What causes schizophrenia

Science in dialogue

How does it come about that a person becomes schizophrenic?

Schizophrenia is a serious mental illness belonging to the group of psychoses. Disturbances in thinking, perception and self-awareness ("I function"), emotional life and drive and movement disorders occur. There may be hallucinations and delusions.

Why in all cultures around one percent of the population - mostly between the ages of puberty and the age of thirty - develops such a psychosis is not clearly understood. An interplay of various factors is discussed, which in each individual case in an individual combination lead to the onset of the disease. An attempt is made to explain this process with the help of various models, including the so-called vulnerability-stress-coping model (vulnerability = vulnerability, coping = stress management behavior). This model assumes that under stress and with an existing predisposition (e.g. genetic) the individual ability to cope with stressful life events reaches its limits and is then expressed in psychotic experience. So there is not one cause that triggers the disease.

We do not yet know all the factors that play a role in the development of schizophrenia. While any person can suffer a psychotic episode under certain circumstances, certain conditions must be met for the development of schizophrenia. Therefore, biomedical research searches intensively for corresponding gene changes, critical moments in the development of the brain and other factors that could be of importance here.

A number of studies have shown that chemical processes in the brain are disrupted in the development of schizophrenia. It is assumed that disturbances in the neurotransmitter system of the brain can be responsible for this. An overfunction of the neurotransmitter dopamine probably plays a major role in this. Dopamine increases the sensitivity of the brain cells to stimuli. What is in principle a sensible reaction in stressful and dangerous situations can lead to psychotic symptoms in people who are prone to schizophrenia. The role of other neurotransmitters such as glutamate and gamma-aminobutyric acid (GABA) is also being explored in more recent studies.

The studies of structural changes and functional disorders of the brain provide evidence that a disorder of brain development can be involved in the development of schizophrenia. Because in some people with schizophrenia there are certain, albeit minor, deviations in the brain structure, e.g. changes in the size of certain brain regions and changes in brain function (e.g. reduced metabolic processes in certain areas).

Brain function examinations indicate that in hallucinations the corresponding brain areas, which are also normally responsible for certain sensory impressions, become spontaneously active. In addition, such examinations and EEG findings show that the function of the frontal lobe, which is responsible for abstract thinking, planned action, attention and similarly complex processes, is changed in people with schizophrenia. This also explains that, on the one hand, the attention of those affected is reduced, but on the other hand, sensory impressions have to be processed by the brain in a more or less "unfiltered" manner, so that the "processing ability" is overloaded and the disturbances in thinking are at least partially explained.

Previous damage to the brain, e.g. due to a lack of oxygen during childbirth or viral infections of the mother during pregnancy, can cause structural damage in the brain, i.e. change the functional interaction of different brain areas, and thus create the biological prerequisites for the development of schizophrenia.

The vulnerability can also be genetic. However, there is no such thing as the schizophrenia gene or a specific genetic change that clearly and necessarily leads to the disease or allows a prediction. In the meantime, however, it has been possible to determine some genes and gene changes that occur more frequently in people with schizophrenia. Some variants of these vulnerability genes that favor the disease can also be found in non-sick people. It is still unclear why the same gene change is linked to an increased risk of schizophrenia in part of the population. It is striking that many of these “risk genes” play a role in the development of the nervous system or in the dopamine metabolism, which strongly supports the neurobiological hypothesis of the development of schizophrenia.

How the genetic predisposition is acquired is still unclear. Because twin studies show that it is obviously not the disease itself that is passed on, but only the genetic predisposition, which can, but does not have to, have an impact in the course of life. In fact, the incidence of identical twins is not 100 percent, but around 40-60 percent.

Follow-up studies have shown that the outbreak of schizophrenia is preceded by stressful life situations in 11-24 percent of cases. In the majority of cases, schizophrenia occurs without any recognizable external trigger factors. Therefore, the meaning and mechanisms of action of psycho-social influences are discussed controversially.

The question was answered by Prof. Dr. Wolfgang Gaebel, spokesman for the Schizophrenia Competence Network.