Causes and Risk Factors of Schizophrenia

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It is not known exactly what causes schizophrenia but a number of factors have been linked to the risk of its development. There is a strong genetic component to this disease but genes are not the only reason a person may develop it. Neurological differences and environmental factors may also play a role. 

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People with schizophrenia can experience a number of symptoms and not everyone will experience the same ones. Symptoms usually start to develop during young adulthood, between late adolescence, around 16 years old, and early 30s. 

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

Common Causes

Multiple factors are being studied that contribute to the risk of developing schizophrenia, including genetics, brain and body risk factors, and environmental and societal factors. 

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.

Schizophrenia is not just associated with one genetic variation but rather a combination of variations in multiple genes. If you have these variations, they leave you vulnerable to schizophrenia if you encounter the right set of 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.

Brain and Body Risk Factors

Those with schizophrenia experience differences in the way the brain is structured and how it functions. Developmental theories of schizophrenia suggest that these differences occur in early brain development, including in the first few months of pregnancy and during adolescence.

Imbalances in certain chemicals in the brain are also associated with schizophrenia. Regulating the levels of these chemicals is the main way schizophrenia is medically treated.

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 the schizophrenia include:

  • Exposure to viruses: Viruses can attack certain regions of the brain and can alter certain brain processes. Some viruses can also alter neurotransmitters—chemical messengers that 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 with 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 that 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.

Genetics

Genetic predisposition to schizophrenia comes from a combination of multiple genetic variations.

Some are common, which by themselves have little effect on the risk of development of schizophrenia. Some are rare and highly penetrant, which means they are traits that are likely to be presented physically in the person that has that particular variant.

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

Deletions or duplications of genetic material have also been identified that increase the risk of schizophrenia. 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.

You can have the genes that have been shown to be associated with schizophrenia but never develop the condition. It is also not yet possible to use genetic information to predict who will develop schizophrenia.

Family History

Genetic variations can be passed down from parent to child and schizophrenia is thought to be largely heritable. This means being related to someone with schizophrenia increases the risk of your developing it.

It is estimated that a child whose both parents have schizophrenia will have a 40% risk of developing the disorder. If a child has one parent with schizophrenia this risk is estimated to be between 8% and 15%. This means that just because someone in a family has schizophrenia it doesn’t mean others will as well.

Brain and Body Risk Factors

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 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 hold information and formulate plans.

Early Disruptions

Developmental theories suggest that something happens in the brain's development to cause these differences. Development during the early stages of pregnancy and changes to the brain that occur during adolescence have both been identified as times when the differences might occur.

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 these theories are not looking at the cause of schizophrenia itself but rather when these differences to the brain's structure and function happen.

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 medication works by blocking these chemicals and are known to be effective in 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 a successful recovery.

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. 

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 bullying, especially if it is recurring, may be linked with increased risk of psychotic experiences. 

Stress may also act to trigger severe 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 worrying drop in job performance.

This by itself is not concerning but if there are other signs, such as social withdrawal, mistrust of others and 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 poor outcomes in terms of recovery. 

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 itself is a risk factor for marijuana use.
  • Cocaine: Cocaine impacts a number of chemicals in the brain. In particular, it acts to increase and release 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 when responding to threatening situations. Amphetamines are thought to 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 disease. It can be confusing to understand why it happens as its exact cause is unknown and it is likely to be as a result of an interaction between a number of factors. While it is hereditable, it is not definite that someone with schizophrenia will pass it on to their children.

If you or a loved one has schizophrenia then know that effective treatments are available and there exist a variety of different options. With a comprehensive treatment plan, symptoms can be managed.

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