Caspi et al.
Caspi et al. (2003)
Longitudinal study on the possible role of the 5-HTT gene in depression after experiences of stressful events
- The 5-HTT gene influences the level of serotonin, which is known to play a role in controlling mood.
- The researchers compared participants with a normal 5-HTT gene and a mutation of the 5-HTT gene with shorter alleles. Both types are quite frequent in humans but the long allele is slightly more frequent (57%).
- The researchers found that participants who carried a mutation of the 5-HTT gene and who had experienced many stressful events were more likely to become depressed after stressful events than those participants who carried the normal 5-HTT gene.
- The 5-HTT gene could indicate a vulnerability to depression after stress and the researchers speculated whether the gene could moderate individual responses to environmental factors.
Evaluation:
- Since a large proportion of the population carries the mutation of the 5-HTT gene that makes them susceptible to depression after traumatic events, it can be difficult to conclude that the gene is a major contribution to depression. People who did not carry the mutation also became depressed.
- The study showed a correlation between the presence of a 5-HTT short allele and depression but it is not possible to establish a cause-effect relationship.
- Genes contribute to some extent to behavioral traits and disorders but it is not clear how environmental factors influence genes. Environmental factors were included in the study (stressful events) but there is no evidence against the idea that it could be the stressful events (environmental factors) that made people depressed.
Much more research is needed before a clear relationship between a gene and a behavioral trait can be established.