In 1952, Goldenhar described a pair of monozygotic twins who were discordant for epibulbar dermoids, auricular appendages, malformations of the auricle, and hemifacial microsomia. Eighteen twin pairs have subseqently been described in which at least one member exhibited these manifestations. We report on an additional pair of discordant dichorionic monozygotic male twins. All of the 5 monozygotic twin pairs for which placental information is available have been discordant and 2 of these had dichorionic membranes. The failure of discordant monozygotic twins to be limited to monochorionic pairs argues against the hypothesis that developmental abnormalities arising from the placental vascular anastomoses that are commonly found in monozygotic twins is the probable explanation for the discordant expression of these traits in twins.
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