genetic similarity

genetic similarity

Human beings are 99.9% genetically similar to each other i.e. you are almost 100% identical to every other person on the planet. However, as we know from experience, there is huge variety amongst human beings in terms of physical appearance, skills, abilities, personalities etc.

kinship studies

Scientific studies in which researchers assess hereditary influence by examining blood relatives to see how much they resemble each other on a specific trait.

Kendler et al

Aim

To investigate the heritability of depression

Research method

Correlation (interviews; twin study)

Participants

42000 twins from Sweden's twin registry

Procedure

The participants were interviewed and assessed for major depressive disorder in accordance with DSM-IV

Results

The researchers estimated from the condordance rates in mono- and dizogotic twins that the heritability of depression is roughly 38% - The rate was higher in females. (MZ male - 31%: MZ female - 44%: DZ Males - 11% DZ females - 16%)

Conclusions

Depression is somewhat heritable, but environment and stress play at least a big a role (predisposition and stress: diathesis stress theory)

Evolutionary: Strengths

- High generalizability
- Adhered to ethical guidelines

Evolutionary: Weaknesses

- No cause & effect relationship
- Self reported data, unreliable results

weissman et al

Aim

To study the potential genetic nature of Major Depressive Disorder over 3 generations

Method

· Sample of 161 grandchildren and their parents and grandparents
· Took place over a twenty year period, looking at families at high and low risk for depression
· The original sample of depressed patients (now, the grandparents) was selected from an outpatient clinic with a specialization in the treatment of mood disorders.
· The non-depressed participants were selected from the same local community. (environment but less able to generalise)
· The original sample of parents and children were interviewed four times during this period.
· The children are now adults and have children of their own - allowing for study of the third generation.
· Data was collected from clinicians, blind to past diagnosis of depression or to data collected in previous interviews.
In order to establish credibility, researcher triangulation (reliability) was used. Children were evaluated by two experienced clinicians - with one being a child psychiatrist and the other a psychologist.

Results

· The inter-rater reliability of their diagnoses were 0.82 for MDD, 0.65 for anxiety disorders and 0.94 for alcohol dependency (more quantifiable).
· High rates of psychiatric disorders in the grandchildren with two generations of major depression. By 12-years-old, 59.2% of the grandchildren were already showing signs of a psychiatric disorder - most commonly anxiety disorders.

· Children had an increased risk of any disorder if depression was observed in both the grandparents and the parents, compared to children where their parents were not depressed. In addition, the severity of a parent's depression was correlated with an increased rate of a mood disorder in the children.

On the other hand, if a parent was depressed but there was no history of depression in the grandparents, there was no significant effect of parental depression on the grandchildren. (one parent has depression)

Conclusions

· Association between parental MDD and child diagnosis is moderated by grandparental MDD status
· Rates of psychopathology are highest in grandchildren of parents and grandparents with a moderately to severely impairing depression
Anxiety disorders are the early sign of psychopathology in the young grandchildren

Evaluation

· The study is longitudinal, increasing the reliability of the data
· The association between parental MDD and child diagnosis is moderated by grandparental MDD status. The amount of time that a child spent with a healthy grandparent may be a confounding variable in the study.
· The use of researcher triangulation increases the credibility of the findings.
· A sample of 161 children is a large sample; however, more research would need to be carried out to confirm the reliability of the findings.
· Although family (kinship) studies indicate a potential genetic link to behaviour, there is no actual genotype studied.
· Are we able to predict mental disorders and prevent mental disorders by diagnosing young children
· Do we intervene and how do we manage?
· Challenge cognitive biases
· No prior knowledge of relationship
Amount of time that a child spent with a healthy grandparent may be a confounding variable in the study

Research Method

Longitudinal family study