In the study, Finnish researchers determined individuals with epilepsy are more likely to have schizophrenia, and a family history of epilepsy is a risk factor for psychosis. However, investigators still do not know if the converse is true, i.e., whether a family history of psychosis is a risk factor for epilepsy.
Scandinavian countries are often optimal for genetic research because they maintain detailed population-based national registries that allow examination of medical and mental care extending for decades.
Past studies have used a variety of investigative techniques to determine that patients with schizophrenia and patients with epilepsy show some similar structural brain and genetic abnormalities. The commonalities suggest the conditions may share a common origin.
To investigate this possibility, researchers conducted a population-based study of parents and their children born in Helsinki, Finland. Using data available in two Finnish national registers, the study included 9,653 families and 23,404 offspring.
Researchers discovered that within this cohort, individuals with epilepsy had a 5.5-fold increase in the risk of having a psychotic disorder, a 6.3-fold increase in the risk of having bipolar disorder, and an 8.5-fold increase in the risk of having schizophrenia.
They also found that epilepsy and psychosis occurred within family clusters. Individuals with a parental history of epilepsy had a two-fold increase in the risk of developing psychosis, compared to individuals without a parental history of epilepsy.
Individuals with a parental history of psychosis had a 2.7-fold increase in the risk of having a diagnosis of epilepsy, compared to individuals without a parental history of psychosis.
Earlier theories that attempted to explain the relationship between epilepsy and psychosis have focused on the idea that epilepsy has a toxic effect on the brain. But researchers now believe that the findings of prior genetic and neurodevelopmental evidence suggest a much more complex association, which likely includes a shared genetic vulnerability.
“Our evidence that epilepsy and psychotic illness may cluster within some families indicates that these disorders may be more closely linked than previously thought. We hope that this epidemiological evidence may contribute to the ongoing efforts to disentangle the complex pathways that lead to these serious illnesses,” said Mary Clarke, Ph.D., first author of the study.
Dr. John Krystal, Editor of Biological Psychiatry, commented: “We have long known that particular types of epilepsy were associated with psychosis. However, the finding that a parental history of psychosis is associated with an increased risk of epilepsy in the offspring strengthens the mechanistic link between the two conditions.”