A mosaic is an organism composed of two or more genetically distinct cell populations derived from a genetically homogeneous zygote. Cutaneous mosaicisms are the clinical expressions of these disorders. The main event which allows the existence of mosaicism is a genetic mutation, either structural or functional. Cutaneous mosaicisms usually manifest by specific patterns on the skin and the archetypic pattern is the system of Blaschko lines, but others include checkerboard, phylloid, large patches without midline separation and lateralization. Since 1901, when Blaschko lines were first described, the study of mosasicism has helped to elucidate the behavior of numerous genetic diseases, generating therapeutic perspectives for these pathologies, including the promising gene therapy.

Epidermolytic ichthyosis is a rare autosomal dominant disease that manifests at birth with fragile blisters and erosions that evolve into hyperkeratotic lesions associated or not with erythroderma. When the disease is associated with a mutation in cytokeratin 1, it may be related to hyperkeratosis of palms and soles, but this is not usually found when cytokeratin 10 is mutated. The disease can present in a mosaic form, due to post zygotic mutation of the gene involved, constituting an individual formed by two populations of genetically distinct cells - one carrier of the mutation and the other without it. We report a case of mosaic epidermolytic ichthyosis diagnosed in a female patient.