Mosaic manifestations of monogenic skin diseases.

A genetic mosaic is defined as an organism which is composed of genetically different cell lines which originate from a homogeneous zygote. Etiologically, cutaneous mosaics can be divided into two large categories, epigenetic mosaicism and genomic mosaicism. Genomic mosaics which have two or more genetically different cell populations are not inherited with the exception of para-dominant inheritance pattern. Epigenetic mosaics have a structurally homogeneous cell population but there are functional differences induced by modifying factors in the form of gene-steering retroviral elements that can be inherited. We distinguish five different manifestation patterns of mosaicism, including the Blaschko lines pattern, patchy pattern without midline separation, checkerboard pattern, phylloid pattern and lateralization pattern. All forms of epigenetic mosaicism, including the various patterns of X-inactivation, appear to be caused by the action of retrotransposons. A new concept is functional autosomal mosaicism transmittable through the action of retrotransposons