## Genetic Basis of Atopic Dermatitis **Key Point:** Filaggrin (FLG) gene mutations are the most well-established genetic risk factor for atopic dermatitis, found in 10–30% of patients with AD in European populations. ### Filaggrin Function Filaggrin is a filament-associated protein essential for: - Aggregation of keratin filaments in the stratum corneum - Formation of the natural moisturizing factor (NMF) - Maintenance of skin barrier integrity - Prevention of transepidermal water loss (TEWL) ### Mechanism of AD Pathogenesis FLG mutations → impaired barrier function → increased TEWL → increased allergen penetration → enhanced immune activation → chronic inflammation **High-Yield:** Loss-of-function FLG mutations lead to a "leaky" skin barrier, which is a hallmark of the "outside-in" hypothesis of atopic dermatitis pathogenesis. ### Other Genetic Associations While FLG is the strongest single-gene association, AD is polygenic: - Genes affecting immune regulation (IL-4, IL-13, STAT3) - Genes affecting barrier proteins (claudins, tight junction proteins) - Genes affecting lipid metabolism (ELOVL3, FADS) **Clinical Pearl:** Not all AD patients carry FLG mutations, indicating that other genetic and environmental factors also contribute significantly to disease development. 
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