 It may also be called congenital hydantoin syndrome, fetal hydantoin syndrome, dilantin embryopathy, or phenytoin embryopathy.Association with EPHX1 has been suggested.About one third of children whose mothers are taking this drug during pregnancy typically have intrauterine growth restriction with a small head and develop minor dysmorphic craniofacial features (microcephaly and mental retardation) and limb defects including hypoplastic nails and distal phalanges (birth defects).