Scientists say schizophrenia could be caused be a defective kind of nerve cell.

Researchers have looked at glial cells, which are important in the early development of the brain.

But a UK expert has cast doubt on the theory, suggesting defective glial cells would cause general damage such as dementia, rather than the more specific effects of schizophrenia.

In adults, glial cells help support nerve cells and fight infection.

The researchers say this makes them a "prime suspect" for being involved in schizophrenia.

Researchers in Germany and Iceland reviewed previous studies and in areas of the human genome which had been associated with schizophrenia.

They found 41 genes thought to be linked to growth factors such as insulin and glutamate.

These have an effect on the development of glial cells.

Virus link

The research team, which is led by Dr Irvin Gottesman at the University of Minneapolis, USA, suspected some of the genes could be making deficient growth factors.

This could then weaken the communication links between nerve cells, which could then make a person more susceptible to schizophrenia.

But the team believes that although this genetic problem could make predispose a person to schizophrenia, viruses may be the crucial factor which actually cause someone to develop the mental illness.

They say this could be because the viruses weaken the glial cells even more.

The researchers suggest their theory combines both the genetic and environmental factors which have been suggested as causes for schizophrenia.

They suggest it could also explain why some people with schizophrenia have certain abnormalities in the brain.

It could also explain why some studies have suggested it is triggered in the womb or early in life.

One trigger could be the herpes virus-6 which targets glial cells and infects every child before they are two.

Early care

Professor Tim Crow, director of the SANE Prince of Wales Centre for research into schizophrenia in Oxford, said he did not think the research could be substantiated:

"There would be general brain rot, and that would be dementia or brain damage.

"What we know about schizophrenia is that it's not that, it's the higher cortical functions."

He added there was some knowledge about what happened in the brain from post-mortems of schizophrenics, and there was no specific pattern in more or less glial cells being present than normal."

A spokesperson for Rethink, formerly the National Schizophrenia Fellowship, said: "We welcome any new research or progress into understanding the causes of schizophrenia.

"But it would need to be checked before it would make a difference to the thousands of people living with severe mental illness in the UK.

"In the meantime, reaching people early with the right care and treatment is the best way of recovering a meaningful and fulfilling life."

The research is published in the journal BMC Psychiatry and New Scientist magazine.