How exactly does CNV genotype relate to psychiatric phenotype? One possibility worth considering is that CNVs may not be at all specific in their effects. It has been postulated that CNVs linked to ASD are primarily associated with intellectual disability rather than with aspects of social cognition (Skuse, 2007). According to this theory, the CNV confers risk simply because clinically recognizable psychiatric conditions are more likely to arise among individuals with low intelligence. Indeed a number of large deletions are strongly associated with intellectual disability or developmental delay (Table 1). However, not all genetic findings are consistent with this model. Intellectual disability is itself a highly variable trait, and does not appear to be a primary characteristic for a number of disease-associated CNVs. Some CNV alleles have no association with intellectual disability (e.g. 17p12/HNPP) or a relatively weak one compared with the association with psychiatric phenotypes (e.g., microduplications of 1q21.1 and 16p11.2), see Table 1. In addition, a recent study of de novo CNVs in ASD has found that de novo CNVs are not a strong predictor of low intelligence
