The causes of schizophrenia, like all mental disorders, are not completely understood or known at this time. Researchers have spent millions of hours (and many hundreds of millions of dollars) studying this condition. The more they learn, the more it becomes evident that the condition is far more complex than anyone realized.
There is no known single cause of schizophrenia. It is likely the result of a complex interplay of dozens of different factors, including biological, specific sets of genes, gut bacteria, neurology, social, psychological, and environmental components.
Yes, schizophrenia — like all mental illness — runs in families. A person who has a family history of schizophrenia (or mental illness in general) is at greater risk for developing this condition (or any mental disorder).
The risk of schizophrenia in the general population is less than 1 percent. According to the National Institute of Mental Health researchers, people who have a close relative with schizophrenia are more likely to develop the disorder than are people who have no relatives with the illness. A child whose parent has schizophrenia has about a 10 percent chance of developing schizophrenia themselves. A monozygotic (identical) twin of a person with schizophrenia has the highest risk — a 40 to 65 percent chance of developing the illness. People who have second-degree relatives (aunts, uncles, grandparents, or cousins) with the disease also develop schizophrenia more often than the general population.
Researchers continue to examine the genetic factors and gene sets connected to schizophrenia. A person’s genes are inherited from their parents, and theirs from their parents before them. It appears that areas of specific genes, gene mutations, and certain sets of genes are implicated in schizophrenia. But it is important to note that no single gene or gene mutation is implicated in schizophrenia. Recent research has found that these genetic differences involve hundreds of different genes and gene mutations, and probably disrupt brain development.
In addition, factors such as prenatal difficulties like intrauterine starvation or viral infections, perinatal complications, and various nonspecific stressors, seem to influence the development of schizophrenia. However, it is not yet understood how the genetic predisposition is transmitted. Nor can it be accurately predicted whether a given person will or will not develop the disorder.
Other recent studies suggest that schizophrenia may result in part when a certain gene that is responsible for making important brain chemicals — primarily dopamine — malfunctions. This problem may affect the part of the brain involved in developing higher functioning skills. Research into this gene and related genes is ongoing, so it is not yet possible to use the genetic information to predict who will develop the disease (Janicak et al., 20140.
In addition, it probably takes more than genes to cause the disorder. Scientists think interactions between genes and the environment are necessary for schizophrenia to develop. Many environmental factors may be involved, such as exposure to viruses or malnutrition before birth, problems during birth, and other not yet known psychosocial factors.
Basic knowledge about brain chemistry and its link to schizophrenia is expanding rapidly. Neurotransmitters, substances that allow communication between nerve cells, have long been thought to be involved in the development of schizophrenia. It is likely, although not yet certain, that the disorder is associated with some imbalance of the complex, interrelated chemical systems of the brain, perhaps involving the neurotransmitters dopamine and glutamate.
Due to the advances in neuroimaging and our understanding of schizophrenia, researchers can study the functioning brain as it carries out activities (this is called functional magnetic resonance imaging). There have been many studies of people with schizophrenia that have found abnormalities in brain structure. In some small but potentially important ways, the brains of people with schizophrenia look different than those of healthy people. For example, fluid-filled cavities at the center of the brain, called ventricles, are larger in some people with schizophrenia. The brains of people with the illness also tend to have less gray matter, and some areas of the brain may have less or more activity.
These types of brain abnormalities are usually subtle and may not be present in everyone with schizophrenia. Nor do these specific abnormalities occur only in individuals with this condition. Microscopic studies of brain tissue after death have also shown small changes in distribution or number of brain cells in people with schizophrenia. It appears that many (but probably not all) of these changes are present before an individual becomes ill, and schizophrenia may be, in part, a disorder in brain development.
Neurobiologists have also found evidence that this condition could be a developmental disorder as a result of faulty connections between the brain’s neurons during fetal development. These faulty connections may lie dormant until puberty. During puberty, the brain is undergoing many changes in its development. It’s thought these changes could trigger the emergence of the faulty neuron connections. There may be ways to identify prenatal factors that may help us eventually inoculate or otherwise prevent these connections from occurring.
While research continues in better understanding the causes of this condition, it’s important to understand that schizophrenia can still be successfully treated.
Learn more: Schizophrenia & Genetics: Research Update