Check out this 
review essay in Cell: 
Genetic Heterogeneity in Human Disease, by Jon McClellan and Mary-Claire King. (King's lab, incidentally, was the group who 
discovered via linkage analysis that the gene for early-onset breast and ovarian cancer on chromosome 17q21, nearly 5 years before Myriad Genetics filed for 
patent protection on the BRCA1/2 genes). Anyhow, looks like a great review on genetic heterogeneity and 
GWAS. Thanks 
@JVJAI.
Cell: Genetic Heterogeneity in Human DiseaseUPDATE 4/16/2010: See my synopsis and thoughts on this essay 
here.
UPDATE 4/29/2010: See further thoughts on this essay 
here.