Studies of individual cases have shown that delusional ideas and psychotic symptoms are rarely transmitted to a healthy individual whose partner displays unhealthy behavior resulting from a psychotic disease; however, a passive person may have a genetic predisposition to psychosis and, as a result, may develop this disorder.
Although Harvey described the first case of phantom pregnancy associated with induced psychosis in 2 sisters in 1651, the term folie à deux dates to a classic report by Lasègue and Falret in 1877.
The sisters were separated and given psychopharmacological treatment.
Peritogiannis et al investigated a case of folie à quatre, which not only presented the issues of close familial ties as a contributing factor, but also the complications of occurrence in rural areas.
Interestingly, rare cases have been reported in which the secondary experienced hallucinations while the primary did not.
Nevertheless, no confirmation of increased susceptibility of females exists today.
Both female and male secondaries are equally affected by female primaries.
Thus, the conclusion has been made that close association contributes more to the development of shared psychotic disorder than age.
Individuals with shared psychotic disorder lack insight and therefore do not seek treatment.