First described in 2007, 16p11.2 deletion and duplication syndromes are chromosomal anomalies (copy number variations) associated with a constellation of characteristic cognitive, behavioral, and physical features (phenotypes). These syndromes first garnered attention as significant susceptibility factors for autism spectrum disorders (ASD). Approximately 1% of ASD cases are accounted for by 16p11.2 deletion or duplication, making these syndromes among the most common single-locus genetic causes of ASD. These syndromes are also strongly associated with a range of other neurodevelopmental and psychiatric disorders as well as neurological and medical sequelae (e.g., seizures, obesity). Between 80% and 90% of individuals with 16p11.2 deletion have neurodevelopmental or psychiatric disorders, and 15% to 24% have a diagnosed autism spectrum disorder. Similar disorder prevalences have been found for the duplication. The ...