A A delusion is a fixed, false belief held with absolute certainty despite strong evidence to the contrary. The belief is also inconsistent with the cultural and religious norms of the affected individual(s).
Shared psychotic disorder is when a delusional belief is transmitted from one person to another or others. Folie a deux is when two people share the delusional belief, folie à trois when three people share it and so on. An entire family can share a delusional belief, in which case the condition is referred to as folie en famille or family madness.
The diagnostic term “shared psychotic disorder” was introduced in the American Psychiatric Association Diagnostic and Statistical Manual Fourth Edition (DSM-4). This term; however, has been removed from DSM-5, and the condition has been subsumed under the category “other specified schizophrenia spectrum” and “other psychotic disorder.”