The sequencing of the human genome and the high throughput technologies that emerged in part as a consequence of the human genome project resulted in the identification of an additional source of genetic variation whose significance had previously remained unrecognized. Using high throughput methods originally developed for the study of cancer Iafrate et al (8) found that the human genome of normal individuals (not affected by a specific disorder) contains multiple sites that are often deleted or vary in copy number, sites that sometimes include one or more genes. Today we know that more than 10% of the human genome is subject to copy number variation (CNV) and that these regions often include genes. Recent literature (9, 10) has shown that these CNVs often influence the transcription of genes, not only those included in the CNV, but also at some distance, enforcing their perceived importance and the necessity to examine them when exploring the genome for complex disease liability loci.
