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Overview and classification of the inherited ichthyoses

Keith Choate, MD, PhD
Section Editor
Jennifer L Hand, MD
Deputy Editor
Rosamaria Corona, MD, DSc


The ichthyoses, also called disorders of keratinization or disorders of cornification, are a heterogeneous group of disorders characterized by a generalized scaling of the skin of varying severity. The great majority of ichthyoses are inherited, but acquired forms can develop in the setting of malignancy, autoimmune or infectious disease, and nutritional deficiency.

The molecular basis and pathophysiology of most inherited ichthyoses has been clarified by the identification of causative mutations in over 50 genes encoding structural proteins or enzymes involved in a broad variety of cellular functions, from DNA repair to skin barrier homeostasis [1]. Abnormalities in any of these components result in a rather stereotypic epidermal response with epidermal hyperplasia and the formation of excess stratum corneum accompanied by abnormal desquamation and visible accumulation of scales on the skin's surface [2].

This topic will review the major types of inherited ichthyoses, utilizing the consensus nomenclature adopted by the 2009 Ichthyosis Consensus Conference [1]. Paraneoplastic ichthyosis is discussed separately. (See "Cutaneous manifestations of internal malignancy", section on 'Acquired ichthyosis'.)


Ichthyosis vulgaris and X-linked ichthyosis are the most common types of ichthyosis, with an estimated incidence of 1 in 250 births and 1:6000 male births, respectively [3,4]. Autosomal recessive congenital ichthyoses, which include lamellar ichthyosis, congenital ichthyosiform erythroderma, and harlequin ichthyosis, are rare; their overall incidence has been estimated at approximately 1 in 200,000 births [5].


The average adult skin surface area is 1.8 m2 and contains nearly 85 billion nucleated cells, requiring daily generation of three billion keratinocytes to achieve simple replacement [6,7]. This cellular demand is met by a population of keratinocyte stem cells that cycle slowly to generate the mitotically active cells of the basal layer of the epidermis, which enter into a pathway of terminal differentiation.

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Literature review current through: Oct 2017. | This topic last updated: Dec 06, 2016.
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