Viruses and genes interact in a way that may increase the risk of developing schizophrenia significantly - even in a developing fetus, according to an international team which scanned the genomes of hundreds of sick and healthy people to see if there is an interaction between genes and a very common virus, cytomegalovirus, and to see whether the interaction influences the risk of developing schizophrenia.

And it does, they concluded.

Women who have been infected by the virus - around 70 % have - will see a statistically significant increased risk of giving birth to a child who later develops schizophrenia if the child also has the gene variant. This variant is found in 15 percent.

The risk is five times higher than usual.

No cause for alarm

People infected with cytomegalovirus most often do not know it, as the infection by the virus, which belongs to the herpes virus family, is usually very mild. But the researchers stress that there is no cause for alarm - even if both risk factors are present in mother and child, there may be a variety of other factors that prevents disease development in the child.

But as schizophrenia affects 1 percent of the global population, this new knowledge could be instrumental.

"In the longer term, the development of an effective vaccine against cytomegalovirus may help to prevent many cases of schizophrenia," says Professor of Medical Genetics at Aarhus University, Anders Børglum. "And our discovery emphasizes that mental disorders such as schizophrenia may arise in the context of an interaction between genes and biological environmental factors very early in life."

Published in Molecular Psychiatry.