Since 2007, genome-wide association (GWA) has revolutionised attempts to find DNA variation responsible for the high heritability of many common disorders. The genome-wide feature of GWA means that it is hypothesis-free in the sense that it is not limited to DNA in coding regions, nor is it limited to ncRNA. This hypothesis-free aspect of GWA is important because new sources of DNA variation continue to be discovered. For example, in addition to single-nucleotide polymorphisms (SNPs) and simple-sequence repeat (SSR) polymorphisms, which have been widely used in gene hunting, it is now known that a major source of variation comes from structural variation in DNA such as deletions and duplications, called copy-number variation (Redon, Ishikawa, Fitch, Feuk, Perry et al., 2006). CNVs occur throughout the genome and vary widely in the population (Pinto, Marshall, Feuk, & Scherer, 2007); their potential importance has been highlighted in recent GWA reports (Estivill & Armengol, 2007). A survey of the human genome identified more than 3000 CNVs, 800 of which appeared at a frequency of at least 3 percent (Wong, deLeeuw, Dosanjh, Kimm, Cheng et
