Hong Kong J Psychiatry 2007;17:64-6


Folie a Famille - a Case Report of Three Sisters
YL Loh, HK Wong

Dr YL Goh, MBBS, M Med (Psychiatry), Department of General Psychiatry, Institute of Mental Health/Woodbridge Hospital, 10 Buangkok View, Singapore 539747.
Dr HK Wong, MBBS, Department of General Psychiatry, Institute of Mental Health/Woodbridge Hospital, 10 Buangkok View, Singapore 539747.

Address for correspondence: Dr YL Goh, Department of Psychiatry, Singapore
General Hospital, Singapore 169608.
Tel: (65) 6321 4344;>
E-mail: goh.yen.li@singhealth.com.sg

Submitted: 27 March 2007; Accepted: 14 May 2007

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Delusional disorders often amaze psychiatrists with their variety of themes. Folie a deux is usually characterised as a shared psychotic or induced delusional disorder between two or more persons in close proximity. It has often been cited in case reports but has not been dealt with in much detail compared with other psychiatric conditions, and folie a trois has had even less attention. Only a small percentage of reported cases involve families and an even smaller fraction of these involve siblings. We hereby describe and discuss a case of folie a famille involving 3 unmarried sisters living together in isolation. This demonstrates how the one sister, who had schizophrenia, induced the other sisters to share the same delusional beliefs. We managed to separate the secondary cases using hospitalisation and medications and achieved improvement and recovery.

Key words: Consanguinity;Psychotic disorders; Schizophrenia, paranoid





The term ‘folie a deux’ means ‘insanity or psychosis of two’. Lasègue and Falret1 coined it in 1877 in their classic paper titled La folie à deux (folie communiquee). It has been described as communicated insanity, contagious insanity, and psychosis of association.2 It is classified as a shared psychotic disorder in Diagnostic and Statistical Manual of Mental Disorders—4th Edition3 and as an induced delusional disorder (folie a deux) in International Classification of Diseases version 10.4

While it is recognised that folie a deux is a rare phenomenon, conditions involving three, four, five persons or the entire family are even rarer.2 Available literature on these conditions is scant and limits mainly to case reports, hence little is known about the prevalence of such conditions.

We describe a case of folie a famille involving three unmarried Chinese sisters X (42 years), Y (41 years), and Z (36 years) living together.

Case Report

In January 2007 the police brought X to the Institute of Mental Health after she created a disturbance at the police station. She had gone to the police station to lodge a report as she was convinced that her house had been rigged with surveillance cameras and that the 3 sisters were being spied upon. She claimed that it was her second sister, Y, who had convinced her about the hidden cameras.

Y first began instilling delusional ideas into X and Z. She believed that the government was installing hidden cameras to spy on the sisters’ activities with the intention of persecuting them. Initially, the other sisters were resistant to Y’s delusional ideas but over the next few months X succumbed to Y’s persistent reinforcement of her delusional ideas, and began to believe that the family was indeed under government surveillance. Z was suspicious of surveillance but was more convinced that it was their neighbours disturbing them. Both X and Y also believed that government officials communicated with them through the television.

X had no psychiatric history. Y had been suffering from paranoid schizophrenia for 5 years, and Z had been treated for paranoid schizophrenia 15 years earlier but had defaulted treatment. They were socially isolated as X and Z were unemployed and seldom ventured out of their home. Y was working, but interacted minimally with her colleagues. The 3 sisters have a close relationship, enmeshed with one another. Their parents are deceased.

X was admitted to the Institute of Mental Health for compulsory treatment under the Mental Disorders and Treatment Act. An initial physical and mental state examination found X to be a dirty, disheveled, and unwashed female. She was irritable and hostile, and harboured persecutory delusions about government surveillance. She was paranoid towards the treating team as we were ‘government doctors’. She denied auditory hallucinations although she was noticed to be talking to herself. X was diagnosed as suffering from paranoid schizophrenia and was separated from her sisters Y and Z upon admission. She was treated with haloperidol 5 mg twice daily. She responded rapidly and was no longer paranoid after 3 weeks of admission but Y remained deluded and Z refused psychiatric treatment.

Following discharge from hospital, the 3 sisters refused to live separately, despite the offer to X and Y of the option of living in psychiatric community hostels. X and Y returned for their psychiatric treatment and both were compliant with their medications. Nonetheless, all the 3 sisters held to their persecutory beliefs that they were under government surveillance. Z adamantly refused psychiatric treatment, as she was suspicious of the psychiatrists.


This case illustrates a case of folie a famille involving 3 unmarried sisters who enmeshed in their relationships with one another, and lived in social isolation.

This could be a case of folie imposee5 in which Y, who suffered from paranoid schizophrenia, was dominant, and X and Z were the recipients.

Y was the primary patient, otherwise described as the ‘inducer’or the ‘principal’.2 X succumbed under pressure and submitted to the persecutory beliefs of her second sister Y. She accepted, supported, and shared the persecutory beliefs of Y in order to gain identification. It was likely that Y, being the sole family breadwinner was now identified as the most important person within their family. Identification has been described by Gralnick6,7 as the mechanism governing this condition. The ‘primary’ case, i.e. the individual who first develops psychotic symptoms, can be distinguished from one or more ‘secondary’ cases, in which the symptoms are induced.8

On the other hand, it could also be a case of folie simultanee as described by Regis in 1881.9 X could have independently developed a psychotic illness, as she was genetically predisposed to psychiatric illnesses, in view of having 2 sisters afflicted with schizophrenia. Arnone et al10 has described how recipients can actually be extremely vulnerable to developing or having a significant mental illness themselves.

Nevertheless, the marked similarities of the delusional beliefs held by all 3 sisters indicate that they accepted, shared, and supported each other’s ideas. This was described by Dewhurst and Todd11 as an essential feature of folie a deux.

This case is similar to instances that were described in the Japanese literature. An analysis of 97 cases in the Japanese literature12 showed that female subjects were more often involved than males. The most common diagnoses for the dominant partner and for the submissive partner were schizophrenia and a paranoid reaction respectively. Delusion is the most common symptom shared by both partners in Japan.

Social isolation has been described as a major risk factor for the development of this condition. Social isolation was reported in 64.3% of the cases identified in the years 1993 to 200510 and 84% from the years 1942 to 1993.13 Other risk factors included passive personality, cognitive impairment, language difficulties, and life events.10 In our case, although X was the eldest sister, she was described by Y as suggestible, shy, suspicious, and anxious. This could have contributed to her susceptibility to succumbing to the persecutory beliefs of Y. It is generally accepted that a dyad composed of a charismatic psychotic inducer and an induced person with dependent character traits is necessary for the development of shared psychosis.14

It is interesting to note the chronological sequence of the illnesses in the 3 sisters. Z, although the youngest, developed schizophrenia first, followed by Y and finally X, who was the eldest.


We would like to thank Dr Chee Kuan Tsee, Emeritus Consultant; Dr Chua Hong Choon, Chief of Department; and A/Prof Chong Siow Ann, Vice Chairman Medical Board (Research) for their invaluable guidance and support.

There is no financial support involved.


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  3. American Psychiatric Association. Diagnostic and statistical manual of mental disorders. 4th ed. Washington DC: American Psychiatric Association; 1994.
  4. The ICD-10 Classification of Mental and Behavioural Disorders. Geneva: World Health Organization; 1992.
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