Heritability of psoriasis in a large twin sample

Background Previous twin studies have shown greater concordance rates for psoriasis in MZ than in DZ twins, and heritability estimates between 66% and 90%. This supports a genetic influence on psoriasis, but also highlights the fact that genes are not the only explanation for the disease. Objectives To study the concordance of psoriasis in a population-based twin sample. Methods Data on psoriasis in 10725 twin pairs, aged 20-71years, from the Danish Twin Registry was collected via a questionnaire survey. The concordance and heritability of psoriasis were estimated. Results In total, 41% of the men and 42% of the women had a lifetime history of psoriasis. The proband-wise concordance for psoriasis was larger in monozygotic than in dizygotic twins, 033 vs. 017. Genetic factors explained 68% (60-75%) of the variation in the susceptibility to psoriasis, whereas the rest of the variation was explained by nonshared environmental factors. Conclusion The results confirm that psoriasis is a complex multifactorial disease controlled by both exogenous and endogenous factors.