Monochorionic-monoamniotic twins discordant for VATER association.

We describe a monozygotic twin discordant for VATER association with single dysplastic kidney and cloacal anomaly, who had no pulmonary hypoplasia. This twin probably had little or no urine output in utero, but still had normal lung development due to production of adequate amniotic fluid by the healthy twin preventing pulmonary hypoplasia. The discordance between monozygotic twins for VATER association indicates that factors other than inherited genetic ones may have a role in the causation of this association.