Combined effects of HLA-Cw6 and cigarette smoking in psoriasis vulgaris: a hospital-based case-control study in China.

BACKGROUND: Psoriasis is not only related to genetic factors but also to environmental factors. However, the combined effect of genetic and environmental factors in the development of psoriasis has still been unclear.
OBJECTIVE: The study was to analyze the combined effect of HLA-Cw6 and smoking on psoriasis vulgaris.
METHODS: A hospital-based case-control was conducted study. One hundred seventy-eight cases and 178 controls received this epidemiological investigation and HLA typing by polymerase chain reaction utilizing sequence-specific primers.
RESULTS: The risk of psoriasis was related to smoking, the adjusted odds ratio (OR) being 2.07 (P < 0.01), and there is a graded positive association between the risk of psoriasis and intensity or duration of smoking. Stressful life events increased the risk of psoriasis (OR = 7.87, P < 0.01). We found the waist-hip ratio (WHR) increased the risk of psoriasis vulgaris, and OR was 2.67 (P < 0.01) in China. Individuals harboring the HLA-Cw6 gene obviously increased the risk of psoriasis, OR being 9.93 (P < 0.01) after adjusted for potential confounder factors, while the OR of psoriasis for HLA-B57 was 2.41 (P < 0.05). Significant combined effect between HLA-Cw6 and HLA-B57 for psoriasis was found (OR = 10.51, P < 0.01). A striking finding is that the risk of psoriasis for smokers with HLA-Cw6 increased about 11-fold than non-smokers without HLA-Cw6, and the risk increased some 20-fold in individuals with HLA-Cw6 having stressful life events compared with one without HLA-Cw6 and stressful life events.
CONCLUSION: Our study suggested that the combined effect between HLA-Cw6 and cigarette smoking or stressful life events may play an important role in the development of psoriasis vulgaris in Han Chinese population.