Biological Explanations for Schizophrenia
BIOLOGICAL EXPLANATIONS OF SCHIZOPHRENIA
There is a strong correlation between a family member having schizophrenia and the chances of a
close relative going on to also develop the disorder.
It is generally believed that the closer you are to the diagnosed individual, the more chance you have
of developing schizophrenia, suggesting genetic influences.
Types of research done in genetic research
● Twin studies
● Adoption studies
● Family studies
GENETICS - TWIN STUDIES
Gottesman (1991) reviewed 40 twin studies and found:
● 48% concordance for MZ twins
● 17% concordance for DZ twins
Shields (1962) found that concordance rates for MZ twins brought up apart are similar to those
brought up together.
TWIN STUDIES CRITICISMS
Loehlin and Nichols (1976) - The higher the concordance rates in MZ twins may be due to the fact
that MZ twins tend to be treated more similarly than DZ twins and so nurture may explain the
concordance rates rather than nature.
Shields (1962) can be criticised because in the studies of twins reared apart - it is unlikely that the
twins spent all of their childhood apart. Some would have been raised by close relatives and may
have gone to the same school - and so would have shared a very similar environment.
The fact that the concordance rates are not 100% means that schizophrenia cannot be a wholly
genetic disorder.
GENETICS - ADOPTION STUDIES
Tienari’s results from their adoption study.
Adopted Children Group Biological mother / biological % of children developing
family schizophrenia
1 Schizophrenic 10%
2 No family history of 1%
schizophrenia
METHODOLOGICAL WEAKNESSES OF CONCORDANCE RATES
Family, twin and adoption studies must be considered cautiously because they are retrospective and
may be biased by knowledge that another family member has been diagnosed.
SAMPLE BIAS
The sample size of twin, family and adoption studies tends to be small and so population validity may
be low. This casts doubt on the generalisability of the findings. The gene mapping study was
conducted on a restricted number of families and has failed to be replicated; which shows the
problems of sample bias.
GENETICS - FAMILY STUDIES
BIOLOGICAL EXPLANATIONS OF SCHIZOPHRENIA
There is a strong correlation between a family member having schizophrenia and the chances of a
close relative going on to also develop the disorder.
It is generally believed that the closer you are to the diagnosed individual, the more chance you have
of developing schizophrenia, suggesting genetic influences.
Types of research done in genetic research
● Twin studies
● Adoption studies
● Family studies
GENETICS - TWIN STUDIES
Gottesman (1991) reviewed 40 twin studies and found:
● 48% concordance for MZ twins
● 17% concordance for DZ twins
Shields (1962) found that concordance rates for MZ twins brought up apart are similar to those
brought up together.
TWIN STUDIES CRITICISMS
Loehlin and Nichols (1976) - The higher the concordance rates in MZ twins may be due to the fact
that MZ twins tend to be treated more similarly than DZ twins and so nurture may explain the
concordance rates rather than nature.
Shields (1962) can be criticised because in the studies of twins reared apart - it is unlikely that the
twins spent all of their childhood apart. Some would have been raised by close relatives and may
have gone to the same school - and so would have shared a very similar environment.
The fact that the concordance rates are not 100% means that schizophrenia cannot be a wholly
genetic disorder.
GENETICS - ADOPTION STUDIES
Tienari’s results from their adoption study.
Adopted Children Group Biological mother / biological % of children developing
family schizophrenia
1 Schizophrenic 10%
2 No family history of 1%
schizophrenia
METHODOLOGICAL WEAKNESSES OF CONCORDANCE RATES
Family, twin and adoption studies must be considered cautiously because they are retrospective and
may be biased by knowledge that another family member has been diagnosed.
SAMPLE BIAS
The sample size of twin, family and adoption studies tends to be small and so population validity may
be low. This casts doubt on the generalisability of the findings. The gene mapping study was
conducted on a restricted number of families and has failed to be replicated; which shows the
problems of sample bias.
GENETICS - FAMILY STUDIES
