Definition:

The ichthyoses represent a large group of cutaneous disorders linked by the common finding of abnormal epidermal differentiation. These disorders are characterized by the cutaneous scaling, which is said to resemble the scales of a fish. Scaling can be localized or generalized and can be associated with a variety of additional cutaneous and/or systemic manifestations. In patients with ichthyosis, the barrier function of the skin is compromised and has a decreased ability to protect against bacterial or chemical assault and to prevent transepidermal water loss. Ichthyosis vulgaris (H00735) is the most frequent type. X-linked ichthyosis (H00134) occurs almost exclusively in boys. Autosomal recessive congenital ichthyosis (H00734) is genetically very heterogeneous and several different genes have been identified. Mutations in keratin genes are the cause of the keratinopathic ichthyoses (H00691), such as epidermolytic ichthyosis.