Discordant phenotype in monozygotic twins with Fryns syndrome.

We report on a pair of monozygotic twins with Fryns syndrome discordant for severity of diaphragmatic defect. Both twins had macrocephaly, "coarse" facial appearance, hypoplasia of distal phalanges, and an extra pair of ribs. Twin A lacked an apparent diaphragmatic defect, and at 1 year of age had mild developmental delay. Twin B had a left congenital diaphragmatic hernia and died neonatally. Absence of diaphragmatic defect in Fryns syndrome may represent a subpopulation of more mildly affected patients whose developmental outcome is currently undetermined.