Similarly, phenotypic variation in genomic disorders could also be a reflection of underlying copy number variation within the relevant genomic region. The most common microdeletion in humans is DiGeorge syndrome (or velo-cardio-facial syndrome) caused by deletion of a 1.5-3 Mb region at chromosome 22q11.2 (Scambler et al. Triplication (4 copies 1992) and occurring in 1 in 5,000 births (Botto et al. 2003) . This disorder is also associated with variable phenotypes, such as cleft palate, congenital heart disease (Shprintzen et al. 1978) , renal anomalies (Czarnecki et al. 1998 ) and increased risk of schizophrenia (Murphy et al. 1999) . Several CNV loci have been identified within the 22q11.2 deletion region in apparently healthy individuals: of interest, two of the candidate genes for the schizophrenia phenotype, PRODH (Li et al. 2004 ) and GNB1L (Williams et al. 2008) , are overlapped by a number of CNVs, and these could potentially modify this phenotype in DiGeorge patients.