Caspi et al (2003)

• Aim:

  To investigate evidence for a gene-environment interaction (G x E) for a mutation of the serotonin transporter gene (5-HTT) in relation to depression.
• Research Method:

  Natural Experiment, IV - stressful life events causes depression
• Procedure:

  • Sample: 847 New Zealand 26-year-olds
  • Participants divided into three groups based on 5-HTT alleles
  • Stressful life events assessed via questionnaire (ages 21-26)
  • Depression symptoms evaluated
• Results:

  • Individuals with one or more short alleles showed more depression symptoms in response to stressful events
  • Effect strongest for those with more stressful life events
  • Gene alone not sufficient; interaction with stress increased depression likelihood
• Conclusion:

  The findings support the diathesis-stress model, demonstrating that genetic vulnerability (short allele) increases the risk of MDD, but only when combined with stressful life events.
• Strengths:

  1. Longitudinal Design: Offers a clear temporal sequence between stress exposure and onset of MDD, aiding in establishing causation.
  2. Focus on Gene–Environment Interaction: Highlights the importance of environmental triggers in expressing genetic vulnerability.
• Limitations:

  • Self-Report Bias: Reliance on participants’ reports for stressful events may introduce inaccuracies or bias.
  • Replication Variability: Subsequent studies have sometimes failed to replicate the strength of the interaction, indicating variability in the effect.