filagryny

Filaggrin proteins, commonly referred to as filaggryns in some languages, are a family of keratinocyte proteins that contribute to the formation and maintenance of the skin’s outer barrier. They are encoded by the FLG gene in humans. Filaggrin is produced as profilaggrin, a large precursor stored in keratohyalin granules of differentiating epidermal cells.

During terminal differentiation, profilaggrin is dephosphorylated and proteolytically processed into multiple filaggrin monomers that bind and aggregate keratin intermediate filaments. This promotes the flattening and compaction of keratinocytes and supports the formation of the cornified cell envelope in the stratum corneum.

Filaggrin breakdown products contribute to natural moisturizing factors (NMFs), such as urocanic acid and pyrrolidone carboxylic acid, helping to maintain skin hydration, acidity, and barrier function.

Expression is highest in the epidermis, especially the stratum granulosum, and is regulated by calcium signaling and differentiation programs. Loss-of-function variants in the FLG gene reduce filaggrin production or processing.

Filaggrin deficiency is a well-established risk factor for barrier disorders, including ichthyosis vulgaris and atopic dermatitis, and is associated with increased transepidermal water loss and allergen sensitization. Management focuses on restoring moisture and barrier integrity with emollients that replenish NMFs and ceramides.