Familial Aggregation of Psoriasis and Co-Aggregation of Autoimmune Diseases in Affected Families.

Psoriasis is considered to result from the interaction of genetic factors and environmental exposure. The evidence for familial aggregation in psoriasis has been reported but population-based studies related to the magnitude of genetic contribution to psoriasis are rare. This study aimed to evaluate the relative risks of psoriasis in individuals with affected relatives and to calculate the proportion of genetic, shared, and non-shared environmental factors contributing to psoriasis. The study cohort included 69,828 patients diagnosed with psoriasis enrolled in National health Insurance in 2010. The adjusted relative risks (RR) for individuals with an affected first-degree relative and affected second-degree relative were 5.50 (95% CI (Confidence Interval), 5.19⁻5.82) and 2.54 (95% CI, 2.08⁻3.12) respectively. For those who have affected first-degree relatives, their RR was 1.45 (95% CI, 1.17⁻1.79) for Sjogren's syndrome and 1.94 (95% CI, 1.15⁻3.27) for systemic sclerosis. This nationwide study ascertains that family history of psoriasis is a risk factor for psoriasis. Individuals with relatives affected by psoriasis have higher risks of developing some autoimmune diseases.