FLG and ichthyosis vulgaris: Null mutations in the filaggrin gene (FLG) are responsible for the common inherited dry skin condition ichthyosis vulgaris and are a major predisposing factor for AD.4, 5 However only approximately 40% of patients with AD in the United Kingdom and around 10% of patients with AD in the rest of the world have filaggrin mutations,6, 7 and conversely, not all persons with filaggrin mutations have AD,8 suggesting that other mechanisms might contribute to filaggrin expression and processing defects and hence to the barrier defect observed in patients with AD.