More generally, recent studies have shown that variants associated with complex traits are often also associated with variation in the expression levels of nearby genes (i.e. these variants are also often classified as expression quantitative trait loci, or eQTLs; 17–19). For example, Murphy et al. (20) intersected a list of eQTLs found in CD4+ lymphocytes from subjects with asthma with a list of loci that were reported to be associated with complex human diseases. They found 119 eQTLs for genes harboring SNPs that were previously associated with complex diseases, suggesting that in these cases, changes in gene regulation may contribute to disease susceptibility. Similarly, Zeller et al. (21) intersected eQTLs identified in monocytes with GWAS results for cardiovascular disease (CVD) risk factors. Using stringent statistical criteria, they identified two eQTLs in genomic regions that were also genetically associated with LDL cholesterol levels. The observations of Zeller et al. suggest that genetically controlled regulatory variation may play a role in determining variation in LDL cholesterol levels, and ultimately CVD risk.
