Doyle believe folie à plusieurs to have been at least a partial factor in the murder of Bridget Cleary. In 1895, Michael Cleary convinced several friends and relatives that his wife, Bridget Cleary, was a changeling who had been replaced by a fairy. They assisted him in physically abusing her to "cast the fairies" out, before he ultimately burned her to death shortly afterwards. Christine and Léa Papin were two French sisters who, as live-in maids, were convicted of murdering their employers wife and daughter in Le Mans, France on February 2, 1933. Born in Yemen in 1963 to Barbados immigrants, June and Jennifer Gibbons were known as "the Silent Twins" for speaking solely to each other in an idioglossia derived from an idiosyncratic, sped-up Bajan Creole dialect that qualified as an example of cryptophasia. The inseparable twins had a longstanding agreement that, if one died, the other must begin to speak and live a normal life, and it was during their 11-year admission to Broadmoor Hospital — where the twins had been indefinitely placed following a series of crimes (e.g. vandalism, petty theft and arson) in 1981 — that they began to believe that it was necessary for one of them to die. Jennifer agreed it should be her, and when the twins were transferred from Broadmoor to the more open Caswell Clinic in Bridgend, Wales in 1993, Jennifer could not be roused upon arrival. She was taken to the hospital where she died soon after of acute myocarditis, or inflammation of the heart.
When stressed, an individuals adrenal gland releases the "stress hormone" cortisol into the body, increasing the brains level of dopamine; this change can be linked to the development of a mental illness, such as a shared delusional disorder.While there is no exact cause of shared psychosis, there are several factors that are contributors depending on different cultures and communities. Taking into consideration the individuals circumstance which entails their environmental changes and relationships. Diagnosis
Shared delusional disorder is often difficult to diagnose. Usually, the person with the condition does not seek out treatment, as they do not realize that their delusion is abnormal, as it comes from someone in a dominant position who they trust. Furthermore, since their delusion comes on gradually and grows in strength over time, their doubt is slowly weakened during this time. Shared delusional disorder is diagnosed using the DSM-5, and according to this, the patient must meet three criteria:
They must have a delusion that develops in the context of a close relationship with an individual with an already established delusion. The delusion must be very similar or even identical to the one already established one that the primary case has. The delusion cannot be better explained by any other psychological disorder, mood disorder with psychological features, a direct result of physiological effects of substance abuse or any general medical condition. Related phenomena
Reports have stated that a phenomenon similar to folie à deux was induced by the military incapacitating agent BZ in the late 1960s.