3. One other biological theory/explanation of schizophrenia

AO1 → Schizophrenia is heritable

• Hiller et al. (2018) → 79% schizophrenia cases = genetic

  • Suggests → significant role of genes → in schizophrenia

• Jessica Wright (2014) → identified as many as 700 genes → possibly linked to the disorder

Strength → Gottesman (1991)

• Examined concordance rates → of people of different genetic similarity

  • Clear relationships → between genetic similarity + two related individuals → both having schizophrenia

Strength → Gottesman (1966)

• Found concordance rates → MZ = 42% + DZ = 9%

  • Shows strong relationship → between biology + schizophrenia → although not 100%

Weakness → concordance rates are not 100%

• Peterson and Mortenser (2006) → the longer person is exposed to city life + the denser the city population = greater risk of developing schizophrenia

  • Suggests rural living → may protect person → from developing schizophrenia → when they already had genetic pre-disposition to it

    • Shows importance of environment + how/why MZs differ so much → in their onset of schizophrenia

    • REMEMBER → concordance rates = never 100%

Gene mutations

• Schizophrenia → can also appear in families → without history of disorder

• DNA code in one gene → may just spontaneously mutate

  • Changes → may be result of environmental factors/errors → during cell division in the womb

Candidate genes → COMT

• Schizophrenia may be due → to deletion of this gene → responsible for breaking down dopamine

  • Results in dopamine levels → being poorly regulated

    • Leading to schizophrenia

Candidate genes → DISC1 gene

• Kim et al. (2012) → people with abnormality in this gene = 1.4x more likely to develop schizophrenia → than those without

  • Gene code → for the creation of GABA → regulates other neurotransmitters → i.e. glutamate + dopamine

Supporting evidence for COMT → Egan et al. (2001)

• Proposes link between decreased dopamine activity → in the PFC + one form of COMT gene

  • Concluded → inheriting two copies of this particular gene → increases chances of schizophrenia → by 50%

Supporting evidence for DISC1 → Dahoun et al. (2017)

DISC1 = associated with pre-synaptic dopamine dysregulation→ key factor in schizophrenia

Diathesis-Stress Model

• Most likely → genes create vulnerability for SZ → rather than cause it:

  • Individual may posses schizophrenia gene = diathesis

  • Condition triggered → by other environmental + biological factors (stress)

  • Much research into triggering factors → found that cannabis = increases risk of schizophrenia → up to 7x

    • Cannabis = interferes with dopamine system

• Still a genetic explanation