Comparative Research Of The Genetic Epidemiology Of Six Common Skin Diseases (Psoriasis Vulgaris/Vitiligo/Alopecia Areata/Keloid/Pityriasis Versicolor/Ephelides)

Genetic epidemiology of dermatology is a newly, interdisciplinary subject which is guided by Genetic epidemiology and based on Dermatology, it is directed by basic theory of Population genetics, conducted by experimental means of Molecular genetics, also, it exerts manners of Epidemiology to collect and process numerical data, and to do Etiology research, furthermore, it binds Biometrics and Mathematical models and numerical methods of computer together, accordingly, it takes great advantages to study and clarify genetic and environmental factors of skin disease(especially chronic skin disease) and the interaction of these two factors. Therefore, drawing assistance from the science of Genetic epidemiology, we chose six kinds of common skin diseases with high incidence into our study, and clarify the law of distribution of these diseases in the crowd, as well as the etiological factors. We also describe the interaction of genetic or environmental factors with the genetic susceptibility of the host. All the work we do would be important in prevention or control of these common diseases.Psoriasis(OMIM: #177900), one of erythema subtype dermatosis, is a common cutaneous disorder characterized by abnormal epidermal proliferation with high relapsing rate. Vitiligo(OMIM: #193200) is an acquired skin disease with topical or generalized depigmentary lesion. Ephelides is a kind of pigmented disease presenting brown spot-pigmented spots, circle, oval or irregularly-shaped patches on face. Alopecia areata(AA.OMIM: %610753) is a common disease of the hair, characterized by topical, non-inflammatory patchy baldness, it presents no symptoms and may relapse and remission. Keloids(OMIM: 148100) are benign, proliferative dermal collagen growths that represent a pathological wound-healing response to skin injury in susceptible persons. Pityriasis versicolor is a chronic common superficial fungal infection of the skin caused by Malassezia furfur. All the six kinds of diseases share the same feature presenting as follows: Firstly, all of them are very common skin disease, in addition to rational symptom such as itch and pain declaimed by Psoriasis and Keloids patients, the other four species often present no symptoms. Secondly, they tend to be recurrent, and difficult to cure radically. Thirdly, appearance of this six kinds of patients are seriously affected, it is usual to cause psychological pressure in these patients. Fourthly, both environmental and genetic factors play an important role in the pathogenesis of these six kinds of diseases, and certain environmental factors are their common trigger. Fifthly, the pathogenesis of this all six kinds of diseases are not yet clear, the origin of each disease deserve a variety of theories, however, there are certain familial aggregation in all the six kinds of diseases. it is a good way to figure out the pathogenesis of the disease,the impact of environmental factors and ways of prevention by taking advantages of genetics epidemiology.Through collecting large number of cases and control, we can analyze the general situations, clinical features, pedigree information, genetic susceptibility and environmental factors of these six species. The purpose of this study is to identify the commonalities and personality characteristics of the disease by comparing their genetic epidemiological characteristics and to gain some experiences of conducting epidemiological survey. Through collaboration of multi-clinical centers, we had collected eligible data by a uniform questionnaire from 1043, 3742, 1032, 550, 503, 1859 patients and their pedigrees, for a total of 8729 copies, respectively for Psoriasis vulgaris, Vitiligo, Alopecia areata. Keloids, Pityriasis versicolor, Ephelides, simultaneously, we got respectively 789, 2120, 1635, 1007, 963, 535 copies, total 7049 copies, in control group. All the data were inputted into a database set up by Epi Info 5.0 package. After proper transformation, the data were statistically analyzed by statistic package of social science (SPSS, version 10.0), statistic analysis of genetic epidemiology (SAGE, version 3.1), Falconer's method in order to estimate heritability of the disease, and Penrose and complex segregation to model the mode of inheritance. Binary logistic regression was used to estimate the associated risk of potential environmental factors underling the disease.Comparison of onset age of the six common skin diseases: Ephelides patients had a peak incidence at the age 10-20 years old (main age of 12.65), which was smallest in the six species. Then, hierarchizedly, the main age of onset were 18.88, 22.58, 25.48, 22.49 respectively for vitiligo, Keloids, Psoriasis vulgaris and Pityriasis versicolor. Patients of all these five diseases had a