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April 1997

How Common Is Pigmentary Mosaicism?-Reply

Author Affiliations

The Ronald O. Perelman Department of Dermatology and the Department of Pediatrics New York University School of Medicine 560 First Ave New York, NY 10016

Arch Dermatol. 1997;133(4):528. doi:10.1001/archderm.1997.03890400133023

In reply  Pigmentary lines of demarcation are indeed a common phenomenon, especially evident in dark-skinned people, and the descriptions by Selmanowitz and Krivo referred to in Krivo's letter are classics in the field. There is no evidence, however, that these lines of demarcation represent genetic mosaicism even of the somatic type. That is to say, there is no reason to believe that there is a genetic difference between the cells on the dark, posterior side of a line of demarcation vs the light, anterior side. Indeed, the presence of a lighter ventrum is a common phenomenon in the animal kingdom, readily evident not only in darkly pigmented humans, but also in other mammals, reptiles, and amphibians. Recent evidence suggests that these differences may be due to the normal function of genes that affect embryonic patterning, such as the product of the agouti locus.1 Since the lines of Blaschko presumably

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