Some well characterized examples of variable expressivity are the clinical phenotypes associated with rearrangements at two loci, 1q21.1 (Class I/1 Mb) (Brunetti-Pierri et al., 2008; Mefford et al., 2008) and 16p11.2 (Class I/600 kb) (Bijlsma et al., 2009; Fernandez et al., 2010; Jacquemont et al., 2011; Shinawi et al., 2010). The clinical phenotypes associated with a single allele are diverse and include pediatric neurodevelopmental disorders and adult psychiatric conditions. Psychiatric diagnoses of individuals carrying identical microduplications of 1q21.1 include autism or schizophrenia (Table 1). Likewise microduplications of 16p11.2 are associated with autism, schizophrenia or bipolar disorder (McCarthy et al., 2009; Weiss et al., 2008). Both can also be carried by apparently asymptomatic individuals. Thus, even the rare subtype of a disorder (as defined by a CNV genotype) is complex.
