A new study led by Johns Hopkins Children’s Center investigators points to liver-damaging hepatitis C infection (HCV) as a possible cause for psychiatric diseases such as schizophrenia, bipolar disorder and major depression.

Observational studies of some psychiatric diseases have long tied viral infections with behavioral symptoms in these disorders, but scientists have been unable to find direct evidence of suspected viruses in the brain. Experts say that’s possibly because viruses may not get directly inside the brain, but may target the brain lining instead.

A team led by Sarven Sabunciyan, a neuroscientist at the Children’s Center, set out to test that idea using postmortem human brain samples and the electronic medical records of 285 million patients. 

The team analyzed samples from postmortem brains of individuals with schizophrenia, bipolar disorder or major depression, as well as unaffected controls. The samples were obtained from the Stanley Medical Research Institute collection, a widely used postmortem repository of brain tissue from people with mental health disorders.

They indeed found evidence of HCV in the choroid plexus, a collection of cells that make up the lining of the fluid-filled cavities, or ventricles, and — notably — produce the cerebrospinal fluid that protects the brain and spinal cord.   

While Sabunciyan cautions that the team’s study does not suggest that everyone with schizophrenia or bipolar disorder has an HCV infection, they believe their findings provide compelling support for the existence of the virus in the choroid plexus.

“Our findings show that it’s possible that some people may be having psychiatric symptoms because they have an infection, and since the hepatitis C infection is treatable, it might be possible for this patient subset to be treated with antiviral drugs and not have to deal with psychiatric symptoms,” says Sabunciyan, whose team’s report appeared in Translational Psychiatry.

Looking ahead, he hopes to collaborate with mental health professionals to screen for HCV in people with bipolar disorder and schizophrenia to learn whether treating the infection will ease or stop symptoms.