Cutaneous mosaicisms: concepts, patterns and classifications.
Bottom Line: 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.
Affiliation: University of Brasilia, BrasiliaDF.
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.
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Mentions: It starts during embryonic development, due to a de novopostzygotic mutation in one of the alleles of a given gene, resultingin an altered allele. From this moment, the individual will have two cellpopulations, one normal, the other sick (Figure5).1,2,7Thus, the characteristics of this disease will bedistributed along the Balschko lines or other mosaic patterns, corresponding tocells containing the mutation.2,5,8The rest of the skin will be normal genotypicallyand phenotypically. In general, this type of mosaicism is not inherited, exceptwhen the mutation affects the gonads. Examples of type 1 segmental mosaicismsinclude epidermolytic hyperkeratosis, type 1 neurofibromatosis, Darier'sdisease, tuberous sclerosis, basal cell nevus syndrome, multiple syringomas andpachyonychia congenita type 1.1,5