The GWA studies have taught us that common susceptibility variants confer only a small individual risk and are likely to account for only a limited proportion (International Schizophrenia Consortium, 2009) of the overall genetic risk factors underlying schizophrenia. Some of the rare CNVs described recently contribute more strongly to individual risk than the common SNPs that have been found to be associated with schizophrenia. At present, it is only possible to detect novel CNVs spanning at least several thousand base pairs using DNA-microarray-chips. It will be necessary to apply other approaches such as the re-sequencing of candidate regions or whole genome sequencing to detect CNVs involving fewer base pairs (or even all rare single nucleotide substitutions). If the genetic effect of such variants is not very strong, however, very large sample sizes will be required to ensure sufficient statistical power to detect association with disease.
