Folie à deux in a Seychellois mother and adult son

Folie a deux, a French term which literally means psychosis of two, was first coined by Lasegue and Falret in 1877 to describe a rare clinical syndrome in which delusions are shared by two or more people who have a close and intimate relationship and are often isolated from the outside world. The phenomenon was later defined by Gralnick (1942) in his classic review of 103 cases as