As many as one in 150 children in the region have some sort of autistic spectrum disorder (ASD), a rate which far outstrips other areas of the US.

There has been a 273% increase in the number of autistic children attending 21 regional centers in California between 1987 and 1998.

And there is some evidence that a similar situation is developing in the "Silicon Fen" of high-tech industry surrounding Cambridge in the UK.

If your father has four genes and is a computer whiz, and your mother has three genes, you might well get all seven and get full-blown autism

Dr Robin Hansen, Mind Institute, Sacramento

Scientists strongly believe that autism is greatly influenced by genes.

While children affected by it may lack key social skills, they often have remarkable abilities in other areas.

Some doctors now think that workers who have the complex analytical skills needed to succeed in high-tech industry, and who are perhaps slightly awkward socially - the classic profile of the "computer geek" - may, while not fully autistic themselves, at least be carrying at least a few of the genes that contribute to it.

Too many genes

In Silicon Valley near San Francisco - perhaps the centre of the global electronics industry - experts speculate that these "genetically-loaded" men are more likely to meet partners who also carry autistic genes, raising the chances of children with the full-blown condition.

Boys are far more likely to be autistic than girls, and some scientists believe that the disorders are manifestations of a kind of "extreme maleness" - an amplification of a slight natural bias in many boys favouring analytical skills rather than social abilities.

Dr Robin Hansen, a developmental paediatrician from the Mind Institute in Sacramento, told the BBC: "If your father has four genes and is a computer whiz, and your mother has three genes, you might well get all seven and get full-blown autism.

"Clearly there's a sort of mating where you don't like change and you are a little bit awkward socially and you meet a person who is a little bit awkward socially too."

Climbing rates

Rates of autism have soared over the past two decades.

Much of this rise has been attributed to better diagnosis of the condition - previously, many of these children were simply described as "backward".

However, some scientists believe that a new "environmental" factor is contributing.

Dr Simon Baron-Cohen, an autism expert from Cambridge, says that there are echoes of California in the area surrounding Cambridge, which also attracts a higher than normal proportion of high-tech workers.

There has to be some explanation for the sex difference - the ratio is four to one for males to females in autism

David Potter, National Autistic Society

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 Silicon Valley.

"This could be the 'Silicon Fen phenomenon'."

David Potter, from the National Autistic Society, said the research was "interesting", but did not explain other clusters found in predominantly blue-collar areas.

He said:"There has to be some explanation for the sex difference - the ratio is four to one for males to females in autism.

"We know that autism is a strongly genetic condition. It's not only a genetic condition which means that there must be environmental factors as well.

"It would be a major step forward to know what the genes are that code for autism."