Research is being done on the causes as we speak, but so far not one single factor has been identified in causing schizophrenia. In individual case studies, multiple factors contribute to the severity of schizophrenia and its form from person to person
A theory regarding the development of schizophrenia is that the levels of the neurotransmitter dopamine are high, and the dopamine systems and neural networks tend to be hyperactive (dopamine hypothesis). Some studies that have examined the genetic sequences of patients with schizophrenia showed a common mutation present in their genomes: the deletion of the COMT gene, which codes for the creation of a catabolic enzyme in charge of breaking down dopamine. Though that mutation is common, not all schizophrenia patients have it. What's more, there is conflicting data that COMT may not have anything to do with schizophrenia.
Dopamine pathway malfunctions and their relations to schizophrenic symptoms.
Conflicting data points to the role of epigenetics in the onset of schizophrenia, how gene expression is modified rather than any change in the genome itself. Epigenetic factors include some kind of compromise during child birth (lack of oxygen, low weight) and prenatal environment (smoking, drinking, or being ill during pregnancy). Since it is a fairly new idea, there is not enough research and information to make definitive conclusions about the role of epigenetics in schizophrenia.
Some scientists believe that brain chemistry and structure makes certain individuals more predisposed to schizophrenia. For example, the brain undergoes changes during puberty that may bring out psychotic symptoms in some whose brain allows it to. Imbalances in the interrelated chemical reactions of the brain may also play a role. People with schizophrenia have been found to have relatively smaller brains with less grey matter and enlarged ventricles. Compromises to the occipital lobe have been linked to not full-blown visual hallucinations, rather trouble of schizophrenic individuals to interpret complex visual stimuli or recognize movement. In the temporal lobe, the auditory center activates during auditory hallucinations, suggesting trouble for the brain in interpreting auditory stimuli.
The top portion shows brain activity in healthy persons. The bottom portion shows decreased activity in the prefrontal cortex of a patient with schizophrenia, an area vital to judgment and decision-making.
Epidemiological studies have shown that it is a heritable disease, confirmed by an agreement rate of 60-70% of monozygotic (identical) twin studies. If an individual's parents have schizophrenia, their chances of developing it are dramatically higher than those whose parents do not. The more schizophrenic relatives one has, the more likely that individual will develop schizophrenia.
The brain scan reveals enlarged ventricles and less grey matter in the schizophrenic twin
It is a long-term illness as well as a spectrum. Signs can be present throughout childhood and early childhood and depending on their family history, but it ultimately is difficult to discern. If the mother has severe schizophrenia, chances are much higher for her offspring to develop schizophrenia as well. First detection is difficult as most patients have not had a previous episode or history of psychosis before the first episode. The incidence of episodes often decreases over a life time, and a stressful environment or not taking medications increases the psychotic episodes' incidence and severity. The symptoms and what forms they take as well as their debilitating effects vary widely among schizophrenic individuals, but they fall into several categories.