Late-onset folie simultanée in a pair of monozygotic twins.

A case-report is presented of folie simultanée in a pair of female monozygotic twins with onset at the remarkable age of 81. The twins demonstrated no evidence of dementia or other psychopathology apart from delusions. Folie simultanée in monozygotic twins provides a model example of the potential role of genotype-environment correlation in the etiology of psychiatric illness.