Key study - Oruč et al. (1997)

• Background

  • there is thought to be both biological and psychological factors associated with the onset of bipolar disorder
  • psychological triggers may include a traumatic effect or other environmental factors
  • if levels of certain neurotransmitters in the brain are too low or high, this can lead to a psychological disorder
  • McGuffin et al. (1994) - genetics is at least partly responsible for the onset of bipolar disorder, but the identification of specific genes is too complex
• Psychology

  • bipolar disorder is the most likely psychological disorders to be inherited
  • genetics are thought to be 80% of the cause
  • however there is still very little information about specific genes
  • dopamine, noradrenaline and serotonin are neurotransmitters associated with the onset
  • if lower serotonin levels are associated with bipolar disorder, it is appropriate to investigate the genes associated with serotonin
• Aim


  To investigate whether the genes encoding for certain serotonin receptors could be involved in susceptibility to bipolar disorder.
• Sample

  • 42 patients with type 1 bipolar
  • from 2 Croatian hospitals
  • 25 females and 17 males
  • 31 - 70 years
  • 16 patients had a first degree relative diagnosed with a major effective disorder
  • control group of 40 with no family history
• Method/procedure

  • matched pairs - matched control group with patients in terms of age and sex
  • DNA testing was carried out to test for polymorphisms in the genes responsible for serotonin receptors and transmitters
  • results of the DNA tests were compared with each other
• Polymorphism


  A variation in a gene or genes.
• Results

  • participants with bipolar were not significantly more likely to have polymorphisms of the genes under investigation than the control group
  • those with a family history of mood disorder were no more likely to have polymorphisms in these genes than other participants
  • serotonin is sexually dimorphic
  • polymorphisms for both genes were more common in women with bipolar than the control group
• Sexually dimorphic

  Any differences between males and females of any species that are not just differences in organs. These differences are caused by either inheriting either male or female patterns of genetic material.
• Conclusions

  Polymorphisms in these genes could be responsible for an increased risk of developing bipolar disorder in females only.
• Evaluation - Strengths

  • quantitative data - comparable and removes researcher bias
  • control and standardization - reliability
  • application due to focus on DNA
• Evaluation - Weaknesses

  • small sample - difficult to generalize
  • reductionist
  • age could be an EV as bipolar is ot fully developed yet