Filaggrin loss-of-function mutations and levels of filaggrin degradation products in adult patients with atopic dermatitis in Croatia

Background: FLG loss-of-function mutations (FLG LOF) represent the strongest genetic risk factor for atopic dermatitis (AD) and are associated with early-onset and more severe disease. The prevalence of FLG mutations varies greatly across Europe. At present, there are no data on FLG mutation prevalence in Croatian AD patients. Objectives: To investigate the prevalence of FLG LOF mutations in adult patients with AD and healthy controls. Next to measure the stratum corneum (SC) levels of filaggrin degradation products (NMF), transepidermal water loss (TEWL) and pH in lesional and non-lesional skin. Methods: We recruited 100 AD patients with moderate to severe disease and 50 healthy controls. They were screened for three FLG mutations (R501X, 2282del4 and R2447X). Samples of the SC for NMF analysis were collected by adhesive tapes. TEWL and skin surface pH levels were determined on the lesional and non-lesional skin. Results: The combined mutation frequency was 4% in the AD group, and all patients with FLG mutations were homozygous carriers. In the control group, no mutations were found. The most common FLG mutation in AD patients was 2282del4 (3%), followed by R501X (1%). As compared to healthy controls, NMF values were strongly reduced in lesional skin; however, no significant difference was found for non-lesional skin. AD patients had elevated TEWL in both lesional and non-lesional skin. The same pattern was observed for pH. Conclusions: Our study expands understanding of the landscape of FLG mutations in the European population. The low frequency of FLG mutations and similar levels of filaggrin degradation products in healthy controls and in non-lesional skin of AD patients suggest that filaggrin deficiency does not confer a major risk for AD in the Croatian population.