Theories About What Causes Schizophrenia

Schizophrenia is an illness of the brain that causes certain characteristics, abnormal experiences, and behaviors. There are several types of schizophrenia that involve different clusters of symptoms. It is possible that slightly different disease processes are involved in the different types of schizophrenia. However, most researchers believe that schizophrenia is a single disease which can have different effects depending on which brain regions are most affected.

Researchers do not yet know exactly what causes some people to develop schizophrenia. There is a very strong genetic component to schizophrenia. However, genes alone do not completely explain the illness.

Most scientists believe that genes don’t cause schizophrenia directly, but do make a person vulnerable to developing the disease. Scientists are studying many possible factors that might cause a person with a genetic predisposition to develop schizophrenia.

Genetic Factors

Parted portrait of young man
Westend61 / Getty Images

The evidence of a genetic predisposition to schizophrenia is overwhelming. The frequency of schizophrenia in the general population is less than 1%. However, being related to someone with schizophrenia greatly increases your risk of developing schizophrenia.

For example, if your brother or sister or one parent has the illness your chance of having schizophrenia is around 10%. If your identical twin has the illness, you have a roughly 50% chance of developing schizophrenia. If both of your parents have schizophrenia, you have a 36% likelihood of developing the illness.

We know these family risks are due to genetics rather than family environment because the risks due to family relationships are the same whether a person is raised in the birth family or not. The children of people with schizophrenia are more frequently given up for adoption because their parents are too ill to care for them.

However, genes alone don’t cause schizophrenia. If they did, then identical twins, who share virtually the same genetic code, would have close to 100% likelihood of sharing the illness, rather than 50%.

Developmental Theories

Developmental theories of schizophrenia say that something goes wrong when the brain is developing. Brain development, from the earliest stage of fetal development through the early years of life, is an extremely complicated process. Millions of neurons are formed, migrate to different regions of the forming brain, and specialize to perform different functions.

The “something” that goes wrong might be a viral infection, a hormonal imbalance, an error in genetic encoding, a nutritional stress, or something else. The common element in all developmental theories is that the causal event occurs during the brain’s development.

Symptoms of schizophrenia typically emerge in late adolescence or early adulthood. How could those symptoms be caused by developmental events that took place decades earlier?

Developmental theories suggest an early disruption causes the brain structure to be disorganized. The start of puberty brings a number of neurological events, including the programmed death of many brain cells, and at that time the abnormalities become critical.

To support developmental theories, there are a number of risk factors for schizophrenia related to critical periods in fetal development, such as:

  • Schizophrenia is more common in winter and spring births.
  • Children whose mothers experienced famine during the first trimester are more likely to develop schizophrenia.
  • Pregnancy and birth complications increase the risk of developing schizophrenia.

However, there is not yet enough evidence that the brains of adults with schizophrenia are disorganized in the ways that developmental theories predict. Also, these theories address the when of schizophrenia’s origin, but not the cause itself.

Infectious Disease Theories

Some researchers now believe that schizophrenia is caused by an interaction of an infectious agent, particularly a virus, with a genetic predisposition to the illness. There are a number of features of known viruses that might make this possible:

  • Viruses can attack certain brain regions and leave others intact.
  • Viruses can alter certain processes within a brain cell without killing the cell.
  • Viruses can infect someone and then lay dormant for many years before causing illness.
  • Viruses can cause minor physical abnormalities, birth complications, and altered fingerprint patterns sometimes found in people with schizophrenia.
  • Viruses can affect neurotransmitters.
  • Some antipsychotic agents are also antiviral agents.

People who have recently developed schizophrenia very often have antibodies to two herpes viruses in their blood, HSV (herpes simplex virus) and CMV (cytomegalovirus). Studies have shown that when these herpes viruses infect someone with a particular set of genes, that person is much more likely to develop schizophrenia.

People with schizophrenia also are more likely to show antibodies to toxoplasmosis gondii, a parasite carried by cats that can also infect humans. Being raised around cats slightly raises a person’s likelihood of developing schizophrenia, and the illness is more common in countries and states where many people have cats as pets.

Infectious disease theories of schizophrenia are very exciting and promising. It is too early to know if researching these theories will reveal the cause of schizophrenia.

Neurochemical Theories

Schizophrenia clearly involves irregularities in the chemicals of the brain (neurochemicals) that allow brain cells to communicate with each other. We know this because blocking certain neurotransmitters with drugs (like amphetamine or PCP) can cause schizophrenia-like symptoms. Also, antipsychotic medications that block the action of the neurotransmitter dopamine can effectively reduce symptoms.

In fact, dopamine imbalance was once thought to cause schizophrenia. However, more recent antipsychotics work without blocking dopamine. Current research indicates that the neurotransmitters GABA and glutamate are involved in the cause of schizophrenia.

The difficulty of neurochemical theories is that most brain processes can affect neurotransmitter levels, and neurotransmitters (of which there are at least 100) all interact with one another.

When we say that one particular neurotransmitter or another is causing schizophrenia, we are basing that claim on a single frame of a very long and complicated motion picture, without being able to see the frames that led up to the change we’re observing.

The medical treatment of schizophrenia today relies almost entirely upon regulating levels of neurotransmitters, and so research in this area is vital to developing more effective treatments.

Stress Theories

Psychological stress has physiological effects and is implicated in causing or contributing to psychiatric disorders including post-traumatic stress disorder. Psychological stress also aggravates diseases like high blood pressure and heart disease.

However, psychological stress has not been shown to cause schizophrenia. This statement doesn’t make sense to many people familiar with schizophrenia. How can it be true?

For one thing, schizophrenia does not become more common after psychological traumas like war, natural disaster, or concentration camp imprisonment.

People’s lives are often filled with loss during the time leading up to the first psychotic episode. However, those losses (like relationships, jobs, school, accidents, etc) were often the result of early-onset symptoms including suspicion, memory disturbance, withdrawal, and loss of motivation.

Being raised in a family with schizophrenia greatly increases the stress and likelihood of abuse and trauma, and children from these homes are more likely to develop the illness themselves. However, the genetic contribution, rather than the psychological stress, explains most of the rate of schizophrenia in children from these families.

It is certainly possible to look in the history of many people with schizophrenia and find past trauma, but many more people with schizophrenia came from loving, supporting homes. One of the many tragedies of schizophrenia is the blame that well-meaning people often assign to parents already heartbroken by the illness of their beloved child.

Stress does play a significant role in the control of the illness, however. People with schizophrenia become very sensitive to stress and change. Psychological stress alone can be enough to trigger an episode. Developing and maintaining a routine is one of the most important aspects of avoiding relapse.

Was this page helpful?
Article Sources
  • Schizophrenia: A Detailed Booklet That Describes Symptoms, Causes, and Treatments, With Information on Getting Help and Coping.National Institutes of Mental Health. (2006)

  • Torrey, E.F. (2006) Surviving Schizophrenia: A Manual for Families, Patients and Providers, 5th Edition. New York: HarperCollins Publishers.

  • What Causes Schizophrenia? (2007) National Institutes of Mental Health.