Biological Explanations for Schizophrenia

Biological Explanation to Schizophrenia

Ø  Has much support

Ø  Doesn’t rule out psychological factors

Ø  Current thinking is – ‘diathesis-stress’ relationship.

Ø  Diathesis-stress relationship =  there are biological predispositions (the diathesis) for Schizophrenia THAT only develops into the disorder if significant psychological stressors (stress) are present. (Gottesman and Riley), 2003

4 different explanations:

Ø  Genetic factors

Ø  Biochemical Factors

Ø  Brain dysfunction/neuroanatomy

Ø  Viral Infection

Family Studies:

Biological relatives – Gottesman 1991 and Kendler 1995 found Schizophrenia is more common in the biological relatives of a schizophrenic.

The closer the degree of relatedness the greater risk

Genetic factors

Twin studies compare the concordance rates for:

•           identical or MZ twins (identical genes, same environment)

•          and fraternal or DZ twins (same environment but not identical genes).

•          Identical twins:

•          Research has consistently shown identical twins have a higher risk of developing schizophrenia if the other twin has it. Gottesman & Shields 1982 – 58%), Gottesman meta-analysis 1991 – 48%

•          Why is this? – Because identical twins share 100% genes.

•          Fraternal twins:

•          Only have a 17% chance

•          Why – because they share only 50% same genes (Janicak at al 2001).

Adoption studies:

Ø  Kety et al 1988 found 14% of biological relatives of adoptees with schizophrenia were classified as schizophrenic, whereas only 2.7% of their adoptive relatives were found to be.

Ø  Insights from molecular biology

Ø  Miyakawa et al (2003) – created genetically modified ‘schizophrenic mouse’ by switching off a specific gene in the brain responsible for making the chemical calcinerurin.

Ø  Mice showed abnormalities e.g. social withdrawal  mirrored behaviour of schizophrenic patients.

Ø  Miyakawa et al (2003) studied DNA families with schizophrenia, found those who had it were more likely to have defective version of the gene. 

Biochemical Factors

The dopamine hypothesis

Ø …