Schizophrenia is generally believed to be caused by a combination of genetics, brain chemistry and environment.
Genes: Scientists have long known that schizophrenia sometimes runs in families. However, there are many people who have schizophrenia who don’t have a family member with the disorder and conversely, many people with one or more family members with the disorder who do not develop it themselves.
In identical twins, if one twin develops schizophrenia, the other twin has a one in two chance of developing it, too. This is true even if they're raised separately.
In non-identical twins, who have different genetic make-ups, when one twin develops schizophrenia, the other only has a one in seven chance of developing the condition.
While this is higher than in the general population, where the chance is about 1 in 100, it suggests genes aren't the only factor influencing the development of schizophrenia.
Scientists believe that many different genes may increase the risk of schizophrenia, but that no single gene causes the disorder by itself. It is not yet possible to use genetic information to predict who will develop schizophrenia.
Problems with certain naturally occurring brain chemicals, including neurotransmitters called dopamine and glutamate, may contribute to schizophrenia. Neuroimaging studies show differences in the brain structure and central nervous system of people with schizophrenia. While researchers aren't certain about the significance of these changes, they indicate that schizophrenia is a brain disease.
Some experts also think problems during brain development before birth may lead to faulty connections. The brain also undergoes major changes during puberty, and these changes could trigger psychotic symptoms in people who are vulnerable due to genetics or brain differences.
Scientists also think that interactions between genes and aspects of the individual’s environment are necessary for schizophrenia to develop. Environmental factors may involve:
- Exposure to viruses
- Malnutrition before birth
- Problems during birth, such as a low birth weight, premature labour, a lack of oxygen (asphyxia) during birth
- Increased immune system activation, such as from inflammation or autoimmune diseases
- Older age of the father
- Taking mind-altering (cannabis, cocaine, LSD or amphetamines) drugs during teen years and young adulthood
The main psychological triggers of schizophrenia are stressful life events, such as:
- losing your job or home
- the end of a relationship
- physical, sexual or emotional abuse
These kinds of experiences, although stressful, don't cause schizophrenia. However, they can trigger its development in someone already vulnerable to it.
- American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (DSM-5®). American Psychiatric Pub.