Unilateral speckled-lentiginous naevus, contralateral verrucous epidermal naevus, and diffuse ichthyosis-like hyperkeratosis: An unusual example of twin spotting?

The genetic concept of twin spotting has been proposed to explain paired mosaic patches in plants and animals and, recently, in humans. We have observed a unilateral, systematized epidermal naevus and a contralateral speckled-lentiginous naevus in an 11-year-old girl. Remarkably this girl suffered also from a diffuse ichthyosis-like hyperkeratosis involving the entire body. We infer that the diffuse skin disorder reflects a state of heterozygosity, whereas the epidermal naevus visualizes loss of heterozygosity for the same mutation, having occurred at an early stage of embryogenesis by somatic recombination. Simultaneously, as a result of this mutational event, one of the daughter cells would have become homozygous for a neighbouring allele giving rise to a mosaic patch of multiple eruptive naevi. In conclusion, this unique case provides further circumstantial evidence that paired mosaic lesions in human skin may represent a twin-spot phenomenon.