determined binding sites. We also observe genes encoding proteins with heterogenous functions that have widespread effects on DNA methylation, e.g., NFKBIE, CDCA7(L), and NLRC5, and for several examples, we suggest plausible mechanisms underlying their effect on DNA methylation.

CONCLUSION

We report hundreds of genes that affect DNA methylation and provide key insights in the principles underlying epigenetic regulation.