Is Schizophrenia Hereditary? - Verywell Health
Researchers think that schizophrenia is genetic, but that's not the only factor involved in determining who gets the condition. Other elements, like a person's environment, also come into play.
Research suggests that schizophrenia's heritability could be between 60% and 80%. However, just because a relative has schizophrenia does not mean you will develop it.
Read on to learn how genetic and environmental factors can interact to make a person more likely to develop schizophrenia.
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How Brain Chemistry Affects Schizophrenia
Researchers think that there are brain differences in people with schizophrenia that lead to the symptoms of the condition. For example, chemicals in the brain called neurotransmitters play a role in many mental health conditions.
In people with schizophrenia, there might be an imbalance in serotonin, dopamine, and glutamate. Since these chemicals are part of how the brain processes sensory information, they could explain some of the key features of schizophrenia, like seeing or hearing things that are not there (hallucinations).
Genetic Causes
The genetics behind schizophrenia are complex. Schizophrenia is believed to be polygenic, meaning there is not just one gene that causes the condition. Instead, researchers have found many different genes and loci (sites within a genome) that can increase the chance of developing schizophrenia. Each of these gene variants increases schizophrenia predisposition by a small amount, and many gene variants in combination increase the risk further.
Schizophrenia affects approximately 1% of people worldwide. There is ongoing research into its causes.
Genome-wide association studies have helped connect specific genetic variants with schizophrenia. A 2014 meta-analysis by the Schizophrenia Working Group is one of the most extensive genetic studies that has been done. It found 108 places in the genes (genetic loci) that are associated with schizophrenia.
Among the 108 loci were genes related to body functions like calcium channel regulation, immunity, dopamine synthesis, and glutamate neuroreceptors.
Over 600 genes are thought to possibly be involved in schizophrenia. More research is needed to understand the roles that each of these genes may play in the risk of schizophrenia.
For example, researchers do not know if certain genetic changes (variants) are linked to certain features of schizophrenia. No specific pattern of passing down genes (Mendelian inheritance) or single-gene cause of schizophrenia has been found yet.
Chance of Developing Schizophrenia
Schizophrenia may run in families. Some estimates have suggested that schizophrenia could be 60% to 80% heritable.
For example, someone who has one parent with schizophrenia has a higher risk of developing it than someone who does not have any parents, siblings, or other close relatives with schizophrenia. If both parents have schizophrenia, a person's risk of developing the condition is 40 times higher than someone in the general population who doesn't have any relatives with schizophrenia.
Twin studies help scientists research and draw conclusions about how genes and heredity affect the risk of disease. Identical twins share 100% of their DNA, and fraternal twins share 50% of their DNA.
A 2018 nationwide twin study in Denmark found that if one identical twin had schizophrenia, the chance that the other twin also did was 33%. For fraternal twins, the chance of both twins having schizophrenia was 7%. The researchers analyzed the data from both samples and estimated that the heritability of schizophrenia was about 79%.
It's important to note that the rate of both identical twins having schizophrenia was relatively low, even though they shared the same DNA. This indicates that there are factors besides genetics that determine whether someone has schizophrenia.
Most of the research on the genetics of schizophrenia has been done on participants of European ancestry. This means the ability to apply the findings to different global populations (generalizability) is probably limited.
That said, a 2019 study on over 57,000 East Asian ancestry participants suggested that genetic risk factors are consistent across populations, but more research is needed.
Environmental Factors That Increase Your Risk
It is not currently possible to use genetics alone to predict who will get schizophrenia.
Many researchers believe that the interactions between genes and the environment likely have a significant role in schizophrenia development. In other words, a person could be more likely to develop schizophrenia due to their genes but may not develop it unless they are exposed to environmental risk factors.
Environmental factors that have been shown to increase schizophrenia risk include:
- Pregnancy and birth complications
- Viral infections
- Advanced parental age
- Trauma
- Social adversities or disadvantages
- Isolation
- Migration
- Urbanicity
- Cannabis or other substance use
Early Warning Signs of Schizophrenia
No matter the reason why a person develops schizophrenia, the sooner the condition is diagnosed, the sooner they can get treatment to help manage the condition.
The early signs and symptoms of schizophrenia can be a bit different depending on how old a person is. Common warning signs of schizophrenia include:
- In young children: Delayed development
- In teens: Depression, isolation, behavioral problems (e.g., stealing) or changes (e.g., bizarre or unusual thoughts or actions), and trouble focusing
- In adults: Restlessness, anxiety, low energy, not taking care of oneself (e.g., personal hygiene), decrease in work performance, suicidal thoughts, and social withdrawal
Summary
Schizophrenia is partly genetic, but other factors like your environment also play a role in your risk of developing the condition. There is still much research to be done on the causes of schizophrenia, including both environmental and genetic factors. The genetics of schizophrenia is an active and ongoing area of research, including trying to use genes to help make better treatments.
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