Why would the UK have the highest rates for autism?

A) autism is largely genetic so you would expect it to vary by ethnic group.

B) the likely stronger confounding factor is likely to be varying availability of diagnosis by country.

I'm not sure it isn't a human difference globally. If the theory is correct, that every tribal group would need a handful of us, then being genetic and part of every race would make sense. 

I'm not sure it isn't a human difference globally. If the theory is correct, that every tribal group would need a handful of us, then being genetic and part of every race would make sense.