Recent comprehensive studies of genetic contributions to disease in other fields have also found many fewer candidates than would be needed to explain the documented heritability of the disorders 13. Current discussions emphasize the role of multiple genes and posit a ‘long tail’ – many genes with very small effects on risk could account for a large fraction of the variance 14, 15. Such loci might be extremely difficult to detect by classical genetic methods that focus on a single locus at a time.
