Biological Explanations

• The Genetic Basis for Sz

  Candidate Genes​

  Early research into this area looked for a single genetic variation in the belief that one faulty gene could explain Sz. ​

  Polygenic

  Sz appears to have a number of different genes are involved. Most likely, genes coding for neurotransmitters, including DA.​
• Genetic Basis for Sz

  Aetiologically heterogenous

  Diff. studies identified diff. candidate genes. Appears that Sz is aetiologically heterogenous, i.e. different combinations of factors. Incl. genetic variation

  Ripke et al study combined all previous data from genome wide studies of Sz. Genetic make-up of 37,000 pts compared to 113,000 controls; 108 separate genetic variations were associated with increased Sz risk
• The role of Mutation ​

  Evd. for the role of mutation comes from a study showing a positive correlation between paternal age (associated w/increased risk of mutation) & Sz risk, increasing from 0.7% fathers under 25 to over 2% in fathers over 50 years old (Brown et al, 2002). ​
• Twin Studies(Research support for the genetic explanation for Sz)

  • Hilker et al (2018) showed a concordance rate of 33% for MZ twins and 7% for Dz twins.​
  • Joseph (2004) calculated that the pooled data for all Sz win studies carried out prior to 2001 showed a concordance rate for Mz twins of 40.4% and 7.4% for Dz twins.​
• Other Factors

  One limitation of the genetic explanation is there is clear evidence to show that environmental factors also increase the risk of developing Sz. ​

  ​factors include both biological and psychological influences. Biological factors include birth complications and smoking THC-rich cannabis in teenage years. Psychological risk factors include childhood trauma which leaves people more vulnerable to adult mental health problems in general.

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  Means genetic factors alone cannot provide a complete explanation for Sz.​
• Neural Correlates​

  Research has identified some neural correlates which may be the cause of Sz on a biological level.

  Neural Correlates​

  Patterns of structure or activity in the brain that occur in conjunction with an experience and may be implicated in the origins of that experience. ​

  Dopamine​

  A NT that generally has an excitatory effect and is linked to the sensation of pleasure. ​

  Negative symptoms - avolition - less activity in the ventral striatum

  Positive - Hallucination - lower activation lvls in superior temporal gyrus
• Dopamine Hypothesis

  Original version of the DA hypothesis focused on the possible role of high levels of DA in the subcortex (central parts of the brain).

  • More recent versions of the DA hypothesis have instead focused on abnormally low levels of DA in the brain’s cortex.
  • Rakic et al (2004) -identified a role for low levels of DA in the PFC in the negative symptoms of Sz. ​
  • Been suggested that cortical hypodopaminergia leads to subcortical hyperdopaminergia – so high and low levels of DA in different brain regions are part of the updated version.​
• Updated Version of the DA Hypothesis​

  Links between abnormal DA levels and symptoms, current versions of the DA hypothesis try to explain the origins of abnormal DA function.

  • ​Both genetic variations and early experiences of stress, both psychological and physical, make some people more sensitive to cortical hypodopaminergia and hence subcortical hyperdopaminergia.
• Evd. for DA

  +support for the idea that DA is involved in Sz.​

  • Amphetamines increase DA and worsen symptoms in people with Sz and induce symptoms in people without.
  • In addition, antipsychotic drugs reduce DA activity and also reduce the intensity of symptoms. Finally, some candidate genes act on the production of DA or DA receptors. ​
  • This strongly suggests that DA is involved in the symptoms of Sz.​
• Evd. for DA

  - One limitation of the DA hypothesis is evd. for the central role of glutamate. ​

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  Post-mortem and live scanning studies consistently found raised levels of the NT glutamate in several brain regions of people with Sz. Several candidate genes for Sz are believed to be involved in glutamate production or processing. ​

  ​This means than an equally strong case can be made for a role for other transmitters.