A recent study, using genetic variants as instrumental variables for body mass index (BMI), provides evidence that higher BMI leads to a higher risk of psoriasis. This supports the prioritization of therapies and lifestyle interventions aimed at controlling weight for the prevention or treatment of this common skin disease. Researchers used a genetic instrument comprising 97 single-nucleotide polymorphisms (SNPs) associated with BMI as a proxy for BMI. 1-sample mendelian randomization (MR) was conducted using individual-level data from 396,495 individuals. 2-sample MR was performed with summary-level data (356,926 individuals) from published BMI and psoriasis genome-wide association studies (GWASs). They found:
- Published observational data showed an association of higher BMI with psoriasis.
- A mean difference in BMI of 1.26 kg/m2 between psoriasis cases and controls was observed in adults, while a 1.55 kg/m2 mean difference was observed in children.
- Overall, a 1 kg/m2 increase in BMI was associated with 4% higher odds of psoriasis (meta-analysis odds ratio [OR] = 1.04).
- MR analyses provided evidence that higher BMI causally increases the odds of psoriasis.
Budu-Aggrey A, Brumpton B, Tyrrell J, et al. Evidence of a causal relationship between body mass index and psoriasis: A mendelian randomization study. [Published online ahead of print January 31, 2019]. PLoS Med. doi:10.1371/journal.pmed.1002739.
The rising prevalence of psoriasis and obesity are important public health concerns. This study presents evidence that a higher body mass index (BMI) increases the risk of psoriasis but there was no causal effect of a psoriasis genetic risk that results in obesity. In addition, there are various possible mechanisms linking obesity with psoriasis, such as the increased production of inflammatory cytokines derived from adipose tissue, which include tumor necrosis alpha, interleukin 6, and leptin. Therefore, the prevention and treatment of psoriasis may come from targeting adiposity levels in addition to immune pathways in the skin. Such an approach may prove useful in the prevention of psoriasis.—Paul S. Yamauchi, MD, PhD; Clinical Assistant Professor of Dermatology David Geffen School of Medicine at UCLA; Harbor-UCLA Medical Center Division of Dermatology; Adjunct Associate Professor John Wayne Cancer Institute.