Psychosis is not a specific illness, but a set of symptoms that results in a disconnect from reality. These symptoms can include hallucinations, like seeing things that are not there, or delusions, which are strong beliefs not shared by others. While family history can increase risk, the cause of psychosis involves a complex interplay between a person’s genetic makeup and their life experiences.
The Role of Genetics in Psychosis
Evidence for a genetic link to psychosis comes from studies of families, twins, and adoptions. For instance, research on individuals with schizophrenia adopted at birth found higher rates of the disorder among their biological relatives, not their adoptive families. This points to a genetic influence. Twin studies show that identical twins, who share all their genes, have a much higher rate of both developing psychosis compared to non-identical twins.
This genetic influence is described by heritability. Heritability estimates for schizophrenia, a common cause of psychosis, can be as high as 80%, meaning a large portion of the risk variation in a population is due to genetic factors. However, the concordance rate for identical twins is around 50%, not 100%, which shows that other influences are at play.
There is no single “psychosis gene.” The genetic risk for psychosis is polygenic, meaning it involves thousands of different genes, each contributing a small amount to an individual’s predisposition. No single gene is powerful enough to cause psychosis on its own. The cumulative effect of these genetic variations creates a higher or lower baseline of risk.
Environmental and Developmental Triggers
While genetics can create a predisposition, they do not act in a vacuum. A range of environmental and developmental factors can also increase the risk of psychosis. These influences can occur at different stages of life and relate to physical development or social experiences.
These risk factors can affect brain development and include:
- Prenatal exposure to infections and complications during birth, such as a lack of oxygen
- Being born during the winter months
- Experiences of trauma or abuse during childhood
- Social isolation or the stress of migration later in life
- Heavy cannabis use, particularly during the teenage years
The Gene-Environment Interaction
The development of psychosis is best understood as a result of the complex interplay between genetics and environment. This concept is explained by the diathesis-stress model. In this model, “diathesis” refers to a pre-existing vulnerability, often genetic, while “stress” refers to environmental events that can trigger the condition.
This interaction means an individual’s genetic makeup can influence how they respond to their environment. A person with a higher genetic predisposition for psychosis may be more sensitive to the effects of stress or substance use. For example, a variation in the AKT1 gene increases the risk of psychosis in individuals who use cannabis, showing how a specific gene and environmental exposure can interact.
The biological mechanism that may underlie this interaction is epigenetics. Epigenetics refers to changes that affect how genes are expressed without changing the DNA sequence itself. Environmental factors like stress, trauma, or substance use can lead to these modifications, which can alter brain development and function in ways that contribute to psychosis risk.
This means life experiences can leave a molecular mark on our genes, influencing their activity. The accumulation of multiple genetic risk factors and exposure to several adverse environmental events can increase the likelihood of psychosis. The timing of these environmental exposures is also important, as different factors have more impact at different stages of brain development.
Understanding Your Personal Risk
For individuals with a family history of psychosis, it is natural to be concerned about personal risk. Having a first-degree relative, such as a parent or sibling, with a disorder like schizophrenia increases the statistical risk. The risk in the general population is about 1%, but it rises to approximately 10% for those with an affected parent.
It is important to put this statistic in perspective. A 10% risk means there is a 90% chance that an individual with a first-degree relative with schizophrenia will not develop the disorder. Most people with a family history of psychosis do not develop it themselves, as the presence of a family history does not determine one’s destiny.
Currently, there is no single genetic test that can definitively predict whether someone will develop psychosis. The condition’s polygenic nature makes such a test impossible with current technology. Polygenic risk scores, which combine the effects of many genetic variants, are used in research but are not yet accurate enough for individual prediction in a clinical setting.
Understanding personal risk is not about getting a simple “yes” or “no” answer from a genetic test. It is about being aware of the combination of genetic and environmental factors that contribute to risk. This knowledge can empower individuals to make informed decisions about their health and lifestyle, but it is not a tool for predicting the future with certainty.