The majority of keratinization disorders are referred to as Mendelian disorders of cornification. This is a very broad group, clinically characterized by hyperkeratosis or visible scaling or both. This chapter deals with the ichthyoses, palmoplantar keratodermas (PPKs) and miscellaneous cornification disorders such as porokeratoses. It is aimed primarily at dermatologists and physician scientists who have to make a clinical diagnosis and provide adequate management for their patients. Therefore a nosology and classification scheme has been chosen that is based on clinicogenetic and morphological features. Clinical diagnoses are then discussed with their molecular pathology. Part of the chapter addresses the management of congenital ichthyoses. Various tables provide an overview on clinical and/or pathophysiologically related groups of diseases. Finally, several cornification disorders are discussed that do not have a genetic basis, but are acquired or are of unknown aetiology (e.g. acquired ichthyoses/PPKs or perforating keratotic disorders).

Keywords genetics, cornification disorders, ichthyoses, palmoplantar keratoderma, PPK, porokeratosis, rare disease, orphan disease, patient organizations, paediatric dermatology, ultrastructure, histology, epidermolytic hyperkeratosis, autosomal recessive congenital ichthyosis