Lots of things run in families, from heirlooms to embarrassing stories to a whole bunch of chronic health conditions. But is schizophrenia one of them? Will you get it if a blood relative has it?

Not necessarily.

In the U.S., most people’s estimated risk of schizophrenia is around 0.33 to 0.75 percent. If you have a “full” sibling with schizophrenia, you’re 10 times more likely to develop it. If both parents have schizophrenia, the chances their child will also have it is about 45 percent.

But according to research, about 85 percent of people with schizophrenia don’t have a family member with it. So why do some people get schizophrenia when others don’t?

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Like a passive-aggressive FB relationship status, “it’s complicated.” No one really knows what causes schizophrenia.

Schizophrenia has its roots in genetics, but research peeps suggest a combo of factors. Neuro pros suggest that emotional trauma, stuff that happens to the developing brain, and lifestyle factors might all play a role in how schizophrenia develops.

Although the DNA lottery definitely affects schizophrenia risk, genes are not solo artists. The world outside can affect what genes do. This is called epigenetics. Which is why not everything is exactly the same for many identical twins, for example.

If your identical twin has schizophrenia, your risk of having it is around 50 percent. That leaves a whole half of identical twins who don’t develop schizophrenia when their same-time sibling has it.

And it’s rarely one gene to rule them all. There are 16 different genes responsible for eye color, for example. So it’s no wonder that something as complex as a brain disorder can have a head-scratching number of different causes.

If your biological parent or “full” sibling has schizophrenia, the likelihood of you also getting schizophrenia is higher than for other folks.

If your parents have it

  • One of your biological parents has schizophrenia: Your risk of also having it is 6 in 100.
  • Both of your biological parents have schizophrenia: Your risk of also having it is 45 in 100.

If your siblings have it

  • If your full sibling (same biological parents) has schizophrenia: a risk of 9 in 100
  • If your identical twin has schizophrenia: a risk of 40 to 50 in 100
  • If your non-identical twin has schizophrenia: a risk of 17 in 100

These figures aren’t fixed. They vary across the world, and science peeps have called for more studies looking at schizophrenia risk in people of African and Latinx ancestry.

What else stirs the pot of schizophrenia?

Brain chemistry

The brain needs a delicate balance of chemicals to do its thing. If one of these is off, like a bad teammate, everybody’s gonna have a bad day. Science bods point to dopamine, glutamate, and serotonin as the MVPs.

These chemicals are part of your brain’s comms team. If they’re passing too much info, too little info, or just wrong info, it distorts how we experience the world. It’s like that one person in the group chat who just has to share every meme they find.

This info processing problem may be why people with schizophrenia may have hallucinations or delusions. Brain imaging studies also suggest differences in the way the brains of some people with schizophrenia use energy.

Brain development

The brain grows from before we’re born until after our teen years. Some of this “growth” involves getting rid of brain connections that aren’t important.

It’s like a bunch of transport networks. You don’t need every possible variation of metro / bus / freeway / tram, but it’s good to have options. Sometimes, a brain’s “city planner” mode can miss routes or add too many.

Brain boffs have found slight differences in the brain architecture of some peeps with schizophrenia. Not everybody with schizophrenia has these differences though, and you can have a different brain build without having a diagnosable disorder.

The environment

Environmental causes help explain cases of schizophrenia where genetics don’t have a to role to play. Our interactions with the world affect our brain chemistry and structure. For example, the brain’s reward system, dopamine, has been linked to schizophrenia.

Social aspects like migrant status and an urban environment can affect the likelihood of having schizophrenia. There are even studies suggesting some infectious nasties like herpes, influenza, rubella, and toxoplasmosis can increase a person’s risk.

Immune system issues

An article in Nature journal describes the idea that the immune system and its effect on the brain could contribute to schizophrenia. Lots of researchers have looked at this, but we’ll level with ya: The immune system, like the brain, is heckin’ complex.

Sometimes, the immune system glitches and attacks the wrong things. This could be pollen (hey, hay fever) or your own body. It might do this and create an auto-inflammatory disorder like Crohn’s, or work in a subtler way and contribute to other disorders, like schizophrenia.

Science is working on an “immunome” (like a genome… or a garden gnome), which in an ideal world will help us decode the immune system and get closer to understanding its effects on your thinkbox. If nothing else, it’ll bump up your Scrabble score further down the line.

Pregnancy and birth complications

The womb is the whole world for a developing fetus, so what goes down in here affects a baby’s risk of acquiring schizophrenia.

Fetal malnutrition, stress, and cytomegalovirus (CMV) have all been linked to a higher risk of schizophrenia developing later in life.

People who develop schizophrenia are more likely to have had issues before and during their birth like:

  • a low birth weight
  • premature labor
  • a lack of oxygen during birth

So your risk might be higher based on a number of factors. What sets the wheels of schizophrenia in motion?

Emotional distress

Serious emotional distress might trigger schizophrenia in someone who already has a high risk for it.

Stressful life events like losing a loved one, a significant negative life change, or experiencing abuse can add to a person’s risk of developing schizophrenia.

Distress doesn’t cause schizophrenia but has been linked with psychosis and can make other symptoms worse. For example, some people with schizophrenia experience hallucinations related to abuse during childhood.

Factors like social isolation that commonly occur as result of or alongside schizophrenia can make symptoms like paranoid thoughts worse.

But it’s really tricky to unpick cause and effect, especially with events that happen early in life.

Substance abuse

Substance use does not directly cause schizophrenia. However, substance misuse might increase a person’s risk of developing schizophrenia.

Certain substances can trigger psychotic episodes in people, including those without a schizophrenia diagnosis. Also, people with schizophrenia can often be more vulnerable to developing problems with substance misuse.

You can’t prevent schizophrenia if your parents have it. Because schizophrenia has a whole bunch of possible causes, there isn’t one definite way to prevent it.

You can reduce your risk of developing schizophrenia by reducing other risk factors. People with schizophrenia can also reduce the symptoms. They can manage their mental health using meds, therapy, and even texting.

Genetics can play a role in schizophrenia development.

But even though the DNA we get has a hand in whether we might end up with schizophrenia, lots of other factors affect the outcome. After all, there are around 700 genes that determine your height alone! (So don’t blame Mom and Dad).

How that gene combo interacts with the world is also very important. So although you might get the same DNA as your twin, you might not both have schizophrenia.