Skin Barrier Function and mRNA Expression Profiles in Patients with Atopic Dermatitis, Ichthyosis Vulgaris, and X-linked Recessive Ichthyosis Aetiopathogenic Differences and the Impact of Moisturizing Treatment

Abstract: Atopic dermatitis (AD), ichthyosis vulgaris (IV), and X-linked recessive ichthyosis (XLRI) are characterized by dry skin and impaired skin barrier. AD and IV are related to loss-of-function mutations in FLG (encoding filaggrin), whereas XLRI is caused by deletions or inactivating mutations in the steroid sulphatase gene (STS). Patients regularly use moisturizing creams, but little is known about the creams’ effects on the skin barrier.The present work combines objective scorings, non-invasive techniques, and molecular analyses of skin biopsies to characterize the skin in 57 patients with AD, IV, or XLRI, and in 14 healthy controls. Patients were classified according to their FLG and STS mutation status: AD with FLG+/+ (n = 14), AD with FLG+/– (n = 14), AD/IV with FLG–/– (n = 15), and XLRI with STS– (n = 14), as well as one man with a novel point mutation. Assessments were conducted at baseline and after four weeks of treatment with three different moisturizers applied to volar forearm skin.At baseline, dryness scoring and non-invasive assessments verified impaired skin barrier function in all patients. In patients with AD/IV, microarray analysis identified 300–3000 up- or downregulated mRNA transcripts involved in signalling pathways important for inflammation and barrier repair. The skin phenotype and number of altered transcripts were correlated with the FLG mutation status, with FLG–/– patients displaying the highest transepidermal water loss (TEWL) and the most altered transcript levels. In contrast, despite an equally dysfunctional skin barrier, only limited changes in mRNA transcripts occurred in XLRI patients. Treatment with moisturizers improved skin dryness similarly in all groups, but TEWL behaved differently: it decreased slightly in the AD/IV group and increased in the XLRI group, especially after urea treatment. Only minute effects on skin pH and mRNA expression were observed.In conclusion, FLG mutations elicit pro-inflammatory mechanisms probably aimed at restoring barrier competence. This does not occur in patients with XLRI, presumably because STS deficiency automatically increases the barrier thickness. Moisturizing treatment improves skin dryness in patients with AD, IV, or XLRI, but does not seem to normalize the altered epidermal gene expression profile in AD/IV patients.