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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 re-uptake of serotonin in brain synapses.


What theory were the aims based upon?

Diathesis-stress theories of depression predict that an individual's reaction to stressful events depends on their genetic make-up.

If an individual has a specific genotype, then interaction with the environment may cause these genes to be expressed.


and how were they assessed?

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.


what were the 3 groups they were divided into?

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.


Which gene of the 5-HTT has the mutation? what percentage of people have it?

The mutation of the 5-HTT gene has the shorter alleles.
Roughly 43% of people have the shorter alleles.


What were the participants asked to do?

asked to fill in a "Stressful life events" questionnaire

asked them about the frequency of 14 different events -
including financial,
health and relationship stressors - between the ages of 21 and 26.

They were also assessed for depression.



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.


When was the effect of the result strongest?

The effect was strongest for those with three or more stressful life events.


When is the likelihood of the formation of depression increased

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.


Describe the Wilhelm et al 2006 study

researchers looked at DNA samples from 127 people who are part of a longitudinal prospective study looking at mental health.

The sample had been monitored for over 25 years.

At five-year intervals, scientists recorded any major life events and signs of depression.

80% of those with two short 5-HTT genes became depressed after three or more negative life events in a year

those with two long genes appeared resilient - only 30% developed the illness in similar situations.

childhood maltreatment predicted adult depression only among individuals carrying a short allele and not among those carrying the longer allele.

much more research is needed before a clear relationship between a gene and a depression can be established.

The researchers have also found evidence to support this in cases of bullying.


what is the study?

correlational, so no cause and effect relationship can be determined.


what assumption does the study make?

assumption that serotonin causes depression


why might the results be skewed?

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 toward depression.

Those who are more resilient, may not recall negative life events as easily.


why was the approach of this study more hollistic than reductionist?

The theory acknowledges the interaction between both biological and environmental factors in depression.


have later studies revealed similar results?



reliability of the study?



inconsistency/ anomalies

There were some participants who did not carry the gene mutation who became depressed; therefore, we cannot say that gene expression alone can cause expression.