Genetic explanation of depression

Family studies
1. The concordance rate of depression in families should be much higher for closer relations that it is for distant realtions
2. Egeland
  1. Amish study: prevalence of bipolar was much higher compared to other populations
Twin studies
1. Peter McGuffin
  1. 214 twin pairs, MZ concordance=46%, DZ concordance= 20%
  2. Allen (1976) support study
    1. Found MZ concordance of 40% and DZ concordance of 11% (similar to McGuffin's study)
      1. Concordance for bipolar depression was much higher: MZ= 72%, DZ= 14%
2. MZ twins= 100% genetic similarity
  1. Concordance should be higher than that of DZ twins
3. DZ twins= 50% genetic similarity
  1. Same genetic similarity as normal siblings
Adoption studies
1. Seperates genetics and environments- more covincing
2. Wender
  1. 71 adult adoptees with depression, 71 adult adoptees without depression (controls)
    1. Results showed that the biological parents of the adoptees are 8x more likely to have depression than the adoptee's adoptive parents.
  2. Psychiatric evaluations were conducted of adoptee's biological and adoptive parents
3. The psychologists have to find adoptees with depression who are serperated from their parents at a young age
  1. This means that sample sizes are small and so ungeneralisable
The idea that depression runs in families and is inherited from our parents
1. Key people: Peter McGuffin, Paul Wender, Egeland and Allen
Strengths
1. Adoption studies separate the role of environment and genetics as the children aren't brought up by depressed parents; environment can't intervene
2. A new revised theory of genetics is that genetics makes an individual prone to depression, but environmental triggers are required. This takes both genetics and environment into account
3. There is compelling evidence, particularly from adoption studies, that indicate a genetic link and so it would be wrong to completely rule out the possibility.
  1. It would be wrong to say genetics don't play any role at all in the formation of depression
4. Stress-diathesis relationship: it has been suggested that genetics make us prone to the disorder, but stress triggers this genetic link- revised and improved theory
Weaknesses
1. Adoption studies- small sample size
2. Twins are often brought up in a more similar environment so it might explain the high concordance rate better than genetics
3. MZ twins have 100% genetic similarity so concordance rates should be 100% (which they aren't, they are actually 46%) so environment must play a part
4. DZ twins and normal siblings both have 50% genetic similarity so they should both have the same concordance rate. In reality, DZ twins have a higher concordance rate for depression so environment could explain it better- DZ twins share a more similar environment to normal siblings
5. Family of closer relations often have a more similar environment so it could explain the higher concordance rate for closer relations compared to distant realtions.
6. So far, search for a gene that causes depression has been unsuccessful

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Genetic explanation of depression

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