Elevated plasma triglycerides increase the risk of psoriasis: a cohort and Mendelian randomization study.

ABSTRACT

BACKGROUND: It is increasingly clear that triglyceride-rich lipoproteins are proinflammatory and cause low-grade systemic inflammation. However, it is currently unknown whether elevated plasma triglycerides are causally related to the development of psoriasis, a skin disorder driven by chronic inflammation. OBJECTIVES: To determine if elevated plasma triglycerides are associated with increased risk of psoriasis in observational and Mendelian randomization analysis. METHODS: Consecutive individuals from the Copenhagen General Population Study were included. We used plasma triglycerides (n = 108 043) and a weighted triglyceride allele score (n = 92 579) on nine known triglyceride-altering genetic variants. Genetic results were replicated in 337 159 individuals from the UK Biobank. Psoriasis was defined using the International Classification of Diseases, version 10 (ICD-10) code for hospital contact in the main analyses, and prescription of topical antipsoriatics for mild psoriasis in the sensitivity analysis. RESULTS: During a follow-up of median (range) 9.3 (0.1-15.1) years from 2003 to 2015 through 2018, 855 (1%) individuals were diagnosed with psoriasis by ICD-10 in the observational analysis and 772 (1%) in the Mendelian randomization analysis. In the observational analysis, the multivariable adjusted hazard ratio for psoriasis by ICD-10 was 1.26 [95% confidence interval (CI) 1.15-1.39] per doubling in plasma triglycerides with a corresponding causal odds ratio of incident psoriasis of 2.10 (95% CI 1.30-3.38). Causality was confirmed from data from the UK Biobank. Results were similar but slightly attenuated when we used topical antipsoriatic prescriptions for mild psoriasis. CONCLUSIONS: Elevated plasma triglycerides are associated with an increased risk of psoriasis in observational and Mendelian randomization analysis.

Psoriasis is a common skin condition, characterized by inflammation in the body (the body's response to an unwanted agent). People with psoriasis often have higher lipid levels in their blood compared with people without psoriasis. Some studies have shown that triglyceride-rich lipoprotein (a certain type of lipid) is irritative to the body and can cause inflammation. However, it is unclear whether high levels of triglycerides in the blood can cause them to penetrate into the skin and trigger the onset of psoriasis. We aimed to test this question in 100,000 people from a Danish population without previously diagnosed psoriasis. Specifically, we measured plasma triglycerides at initial examination and at the same time assessed the same people for genetic variants that impact on the concentration of plasma triglycerides. Importantly, genetic variants are inherited by chance, meaning that we could look specifically at whether a change in triglycerides was the mechanism that causes psoriasis. Next, we observed these people for about 10 years and noted any new occurrence of psoriasis during follow-up. We found that the risk of developing psoriasis was higher both as a function of plasma triglyceride concentration and the genetic variants that increase plasma triglyceride concentration. Overall, our study findings suggest that high levels of triglycerides in the blood could be a causal risk factor for the development of psoriasis.