1) Genetic Factors
Gottesman: Schizophrenia is more common in the biological relatives of a Schizophrenic, the closer the degree of genetic relatedness, the greater the risk. If a parent has schizophrenia the chance of child having it is 10%
MZ twins have 48% chance risk of developing Schizophrenia if their twin has the disorder, whereas DZ twins 17% chance of having Schizophrenia if their twin has the disorder, that’s more than double!
Kety et al: 14% of the biological relatives of adoptees with Schizophrenia were classified as Schizophrenic, whereas only 2.7% of the adoptive relatives were found to be Schizophrenics.
Researchers studies DNA from human families affected by schizophrenia and found that those with Schizophrenia were more likely to have a defective version of a gene called PPP3CC; which is associated with calcineurin.
Attempts to explain Schizophrenia in terms of one biological cause are challenged by the fact that there are many types of Schizophrenia. (Crow: Type 1 is characterised by positive symptoms, Type 2 is characterised by negative symptoms)
Another issue is whether the causes identified are proximate (direct) symptoms i.e. enlarged ventricles or ultimate (indirect) symptoms i.e. biological.
Genetic explanations cannot account for patients who have no family history of the disorder.
2) Biochemical Factors
Comer: The Dopamine Hypothesis; Schizophrenics are thought to have high number of D2 receptors on postsynaptic neurones, resulting in more of the neurotransmitter Dopamine binding and more neurones/ action potentials firing through bodies axons. Result is ‘attentional deficit’
Evidence to support the Dopamine Hypothesis is
i. Antipsychotic/antischizophrenic drugs; called Phenothiazines, which bind to D2 receptors, blocking Dopamine from binding, reducing the ‘attentional deficit’ effect. ii. Parkinson’s Disease; have low levels of Dopamine so