Introduction




(1)
Department of Dermatology, Freiburg University Medical Center, Freiburg, Germany

 



Abstract

In biology, the term mosaic means an organism that is composed of two or more genetically different cell lines originating from one homogeneous zygote. Mosaicism can occur in all pluricellular living organisms. Molecular genetics has provided evidence that every human being represents, to some degree, a mosaic. In dermatology, the concept of mosaicism has helped solving the following problems: How to find a workable definition of the term nevus; why different types of nevi may sometimes occur as twin spots; why the arrangement of nevi can neither be called “dermatomal” nor “zosteriform”; why we can discriminate, in autosomal dominant skin disorders, three different categories of postzygotic mosaicism; why some segmentally arranged skin disorders are heritable whereas others are not; why a segmental distribution of autosomal dominant skin disorders implies an increased risk for the next generation; why patients born with a severe Mendelian skin disorder may develop, later in life, patchy areas of healthy skin; why common skin disorders such as atopic dermatitis or lichen planus are sometimes superimposed by a rather pronounced linear or otherwise segmental involvement; and why all types of skin cancer reflect mosaicsm.


Since ancient times, a mosaic denotes a piece of artwork made by placing colored squares in a pattern creating a picture. In modern biology, the term mosaic is used in a metaphoric way. It means an organism that is composed of two or more genetically different cell lines originating from one homogeneous zygote. Mosaicism can occur in all pluricellular living organisms. In human genetics, a well-known example is functional mosaicism in women because one of the X chromosomes is randomly inactivated at an early developmental stage. Mosaicism can involve all organs but is most easily noted in the skin because this organ is right before our eyes.

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Oct 15, 2016 | Posted by in Dermatology | Comments Off on Introduction

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