Two unrelated families are presented in which only one monozygotic twin demonstrated ichthyosis hystrix, while a nontwin sibling showed ichthyosis vulgaris. Zygosity in the twins was determined by using physical traits, placental characteristics, blood typing, dermatoglyphics, and skin grafting.
Adam JE, Richards R. Ichthyosis HystrixEpidermolytic Hyperkeratosis; Discordant in Monozygotic Twins. Arch Dermatol. 1973;107(2):278-282. doi:10.1001/archderm.1973.01620170086025