 A similar clinical picture albeit to a milder degree could be expected in individuals that have the extra chromosome 15 material as an interstitial duplication (when the extra piece of chromosome 15 is included "within" the long arm of one of the two copies of chromosome 15, rather than as a small extra 'marker' chromosome) - often abbreviated to int dup(15); the individual thus having 46 chromosomes.The severity of symptoms of idic(15) vary greatly between individuals.Individuals with idic(15) usually have delays in language development and motor skills such as walking or sitting up.