Gottesman et al. (2010) Disorders in Offspring with Two Psychiatically Ill Parents

Aim of Study

To investigate in a large sample the probability of a child, with 2 parents with a psychiatric illness, being diagnosed with a mental disorder, in particular, the one that their parents have

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Sample

  • 2.6 million people born in Denmark
  • Alive in 1968 
  • Had a link to their parents 
  • Aged over 10 before 01/01/07
  • Danish Civil Register
  • Danish Psychiatric Central Register
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Research Method

National register-based cohort study

Psychiatric Central Register and National Statistics identified people who had ever received a diagnosis of schizophrenia, bipolar affective disorder or unipolar depressive disorder using the ICD-8 and ICD-10

Groups: Both parents with same disorder, one parent with disorder, neither parent admitted, no data on parent diagnoses (General population used for comparison)

Groups were not mutually exclusive

Group of 1 parent with schizophrenia and 1 with bipolar disorder  used to give more info about the genetic overlap in these disorders

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Key Findings

Risk of Schizophrenia:

  • Both parents with schizophrenia= 27.3% (39.2% incl. schizophrenia-related disorders)
  • One parent with schizophrenia= 7%
  • Neither parent diagnosed= 0.86%
  • One schizophrenic parent and one bipolar parent=15.6%

Risk of bipolar disorder:

  • Both parents with bipolar= 24.9% (36% incl. unipolar depressive disorder)
  • One parent with bipolar=4.4%
  • Neither parent diagnosed=0.48%
  • One schizophrenic parent and one bipolar parent= 11.7%

Maximal risk of any psychiatric disorder with both schizophrenic or both bipolar parents were 67.5% and 44.2% respectively

General population: cumulative incidence was 14.1%, 1 in 7 had been admitted by 52 yrs old

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Conclusions

  • Children with two parents diagnosed with psychosis have a very high chance of also developing psychosis
  • Risk of schizophrenia is higher if both parents have been admitted with the same diagnosis compared to if only one parent or no parents have been admitted with the diagnosis
  • Risk of bipolar disorder or unipolar depressive disorder is higher if both parents have been admitted with the same diagnosis than if only one parent or no parents have been diagnosed
  • Evidence to support genetic explanation of mental illness
  • Patterns of transmission may support evolving assumptions about genetic overlap for traditional categories of psychosis
  • Risks of psychosis may be informative for counselling and making personal decisions such as family planning or health insurance
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Evaluation Strengths

  • High Validity- diagnosis used ICD-8 and ICD-10
  • High ecological validity- used secondary data that already exists so nothing was manipulated
  • Large, representative sample
  • Reliable- consistent collection fo data
  • Quantitative data- scientific, analyses, trends
  • Ethical- data anonymised, was approved by Danish Data Protection Agency, research  was in public domain
  • His study supported the previous smaller studies
  • Researchers more about schizophrenia, bipolar and unipolar depressive disorder
  • Information can help make family planning decisions
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Evaluation Weaknesses

  • Difficult to rule out influence of shared environment (nature vs nurture)
  • People with bipolar and unipolar depression are less likely to be admitted and more likely to be treated by GPs or as outpatients
  • Needs to be concurrent validity in terms of adoption & twin studies before making any conclusions about genetic determinism
  • Ethnocentrism-may only apply in Denmark
  • Implications for health insurance and may affect adoption from schizophrenic parents
  • There might be discrimination against schizophrenic people having children (Eugenics?)
  • Problems using information from countries where healthcare is funded by the public may differ in countries where people pay for their healthcare
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