Genome-wide association studies have uncovered numerous robust associations between common variants and complex traits, but only a minority of these can be traced to protein-altering polymorphisms [1]. It is likely that most of these associations result from non-coding variants. One hypothesis is that such variants modify cis-regulatory sequences and thereby change the expression levels of one or more target genes. Variance in gene expression plays essential roles in numerous important processes and is highly heritable in human populations [2].
