Trisomy 18 in monozygotic twins with discordant phenotypes.

The incidence of trisomy 18 in monozygotic twins is approximately 1 per million. We report a pair of liveborn monozygotic twins with trisomy 18. Both twins had esophageal atresia with tracheoesophageal fistula (type C) and intrauterine growth retardation. Twin A had cleft lip, choanal atresia and perimembranous ventricular septal defect. Twin B had hypoplastic left heart syndrome. The twins died without aggressive intervention at the age of 2 months and 52 hours, respectively. These 2 babies had significantly discordant phenotypes, which suggests an epigenetic or environmental effect. Bioethical considerations remain important in the care of babies with multiple congenital anomalies.