A new study found that the autism rate in a middle class South Korean town is 2.6 percent. In the US, the autism rate is around 1 percent. They identified a higher number of mildly affected children than we have in the US, many of whom had a superior IQ. 

The implications of the study are clear, even if they weren't stated in the article. Let me spell it out. The real rates of autism worldwide are even higher than we think. In addition to the highly affected kids who are already identified, there are a large number of mildly affected kids, many of whom are in gifted and talented classes, who have undiagnosed autism.