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.