Bidirectional causal relationships between the skin microbiome and psoriasis: Insights from Mendelian randomization analysis.

Psoriasis is a chronic inflammatory skin disease affecting 2% of the global population. Recent research suggests the skin microbiome plays a critical role in psoriasis. Skin microbiome data were obtained from the KORA FF4 study in Germany, and psoriasis data from FinnGen genome-wide association study summary statistics. Forward and reverse 2-sample Mendelian randomization (MR) analyses were conducted to assess causal relationships. Forward MR analysis identified several microbial features as risk factors for psoriasis, including the family Neisseriaceae in sebaceous skin (OR = 1.036, 95% CI: 1.010-1.062, P = .0054), ASV011 in dry skin (OR = 1.024, 95% CI: 1.000-1.048, P = .0490), and the order Clostridiales in moist skin (OR = 1.016, 95% CI: 1.000-1.032, P = .0449). Protective features included ASV016 (OR = 0.972, 95% CI: 0.949-0.994, P = .0136) and ASV053 (OR = 0.973, 95% CI: 0.954-0.992, P = .0054) in dry skin. Reverse MR analysis confirmed psoriasis as a significant risk factor for changes in the skin microbiome, with notable associations in the dry skin region for asv002 (OR = 1.266, 95% CI: 1.061-1.510, P = .027) and genus: Haemophilus (OR = 1.364, 95% CI: 1.065-1.746, P = .013). This study reveals bidirectional causal relationships between the skin microbiome and psoriasis, highlighting specific microbial features such as Neisseriaceae and Clostridiales as potential risk factors. Further research is needed to develop treatments that modulate the skin microbiome to improve psoriasis outcomes.