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Biological explanations of
Schizophrenia (2)
GENETICS
What does
this mean?
In pairs discuss and
write up a conclusion
based on this data
Gottesman, (1991)
Role of genetics

The fact that schizophrenia tends to run in families led to the inference that it has a genetic
basis.

According to the genetic hypothesis, the more closely related the family member to the
person with schizophrenia the greater their chance of developing the disorder.

Concordance rates, which show the percentage of family members developing
schizophrenia, are investigated as research evidence. The comparison is the 1% probability
of schizophrenia in the general population.

The greater the degree of genetic relatedness the higher the risk of developing the disorder,
which suggests that there is a genetic link.
Research evidence: Twin Studies

In twin studies the researchers want to establish the probability that the
other twin is also has schizophrenia

Gottesman’s (1991) analysis of twin studies revealed 48% concordance for
monozygotic (MZ; identical) twins and only 17% for dizygotic (DZ; fraternal)
twins.

MZ twins share 100% DNA

DZ twins share 50% DNA (like other siblings)
Stop: Let’s Read Gottesman and Shield’s
(1966) Study
Twin study
What is the diathesis stress model?
Make notes on his model
What does this suggest about the genetic explanation?
Family studies

Kendler (1985) has shown that first degree relatives of those with
schizophrenia are 18 times more at risk than the general population.

Gottesman & Bertelsen (1989). If your parent is an identical twin who has
schizophrenia then you have a 17% chance of getting it too. However, if
your parent does not have the disorder, but their identical twin does, then
your chance of getting the disorder is still 17%.

What does this tell us?

Genetic predisposition?
Adoption studies
Finnish Adoption Study (Tienari,1969)

identified adopted offspring of biological mothers who had been
diagnosed with schizophrenia (112 index cases), plus a matched control
group of 135 adopted offspring of mothers who had not been diagnosed
with any mental disorder.

Adoptees ranged from 5-7 years at the start of the study and all had
begun separation from their mother before the age of 4.

The study reported that 7% of the index adoptees developed
schizophrenia, compared to 1.5% of the controls

-this suggests genetics play a role in the development of schizophrenia.
Molecular Genetics
McGuffin and Stuart (1980’s) HLA gene, a gene important in the body’s immune system was
associated with Schizophrenia but no further research supported this.
Hong (2001) TPH gene that is involved in the production of enzymes found variations in this
gene in patients that had Schizophrenia.
Tamminga and Schulz (1991)Research has failed to isolate a single recessive or dominant gene
that that seems to cause the illness.
However
Kelly and Murray (2000) suggest that each of the genes identified by molecular genetics is not
innocent in itself, however people who inherit a number of them are at high risk of developing
Schizophrenia.
Stop: Read Page 39 and 40, regarding
Tiwari (2010)
What do the findings suggest about the genetic explanation?
Common Variants pg.40
There are common variants that interact and alleles involved will be shared
by unrelated individuals.
Alleles: an alternative form of the gene, a gene can have more than one
variant.
This is possibly why twin studies show some evidence for genetic underpinning
in Schizophrenia but do not uncover gene responsibility.
SODAR
S: Supporting Evidence
O: Opposing Evidence
D: Different Theories
A: Application
R: Reductionist