Schizophrenia and Epilepsy May be Linked, Shared Cause Not Yet Known

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A recent study published in the journal Epilepsia indicates that there is a bidirectional relationship between schizophrenia and epilepsy [1]. This means that people with schizophrenia are at a higher risk of developing epilepsy, and those with epilepsy face a higher risk of developing schizophrenia. The fact that each disorder acts as a risk factor for the other indicates that the two may share some underlying causative factors, be they genetic, environmental, or neurological in origin.

Schizophrenia is a complex disease, characterized most commonly in the popular imagination by delusions and hallucinations but equally likely to impede sufferer’s abilities to think clearly, exhibit appropriate emotional responses to events, and therefore function normally in a social setting. Although there is a strong heritable, and therefore genetic, component in schizophrenia, not all of the genetic sequences that may contribute to schizophrenia have been identified. Currently, most experts think that interactions between genes and the environment, similar to autism, are necessary for schizophrenia to develop.

Epilepsy is a brain disorder in which a person suffers repeated seizures over time. Seizures are the results of abnormal brain activity, the causes of which are often not easily identifiable. Both epilepsy and psychosis — including schizophrenia — are thus symptoms of an underlying neurological dysfunction, such as may be caused by brain damage or even a mutation in a gene regulating neuronal development or the transmission of neurotransmitters.

In this recent work, Taiwanise researchers analyzed the records from National Health Insurance Research Database of Taiwan to identify people diagnosed with either schizophrenia or epilepsy between 1999 and 2008. Since its institution in 1995, the National Health Insurance system in Taiwan has been contracted with over 90% of health care providers in that country. Thus 99% of the 23 million people in Taiwan are registered in the database. The researchers identified 5,195 people with known schizophrenia but no known epilepsy, and 11,527 people with epilepsy and no known schizophrenia. Control groups four times larger than each experimental group were used for comparison. They then followed the patients to see how many schizophrenics developed epilepsy, and vice versa, compared to controls over approximately five years.

They found that people with schizophrenia were almost six times more likely to develop epilepsy than controls, and epileptics were over seven times more likely to develop schizophrenia than controls. Similar findings have been reported in longitudinal studies done in Denmark and Finland, and bidirectional relationships between epilepsy and other psychiatric disorders, primarily mood and depressive disorders, have also been established [2-7]. These findings provide evidence that neurotransmitters such as serotonin, norepinephrine and/or dopamine play a role in regulating the pathophysiologic relationship between mood/depressive disorders and epilepsy.

The authors note that the cause of the association between schizophrenia and epilepsy remains unclear. Additionally, they cite several limitations to the study, including accuracy of medical coding in the claims data, sampling bias (patients with schizophrenia or epilepsy who have not been diagnosed in the comparison group), and other medical conditions that may also associate with schizophrenia or other psychosis.

Lead author I-Ching Chou, M.D., with China Medical University Hospital and Associate Professor with China Medical University in Taichung, Taiwan, said [8]:

Our research results show a strong bidirectional relation between schizophrenia and epilepsy. This relationship may be due to common pathogenesis in these diseases such as genetic susceptibility and environmental factors, but further investigation of the pathological mechanisms are needed.

References

1. Chang et al. Bidirectional relation between schizophrenia and epilepsy: A population-based retrospective cohort study. Epilepsia. 2011 Sep 19. [Epub ahead of print]
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2. Qin et al. Risk for schizophrenia and schizophrenia-like psychosis among patients with epilepsy: population based cohort study. BMJ. 2005 Jul 2;331(7507):23. Epub 2005 Jun 17.
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3. Makikyro et al. Comorbidity of hospital-treated psychiatric and physical disorders with special reference to schizophrenia: a 28 year follow-up of the 1966 northern Finland general population birth cohort. Public Health. 1998 Jul;112(4):221-8.
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6. Kanner AM. (2008b) Mood disorder and epilepsy: a neurobiologic perspective of their relationship. Dialogues Clin Neurosci. 2008;10(1):39-45.
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7. Kanner AM. (2009) Depression and epilepsy: a review of multiple facets of their close relation. Neurol Clin. 2009 Nov;27(4):865-80.
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8. Study finds bidirectional relationship between schizophrenia and epilepsy. EurekAlert! 2011 Sep 19.