Caspi et al. (2003) Influence of Life Stress on
Depression: Moderation by a Polymorphism in the
5-HTT Gene
Aims: Results Conclusions:
The main aim was to see why stressful experiences lead to depression in some people but not Measure 1 - stressful life events The 5-HTT gene interacts with life events to predict
others ● No stressful life events: 30% depressive symptoms, an increase in symptoms, diagnosis
The researchers wanted to investigate whether stressful life events were more likely to lead to ● One stressful life event: 25% of depression, new-onset diagnoses, suicidality and an
depression in people with a certain variation of the 5-HTT gene (a gene linked to the amount ● Two stressful life events: 20% informant’s report of depressed behaviour
of serotonin available in the brain) ● Three stressful life events: 11% Those carrying an (l) allele were less likely to develop
● Four or more stressful life events: 15% depression or suicidality
There were no differences across the three groups in terms of the Furthermore, the (l) allele moderated the effects of
number of stressful life events experienced, suggesting that the probable or significant childhood maltreatment
Procedure: 5-HTTLPR genotype did not influence exposure to stressful life
The study was longitudinal, and therefore investigated participants at ages 3, 5, 7, 9, 11, 13, events
15, 18, 21 and virtually all again at age 26 (only 96% of the original cohort) Measure 2 - depression
Participants were not recruited by researchers, but taken from a previous study of 1,037 DSM-IV depressive episode experienced in past year:
●
Strengths:
people, which was the Dunedin Multidisciplinary Health and Development Study 17%
There were 847 participants, so it was a very large sample
In this study 847 Caucasian non-Maori study members were selected from the previous ● Past-year suicide attempt: 3%
therefore easy to generalise
group of 1,037 participants Analysis
Information is useful to doctors as it provides explanation
They were divided into three groups based off the version of the 5-HTT gene they had ● Individuals carrying an (s) allele had a significantly
for a wide range of causes
● Group 1 (n=147, 17%): two copies of the short (s) allele of the 5-HTTLPR genotype stronger interaction between life events and self
● Group 2 (n=435, 51%): one copy of the short (s) allele, and one copy of the long (l) reported depression at age 26
allele of the 5-HTTLPR genotype ● Individuals carrying an (s) allele whose life events Weaknesses:
● Group 3 (n=265, 31%): two copies of the long (l) allele of the 5-HTTLPR genotype occurred after their 21st birthday experienced increases Researchers thought there was a chance some people
Measure 1 - stressful life events in depressive symptoms from 21 to 26 years old were naturally more likely to put themselves in situations
● For each of the groups, the stressful life events occurring after their 21st birthday ● Life events that occurred after their 21st birthday where stressful life events might happen as the short
but before their 26th birthdays were recorded using a life-history calendar predicted more cases of new depression at 26 years old version of the 5-HTT gene might be a natural factor that
● The 14 life events included; employment, financial, housing, health and for those individuals carrying an (s) allele makes people prone to situations that are stressful,
relationship stressors ● Stressful life events predicted major depression among therefore the gene and life events may not be causing
Measure 2 - depression carriers of an (s) allele depression as such, but instead the person is in more
● For each of the groups at age 26, the depressive symptoms for the past year were ● Stressful life events predicted informant reports of stressful situations that could cause depression
assessed using the Diagnostic Interview Schedule depression among carriers of an (s) allele (ruling out The evidence from the questionnaires is self-report data,
● For each of the groups at age 26, an informant was asked via questionnaire about self-report bias) which might not be reliable as some people exaggerate
their depressive symptoms for the past year for 96% of the participants ● Stressful life events predicted suicide ideation among their symptoms of depression, while others might not want
carriers of an (s) allele to ‘make a big deal’ out of them
Depression: Moderation by a Polymorphism in the
5-HTT Gene
Aims: Results Conclusions:
The main aim was to see why stressful experiences lead to depression in some people but not Measure 1 - stressful life events The 5-HTT gene interacts with life events to predict
others ● No stressful life events: 30% depressive symptoms, an increase in symptoms, diagnosis
The researchers wanted to investigate whether stressful life events were more likely to lead to ● One stressful life event: 25% of depression, new-onset diagnoses, suicidality and an
depression in people with a certain variation of the 5-HTT gene (a gene linked to the amount ● Two stressful life events: 20% informant’s report of depressed behaviour
of serotonin available in the brain) ● Three stressful life events: 11% Those carrying an (l) allele were less likely to develop
● Four or more stressful life events: 15% depression or suicidality
There were no differences across the three groups in terms of the Furthermore, the (l) allele moderated the effects of
number of stressful life events experienced, suggesting that the probable or significant childhood maltreatment
Procedure: 5-HTTLPR genotype did not influence exposure to stressful life
The study was longitudinal, and therefore investigated participants at ages 3, 5, 7, 9, 11, 13, events
15, 18, 21 and virtually all again at age 26 (only 96% of the original cohort) Measure 2 - depression
Participants were not recruited by researchers, but taken from a previous study of 1,037 DSM-IV depressive episode experienced in past year:
●
Strengths:
people, which was the Dunedin Multidisciplinary Health and Development Study 17%
There were 847 participants, so it was a very large sample
In this study 847 Caucasian non-Maori study members were selected from the previous ● Past-year suicide attempt: 3%
therefore easy to generalise
group of 1,037 participants Analysis
Information is useful to doctors as it provides explanation
They were divided into three groups based off the version of the 5-HTT gene they had ● Individuals carrying an (s) allele had a significantly
for a wide range of causes
● Group 1 (n=147, 17%): two copies of the short (s) allele of the 5-HTTLPR genotype stronger interaction between life events and self
● Group 2 (n=435, 51%): one copy of the short (s) allele, and one copy of the long (l) reported depression at age 26
allele of the 5-HTTLPR genotype ● Individuals carrying an (s) allele whose life events Weaknesses:
● Group 3 (n=265, 31%): two copies of the long (l) allele of the 5-HTTLPR genotype occurred after their 21st birthday experienced increases Researchers thought there was a chance some people
Measure 1 - stressful life events in depressive symptoms from 21 to 26 years old were naturally more likely to put themselves in situations
● For each of the groups, the stressful life events occurring after their 21st birthday ● Life events that occurred after their 21st birthday where stressful life events might happen as the short
but before their 26th birthdays were recorded using a life-history calendar predicted more cases of new depression at 26 years old version of the 5-HTT gene might be a natural factor that
● The 14 life events included; employment, financial, housing, health and for those individuals carrying an (s) allele makes people prone to situations that are stressful,
relationship stressors ● Stressful life events predicted major depression among therefore the gene and life events may not be causing
Measure 2 - depression carriers of an (s) allele depression as such, but instead the person is in more
● For each of the groups at age 26, the depressive symptoms for the past year were ● Stressful life events predicted informant reports of stressful situations that could cause depression
assessed using the Diagnostic Interview Schedule depression among carriers of an (s) allele (ruling out The evidence from the questionnaires is self-report data,
● For each of the groups at age 26, an informant was asked via questionnaire about self-report bias) which might not be reliable as some people exaggerate
their depressive symptoms for the past year for 96% of the participants ● Stressful life events predicted suicide ideation among their symptoms of depression, while others might not want
carriers of an (s) allele to ‘make a big deal’ out of them
