Schizophrenia: Genetics


The suggestion here is that schizophrenia runs in families. By studying family members and the occurrence of schizophrenia, this can be investigated. Gottesman (1991) found that if a person has schizophrenia, the following concordance rates apply:

  • Identical twins: 48%
  • Non-identical twins: 17%
  • Children: 13%
  • Siblings: 9%
  • Parents: 6%
  • Half-siblings: 6%
  • Grandchildren: 5%
  • Nephews/nieces: 4%
  • Uncles/aunts: 2%
  • First cousins: 2%
  • General population: 1%

This means that if a person has the disorder, there is a 48% chance that their identical twin (if they have one) will also have it. The more genes the person shares with the sufferer, the more likely they are to have the disorder, suggesting there may be a genetic basis for schizophrenia. Schizophrenia is thought to be polygenic, with lots of different genes contributing to an increased risk of developing it. It is also aetiologically heterogeneous, meaning different combinations of genes are implicated in the disorder. Ripke et al (2014) found 108 genetic variations associated with schizophrenia.

Schizophrenia: Genetics, figure 1


  • Tienari et al (2004) found that adopted children of biological mothers with schizophrenia were more likely to develop the disorder themselves than adopted children of mothers without schizophrenia, supporting the genetic link
  • It may be that the increased concordance rates in the Gottesman study were due to the increased chance of sharing the same environment as the person with schizophrenia. For example, identical twins share the same environment (and may be treated similarly), whereas first cousins would not. This means that it can’t be concluded that genetics has caused schizophrenia.
  • As identical twins share 100% of their genes, it would be expected that the concordance rate for schizophrenia would be 100% if it was purely genetic. As it is only around 50%, this suggests other influences are playing a part.

The Dopamine Hypothesis

Dopamine is a neurotransmitter, the levels of which seem to be associated with schizophrenia symptoms.

Hyperdopaminergia: This refers to higher than usual levels of dopamine in the subcortex (central areas of the brain). This is linked with positive symptoms such as hallucinations. There may be a higher number of dopamine receptors, causing over-activity of dopamine, causing sensory hallucinations.

Hypodopamineriga: This refers to lower than usual levels of dopamine in the cortex (outer part of the brain), where less dopamine is being transmitted across synapses. This is linked with negative symptoms, as there is a reducing in normal functioning.


  • Curran et al (2004) found that dopamine agonists (drugs which increase activity) produce schizophrenia-type symptoms in patients, supporting the hypodopaminergia aspect of the dopamine hypothesis.
  • Tauscher et al (2014) found that giving patients antipsychotic drugs which lower dopamine levels (antagonists- reducing activity) reduced the occurrence of positive symptoms, supporting the hyperdopaminergia aspect of the hypothesis.
  • There is likely to be other neurotransmitters involved in schizophrenia, some identified the Ripke’s genetic study, weakening the dopamine hypothesis as an incomplete explanation of schizophrenia.

Neural Correlates

There is growing evidence that schizophrenia is down to abnormalities in the brain. The structure or functioning of the brain is correlated (associated) with positive and negative symptoms.

Schizophrenia: Genetics, figure 1

Negative symptoms: The ventral striatum is involved with reward anticipation. Schizophrenia patients have been found to have less activity in this region- the lower the activity, the more severe the negative symptoms. This could explain avolition (loss of motivation).

Positive symptoms: Allen et al (2007) scanned the brains of patients experiencing hallucinations whilst they completed an auditory processing task. Lower activation levels were found in the superior temporal gyrus and anterior cingulate gyrus, and they made more errors, compared to a control group. Auditory hallucinations are therefore correlated with reduced activity in these areas.


  • The fact that there is a correlation between brain areas and symptoms does not mean that the neural mechanism has caused the symptoms. It may be that the difference in activity levels could be a consequence of the disorder.
  • Neural explanations have been criticised as reductionist, explaining schizophrenia at quite a simplistic level of explanation. The role of upbringing, learning and emotions is not considered, weakening this as a full explanation.

Family Dysfunction

Family dysfunction refers to the workings of dysfunctional families, and the effects of being brought up in one, contributing to schizophrenia.

Schizophrenogenic mother: Proposed by Fromm-Reichmann (1948), who noted that many of her patients with schizophrenia described a particular type of parent, which she termed ‘schizophrenogenic’. These characteristics are:

  • Cold
  • Uncaring
  • Rejecting
  • Unemotional
  • Controlling
  • Suspicious
  • Creates tension and secrecy

This leads to an atmosphere of distrust and the development of paranoid thoughts which become delusions.

Double-bind theory: Bateson et al (1956) suggest that children who frequently receive contradictory messages from their parents are more likely to develop schizophrenia, because this prevents them from developing an internally coherent construction of reality. For example, if a mother tells her son that she loves him, yet at the same time turns her head away in disgust, the child receives two conflicting messages about their relationship on different communicative levels, one of affection on the verbal level and one of animosity on the non-verbal level (one invalidates the other). The child is unable to decide what is ‘good’ behaviour, and is often punished for ‘wrong’ behaviour. This may lead to the child developing a false concept of reality and an inability to communicate effectively, explaining delusions, hallucinations and disorganised speech Bateson did not suggest that double bind communication caused schizophrenia on its own, but it may be a contributing factor.

Expressed emotion: Another family variable associated with schizophrenia is a negative emotional climate, or more specifically, a high degree of ‘expressed emotions’. Expressed emotion is a family communication style that involves criticism, hostility and emotional over-involvement. High levels of this may influence relapse rates, or the onset of schizophrenia in a vulnerable person. The negative emotional climate in these families arouses the patient and leads to stress beyond his or her already impaired coping mechanisms, triggering a schizophrenic episode.

Schizophrenia: Genetics, figure 1


  • Berry et al (2008) found that 69% of women and 59% of men with schizophrenia in their sample had a history of physical and/or sexual abuse in childhood, supporting that family dysfunction is a risk factor in developing schizophrenia.
  • Research in this area is often retrospective, meaning that patients with the disorder are asked to think back to their childhood and explain what it was like. Such recollections are unlikely to be completely trustworthy, therefore reducing the validity of the evidence and therefore the explanation.
  • There is hardly any evidence supporting the particular explanations of the schizophrenogenic mother or the double-bind theory, and it leads to the blame for the disorder being put on the parents, which many psychiatrists today find unacceptable.

Cognitive Explanations

Schizophrenia: Genetics, figure 1

Cognitive explanations focus on the role of dysfunctional thought processing contributing to schizophrenia symptoms. These faulty thoughts may be due to abnormal biological functioning (as seen in the examples of neural correlates). Frith et al (1992) identified two main kinds of dysfunctional/faulty thought processing:

  • Metarepresentation: the ability to reflect on, and have insight into, our own intentions and the actions of others. Dysfunction in this area could mean that the individual is unable to recognise that their own thoughts are actually theirs, so leading to hallucinations (voices) and delusions (thought insertion).
  • Central control: the ability to suppress automatic responses/triggers in response to stimuli. Dysfunction in this area could mean that the individual cannot suppress automatic thoughts that get triggered by other thoughts. This could explain disorganised speech and disordered thinking.


  • Stirling et al (2006) found that participants with schizophrenia took much longer than participants without schizophrenia to complete a Stroop test (a test where the colour a word is written in must be named, even though the word is a different colour). This supports that schizophrenia sufferers have problems with central control (ability to supress automatic thoughts).
  • Abnormal cognitions may be one of the effects/consequences of schizophrenia, rather that actually causing the development of it in the first place. This weakens cognitive explanations, as they are unlikely to be a complete explanation of the disorder.