Mosaicism and epidermal nevi

Abstract

In the field of biology, a mosaic is an organism consisting of genetically different cells that have arisen from a homogeneous zygote. By contrast, a chimera develops from genetically different cell populations that originate from different zygotes. Genetic mosaics can affect all organs, but are particularly easy to recognize on the skin. For this reason, the concept of mosaicism is of peculiar importance in dermatology. In numerous dermatoses, their mosaic nature has already been proven on a cytogenetic or molecular level. Today, all nevi can be defined as genetic mosaics. On the other hand, it goes without saying that not all mosaics should be regarded as nevi, because otherwise one would have to apply the term nevus to a basal cell carcinoma or a melanoma. Examples of genomic mosaics are segmental manifestations of neurofibromatosis 1, tuberous sclerosis, or Darier disease, whereas incontinentia pigmenti, focal dermal hypoplasia, and CHILD syndrome reflect functional X-chromosome mosaicism.