Monozygotic Turner syndrome twins--correlation of phenotype severity and heart defect.

We report on monozygotic twins with Turner syndrome (45,X) with discordant phenotypes. One twin had severe neck webbing and extremity edema and died of severe coarctation of the aorta. The other twin had fewer craniofacial anomalies and no congenital heart defect, suggesting a pathogenetic relationship between cardiac abnormality and phenotype severity.