Psychoses are serious psychiatric disorders characterised by the inability to differentiate reality from unreality. Major symptoms are disorganised thoughts, delusions, hallucinations, and persistent profound sadness or euphoric mood without apparent reason. They are split into a group of known organic and a group of unknown causes. The latter are termed major psychoses and affect approximately 2% of the human population. The subdivision of major psychoses into schizophrenia and bipolar disorder is a matter of debate. In search of the aetiology of these disorders, different models have been applied, mainly medical, Darwinian, Mendelian, psychogenic, and genomic paradigms. These approaches, their results and the widely accepted neurodevelopmental hypothesis of schizophrenia are summarised in this article. More details can be found in other articles in this encyclopedia, references and in a list for further reading.

Key Concepts:

  • Psychoses are caused by known or postulated brain disorders.

  • The classification of psychoses is based on aetiology and course.

  • Schizophrenia and bipolar disorder (manic‚Äźdepressive illness) are two major psychoses of postulated but unknown organic origin.

  • Major psychoses are polygenic disorders with heritability estimates of approximately 80%.

  • Genome research has identified several genes associated with schizophrenia or bipolar disorder which are, in part, identical.

  • Brain imaging revealed partly overlapping volume reductions in schizophrenia as well as in bipolar disorder.

  • Genes associated with schizophrenia or bipolar disorder play a role in neurodevelopment and synaptic regulation.

  • Dopamine hyperactivity, neurodevelopment, inflammation, neurodegeneration and synaptic dysregulation have been implicated in the aetiology of major psychoses.

Keywords: bipolar disorder; euthanasia; linkage studies; polygenic model; schizophrenia

Figure 1.

Disease concepts of major psychoses.

Figure 2.

Family and twin studies in major psychoses. Data of pooled samples from Gottesman and Craddock and Jones . Estimates of risk in second‐degree relatives of bipolar probands are not given because of lack of reliable data. Concordance rates for bipolar disorder are derived from Bertelsen et al..

Figure 3.

MFT model. The MFT model consists of several genes and environmental factors and assumes that the total liability is normally distributed in the population, such that those whose liability exceeds a certain threshold develop schizophrenia. Courtesy of Irving I. Gottesman.

Figure 4.

Summary of genome‐wide linkage studies in schizophrenia (Copyright © 2005 Patrick F. Sullivan). The locations on the genome and several candidate genes for schizophrenia are displayed on the x‐axis. The bars indicate the probability of linkage between schizophrenia and a chromosomal location. Height and colour of the bars are proportional to the −log10(P‐value) and the width gives the size of the chromosomal location.

Reproduced from Sullivan 2005. © PLoS.


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Further Reading

Craddock N and Sklar P (2013) Genetics of bipolar disorder. Lancet 381(9878): 1654–1662.

Goodwin FK and Jamison KR (2007) Manic‐Depressive Illness: Bipolar Disorders and Recurrent Depression, 2nd edn. New York, NY: Oxford University Press.

McGuffin P, Gottesman II and Owen MJ (2002) Psychiatric Genetics and Genomics. New York, NY: Oxford University Press.

Moises HW and Gottesman II (2000) Genetics, risk factors and personality factors. Henn F, Sartorius H, Helmchen H and Lauter N (eds) Contemporary Psychiatry, vol. 3. pp 47–59. Heidelberg/New York, NY: Springer.

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Ritsner MS (2011) Handbook of Schizophrenia Spectrum Disorders. Heidelberg: Springer.

Sullivan PF, Kendler KS and Neale MC (2003) Schizophrenia as a complex trait: evidence from meta‐analysis of twin studies. Archives of General Psychiatry 60: 1187–1192.

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Moises, Hans W(Oct 2013) Psychoses. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0005245.pub2]