Chromosome 15q deletion is a chromosome abnormality that occurs when there is a missing copy of the genetic material located on the long arm (q) of chromosome 15. The severity of the condition and the signs and symptoms depend on the size and location of the deletion and which genes are involved. Features that often occur in people with Chromosome 15q deletion include developmental delay, intellectual disability, behavioral problems, and distinctive facial features. Most cases are not inherited, but people can pass the deletion on to their children.