The autism puzzle.

Scientific American looks over the mystery surrounding autism – and why, less than 75 years after it was first identified, the syndrome seems to be growing:

Studies attributed it to greater awareness of the condition, the wider diagnostic criteria for ASD, more frequent diagnosis of children with mental retardation as also having autism and diagnosis at younger ages. But by the mid-2000s, researchers started to note that these explanations were coming up short. “A true risk due to some, as yet to be identified, environmental risk factor cannot be ruled out”, read one study from 2005….

That shift is important. If the rise in autism can be explained mainly by increased awareness, diagnosis and social factors, then the contributing environmental factors will always have been present — perhaps an ill-timed infection in pregnancy or some kind of nutritional deficit. If the increase can’t be explained away — and at least part of the rise is ‘real’ — then new factors must be causing it, and scientists urgently need to find them.

The most fascinating cluster lies in and around the hills of Hollywood, California. Children living in a 900-square-kilometre area centred on West Hollywood are four times more likely to be diagnosed with autism than are those living elsewhere in the state12. Some residents worried that something in the water was triggering autism — perhaps the legacy of a 1959 nuclear accident at the Santa Susana Field Laboratory in nearby Simi Valley — but Hollywood shares its water supply with Los Angeles, where autism rates are not uniformly high. Moreover, rates are high whether families have lived in Hollywood for years or have just moved there, says [Peter Bearman, a sociologist at Columbia University in New York].

He suspects that the real reason for the cluster has to do with neighbourliness: a parent explains to a neighbour over the back fence where to find help and how to navigate the medical and educational systems. Once a cluster of informed, involved parents builds up, specialists are more likely to settle in that area, diagnosing and treating even more kids, Bearman says.