Genetics - Biological Explanations of Schizophrenia

Question 1

Biological Explanation - Genetics - A01

Answer 1

• Three genes: COMT, DRD4, AKT1 have all been associated with excess dopamine in specific D2 receptors, leading to acute episodes, positive symptoms and negative symptoms.
• Researchers (2016) have identified the C4 gene that increases the risk of schizophrenia.
  -After conducting studies in both humans and mice, the researchers found that C4, appears to be involved in eliminating the connections between neurons — a process called “synaptic
  pruning,” which, in humans, happens naturally in the teen years.

-It’s possible that excessive or inappropriate “pruning” of neural connections could lead to the development of schizophrenia.

Question 2

A03 - Is schizophrenia linked to just one gene?

Answer 2

• Although COMT, DRD4, AKT1 and C4 have been identified in the onset of sz, they may not be responsible in isolation for its causation.

-The genes may all contribute in some way and therefore, it may be the combination of genes (a polygenic disorder) that produces the
varied symptoms of schizophrenia.

• The environmental influences on these genes also need to be considered, therefore to attribute the causation of a sz to a single gene is highly reductionist and unlikely.

Question 3

A03 - Adoption studies

Answer 3

• Tienari et al (2000) investigated 164 adoptees whose biological mothers had been diagnosed with schizophrenia:
  6.7% also received a diagnosis of schizophrenia, compared to just 2% of the 197 control adoptees
  -The investigators concluded that these findings showed that the genetic liability to schizophrenia had been ‘decisively confirmed’.

-However, in countries such as Denmark and the US, potential
adoptive parents would have been informed of the genetic background of children prior to selection for adoption.

-Hence, the adoptive parents’ knowledge of possible disorders may
have produced a self-fulfilling prophecy.
-Likewise, the 2% of control adoptees developing sz
is twice the prevalence of the normal sz population, therefore we must question this study’s claims as being decisive.
-There are potential other factors other than genetics that may have
caused the onset of sz.

Question 4

A03 - Genetics - Twin studies

Answer 4

Gottesman and Shields found:
- A concordance rate of 42% in MZ twins – where both twin 1 and twin 2 have schizophrenia.
- A concordance rate of 9% in MZ twins – where both twin 1 and twin 2 have schizophrenia.
- A concordance rate of 79% in MZ twins – where twin 1 has schizophrenia and twin two has some form of diagnosed or recognised disorder.

• This supports the idea that there may be a genetic vulnerability to developing schizophrenia, but as it is not prevalent in 100% of twin 2 MZ twins, (even though they share 100% genes)
  there must be an environmental influence.
• Therefore, the diathesis-stress model which has a
  focus on a biological predisposition combined with an environmental stressor may be a more holistic explanation for the onset of sz.