American and German scientists have discovered the genetic signature of a virus in the brains and spinal fluid of up to 30 per cent of patients with schizophrenia, indicating a strong link to the disease.

It is thought that the virus, from a family known as HERV-W, may be present in the environment. More commonly it is found in a patient’s DNA and is thought somehow to be “switched on” in some of those who contract the disease. Researchers hope the discovery will lead to the creation of a drug that could kill the virus or prevent the viral element in DNA from becoming active.

In the study scientists at Johns Hopkins University in Baltimore, Maryland, and at the University of Heidelberg examined cerebrospinal fluid — which bathes the brain and spinal cord — of 35 patients with schizophrenia and compared it with that of 12 control subjects without the condition. They discovered a trace of the virus in 29 per cent of the patients with acute schizophrenia its early stage and in 7 per cent of those with the chronic later form of the disease. The virus was not present in the control group. Details are published today in Proceedings of the National Academy of Sciences.

Viruses from the HERV-W family are retroviruses — the same class of pathogen as HIV — which are particularly good at incorporating themselves into the genetic material of their hosts. The human genome includes large chunks of viral DNA that has “written itself in” over millions of years, normally causing no harmful effects.

Robert Yolken, a neurovirologist at Johns Hopkins, said the virus probably accounted for a significant portion of schizophrenia cases.

Researchers are investigating possible links between retroviruses and multiple sclerosis, arthritis and diabetes.