Strengths and limitations
MR, melanoma, CM, psoriasis
ERYTHRODERMIC PSORIASIS, PUSTULAR PSORIASIS, MELANOMA, PSORIASIS, ARTHRITIC PSORIASIS, PSORIASIS VULGARIS, PSORIATIC ARTHRITIS, REGRESSION
This study had several advantages. To determine the causal relationship between psoriasis and CM without the interference of confounding factors, we performed bidirectional MR analysis. Bidirectional Mendelian randomization analysis is an extension of standard Mendelian randomization analysis. Compared with the latter, the former can investigate whether there is a two-way causal relationship between exposure variables and outcome variables. In addition, genetic variation in CM was derived from the largest available GWAS meta-analysis, ensuring the strength of instruments in MR analyses. We detected and excluded horizontal poly-tropism using MR-PRESSO and MR–Egger regression intercept tests. Finally, there was no overlap between the GWAS summary data for psoriasis and the meta-analysis GWAS summary data for CM, which led to low heterogeneity, low bias, and high accuracy in our study.We also acknowledge some limitations. First, most of the data used in the analysis mainly came from individuals with European ancestry, which restricts the applicability of our findings to other ethnic groups. Second, due to the lack of detailed clinical data, we were unable to conduct a subgroup analysis, for example, to distinguish between psoriasis vulgaris, arthritic psoriasis, pustular psoriasis, and erythrodermic psoriasis; explore non-linear relationships; or to sort by the severity of psoriasis. A population-based study in Denmark suggested a modestly increased risk of melanoma in patients with mild psoriasis and no increased risk in patients with severe psoriasis and psoriatic arthritis (