biological explanation for SZ - genetics

• schizophrenia may run in families according to who

  hiker (2018)

  • heritability of SZ is 79% so likely that within the population of SZ 79% have inherited SZ through genes
  • SZ occurs in 1% of the population but if you have a 1st degree relative with SZ, chances of getting it increase suggesting there is a genetic factors (e.g: fraternal twins have a 17% chance of getting SZ)
• gene mutations

  SZ may appear in the absence of a family history of the disorder

  • DNA code in 1 or more genes may mutate and these changes may result from an environmental factor or an error during cell division (e.g: deletion or duplication of strand DNA)
• what are candidate genes

  specific genes identified that are linked to presence of SZ

  • COMT gene
  • DISC-1 gene
• what is the COMT gene

  link between SZ & digeorge syndrome may be the deletion of COMT gene

  • gene provides instructions for creation of catechol-o-methyltransferase - enzyme which breaks down NT such as dopamine in PFC
• what does deletion of COMT gene mean

  dopamine levels are poorly regulated resulting in SZ symptoms
• what is the DISC-1 gene

  people with an abnormality to the gene DISC-1 (disrupted-in-schizophrenia 1) are 1.4x more likely to develop SZ than people without abnormality - kim et al (!012)
• what does the DISC-1 gene code for

  creation of GABA - a neurotransmitter which regulates other NT such as glutamate and dopamine in the limbic system
• strength

  • research support for genetic explanation of SZ
  • gottesman (1991) analysed the concordance rates for people of different genetic similarity. there is a clear relationship between genetic similarity & increase in 2 related individuals both having SZ - MZ twins have a 48% concordance rate & parents and children have a 9% concordance
  • shows while SZ is not entirely a genetic disorder, fact that concordance rate is greater for MZs than DZs shows genetics play a significant part
• weakness (counterpoint)

  • MZ twins likely to be treated more similarly than DZ twins
  • due to their physical similarity and that they are the same sex this leads to a more similar living experience
  • this reduces validity of conclusion that greater amount of shared DNA is responsible for similar disorders & this explains the closer concordance MZ twins display
• strength

  • research evidence to show there are candidate genes for SZ
  • in a review of 14 studies, dahoun (2017) concluded that DISC-1 is associated with presynaptic dopamine dysregulation a key factors in SZ and egan (2001) proposed a link between decreased dopamine activity in PFC and one form of the COMT gene
  • shows how genetic variations underpin neurochemical differences which can predispose a person towards SZ
• weakness

  • concordance rate is far from 100% even for MZ twins
  • pedersen and mortensen's (2006) research demonstrates that the longer a person has been exposed to the city life and the denser the population is in that city, the greater the risk of developing SZ which suggests rural living may help protect a person from developing a disorder to which they are genetically predisposed
  • shows that environmental risk factors can affect individuals accounting for how its possible for MZs to differ in terms of onset of SZ