Caspi et al (2003)

Question 1

Aim

Answer 1

To determine whether there is evidence for a gene-environment interaction for a mutation of the serotonin transporter gene - 5-HTT. The serotonin transporter is involved in the reuptake of serotonin in brain synapses

Question 2

Participants

Answer 2

• 847 New Zealand 26-year-olds
• All members of a cohort that had been assessed for mental health on an every-other-year basis until they were 21
• Divided into three groups based on their 5-HTT alleles: Group 1 had two short alleles; Group 2 had one short and one long allele; Group 3 had two long alleles

Question 3

Method

Answer 3

• Participants were asked to fill in a “Stressful life events” questionnaire which asked them about the frequency of 14 different events - including financial, employment, health, and relationship stressors - between the ages of 21 and 26
• Also assessed for depression

Question 4

Results

Answer 4

• People who had inherited one or more short versions of the allele demonstrated more symptoms of depression and suicidal ideation in response to stressful life events
• Effect was strongest for those with three or more stressful life events
• Simply inheriting the gene was not enough to lead to depression, but the genes’ interaction with stressful life events increased one’s likelihood of developing depression

Question 5

Conclusion

Answer 5

Much more research is needed before a clear relationship between a gene and a depression can be established as there are opposing studies

Question 6

Evaluation

Answer 6

• Study is correlational, so no cause and effect relationship can be determined
• Study makes the assumption that serotonin causes depression
• Information about life-events was self-reported. It may be the salience of the negative life events which plays a role in depression - that is, those that recalled them more easily may have a tendency towards depression. Those who are more resilient, may not recall negative life events as easily.
• Theory acknowledges the interaction between both biological and environmental factors in depression. This is a more holistic approach, not reductionist.
• Later studies have not been able to show similar results. It appears that the study has low reliability.
• Some participants who did not carry the gene mutation became depressed; therefore, we cannot say that gene expression alone can cause depression