Genetic predisposition: Substantial evidence suggests
that there is a genetically inherited predisposition to schizophrenia.
For example, there is a concordance rate of about 48 percent for
identical twins. The concordance rate for fraternal twins is
considerably less, about 17 percent. Concordance rate
refers to the percentage of both people in a pair having a
certain trait or disorder. A person who has two parents with
schizophrenia has about a 46 percent chance of developing schizophrenia.
This probability is very high compared to the roughly 1 percent chance
of developing schizophrenia in the general population.
Neurotransmitters: Some researchers have proposed
that schizophrenia is related to an overabundance of the
neurotransmitter dopamine in the brain. Other researchers have suggested
that both serotonin and dopamine may be implicated. The neurotransmitter
glutamate may also play a role in the disorder. Underdevelopment of
glutamate neurons results in the overactivity of dopamine neurons.
Brain structure: Some researchers have suggested that
schizophrenia may involve an inability to filter out irrelevant
information, which leads to being overwhelmed by stimuli. With this idea
in mind, researchers have looked for brain abnormalities in
schizophrenia patients. The brains of people with schizophrenia do
differ structurally from the brains of normal people in several ways.
For example, they are more likely to have enlarged ventricles, or
fluid-filled spaces. They are also more likely to have abnormalities in
the thalamus and reduced hippocampus volume.
Brain injury: Another line of research
suggests that injuries to the brain during sensitive periods of
development can make people susceptible to schizophrenia later on in
life. For example, researchers believe that viral infections or
malnutrition during the prenatal period and complications during the
birthing process can increase the later risk of schizophrenia. Some
researchers have suggested that abnormal brain development during
adolescence may also play a role in
Many researchers believe stress plays a role in bringing on
schizophrenia in people who are already biologically vulnerable to this