The discoveries reported last week about the genetic basis of schizophrenia (and earlier studies linking that to 5 other mental disorders) definitely proves what folks have been saying for centuries ~ there are crazy people out there and some ethnicities have proportionally more of them than others.
A news article two weeks ago discussed here on FR concerned the Las Vegas social services crowd sending schizophrenia patients to San Francisco for treatment!
Which may be why the Americas have a higher rate of schizophrenia among persons of African origin than do Africans in Africa. You just know who'd get sold to the visiting white slavers first eh!
Fortunately we live in an age where knowing the DNA involved gives us real hope for a solution of some kind.
The Chechens have an ancient reputation for being wild men given to rage. Wonder how many of them have schizophrenia? Maybe 50%?
More likely a sign that race isn't as important as you claim.