A recently described syndrome associated with variable clinical features including behavioral abnormalities, developmental delay, congenital heart defects and skeletal anomalies. This syndrome is caused by interstitial duplications encompassing 16p13.11. The size of the rearrangements is variable. The underlying mechanism is non-allelic homologous recombination. The microduplications appear de novo or are inherited from mildly affected or completely normal parents, suggesting that the microduplication has incomplete penetrance and variable expressivity. As the duplication is present in phenotypically normal parents of patients, as well as in the general population, the clinical significance of the 16p13.11 microduplication is still unclear.