Caspi et al. (2003)

What is 5-HTT? (2)

• Serotonin transporter gene (5-HTT)

• Involved in the reuptake of serotonin in brain synapses

Aim

To determine whether there is evidence for a gene-environment interaction (G x E) for a mutation of 5-HTT

Methodology (2)

• longitudinal Correlational study

• Questionnaire

Participants (2)

• Sample of 847 New Zealand

• 26-year-olds

Procedure (7)

• All participants were members of a cohort that had been assessed for mental health on a three-year basis until they were 21

• Divided into 3 groups based on their 5-HTT alleles:

  • Group 1 - 2 long alleles

  • Group 2 - short and long allele

  • Group 3 - 2 short alleles

• 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

• Assessed for depression

Results (2)

• People who had one or more short versions of the allele demonstrated more symptoms of depression and suicidal ideation in response to stressful life events

• The effect was strongest for those with 3+ stressful life events.

Implication (1)

Simply inheriting the gene was not enough to lead to depression, but the gene’s interaction with stressful life events increased one’s likelihood of developing depression

Strengths (1)

• Acknowledges the interaction between both biological and environmental factors in depression (holistic approach)

Limitations (4)

• Cannot determine a cause-and-effect relationship because it is a correlational study

• The study assumes that serotonin may cause depression

• Later studies have not been able to show similar results (low reliability)

• Some participants did not have the gene mutation and became depressed; therefore, we cannot say that gene expression alone can cause depression