Causes and Risk Factors of Schizophrenia

It is not known exactly what causes schizophrenia, but a number of risk factors have been linked to the disorder. There is a strong genetic component to schizophrenia, and altered brain development and environmental factors may also play a role. 

People with schizophrenia can experience a number of symptoms and not everyone will experience all of them. Symptoms usually start to develop during young adulthood, between late adolescence and early 30s. 

Schizophrenia tends to emerge slightly earlier in men than in women but both develop schizophrenia at approximately equal rates.

Genetics

Genes are considered to be a strong risk factor for schizophrenia. Having certain genetic variations—or alterations in your genes—predisposes you to develop the disease. If you have these variations, they leave you vulnerable to schizophrenia if you encounter other contributing factors. It isn't yet clear exactly how genetic variations are linked to the development of schizophrenia or how they interact with other factors.

Schizophrenia is not just associated with one genetic variation, but rather a combination of variations in multiple genes. Some have little effect on the risk of development of schizophrenia by themselves. Some are highly penetrant, which means they are highly likely to cause the disorder.

Studies have identified over a hundred genetic variations that are associated with schizophrenia. Some of these are not specific to schizophrenia and could lead to increased vulnerability to several psychiatric disorders.

Deletions or duplications of genetic material that increase the risk of schizophrenia have been identified. For example, a small deletion in a part of chromosome 22 has been linked to schizophrenia. Studies have shown that those who have this deletion are 10 to 20 times more likely to have schizophrenia than the general population.

The way in which these changes in genes are linked to schizophrenia is highly complex and is an active area of research. It is thought that new fields, such as genome sequencing, are likely to lead to a greater understanding of this disease.

Family History

Genetic variations can be passed down from parent to child, and schizophrenia is thought to be largely heritable. Being related to someone who has schizophrenia increases your risk of developing it. However, just because someone in a family has schizophrenia doesn’t mean others will develop it as well.

If a child has one parent with schizophrenia, their risk of developing the disorder is estimated to be between 8% and 15%. It is estimated that a child who has both parents with schizophrenia will have about a 40% risk of developing the disorder. 

Physical Development Risk Factors

People who have schizophrenia can have alterations in brain structure and function. Developmental theories of schizophrenia suggest that these differences occur during early brain development, possibly during the first few months of pregnancy and during adolescence.

Imbalances in certain chemicals in the brain called neurotransmitters are also associated with schizophrenia.

Brain images of those with schizophrenia show that in certain areas there are differences in gray matter (areas dense with nerve cell bodies) and white matter (areas dense with insulated nerve fibers). For example, studies of those with schizophrenia have shown a loss of gray matter in an area called the prefrontal cortex, thought to be where we formulate plans.

Early Disruptions

Factors that might impact the development of the brain during the early stages of pregnancy include exposure to environmental and societal factors; such as exposure to infection and nutritional problems.

The way the brain develops is a very complex process and research is looking at ways this development can go awry in schizophrenia.

Neurochemicals

Chemicals of the brain—also known as neurochemicals or neurotransmitters—allow brain cells to communicate with each other. Imbalances in certain chemicals, including dopamine, glutamate, and serotonin, have been linked to schizophrenia.

Antipsychotic medications that influence these chemicals are effective in controlling symptoms such as hallucinations and paranoia. These types of medication do not work for all the symptoms of schizophrenia. A comprehensive treatment plan that involves other forms of treatment is important for managing the condition.

Lifestyle Risk Factors 

Certain factors connected to lifestyle are thought to be associated with schizophrenia. However, it is not thought that these factors cause schizophrenia themselves. Instead these factors can trigger schizophrenia and its symptoms in those already at risk. 

Environmental Factors

Scientists think that interactions between environmental factors and genetic variations play a role in the development of schizophrenia.

Environmental factors that are thought to have a link to schizophrenia include:

• Exposure to viruses: Viral infections can damage certain regions of the brain and can alter certain brain processes. Some viruses can also alter neurotransmitter systems, affecting the way these chemical messengers carry signals between nerve cells in the brain.
• Prenatal complications; Schizophrenia has been associated with exposure to some viruses before birth, including maternal rubella (German measles), influenza, and chickenpox.
• Exposure to toxins; Exposure to harmful toxins, such as alcohol and lead, are thought to be potential risk factors for the development of schizophrenia. This includes exposure during fetal development.

Societal Factors

A number of societal factors have been proposed to have a link to the risk of developing schizophrenia in those predisposed genetically to the disease.

These include:

• Nutritional problems before birth: There is evidence that prenatal exposure to hunger is linked with increased risk. Children who were conceived or in the early stages of fetal development during famine have been shown to be more likely to develop schizophrenia.
• Living in a highly-populated area: Schizophrenia tends to be higher among those who live in urban communities. However, it is not clear whether urban areas are a risk factor themselves or whether those with increased genetic risk are more likely to live in these types of areas.

Stress

Psychological stress from difficult experiences is considered a trigger of numerous psychiatric disorders, including schizophrenia. Studies have shown that experiencing trauma as a child, such as maltreatment or severe bullying, especially if it is recurring, may be linked with an increased risk of psychotic experiences. 

Stress may also act to trigger episodes in those already experiencing symptoms of schizophrenia. For example, going into crowded areas, such as busy streets, may trigger paranoid thoughts for those who experience paranoid delusions.

Life-Changing Events

Severe changes in people’s lives, such as bereavement or the end of a serious relationship, have been identified as a trigger for those experiencing schizophrenia. Other life-changing events, such as the loss of a job, could be connected to the early warning signs of schizophrenia, which include a drop in job performance.

If there are other associated signs of schizophrenia, such as social withdrawal, mistrust of others, or a recent decline in self-care, then you should talk to a mental health professional. 

Drug Abuse

There is a high prevalence of substance abuse among people with schizophrenia. This comorbidity—when someone has two or more conditions at the same time—is linked to worse outcomes. 

It is also known that certain drugs, though they do not directly cause schizophrenia, can increase the risk of developing the disorder.  Certain drugs may trigger symptoms of schizophrenia, and in most cases, continual use increases this risk.

In particular, these drugs are:

• Cannabis: The relationship between cannabis and schizophrenia is the subject of intense research and debate. There is evidence that cannabis use increases the risk of developing psychoses. However, there is also evidence that having schizophrenia is a risk factor for marijuana use.
• Cocaine: Cocaine impacts a number of chemicals in the brain, including dopamine. Continual use of the drug can lead to symptoms such as paranoia, hallucinations, and delusions. 
• LSD: LSD is a psychedelic drug that alters thinking and perception. Users experience hallucinations, in which they experience things that are not there.
• Amphetamines: Intoxication with amphetamines causes symptoms such as hallucinations and paranoia and can increase aggression, especially in perceived threatening situations. Amphetamines are thought to sometimes exacerbate symptoms of schizophrenia. 

Drugs such as cocaine and amphetamines have also been shown to lead to psychosis and can cause a relapse for those recovering from an earlier episode.

A Word From Verywell

Schizophrenia is a complex disorder. Its exact cause is unknown, and it is likely to result from an interaction between a number of factors. While it can be hereditary, it is not definite that someone with schizophrenia will pass it on to their children.

If you or a loved one has schizophrenia, it's important that you know that effective treatments are available. With a comprehensive treatment plan, your symptoms can be managed.