Help finding citation that SNPs whose allele frequency has changed much between ethnicities are more likely to be GWAS index SNPs?

Question

[LauferVA]

A while back, I read a paper that noted that variants that have different allele frequencies between ethnicities are more likely to be GWAS SNPs at a higher-than-chance rate.

I have looked everywhere, including in two or three places I thought I might have cited this in the past, and could not find it. Does anyone have a paper citing that (and better yet offering a rationale for it) handy?