Genetic explanation of depression

Genetic explanation of depression

1. Family studies

   • The concordance rate of depression in families should be much higher for closer relations that it is for distant realtions
   • Egeland
     • Amish study: prevalence of bipolar was much higher compared to other populations

2. Twin studies

   • Peter McGuffin
     • 214 twin pairs, MZ concordance=46%, DZ concordance= 20%
     • Allen (1976) support study
       • Found MZ concordance of 40% and DZ concordance of 11% (similar to McGuffin's study)
         • Concordance for bipolar depression was much higher: MZ= 72%, DZ= 14%
   • MZ twins= 100% genetic similarity
     • Concordance should be higher than that of DZ twins
   • DZ twins= 50% genetic similarity
     • Same genetic similarity as normal siblings

3. Adoption studies

   • Seperates genetics and environments- more covincing
   • Wender
     • 71 adult adoptees with depression, 71 adult adoptees without depression (controls)
       • Results showed that the biological parents of the adoptees are 8x more likely to have depression than the adoptee's adoptive parents.
     • Psychiatric evaluations were conducted of adoptee's biological and adoptive parents
   • The psychologists have to find adoptees with depression who are serperated from their parents at a young age
     • This means that sample sizes are small and so ungeneralisable

4. The idea that depression runs in families and is inherited from our parents

   • Key people: Peter McGuffin, Paul Wender, Egeland and Allen

5. Strengths

   • Adoption studies separate the role of environment and genetics as the children aren't brought up by depressed parents; environment can't intervene
   • 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
   • 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.
     • It would be wrong to say genetics don't play any role at all in the formation of depression
   • 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

6. Weaknesses

   • Adoption studies- small sample size
   • Twins are often brought up in a more similar environment so it might explain the high concordance rate better than genetics
   • 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
   • 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
   • 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.
   • So far, search for a gene that causes depression has been unsuccessful