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What Causes Schizophrenia?

Medically Reviewed by Jennifer Casarella, MD on June 29, 2020

If you know someone with schizophrenia, you probably want to know why they have it. The truth is, doctors don’t know what causes this mental illness.

Research shows it takes a combination of genetics and your environment to trigger the disease. Knowing what increases the chances can help you put together a better picture of your odds of getting schizophrenia.

Is Schizophrenia Genetic?

Think of your genes as a blueprint for your body. If there’s a change to these instructions, it can sometimes increase your odds for developing diseases like schizophrenia.

Doctors don’t think there’s just one “schizophrenia gene.” Instead, they think it takes many genetic changes, or mutations, to raise your chances of having the mental illness.

You’re more likely to get schizophrenia if someone in your family has it. If it’s a parent, brother, or sister, your chances go up by 10%. If both your parents have it, you have a 40% chance of getting it.

What Are Your Chances of Getting Schizophrenia Genetically?

Your chances are highest -- 50% -- if you have an identical twin with the disorder.

But some people with schizophrenia have no history of it in their family. Scientists think that in these cases, a gene may have changed and made the condition more likely.

Genetic Causes of Schizophrenia

Many genes play a role in your odds of getting schizophrenia. A change to any of them can do it. But usually, it’s several small changes that add up and lead to a higher risk. Doctors aren’t sure how genetic changes lead to schizophrenia. But they’ve found that people who have the disorder may be more likely to have problems in their genes that may interfere with brain development.

The Role of Brain Chemistry and Structure in Schizophrenia

Scientists are looking at possible differences in brain structure and function in people with and people without schizophrenia. In people with schizophrenia, they found that:

  • Spaces in the brain, called ventricles, were larger.
  • Parts of the brain that deal with memory, known as the medial temporal lobes, were smaller.
  • There were fewer connections between brain cells.

People with schizophrenia also tend to have differences in brain chemicals called neurotransmitters. These control communication within the brain.

Studies show that these neurotransmitters are either too active or not active enough in people with schizophrenia.

Doctors also believe the brain loses tissue over time. And imaging tools, like PET scans and MRIs, show that people who have schizophrenia have less “gray matter” -- the part of the brain that contains nerve cells -- over time.

Studies of brain tissue in people with schizophrenia after death even show that their brain structure is often different than it was at birth.

Brain Messenger Chemicals

Two brain chemicals, dopamine and glutamate, carry messages to cells along brain pathways that doctors believe control thinking, perception, and motivation.

Dopamine gets a lot of attention in brain research because it’s been linked to addiction. It also plays a role in other psychiatric and movement disorders, like Parkinson’s disease.

In schizophrenia, dopamine is tied to hallucinations and delusions. That’s because brain areas that "run" on dopamine may become overactive. Antipsychotic drugs stop this.

Glutamate is a chemical involved in the part of the brain that forms memories and helps us learn new things. It also tells parts of the brain what to do.

One study found that people who are at risk for developing schizophrenia may have too much glutamate activity in certain areas of the brain at first. As the disease gets worse, those brain areas may have too little glutamate activity.

Doctors are working to find out how brain circuits that use these chemicals work together or are related to each other.

Brain Imaging

Thanks to technology, doctors can see changes in specific areas of the brain. They can also map the possible loss of brain tissue.

One study showed that brain tissue loss in young people at risk of getting the illness was linked to psychotic symptoms like hallucinations.

Another study compared MRI pictures of the brains of youths about age 14 who had no symptoms of schizophrenia with those who did. It found that the teens who had symptoms lost more brain tissue over a 5-year period than the others. Research shows that adults who have schizophrenia also may lose grey matter.

The Default Mode Network

When we’re just hanging out -- the dishes are done, we’ve finished our homework, or we've completed a tough project at work -- our thoughts are free to roam. This “default mode” allows us time to daydream, reflect, and plan. It helps us process our thoughts and memories. Scientists call this the default mode network. When we’re not focused on a given task, it “lights up."

If you have schizophrenia, your default mode network seems to be in overdrive. You may not be able to pay attention or remember information in this mode, one study shows.

Environmental Triggers

Genetic changes can interact with things in your environment to boost your odds of getting schizophrenia. If you were exposed to certain viral infections before you were born, research suggests that your chances may go up. This could also be true if you didn’t get proper nutrition while your mother was pregnant with you, especially during their first 6 months of pregnancy. These are both theories; they haven’t been proved by scientific studies.

Studies show that taking certain mind-altering drugs called psychoactive or psychotropic drugs, such as methamphetamine or LSD, can make you more likely to get schizophrenia. Some research has shown that marijuana use has a similar risk. The younger you start and the more often you use these drugs, the more likely you are to have symptoms like hallucinations, delusions, inappropriate emotions, and trouble thinking clearly.

Other Risk Factors for Schizophrenia

  • An older father
  • Problems with your immune system, like inflammation or an autoimmune disease
  • Taking mind-altering drugs as a teen
  • Complications during pregnancy or birth such as:
    • Low birth weight
    • Premature labor
    • Exposure to toxins, bacteria, or viruses
    • Lack of oxygen during birth
  • Living in a low-income urban area
WebMD Medical Reference

Sources

SOURCES:

National Alliance on Mental Illness: “Schizophrenia.”

National Institute of Mental Health: “Schizophrenia.”

Medscape: “Schizophrenia.”

Mayo Clinic: “Schizophrenia.”

Genetics Home Reference: “Schizophrenia.”

Mayo Clinic: “Schizophrenia.”

National Health Service (U.K.): “Schizophrenia.”

World Health Organization: “Breaking the Vicious Cycle Between Mental Ill-Health and Poverty.”

Biomolecules & Therapeutics: “Glutamate Receptor Abnormalities in Schizophrenia: Implications for Innovative Treatments.”

Frontiers in Psychiatry: “The role of dopamine in schizophrenia from a neurobiological and evolutionary perspective: old fashioned, but still in vogue.”

Vaibhav A. Diwadkar, PhD, associate professor, psychiatry and behavioral neurosciences; co-director, Brain Imaging Research division, Wayne State University School of Medicine, Detroit.

Columbia University Medical Center: “High Levels of Glutamate in Brain May Kick-Start Schizophrenia.”

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