Recent advances in understanding inherited disorders of keratinization.

The ichthyoses are a heterogeneous group of skin diseases characterized by localized or generalized scaling or both. Other common manifestations include palmoplantar keratoderma, erythroderma, recurrent infections, and hypohidrosis. Abnormal barrier function is a cardinal feature of the ichthyoses, which results in compensatory hyperproliferation and transepidermal water loss. Barrier function is maintained primarily by the stratum corneum, which is composed of cornified cells surrounded by a corneocyte lipid envelope and intercellular lipid layers. The lipid components are composed primarily of ceramides. Human genetics has advanced our understanding of the role of the epidermal lipid barrier, and a series of discoveries in animals and humans revealed mutations in novel genes causing disorders of keratinization. Recently, next-generation sequencing has further expanded our knowledge, identifying novel mutations that disrupt the ceramide pathway and result in disorders of keratinization. This review focuses on new findings in ichthyoses caused by mutations involving lipid synthesis or function or both.