topic 3 - Caspi et al (2003) Influence of Life Stress on Depression: Moderation by a Polymorphism in the 5-HTT Gene Flashcards
what is the background of the study?
lots of research evidence suggests that stressful life experiences cause depression but not everyone who experiences stressful life events become depressed. this study looks at the genetic explanation of depression and whether a gene is linked to the neurotransmitter serotonin which is a brain chemical known to be involved in depression which makes some people more likely to become depressed after stressful life events than others.
the SSRI helps increase the amount of serotonin available in the brain and reduce the symptoms of depression. therefore, if low levels of serotonin cause depression then maybe the genes that cause someone to have lower levels of serotonin than the rest of the population could explain why some people are more likely to become depressed after stressful life events.
what is the aim of the study?
capsi et al aimed to investigate why stressful life events seemed to lead to depression in some people and not others. Then they investigated whether stressful life events were more likely to lead to depression in people with a certain variation of the 5-HTT gene.
what is the 5-HTT gene?
it is gene linked to the amount of serotonin available in the brain
what is the gene being investigated?
5-HTT gene
what procedure was conducted in this study? give specifics.
participants were taken from the Dunedin Multidisciplinary Health and Development Study, they were a group of children who have been studied since birth.
in total 847 members from the group took part int eh study. They were divided into 3 groups based on the version of the 5-HTT gene they had.
17% of the participants were in group 1 and they had two copies of the short version of the gene.
51% of the participants were in group 2 and they had one copy of the short version and one copy of the long version of the gene
31% of the participants were in group 3 and they had two copies of the long version of the gene.
it was a longitudinal study, so each participants completed a questionnaire individually that measured the life vents that occurred between their 21st and 26th birthdays. The events could include issues with finances, health and relationship. Another questionnaire was conducted to asses whether they had any symptoms of depression in the year before their 26th birthday which gave the researches quantitative data in the form of a ‘depression score’.
where were the participants from?
participants were members of the Dunedin Multidisciplinary Health and Development Study.
how many people took part in the study?
847
what were the different versions of the 5-HTT gene?
in group one they had two copies of the short version of the gene
in group 2 they had one copy of the short version and one copy of the long version of the gene.
in group 3 they had two copies of the long version of the gene
what is a longitudinal study? define it.
it is a study where the sample people are tested over a period of time to investigate changes.
what were the results of the study?
participants who had at lead one short version of the 5-HTT gene and experienced stressful life events between the ages of 21 and 26 showed a significant increase in symptoms of depression after the event occurred until they were 26 years old.
participants with a short version of the 5-HTT gene and who experienced stressful life events were more likely to be diagnosed with depression than participants with two long versions of the gene.
participants with the short version of the gene were more likely to develop suicidal thoughts after a stressful life.
participants with two short versions of the 5-HTT gene were most likely to report severe depressive symptoms if they suffered a number of stressful events, this included a higher report of suicidal thoughts or attempts if they faced more than three stressful life events.
what version of the gene were more likely to become depressed in the studies results?
the two copies of the short version of the 5-HTT gene
what is the conclusion of the study?
the evidence seems to suggest that there is a connection between life events and genetic influences in causing depression. This suggests that nature and nurture work together to increase the likelihood of a person developing depression.
A person needs to have both a stressful life and the specific type of the 5-HTT gene in order to become depressed.
what are the strengths of the study?
one strength of this study is that there was a large number of participants (847). This means generalising the results from the study should be easier than if the sample is very small.
another strength is that someone with depression could have a different cause of depression and this could be useful information for doctors. Doctors should look at the variety of factors in their patients, including whether they have been through stressful events and whether they have two copies of the short version of the 5-HTT gene to understand why they have become depressed. This can also explain why some people become depressed after a stressful life event while others don’t.
what are the weaknesses of the study?
one weakness of the study is that the researchers thought there was a chance that some people were naturally more likely to put themselves in stressful situations. the short version of the 5-HTT gene might be a natural factor that makes people prone to situations that are stressful. therefore, the gene and life events may not be causing depression as such, but instead the person is in more stressful situations that could cause depression.
another weakness of the study if the evidence from the questionnaire may not be reliable because some of the participants may ‘exaggerate’ their symptoms while other may not want to make a big deal out of them.
