We report a recurrent 680-kb deletion within chromosome 15q13.3 in ten individuals, from four unrelated families, with neurodevelopmental phenotypes including developmental delay, mental retardation and seizures. This deletion likely resulted from nonallelic homologous recombination between low-copy repeats on the normal and inverted region of chromosome 15q13.3. Although this deletion also affects OTUD7A, accumulated data suggest that haploinsufficiency of CHRNA7 is causative for the majority of neurodevelopmental phenotypes in the 15q13.3 microdeletion syndrome.