Schizophrenia is one of the many types of mental illnesses that has been discovered in the world.
1) The dopamine hypothesis:
High levels of the neurotransmitter dopamine have been found in people displaying positive symptoms of schizophrenia, that include hallucinations, delusions and disordered thinking (knight's move thinking). However, low levels have been found in people that are suffering from the negative symptoms of the disorder; e.g. catatonic behaviour, anhedonia and avolition etc.
2) Structural abnormalities in the brain:
A few have been found, and enlarged left ventricles in the brain are one of them.