Keratosis pilaris and filaggrin loss-of-function mutations in patients with atopic dermatitis - Results of a Finnish cross-sectional study.

Keratosis pilaris (KP) associates with epidermal barrier defects in atopic dermatitis (AD) but its role in disease severity and concomitant atopic diseases seems to vary between populations. We performed a cross-sectional observational study with 502 randomly selected AD patients of a Finnish tertiary health care center. At a single clinical examination, disease severity (Rajka Langeland severity score and EASI), clinical signs and patient history were evaluated and total IgE levels and frequent filaggrin (FLG) loss-of-function mutations were investigated. There was no link with disease severity (p = 0.649, 95% CI 0.569-0.654), asthma (p = 0.230, 95% CI 0.206-0.281) or atopic sensitization (p = 0.351, 95% CI 0.309-0.392). Keratosis pilaris was significantly associated with palmar hyperlinearity (p < 0.000, 95% CI 0.000-0.006, OR 4.664, 95% CI 2.072-10.496) and the filaggrin loss-of-function mutation 2282del4 (p < 0.000, 95% CI 0.000-0.009, OR 4.917, 95%CI 1.961-12.330). The prevalence of KP in the cohort was generally low and KP seems to be infrequent in Finnish AD patients. This may be explained by the fact that the tested FLG loss-of-function mutations are rarer in the Finnish population compared for example, with central Europe or Asia. Mutations in other locations of the FLG gene or other genes of the epidermal barrier may play a more important role.