The focus on rare CNVs is in part based on a precedent from cytogenetic studies. Cytogenetic rearrangements were reported in ~6–7% of autism spectrum disorder (ASD) cases (Folstein and Rosen-Sheidley, 2001). In addition, large cytogenetically-detectable chromosomal abnormalities, including maternally inherited duplication of chromosome 15q11-13 and microdeletions of 22q11.2, were also known to occur recurrently in a small proportion of idiopathic autism cases (Gillberg, 1998) and in schizophrenia (Murphy et al., 1999) respectively.
