AO1

• Family studies

  • Gottesman et al. conducted a large-scale family study. He found that the risk of developing schizophrenia was highest in monozygotic twins. Concordance rates of 48%
  • Someone with an aunt with schizophrenia has a 2% chance of developing schizophrenia, 9% for a sibling and 48% for an identical twin.
  • Even fraternal twins have a 17% chance of developing schizophrenia. This is a strong concordance rate as the general population only has a 1% chance of developing schizophrenia.
• Candidate genes

  • Schizophrenia is polygenic, meaning multiple genes can cause it.
  • It is thought that dopamine has a role in schizophrenia. Therefore, it may be that the genetic coding for the neurotransmitters of dopamine is affected in those with schizophrenia.
• candidate genes

  • Ripke et al. combined data from studies that looked at the whole human genome of schizophrenia. The genetic makeup of 37,000 people with a diagnosis of schizophrenia was compared to a control group of 113,000. There were 108 separate genetic variations found to be related to a slight increase in risk of SZ.
  • Early research looked unsuccessfully for a single genetic variation. Schizophrenia is aetiologically heterogeneous, meaning the risk is affected by different combinations.
• • Mutation of the DNA in parents may be due to radiation, poison or viral infection that can cause schizophrenia in a child. The evidence comes from positive correlations between paternal age and risk of schizophrenia.
  • Increased age also increases the risk of sperm mutation.
  • This increases from around 0.7% of fathers under 25 to over 2% in fathers over 50. (Brown et al)
  • The older the sperm, the more likely you are to develop schizophrenia.
  • Sperm can also be mutated from radiation, perhaps such through a phone in your pocket.
• Hyperdopaminergia is when there is higher than usual levels of dopamine in the subcortex. This is linked with the positive symptoms such as hallucinations. There may be a higher number of dopamine receptors causing over activities of dopamine resulting in sensory hallucinations.

  Hypodopaminergia is when there are lower than usual levels of dopamine in the cortex where less dopamine is produced. Dopamine is transmitted across synapses. This is linked with negative symptoms as there is reduction in normal functioning.
• The original dopamine hypothesis focused on the role of high levels of activity of dopamine in the subcortex. This is the central areas of the brain. For example, an excess of dopamine in Broca's area may be associated with speech poverty or auditory hallucinations.

  The updated dopamine hypothesis suggests that the abnormal functioning in the brain cortex Goldman and Rakin et al have identified low levels of dopamine in the prefrontal cortex. This may explain the negative symptoms of schizophrenia.