The genetic epidemiology of psoriasis vulgaris in Chinese Han.
BACKGROUND: The aim of this study was to explore the effects of genetic factors on the onset of psoriasis vulgaris and to develop a possible genetic model of psoriasis in Chinese Han. METHODS: Data for 1043 patients with psoriasis vulgaris were obtained by questionnaire. Complex segregation analysis and heritability were performed using Penrose's method, Falconer's method, and the EPI INFO 6.0 and SAGE-REGTL programs. RESULTS: (1) For male and female patients, the peak ages of initial onset were 30-39 and 10-19 years, respectively, with the mean age of initial onset being 27.69 +/- 12.32 years in males and 23.26 +/- 12.56 years in females. (2) Of 1043 patients with psoriasis, 326 (31.26%) were reported to have a family history of psoriasis. The onset for males with a family history of psoriasis was earlier than that for those without a family history (P < 0.01). The morbidities of first-degree relatives were 7.67% in patients with type I psoriasis and 5.27% in patients with type II (P < 0.01), and those of second-degree relatives were 1.04% in type I and 0.24% in type II (P < 0.01). (3) The onset of psoriasis was earlier in females than in males in type I psoriasis (P < 0.01), but this was not the case in type II (P > 0.05). (4) The prevalence of psoriasis in first- and second-degree relatives of the proband with psoriasis was 7.24 and 0.95%, respectively; higher than that in the general population (0.146%). (5) The heritability of psoriasis in first- and second-degree relatives was 67.04 and 46.59%, respectively. The Mendelian, no-major-gene and environment model was rejected by complex segregation analysis. CONCLUSION: Psoriasis vulgaris follows a pattern of polygenetic or multifactorial inheritance rather than single-gene inheritance.