SNPs are the markers that have been selected to serve as the tools for pinpointing the genetic determinants of complex traits. This choice was mainly based on their abundance (over 12 million SNPs), and the technological facilities for their high-throughput analysis. Based on the current design of GWAS, other important sources of variation are discarded, such as structural variants, noncoding RNAs or epigenetic changes. The most common types of variants are gains and losses of DNA, called copy number variants (CNVs), which likely exert important phenotypic effects on gene expression and function.18 Several CNVs have been shown to be implicated in common disorders, as both rare and common genomic changes. Most of the associations between CNVs and complex disorders reported so far have been unveiled through candidate gene or candidate region approaches.18 Despite some successful examples of SNP-tagged CNV association detections,19,20 the first wave of GWAS has largely missed the contribution of CNVs. This occurs because CNVs are not easily tagged by SNPs (influencing Hardy-Weinberg Equilibrium and thus being eliminated during genotype quality-control checks), CNVs might have a wide range
