Filaggrin (filament-aggregating protein) is a critical structural protein in the epidermis and epithelial barriers that aggregates keratin filaments and is broken down into natural moisturizing factors. Loss-of-function mutations in the filaggrin gene (FLG) compromise barrier integrity and are the strongest known genetic risk factor for atopic dermatitis and progression along the atopic march.
Filaggrin is expressed in the stratum granulosum and broken down during terminal differentiation into free amino acids (particularly histidine) that form natural moisturizing factors and contribute to skin pH regulation. These breakdown products maintain barrier hydration, pH gradient (acidic surface inhibits pathogen colonization), and antimicrobial defense. Filaggrin deficiency increases transepidermal water loss, raises skin pH (favoring Staphylococcus aureus), allows allergen penetration, and promotes Th2 immune polarization. This initiates the atopic march: atopic dermatitis in infancy → food allergies in early childhood → asthma in adolescence → allergic rhinitis and nasal polyps in adulthood.
Filaggrin SNPs identify patients at highest risk for atopic march progression who require aggressive barrier restoration from infancy. Treatment cannot fix genetic deficiency but must compensate through: L-histidine supplementation (filaggrin breakdown product), topical barrier repair (ceramides, fatty acids), pH normalization, microbiome support (reducing S. aureus), and anti-inflammatory interventions (omega-3, curcumin, vitamin D3). Understanding filaggrin deficiency explains why atopic conditions cluster in individuals—it's a shared barrier defect manifesting at different epithelial sites (skin, gut, airways) over time. Complete patient history must include atopic timeline to identify this pattern.
- Filaggrin aggregates keratin filaments in epidermis and epithelial barriers
- Broken down into histidine and other amino acids forming natural moisturizing factors
- Loss-of-function FLG mutations strongest genetic risk for atopic dermatitis
- Filaggrin deficiency increases transepidermal water loss and skin pH
- Elevated pH favors Staphylococcus aureus colonization
- Barrier compromise allows allergen penetration triggering Th2 polarization
- Atopic march sequence: atopic dermatitis → food allergies → asthma → rhinitis/polyps
- L-histidine supplementation can partially compensate for filaggrin deficiency
- Barrier restoration must be lifelong in FLG-deficient individuals
- Cold dry climate, pollution, soaps exacerbate filaggrin-deficient barriers
- atopic dermatitis — filaggrin loss-of-function mutations are strongest genetic risk factor for atopic dermatitis
- atopic march — filaggrin deficiency initiates atopic march through barrier compromise and Th2 polarization
- barrier dysfunction — filaggrin is essential for epithelial barrier integrity; deficiency causes increased permeability
- Th2 — filaggrin deficiency allows allergen penetration triggering Th2 immune polarization
- chronic rhinosinusitis — filaggrin SNPs predispose to chronic rhinosinusitis as end stage of atopic march
- nasal polyps — nasal polyps commonly develop in filaggrin-deficient patients with chronic rhinosinusitis
- asthma — airway barrier deficiency from filaggrin mutations predisposes to asthma development
- food sensitivities — early gut barrier compromise in filaggrin deficiency promotes food allergy development
- Staphylococcus aureus — elevated skin pH from filaggrin deficiency favors S. aureus colonization, worsening inflammation
- L-histidine — histidine is major filaggrin breakdown product; supplementation compensates for deficiency
- vitamin D3 — vitamin D3 deficiency with filaggrin SNPs synergistically impairs barrier and immune function
- pollution — environmental pollution directly damages filaggrin-deficient epithelium, accelerating atopic progression
- SNPs — filaggrin SNPs (FLG gene) are among most clinically significant polymorphisms in cPNI
- keratinocytes — filaggrin is produced by keratinocytes during terminal differentiation in stratum granulosum
- tight junctions — filaggrin deficiency compromises tight junction integrity in epithelial barriers
- pH regulation — filaggrin breakdown products maintain acidic skin pH critical for barrier defense
- natural killer cell — barrier compromise from filaggrin deficiency alters NK cell function and immune surveillance
- microbiome — filaggrin deficiency shifts skin and mucosal microbiome toward pathogenic dysbiosis
- ceramide — topical ceramides are essential to compensate for barrier defects in filaggrin deficiency
- allergen — filaggrin-deficient barriers allow allergen penetration initiating sensitization