Caspi et al (2003)

Aim: To investigate the role that gene mutation and epigenetics may play in major depressive disorder.

 

Method: Correlational experiment (a bit like quasi but not as much cause and effect)

 

Procedure:

Aetiology: study of cause

 

Biological aetiology (biological explanation) of … (uses genetics)

 

Diathesis-stress model - GENETIC PREDISPOSITION of something, in this case, depression, the gene alone does not cause depression, you need life events to trigger the predisposition.

 

Caspi never told the participants whether they have the disposition. (confirmation bias)

 

Stress threshold is different for everyone

 

5HTT is a serotonin transporter gene. Serotonin is shown to be linked to depression through other studies.

 

Participants: Dunedin Multidisciplinary Health and Development Study. There were 1037 children (52% male) has been assessed at ages 3, 5, 7, 9, 11, 13, 15, 18, 21 and was virtually intact (96%) at the age of 26 years. A total of 847 Caucasian non-Maori study members, without stratification confounds, were divided into three groups based on the basis of their 5-HTTLPR genotype.

 

(short/short) = 147 - 17%

(Short/long) = 435 - 51%

(long/long) = 265 - 31%

 

No difference in the frequency of the sexes.

 

Stressful life events between the age of 21-26 years old.  Using it as a life history calendar. (eg. Finance, health, relationship, housing etc). Out of the cohort, 25% had one, 20% had 2, 11% had 3 and 15% had 4 or more. There was no relationship between the genotype and the number of life events. They tested and diagnosed the participants with depression using DSM IV. 17% of the participants met the DSM IV criteria for a major depressive episode. (58% female versus 42% male; odds ration = 1.6. 3% reported past-year suicide attempts or recurrent thoughts about suicide in the context of a depressive episode. They also collected informant reports from close family members.

 

It is shown that more stressful life events, the more people that have depression. If you have (s/s) you are more likely to have depression than people with (l/l) despite having the same amount of cumulative stressful life events, the higher the number of events, the bigger the difference. Short/short is more sensitive and responsive to the accumulative stressful life event.

 

 

Results:

Stressful life events between the age of 21-26 years old.  Using it as a life history calendar. (eg. Finance, health, relationship, housing etc). Out of the cohort, 25% had one, 20% had 2, 11% had 3 and 15% had 4 or more. There were no relationship between the genotype and the number of life events. They tested and diagnosed the participants with depression using DSM IV. 17% of the participants met the DSM IV criteria for a major depressive episodes. (58% female versus 42% male; odds ration = 1.6. 3% reported past-year suicide attempts or recurrent thoughts about suicide in the context of a depressive episode. They also collected informant report from close family members.

 

It is shown that the more stressful life events, the more people that have depression. If you have (s/s) you are more likely to have depression than people with (l/l) despite having the same amount of cumulative stressful life events, the higher the number of events, the bigger the difference. Short/short is more sensitive and responsive to the accumulative stressful life event.

 

 

 

Conclusion:

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.

 

 

Evaluation:

  • Stressful life event is not specified with criteria and ranking. Different life events have different impact (family member dying vs scakov quitting twitch, both r stressful but not the same) dependent on the person and the nature of the event. It is measured by number and not the severity. Difficult to quantify. HOW DO WE OPERATIONALISE THIS? All stressful life events were treated equally.

  • The study makes the assumption that serotonin causes depression.

  • Classifying depression - subjective

  • Used DSM IV, self-report about symptoms, close friends/relative to report on possible depression symptoms, suicidal ideation/attempt.

  • Sampling bias, NZ, Caucasian, similar socioeconomic status, cultural values, many have had similar stressful life events, age.

  • CORRELATIONAL STUDY, NOT CAUSE AND EFFECT

  • TOO REDUCTIONIST, REDUCE EVERYTHING DOWN TO NUMBERS, MAYBE DON'T DO IT, DEPRESSION CAN BE TOO COMPLICATED.

  • THE PARTICIPANTS WERE NEVER TOLD ABOUT THEIR GENES!!!!!!!!!!!!!!!!!

Caspi, A., Sugden, K., Moffitt, T. E., Taylor, A., Craig, I. W., Harrington, H., McClay, J., Mill, J., Martin, J., Braithwaite, A., & Poulton, R. (2003). Influence of life stress on depression: moderation by a polymorphism in the 5-HTT gene. Science (New York, N.Y.), 301(5631), 386–389. https://doi.org/10.1126/science.1083968