peak onset age at 10-30 years old, while Alopecia areata had a relatively late age of onset, at a peak of 20-40 years, with an average age of 28.98 years; More than 80% of the total patients had a age of onset less than 30 years old. Moreover, the higher degree of heritability they were, the smaller age of onset they had, and vice versa.Comparison of onset age by gender of the six common skin diseases: The number of male patients was greater than female in Psoriasis vulgaris and Pityriasis versicolor, the onset age in male was significantly later than that in female. while, there were more females patients than males in Ephelides, the age of onset in women was later than that in men. The incidence ratio in different sex groups were basically the same, and the onset of age appeared no difference in Vitiligo, Alopecia areata and Keloid patients.Comparison of seasonal distribution of the six common skin diseases: More than 60% of the Psoriasis patients happened in spring and winter. While Vitiligo, , Freckle had always occurred in summer with, respectively, 39.44%, 71.37%, 51.91% of the total sick number in this season, Alopecia Areata and Keloid happened in all four seasons, and the incidence was almost the same in different season.Familial aggregation analysis of six common skin diseases: 50.56% of all the Ephelides patients had family history, followed by Psoriasis vulgaris 29.53%, Keloid 27.82%. Pityriasis versicolor 21.07%, Vitiligo 14.38%, Alopecia areata 8.43%. The onset age made no difference in Vitiligo, Alopecia areata, Keloid patients with or without family history, while the mean age of onset in Psoriasis, Pityriasis versicolor, Freckle patients with a family history (24.51±12.23,19.40±10.16,12.22±4.25, respectively) was earlier than those without family history (26.08±12.84,23.77±10.23,13.25±4.06, respectively) through t Test. The pathogenetic conditions in Psoriasis vulgaris, Alopecia areata, Pityriasis versicolor patients with or without family history appear no discrimination. Among Keloid patients with a family history, the percentage with severe illness was significantly greater than in patients with no family history, indicating that the condition in patients with a family history was more serious than that in patients without family history. In addition, the prevalence and heritability of these diseases in first-, second- and third-degree relatives of the proband gradually reduce. Based on the REGTL results, a polygenic additive model was the best genetic model for Psoriasis vulgaris, Alopecia areata, piand Vitiligo (excluding Universal Vitiligo).Comparison of influenction factors of the six common skin diseases: Unmarried individuals were less susceptible to Alopecia Areata than those married, psychological factors such as tension, depression / anxiety, insomnia, as well as spicy food, hair dyes and fatigue were positively associated with Alopecia Areata. Among Keloids, age, occupation, family history, trauma and traumatic surgery were the risk factors. Among pityriasis versicolor, age, occupation, family history, heat, keeping a pet were the risk factors. Psychological factors such as mental stress, depression, insomnia, as well as fatigue, hair dyes were closely correlated with the developing of Psoriasis vulgaris, Vitiligo and Alopecia areata. Sunlight was closely related with the developing of pigmented diseases, including Vitiligo and Ephelides. Trauma was associated with the incidence of Vitiligo, Keloids.In summary, we draw the conclusion that the age of onset affected by family history and heritability altered in different skin disorder. The number of male patients was greater than female in Psoriasis and Pityriasis versicolor, the age of onset in male was significantly later than that in female. While there were more females patients than males in Ephelides, the age of onset in women was later than that in men. The incidence ratio in different sex group was basically the same in Vitiligo, Alopecia areata and Keloid patients. Vitiligo, Pityriasis versicolor, Freckle had always occurred in summer, while More than 60% of the Psoriasis patients happened in spring and winter. Among Keloid patients with a family history, the percentage with severe illness was significantly greater than in patients with no family history. The prevalence and heritability of these diseases in first-, second- and third-degree relatives of the proband gradually reduce. Based on the REGTL results, a polygenic additive model was the best genetic model for Psoriasis vulgaris, Alopecia areata, Pityriasis versicolor and Vitiligo(excluding Universal Vitiligo). Psychological factors were closely correlated with the developing of Psoriasis vulgaris, Vitiligo and Alopecia areata. Sunlight was closely related with the developing of pigmented diseases, including Vitiligo and Ephelides. Trauma was associated with the incidence of Vitiligo, Keloids, and Pityriasis versicolor.