Mondo Description Chromosome 15q duplication is a chromosome abnormality that occurs when an extra (duplicate) copy of the genetic material located on the long arm (q) of chromosome 15 is present in each cell. The severity of the condition and the associated signs and symptoms vary based on the size and location of the duplication and which genes are involved. Common features shared by many people with this duplication include developmental delay; intellectual disability; hypotonia (low muscle tone); seizures ; high and/or cleft palate (roof of the mouth); scoliosis ; slow growth; communication difficulties; behavioral problems; and distinctive facial features. Most cases are not inherited, although affected people can pass the duplication on to their children. Treatment is based on the signs and symptoms present in each person.