Melanotic macules following Blaschko's lines in McCune-Albright syndrome

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Abstract
Summary Hyperpigmented macules are a characteristic feature of neurofibromatosis and the McCune-Albright syndrome. Whereas neurofibromatosis 1 has an autosomal dominant mode of inheritance, it has been suggested that McCune–Albright syndrome is the result of a lethal gene surviving by mosaicism. Recent molecular studies have supported this concept by providing evidence of a somatic mutation of the gene encoding the G protein. We report two patients with McCune–Albright syndrome whose melanotic macules show a clear relation to the lines of Blaschko. The lines of Blaschko are thought to represent the dorso-ventral outgrowth of two different cell populations during embryogenesis, thus reflecting genetic mosaicism. A survey of published photographs of patients with McCune–Albright syndrome in the literature revealed additional cases with macules following Blaschko's lines. In other cases, the configuration of the macules was reminiscent of the flag-like rectangular pattern of pigmentation found in human chimaeras. A very early somatic mutation may have similar effects on the pigmentation pattern as a chimaeric state, which is the result of the double fertilization of an ovum. Café-au-lait spots in 10 of our own patients with neurofibromatosis 1 could not be associated with either Blaschko's lines or the rectangular pattern of pigmentation in chimaeras. We conclude that, in contrast with the calé-au-lait spots in autosomal dominant neurofibromatosis 1. the configuration pattern of melanotic macules in McCune–Albright syndrome in many cases characteristically reflects the mosaic state of the organism.

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