Filaggrins are an important class of the intermediate filament-associated proteins which interact with keratin intermediate filaments (Ifs) of terminally differentiating mammalian epidermis. Filaggrins exhibit wide species variations. Filaggrin also appears to be a target molecule for rheumatoid arthritis-specific auto-antibodies in humans. Profilaggrin is a key protein component of the keratohyalin granules of mammalian epidermis. It is primarily expressed as a large polyprotein precursor which is later proteolytically processed into individual functional filaggrin molecules. Persons with truncation mutations in the filaggrin gene, are strongly predisposed to a severe form of dry skin, (ichthyosis vulgaris), and/or eczema. It was shown that approximately 50 % of all severe cases of eczema may have at least one mutated filaggrin gene. Truncation mutations R501X and 2284del4 are the most widespread mutations in the caucasian population, with 7-10 % of the caucasian population carrying at least one copy of these mutations. R501X and 2284del4 are not usually found in non-caucasian individuals, nevertheless novel mutations (3321delA and S2554X) have been found in Japanese populations that yield similar effects Synonyms: Filaggrin, FLG, ATOD2