Biological Explanations for Schizophrenia

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Biological Explanations: Genetics & Family Studies

Biological explanations have received the most research support to date (Comer, 2013). In particular, the role of genetics and neural correlates such as dopamine.

‘Diathesis-stress’ relationship

The importance of biological explanations for schizophrenia does not deny the importance of psychological factors that play in the onset of this disorder.
Current thinking is that a ‘diathesis-stress’ relationship may be at work, with a biological predisposition for schizophrenia only developing into the disorder if other significant psychological stressors are present in a person’s life.

Genetic factors

One possible explanation of schizophrenia may be heredity i.e. genetics.
Schizophrenia tends to run in families, but only among individuals who are genetically related rather than related by marriage. The risk of developing the disorder among individuals who have family members with schizophrenia is higher than it is for those who do not.

Combination of genes

No one gene is thought to be responsible for this disorder – it’s more likely that different combinations of genes make individuals more vulnerable to schizophrenia. Having these genes does not necessarily mean an individual will develop schizophrenia.

Family studies

Family studies (Gottesman and Shields, 1991) find individuals who have schizophrenia and determine whether their biological relatives are similarly affected more often than non-biological relatives.
Family studies have established that schizophrenia is more common among biological relatives of a person with schizophrenia, and that the closer the degree of genetic relatedness, the greater the risk.

Gottesman and Shield

For example, in Gottesman and Shield’s study, children with two schizophrenic parents had a concordance rate of 46%, children with one schizophrenic parent a rate of 13% and siblings (where a brother or sister had schizophrenia) a concordance rate of 9%.

Biological Explanations: Twin & Adoption Studies

Biological explanations have received the most research support to date (Comer, 2013), in particular the role of genetics and neural correlates such as dopamine.

Twin studies

If monozygotic (MZ – genetically identical) twins are more concordant than dizygotic (DZ – who share only 50% of their genes), then this suggests that the greater similarity is due to genetic factors.
Joseph (2004) calculated that the pooled data for all schizophrenia twin studies carried out prior to 2001 showed a concordance rate for MZ twins of 40.4% and 7.4% for DZ twins.

Lower concordance rate for MZ twins

More recently, methodologically sound studies (e.g. those using ‘blind’ diagnoses where the researchers assessing do not know whether the twins are MZ or DZ) have tended to report a lower concordance rate for MZ twins than earlier studies.
Despite this, however, such studies still support the genetic position because they show a concordance rate for MZ twins that is many times higher than for DZ twins.

Adoption studies

Because of the difficulties of disentangling genetic and environmental influences for individuals who share genes and environment, studies of genetically related individuals who have been reared apart are used.

Tienari et al (2000)

Probably the most methodologically sound study of this type was carried out by Tienari et al (2000) in Finland.
Of the 164 adoptees whose biological mothers had been diagnosed with schizophrenia, 11 (6.7%) also received a diagnosis of schizophrenia, compared to just 4 (2%) of the 197 controls adoptees (those born to non-schizophrenic mothers). The investigators concluded that these findings showed that the genetic liability to schizophrenia had been ‘decisively confirmed.’

Evaluation of biological explanations

Strengths
- There is overwhelming evidence to suggest that genetic factors make some people much more vulnerable to developing the disorder than others.
Limitations
- Could be explained by common family backgrounds and experiences rather than genetics (nature/nurture).
- MZ twins treated more similarly than DZ twins.
- Adoptees may be selectively placed with families.