title: Does normal developmental expression of psychosis combine with environmental risk to cause persistence of psychosis? A psychosis proneness-persistence model.
abstract: BACKGROUND
  Research suggests that low-grade psychotic experiences in the general population are a common but transitory developmental phenomenon. Using two independent general population samples, the hypothesis was examined that common, non-clinical developmental expression of psychosis may become abnormally persistent when synergistically combined with developmental exposures that may impact on behavioural and neurotransmitter sensitization such as cannabis, trauma and urbanicity.
  
  
  METHODS
  The amount of synergism was estimated from the additive statistical interaction between baseline cannabis use, childhood trauma and urbanicity on the one hand, and baseline psychotic experiences on the other, in predicting 3-year follow-up psychotic experiences, using data from two large, longitudinal, random population samples from the Netherlands [The Netherlands Mental Health Survey and Incidence Study (NEMESIS)] and Germany [The Early Developmental Stages of Psychopathology (EDSP) study].
  
  
  RESULTS
  The 3-year persistence rates of psychotic experiences were low at 26% in NEMESIS and 31% in EDSP. However, persistence rates were progressively higher with greater baseline number of environmental exposures in predicting follow-up psychotic experiences (chi2=6.9, df=1, p=0.009 in NEMESIS and chi2=4.2, df=1, p=0.04 in EDSP). Between 21% and 83% (NEMESIS) and 29% and 51% (EDSP) of the subjects exposed to both environmental exposures and psychotic experiences at baseline had persistence of psychotic experiences at follow-up because of the synergistic action of the two factors.
  
  
  CONCLUSIONS
  The findings suggest that environmental risks for psychosis act additively, and that the level of environmental risk combines synergistically with non-clinical developmental expression of psychosis to cause abnormal persistence and, eventually, need for care.
authors.affiliation: INSERM U 657, University Victor Segalen Bordeaux 2, IFR99 of Public Health, Bordeaux, France.
authors.forename: Audrey
authors.initials: A
authors.lastname: Cougnard
authors.forename: Machteld
authors.initials: M
authors.lastname: Marcelis
authors.forename: Inez
authors.initials: I
authors.lastname: Myin-Germeys
authors.forename: Ron
authors.initials: R
authors.lastname: De Graaf
authors.forename: Wilma
authors.initials: W
authors.lastname: Vollebergh
authors.forename: Lydia
authors.initials: L
authors.lastname: Krabbendam
authors.forename: Roselind
authors.initials: R
authors.lastname: Lieb
authors.forename: Hans-Ulrich
authors.initials: HU
authors.lastname: Wittchen
authors.forename: Cécile
authors.initials: C
authors.lastname: Henquet
authors.forename: Janneke
authors.initials: J
authors.lastname: Spauwen
authors.forename: Jim
authors.initials: J
authors.lastname: Van Os
mesh_terms: D000293:Adolescent; D000328:Adult; D003702:Delusions / Q000175:diagnosis / Q000453:epidemiology / Q000523:psychology; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006212:Hallucinations / Q000175:diagnosis / Q000453:epidemiology / Q000523:psychology; D006801:Humans; D015994:Incidence; D008297:Male; D011618:Psychotic Disorders / Q000175:diagnosis / Q000453:epidemiology / Q000523:psychology*; D012307:Risk Factors; D012720:Severity of Illness Index; D012931:Social Environment; D019966:Substance-Related Disorders / Q000453:epidemiology; D011795:Surveys and Questionnaires