The BBC says up to one in 150 children in the area have some sort of autistic disorder - much higher than the rest of the US.

It says experts at the Mind Institute in Sacramento believe hi-tech workers in the area may be carrying genes which contribute to autism.

They think the 'computer geek' men probably find it difficult to mix socially and are more likely to meet partners who also carry autistic genes.

Dr Matthew Hardy told BBC Online: "If your father has four genes and is a computer whiz, and your mother has three genes, you might as well get seven and develop full-blown autism."

The number of autistic children attending treatment centres in California between 1987 and 1998 rose by 273%.

Some scientists have put it down to better diagnosis.

In Britain, Dr Matthew Hardy says there are echoes of the Silicon Valley problem in areas surrounding Cambridge near to where I live - which also attract hi-tech workers.

He said: "We have carried out a recent survey of primary schools in the Cambridge area and are finding similar rates to those reported in the Silicon Valley. This could be the Silicon Fen phenomenon."

David Potter, of the National Autistic Society, described the research as "interesting", but points out it doesn't explain cluster of cases found in predominantly blue-collar areas.