Genetic and Clinical Mosaicism in a Type of Epidermal Nevus

Background: Many skin disorders are characterized by a mosaic pattern, often with alternating stripes of affected and unaffected skin that follow the lines of Blaschko. These nonrandom patterns may be caused by a postzygotic mutation during embryogenesis. We studied the genetic basis of one such disorder, epidermal nevus of the epidermolytic hyperkeratotic type. Epidermolytic hyperkeratosis is an autosomal dominant blistering skin disease arising from mutations in the genes for keratin (K) 1 and 10. The offspring of patients with epidermal nevi may have generalized epidermolytic hyperkeratosis. Methods: We studied the K1 and K10 genes in blood and in the keratinocytes and fibroblasts of lesional and nonlesional skin from three patients with epidermal nevi and four of their offspring with epidermolytic hyperkeratosis. Results: In the patients with epidermal nevi, point mutations in 50 percent of the K10 alleles of epidermal cells were found in keratinocytes from lesional skin; no mutations were detected in normal skin. This mutation was absent or underrepresented in blood and skin fibroblasts. In the offspring with epidermolytic hyperkeratosis, the same mutations as those in the parents were found in 50 percent of the K10 alleles from all cell types examined. Conclusions: Epidermal nevus of the epidermolytic hyperkeratotic type is a mosaic genetic disorder of suprabasal keratin. The correlation of mutations in the K10 gene with lesional skin and the correlation of the normal gene with normal skin provide evidence that genetic mosaicism can cause clinical mosaicism., Many skin disorders are characterized by a mosaic pattern, often with alternating stripes of affected and unaffected skin. These stripes are referred to as lines of Blaschko¹. They do not follow the vascular, neural, or lymphatic structures of the skin, nor do they correlate with dermatomes (Figure 1). This pattern has been attributed to the clonal proliferation of two genetically distinct groups of cells that arise from a postzygotic mutation during embryogenesis². Skin diseases exhibiting such patterns are often linked to the X chromosome³. Examples are focal dermal hypoplasia, the Conradi-Hunermann syndrome, incontinentia pigmenti, and the carrier…