Heritability of psoriasis in a large twin sample

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.

To study the concordance of psoriasis in a population-based twin sample.

Data on psoriasis in 10 725 twin pairs, aged 20-71 years, from the Danish Twin Registry was collected via a questionnaire survey. The concordance and heritability of psoriasis were estimated.

In total, 4·1% of the men and 4·2% of the women had a lifetime history of psoriasis. The proband-wise concordance for psoriasis was larger in monozygotic than in dizygotic twins, 0·33 vs. 0·17. 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.

The results confirm that psoriasis is a complex multifactorial disease controlled by both exogenous and endogenous factors.